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1 Polyhedron 27 (2008) Contents lists available at ScienceDirect Polyhedron journal homepage: A systematic investigation of the CuCl 2 /H 2 mal/phen reaction system (H 2 mal = malonic acid): Solution and solid state studies of its products Catherine Gkioni a, Athanassios K. Boudalis a, Yiannis Sanakis a, Leondios Leondiadis b, Vassilis Psycharis a, Catherine P. Raptopoulou a, * a Institute of Materials Science, NCSR Demokritos", Aghia Paraskevi, Athens, Greece b Institute of Radioisotopes-Radiodiagnostic Products, NCSR Demokritos", Aghia Paraskevi, Athens, Greece article info abstract Article history: Received 7 March 2008 Accepted 23 April 2008 Available online 12 June 2008 Keywords: Copper(II) complexes Malonato complexes 1,10-Phenanthroline Mass spectrometry Dynamic combinatorial chemistry The systematic investigation of the parameter space of the CuCl 2 /H 2 mal/phen reaction system in MeOH resulted in the isolation of seven different complexes either as mixtures or in pure form, six of which have been structurally characterized. The molar ratios of the reactants and the crystallization methods have been systematically varied, leading to the isolation of compounds [Cu(H 2 O)(phen)(mal)] (1), [Cu(MeOH) (phen)(mal)] (2), [Cu 2 Li 2 Cl 2 (phen) 2 (mal) 2 (MeOH) 4 ] (3), [Cu 2 (phen) 4 (mal)][cucl(phen)(mal)](oh) (4), [CuCl(phen) 2 ]Cl (5), and [CuCl(phen)(mal)][CuCl(phen) 2 ][Cu(phen) 2 (Hmal)]Cl (6). The coordination versatility of the malonato ligand has been confirmed by the presence of three different coordination modes and its two deprotonation states in compounds 1 6. Solution studies on methanolic solutions of 2 4 and 6 by mass spectrometry revealed the absence of parent ion peak and the presence of fragment ions of low relative abundance not previously found in their crystal structure, thus indicating decomposition and rearrangement/reorganization of the complexes in solution and confirming the dynamic character of their solutions. Compounds 3 and 4 have been also studied in the solid state by EPR spectroscopy and magnetic measurements. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction * Corresponding author. Tel.: ; fax: address: craptop@ims.demokritos.gr (C.P. Raptopoulou). The coordination chemistry of the aliphatic a-x dicarboxylates of the general formula OOC (CH 2 ) n COO has been widely investigated because it has found to exhibit a high coordination versatility. This is mainly due to (i) the presence of two carboxylato groups, (ii) the conformational freedom of the carbon skeleton (for n P 1), giving rise to various relative orientation of the two carboxylato moieties, (iii) the possibility to obtain mono- or di-anionic forms, (iv) the probability of triply coordinated oxygen atoms, and (v) the possibility to form secondary building blocks [1]. Thus, while oxalates (n =0, H 2 ox), act as rigid bridging ligands, giving rise to structures with dimensionalities ranging from zero to three [2], with the 2D honeycomb structure being the predominant one [3], the malonato ion (n =1, H 2 mal), offers the additional advantage of the relative location of the two carboxylato groups in the 1,3 positions supporting simultaneous chelating bidentate and various carboxylato-bridging coordination modes, thus leading to structures with variable architectures [4]. When combined with other bridging and/or chelating ligands, the malonato ion has afforded mononuclear, dinuclear, trinuclear, tetranuclear as well as 1D, 2D and 3D structures [5 11]. One of our areas of interest lies in the field of structure/properties relationship. For that purpose we have been embarked on the systematic exploration of the parameter space of reaction systems involving first-row transition-metal ions and various ligands, by varying several degrees of freedom, like ligand substituents [12], solvent [13], crystallization method [14], as well as reactivity of metal clusters [15]. The isolation of one or more products from these systems in a pure form is also of prime importance, since a parallel area of interest is the physical study of these products in the solid state. The coordination versatility of the malonato ligand and its substituted derivatives, which can lead to novel metal ion topologies and cluster nuclearities bearing interesting physical properties, has prompted us to investigate their coordination chemistry. We have previously reported our results concerning the copper(ii) coordination chemistry of methyl-malonic acid (HOOC CH(CH 3 ) COOH) in the presence of 1,10-phen and 2,2 0 - bpy [16]. Herein we present a systematic investigation of the parameter space of the CuCl 2 /H 2 mal/phen reaction system in MeOH, and we examine the products that result from variations of two degrees of freedom", i.e. the reaction mixture stoichiometry and the crystallization method (Table 1). Apart from crystallographic studies of products that result as single-crystals, we /$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi: /j.poly

2 2316 C. Gkioni et al. / Polyhedron 27 (2008) Table 1 The crystallographically characterized products from the CuCl 2 /H 2 mal/phen reaction system in MeOH Complex Formula 1 [Cu(H 2 O)(phen)(mal)] H 2 O 2 [Cu(MeOH)(phen)(mal)] 3 [Cu 2 Li 2 Cl 2 (phen) 2 (mal) 2 (MeOH) 4 ] 4 [Cu 2 (phen) 4 (mal)][cucl(phen)(mal)](oh) 4.4(MeOH) 0.4(H 2 O) 5 [CuCl(phen) 2 ]Cl MeOH 6 [CuCl(phen)(mal)][CuCl(phen) 2 ][Cu(phen) 2 (Hmal)]Cl 2MeOH 2H 2 O conduct solution studies of some of the isolated products by means of mass spectrometry. 2. Experimental 2.1. General and spectroscopic measurements All manipulations were performed under aerobic conditions using materials as received (Aldrich Co.). All chemicals and solvents were of reagent grade. Elemental analysis for C, H, and N was performed on a Perkin Elmer 2400/II automatic analyzer. IR spectra were recorded from KBr pellets in the range cm 1 on a Bruker Equinox 55/S FT-IR spectrophotometer. Electron-spray ionization mass spectra of 2 4 and 6 were recorded on an AQA Navigator, Finnigan mass spectrometer. Test solutions in 50% aqueous methanol were infused into the electrospray interface at a flow rate of 0.1 ml min 1, using a Harvant Syringe pump. Negative or positive ion ESI spectra were acquired by adjusting the needle and cone voltages accordingly. Hot nitrogen gas (Dominic- Hunter UHPLCMS-10) was used for desolvation at 170 C. Variable-temperature magnetic susceptibility measurements were carried out on polycrystalline samples of 3 and 4 in the K temperature range using a Quantum Design MPMS SQUID magnetometer under a magnetic field of 1 T. Diamagnetic corrections for the complexes were estimated from Pascal s constants. The magnetic susceptibility has been computed by exact calculation of the energy levels associated with the spin Hamiltonian, through diagonalization of the full matrix with a general-symmetry program [17]. Least-squares fittings were accomplished with an adapted version of the function-minimization program MINUIT [18]. The error factor R is defined as R ¼ P ðxexp x calc Þ 2, where N is Nx 2 exp the number of experimental points. X-band EPR spectra were recorded on a Bruker ER 200D EPR spectrometer equipped with an Oxford Instruments ESR900 cryostat, a Bruker NMR Gaussmeter and an Anritsu microwave frequency counter Compound preparation [Cu(H 2 O)(phen)(mal)] H 2 O(1 H 2 O) Solid phen H 2 O (0.099 g, 0.50 mmol) and CuCl 2 6H 2 O (0.085 g, 0.50 mmol) were added to a refluxing solution of H 2 mal (0.052 g, 0.50 mmol) and LiOH H 2 O (0.042 g, 1.0 mmol) in methanol (20 ml). The colour of the solution immediately turned to sky-blue and the reflux continued for 15 min, during which time no noticeable colour change or solid precipitation was observed. Slow evaporation of the sky-blue solution afforded large X-ray quality blue prismatic crystals of 1 after 4 days (yield: g, 7.14%). The crystals were collected by filtration and dried in vacuo. The resulting powder was analyzed as solvent-free. Anal. Calc. for C 15 H 12 CuN 2 O 5 : C, 49.52; H, 3.32; N, Found: C, 49.37; H, 3.34; N, 7.66%. FT-IR (KBr discs, cm 1 ): 3480(m), 3050(s), 2980(sh), 2910(sh), 1590(vs), 1520(vs), 1495(sh), 1428(s), 1380(vs), 1340(s), 1282(s), 1224(m), 1209(m), 1143(m), 1110(m), 1050(m), 1033(m), 980(m), 955(m), 855(vs), 792(w), 778(m), 725(vs), 645(m), 430(m) [Cu(MeOH)(phen)(mal)] (2) Method A. A procedure same as for the synthesis of 1 was followed and X-ray quality blue prismatic crystals of 2 were obtained by layering of Et 2 O (2:1 v/v) to the sky-blue reaction solution (yield: g, 7.94%). The crystals were collected by filtration and dried in vacuo. Anal. Calc. for C 16 H 14 CuN 2 O 5 : C, 50.86; H, 3.73; N, Found: C, 50.70; H, 3.71; N, 7.38%. FT-IR (KBr discs, cm 1 ): 3490(s), 3407(vs), 3279(s), 3050(s), 2980(sh), 2910(sh), 1592(vs), 1520(vs), 1494(sh), 1428(s), 1381(vs), 1364(sh), 1343(s), 1282(s), 1224(m), 1209(m), 1144(m), 1108(m), 1049(m), 1033(m), 981(m), 955(m), 855(vs), 792(w), 779(m), 725(vs), 647(m), 430(m) Method B. Solid phen H 2 O (0.049 g, 0.25 mmol) and CuCl 2 6H 2 O (0.043 g, 0.25 mmol) were added to a refluxing solution of H 2 mal (0.052 g, 0.50 mmol) and LiOH H 2 O (0.042 g, 1.0 mmol) in methanol (20 ml). The colour of the solution immediately turned to sky-blue and the reflux continued for 15 min, during which time no noticeable colour change or solid precipitation was observed. X-ray quality blue prismatic crystals of 2 were obtained either by layering or by vapour diffusion of Et 2 O (2:1 v/v) to the reaction mixture. The identity of the products in each case was established by unit cell determination [a = 7.074(9), b = 11.84(2), c = 18.38(2) Å, b = 95.35(4), V = 1533(6) Å 3 (crystals from vapour diffusion) and a = 7.09(2), b = 11.86(3), c = 18.40(4) Å, b = (3), V = 1540(10) Å 3 (crystals from layering), see Table 2] [Cu 2 Li 2 Cl 2 (phen) 2 (mal) 2 (MeOH) 4 ](3) Method A. A procedure same as for the synthesis of 1 was followed, and X-ray quality light-blue crystals of 3 (yield: g, 3.32%), along with large blue prismatic crystals of 2, were obtained by vapour diffusion of Et 2 O (2:1 v/v) to the sky-blue reaction solution. The crystals were separated manually and dried in vacuo. Anal. Calc. for C 34 H 36 Cl 2 Cu 2 Li 2 N 4 O 12 : C, 45.15; H, 4.01; N, Found: C, 45.01; H, 3.99; N, 6.17%. FT-IR (KBr discs, cm 1 ): 3426(vs), 3066(sh), 1618(vs), 1518(s), 1489(m), 1421(vs), 1342(sh), 1331(s), 1312(sh), 1272(sh), 1252(sh), 1217(m), 1198(w), 1165(m), 1140(s), 1105(m), 1050(w), 1035(w), 1002(w), 970(s), 947(m), 874(m), 852(vs), 837(m), 785(m), 725(vs), 649(w), 577(s), 493(w), 472(w), 430(w) Method B. Solid phen H 2 O (0.099 g, 0.50 mmol) and CuCl 2 6H 2 O (0.128 g, 0.75 mmol) were added to a refluxing solution of H 2 mal (0.052 g, 0.50 mmol) and LiOH H 2 O (0.042 g, 1.0 mmol) in methanol (20 ml). The colour of the solution immediately turned to sky-blue and the reflux continued for 15 min, during which time no noticeable colour change or solid precipitation was observed. X-ray quality light-blue prismatic crystals of 3, along with small portions of a green powder, were obtained either by layering or by vapour diffusion of Et 2 O (2:1 v/v) to the reaction mixture. The identity of the product was established by unit cell determination (a = 8.40(1), b = 8.75(2), c = 14.32(2) Å, a = (4), b = 76.65(4), c = 69.93(4), V = 962(6) Å 3, see Table 2) [Cu 2 (phen) 4 (mal)][cucl(phen)(mal)](oh) 4.4(MeOH) 0.4(H 2 O) (4 4.4MeOH 0.4H 2 O) Method A. Solid phen H 2 O (0.099 g, 0.50 mmol) and CuCl 2 6H 2 O (0.043 g, 0.25 mmol) were added to a refluxing solution of H 2 mal (0.052 g, 0.50 mmol) and LiOH H 2 O (0.042 g, 1.0 mmol) in methanol (20 ml). The colour of the solution immediately turned to sky-blue and the reflux continued for 15 min, during which time a white precipitate was formed and removed by filtration. X-ray quality blue-turquoise crystals of 4 were obtained by slow vapour diffusion of Et 2 O (2:1 v/v) to the sky-blue reaction solution (yield: g, 14.47%). The same reaction mixture when layered with Et 2 O (2:1 v/v) leads to the formation of a mixture of 2

3 C. Gkioni et al. / Polyhedron 27 (2008) and 3. The crystals of 4 were collected by filtration and dried in vacuo. The resulting powder was analyzed as solvent-free. Anal. Calc. for C 66 H 51 ClCu 3 N 10 O 9 : C, 58.54; H, 3.80; N, Found: C, 58.36; H, 3.81; N, 10.31%. FT-IR (KBr discs, cm 1 ): 3406(vs), 3053 (m), 1582(vs), 1518(vs), 1494(w), 1427(vs), 1355(m), 1341(m), 1247(w), 1224(w), 1144(w), 1105(w), 959(w), 938(w), 851(vs), 779(w), 723(vs), 648(m), 428(w) Method B. Solid phen H 2 O (0.099 g, 0.50 mmol) and CuCl 2 6H 2 O (0.043 g, 0.25 mmol) were added to a refluxing solution of H 2 mal (0.026 g, 0.25 mmol) and LiOH H 2 O (0.021 g, 0.50 mmol) in methanol (20 ml). The colour of the solution immediately turned to sky-blue and the reflux continued for 15 min, during which time no noticeable colour change or solid precipitation was observed. X-ray quality blue-turquoise crystals of 4 were obtained by layering of Et 2 O (2:1 v/v) to the reaction mixture. The identity of the crystals was established by FT-IR spectroscopy Method C. Solid phen H 2 O (0.165 g, 0.83 mmol) and CuCl 2 6H 2 O (0.085 g, 0.50 mmol) were added to a refluxing solution of H 2 mal (0.034 g, 0.33 mmol) and LiOH H 2 O (0.028 g, 0.66 mmol) in methanol (20 ml). The colour of the solution immediately turned to sky-blue and the reflux continued for 15 min, during which time no noticeable colour change or solid precipitation was observed. X-ray quality blue-turquoise crystals of 4, along with blue prismatic crystals of 2, light-blue prismatic crystals of 3, green prismatic crystals of 5 and green needle-like crystals of 7, were obtained by vapour diffusion of Et 2 O (2:1 v/v) to the sky-blue reaction mixture. The crystals were separated manually and they were identified by FT-IR spectroscopy [CuCl(phen) 2 ]Cl MeOH (5 MeOH) A procedure as for the synthesis of 4 was followed (Method A), the only difference being the rapid rate of vapour diffusion of Et 2 O to the sky-blue reaction mixture. As a result a mixture of large X-ray quality green prismatic crystals of 5, blue-turquoise crystals and light-green needle-like crystals was formed which were separated manually. The blue-turquoise crystals and the light-green needles were identified by FT-IR spectroscopy as 4 and as a copper phenanthrolinato complex (7), respectively. Compounds 5 and 7 present similar infrared spectra (see below) and presumably they have analogous molecular structures with different unit cell parameters and/or solvate molecules. The crystals of 5 were separated manually and were dried in vacuo. The resulting powder was analyzed as solvent-free. Anal. Calc. for C 24 H 16 Cl 2 Cu 2 N 4 : C, 51.62; H, 2.89; N, Found: C, 51.46; H, 2.88; N, 9.99%. FT-IR (KBr discs, cm 1 ) for 5: 3521(m), 3364(m), 2987(m), 1625(m), 1605(m), 1583(m), 1518(vs), 1494(m), 1427(vs), 1339(m), 1309(w), 1227 (m), 1209(w), 1144(m), 1105(m), 1034(w), 956(vw), 911(vw), 869(sh), 856(vs), 782(m), 723(vs), 649(m), 614(m), 588(m), 428 (m). FT-IR (KBr discs, cm 1 ) for 7: 3416(vs), 3051(w), 2921(w), 1626(m), 1605(w), 1584(m), 1518(s), 1494(w), 1427(vs), 1339(w), 1308(w), 1225(w), 1144(m), 1105(m), 869(sh), 852(vs), 780(m), 723(vs), 648(w), 429(w) [CuCl(phen)(mal)][CuCl(phen) 2 ][Cu(phen) 2 (Hmal)]Cl 2MeOH 2H 2 O(6 2MeOH 2H 2 O) Method A. Solid phen H 2 O (0.099 g, 0.50 mmol) and CuCl 2 6H 2 O (0.043 g, 0.25 mmol) were added to a refluxing solution of H 2 mal (0.026 g, 0.25 mmol) and LiOH H 2 O (0.021 g, 0.50 mmol) in methanol (20 ml). The colour of the solution immediately turned to sky-blue and the reflux continued for 15 min, during which time no noticeable colour change or solid precipitation was observed. X-ray quality blue-turquoise crystals of 6 were obtained by slow vapour diffusion of Et 2 O (2:1 v/v) to the sky-blue reaction solution (yield: g, 5.70%), along with large green crystals and light green needle-like crystals which were identified as 5 and 7, respectively, by FT-IR spectroscopy. The crystals of 6 were separated manually and dried in vacuo. The resulting powder was analyzed as solvent-free. Anal. Calc. for C 66 H 45 Cl 3 Cu 3 N 10 O 8 :C, 56.50; H, 3.23; N, Found: C, 56.33; H, 3.24; N, 9.95%. FT-IR (KBr discs, cm 1 ): 3347(s), 3058(m), 2930(sh), 2817(w), 1714(s), 1605(vs), 1583(sh), 1518(vs), 1493(m), 1428(vs), 1372(m), 1340 (m), 1274(m), 1255(w), 1225(w), 1208(w), 1152(m), 1106(m), 1030(m), 999(vw), 970(w), 938(w), 912(w), 869(sh), 851(vs), 779 (w), 724(vs), 672(w), 648(m), 582(w), 507(w), 474(w), 429(m) Method B. The procedure was the same as above but 0.25 mmol of LiOH H 2 O were used instead. Layer or slow vapour diffusion of Et 2 O (2:1 v/v) to the sky-blue solution afforded blue-turquoise crystals of 6 whose identity was confirmed by unit cell determination. (a = 14.05(1), b = 15.18(2), c = 17.22(2) Å, a = 68.28(3), b = 74.44(3), c = 72.89(3), V = 3209(9) Å 3, see below, X-ray crystallography) Single-crystal X-ray crystallography Blue prismatic crystals of 1 ( mm) and 2 ( mm) were mounted in air. A light-blue prismatic crystal of 3 ( mm), a blue-turquoise crystal of 4 ( mm), a green crystal of 5 ( mm) and a blue-turquoise crystal of 6 ( mm) were mounted in capillaries. Diffraction measurements were made on a Crystal Logic Dual Goniometer diffractometer using graphite monochromated Mo radiation (for 1 3, 5 and 6) and on a P2 1 Nicolet diffractometer upgraded by Crystal Logic using graphite monochromated Cu radiation (for 4). Important crystal data and parameters for data collection for 2 4 are reported in Table 2. Unit cell dimensions were determined and refined by using the angular settings of 25 automatically centered reflections in the range 11 <2h <23 (for 1 3, 5 and 6) and in the range 22 <2h <54 (for 4). Three standard reflections monitored every 97 reflections showed less than 3% intensity fluctuation and no decay. Lorentz, polarization and psi-scan absorption corrections (for 4 only) were applied using Crystal Logic software. The structures were solved by direct methods using SHELXS-97 [19] and refined by full matrix least-squares techniques on F 2 with SHELXL-97 [20]. For compounds 1, 5 and 6 only preliminary crystallographic determination was performed. The molecular structures of 1 and 5 are known, although in different space groups, but their characterization was crucial from the chemical point of view in terms of the species isolated from the reaction mixture examined. Thus we felt that the complete structural characterization of 1 and 5 would not add any further potential to our investigation. On the other hand, the crystals of the new compound 6 were of poor quality showing large x-widths with shoulders on one side, a fact that is also reflected to the quality of the crystallographic data (see below), while our repeating efforts to improve the quality of the crystals of 6 were unsuccessful. Even so, the structural characterization of 6 was valuable, since complex 6 constitutes the only isolated species containing the Hmal anion; an observation very helpful for the interpretation of the Mass Spectra (see below). Further experimental crystallographic details for 1 H 2 O: C 15 H 15 CuN 2 O 6 ; f w = ; space group triclinic P 1; a = 8.093(6) Å, b = (8) Å, c = (1) Å, a = 88.39(3), b = 79.82(3), c = 74.94(2), V = Å 3, Z =4; q calc = g cm 3 ; l(mo Ka) = 1.49 mm 1 ; T =25 C; 2h max =34 ; scan speed 4.0 /min; scan range a 1 a 2 separation; reflections collected/ unique/used, 1949/1754 [R int = ]/1754; 273 parameters refined; (D/r) max = 0.004; (Dq) max /(Dq) min = 0.506/ e/å 3 ; R 1 / wr 2 for 1670 reflections with I >2r(I), (for all data), / , (0.0522/0.1363). Only the metal and the coordinated atoms

4 2318 C. Gkioni et al. / Polyhedron 27 (2008) Table 2 Crystallographic data for complexes MeOH 0.4H 2 O MeOH 0.4H 2 O Formula C 16 H 14 CuN 2 O 5 C 34 H 36 Cl 2 Cu 2 Li 2 N 4 O 12 C 70.4 H 63.4 ClCu 3 N 10 O 13.8 Fw Space group P2 1 /c P1 P2 1 /n T ( C) k (Å) Mo Ka ( ) Mo Ka ( ) Cu Ka (1.5418) a (Å) 7.061(3) 8.372(2) (8) b (Å) (4) 8.696(7) (13) c (Å) (7) (9) (11) a ( ) 84.15(3) b ( ) 95.45(2) 76.60(2) (2) c ( ) 69.93(3) V (Å 3 ) (1) (6) Z q calc (g cm 3 ) l (Mo Ka) (mm 1 ) a R b c d wr 2 a b c d a w = 1/[r 2 (F 2 o)+(ap) 2 + bp] and P = (max)(f 2 o,0) + (2F 2 c)/3. R 1 = P (jf o j jf c j)/ P (jf o j) and wr 2 ={ P [w(f 2 o F 2 c) 2 ]/ P [w(f 2 o) 2 ]} 1/2. b c d For 2401 reflections with I >2r(I). For 3139 reflections with I >2r(I). For 7283 reflections with I >2r(I). were refined anisotropically, the rest were refined isotropically. No H-atoms were included in the refinement. Further experimental crystallographic details for 2: 2h max =50, scan speed 4.5 /min; scan range a 1 a 2 separation; reflections collected/unique/used, 2910/2680 [R int = ]/2680; 273 parameters refined; (D/ r) max = 0.006; (Dq) max /(Dq) min = 0.255/ e/å 3 ; R 1 /wr 2 (for all data), / Hydrogen atoms were located by difference maps and were refined isotropically. All non-h atoms were refined anisotropically. Further experimental crystallographic details for 3: 2h max =50, scan speed 4.0 /min; scan range a 1 a 2 separation; reflections collected/unique/used, 3586/3336 [R int = ]/3336; 303 parameters refined; (D/r) max = 0.004; (Dq) max /(Dq) min = 0.727/ e/å 3 ; R/R w (for all data), / Hydrogen atoms were located by difference maps and were refined isotropically, except those of the methyl groups which were introduced at calculated positions as riding on bonded atoms. All non-h atoms were refined anisotropically. Further experimental crystallographic details for 4: 2h max = 116.5, scan speed 1.5 /min; scan range a 1 a 2 separation; reflections collected/unique/ used, 9984/9675 [R int = ]/9675; 903 parameters refined; (D/r) max = 0.006; (Dq) max /(Dq) min = 0.575/ e/å 3 ; R 1 /wr 2 (for all data), / Hydrogen atoms were introduced at calculated positions as riding on bonded atoms. All non-h atoms were refined anisotropically, except of the methanol and water solvate molecules which were refined isotropically with fixed occupation factors. Further experimental crystallographic details for 5 MeOH: C 25 H 20 Cl 2 CuN 4 O; f w = ; space group monoclinic P2 1 /n; a = (8) Å, b = (6) Å, c = (7) Å, b = (2), V = 2285(3) Å 3, Z = 4. Further experimental crystallographic details for 6 2MeOH 2H 2 O: C 68 H 57 -Cl 3 Cu 3 N 10 O 12 ; f w = ; space group triclinic P1; a = (2) Å, b = 15.24(2) Å, c = (2) Å, a = 69.09(3), b = 74.53(4), c = 73.04(4), V = 3202(9) Å 3, Z =2; q calc = g cm 3 ; l(mo Ka) = mm 1 ; T =25 C; 2h max = 38.5 ; scan speed 2.0 /min; scan range a 1 a 2 separation; reflections collected/unique/used, 5415/5125 [R int = ]/ 5415; 632 parameters refined; (D/r) max = 0.001; (Dq) max / (Dq) min = 3.501/ e/å 3 ; R 1 /wr 2 for 3914 reflections with I > 2r(I), (for all data), /0.2392, (0.1206/0.2657). All non-h atoms were refined anisotropically, except of the solvate molecules and those of the [Cu(phen) 2 (Hmal)] + cation which were refined isotropically (only the copper ion was refined anisotropically). No H- atoms were included in the refinement. 3. Results and discussion 3.1. Syntheses In order to explore the parameter space of the CuCl 2 /H 2 mal/ phen reaction system in methanol, we first employed the 1:1:1 molar ratio reaction in the presence of stoichiometric amounts of LiOH H 2 O to ensure deprotonation of the malonic acid. Three species have been isolated from the same sky-blue reaction mixture depending on the crystallization method employed: (i) slow evaporation afforded the mononuclear complex [Cu(H 2 O)(phen)(mal)] (1), (ii) layering of Et 2 O afforded the analogous mononuclear complex [Cu(MeOH)(phen)(mal)] (2) (see Section 2, Method A), and (iii) vapour diffusion of Et 2 O led to the heterometallic tetranuclear complex [Cu 2 Li 2 Cl 2 (phen) 2 (mal) 2 (MeOH) 4 ] (3) (see Section 2, Method A). The 1:1:1 stoichiometry initially employed in the Cu II /H 2 mal/phen reaction system is reflected to the stoichiometry of the three products. A summary of the reactions employed and the complexes isolated is depicted in Scheme 1. To further explore the parameter space of the above reaction system we varied the molar ratios of the reactants, first by systematically increasing each one s molar ratio, leaving at the same time all other parameters unchanged. Thus, the 1.5:1:1 respective molar ratio led to the isolation of complex 3 regardless of the crystallization method (see Section 2, Method B) along with small portions of green powder which is probably a copper(ii) phenanthrolinato complex (based on its colour). The excess of the Cu II ions in the reaction mixture is not reflected to the Cu II /H 2 mal/phen stoichiometry in 3, but it promoted the isolation of a non-malonato complex (green powder). The 1:2:1 respective molar ratio led to 2 regardless of the crystallization method (see Section 2, Method B). Thus, excess of H 2 mal in the reaction mixture afforded exclusively 2 without pushing the equilibrium to the isolation of other complexes from the reaction mixture. On the contrary, the 1:1:2 Cu II / H 2 mal/phen molar ratio reaction afforded several products depending on the crystallization method: (i) layering of Et 2 Oto the sky-blue solution afforded compound [Cu 2 (phen) 4 (mal)]- [CuCl(phen)(mal)](OH) (4) (seesection2, Method B), and (ii) vapour diffusion of Et 2 O to the same reaction mixture afforded a mixture of [CuCl(phen) 2 ]Cl (5), [CuCl(phen)(mal)][CuCl(phen) 2 ][Cu(phen) 2 - (Hmal)]Cl (6) (see Section 2, Method A), and light-green microcrystalline needles (7) showing superimposable IR spectra with 5. Thus,

5 C. Gkioni et al. / Polyhedron 27 (2008) Scheme 1. Diagram of the reaction pathways, showing the various combinations of stoichiometries and crystallization methods, and the products obtained by each. The 1.5:1:2.5:2 system leads to 2 5 and 7, and is not shown for simplicity. from a chemical point of view, we conclude that complexes 5 and 7 are identical, although they present different crystal structure parameters. The excess of phen in the reaction mixture seems as the most determinant factor since it pushes the equilibrium to the isolation of phen-rich complexes (see molecular structures of 4, 5 and 6). In a next step, we varied the molar ratios of the reactants by simultaneously increasing the H 2 mal and phen, leaving at the same time all other parameters unchanged. Thus, the 1:2:2 respective molar ratio led to the isolation of different mixtures of products depending on the crystallization method: (i) layering of Et 2 O afforded a mixture of 2 and 3, (ii) slow vapour diffusion of Et 2 O afforded exclusively compound 4, and (iii) rapid vapour diffusion of Et 2 O afforded a mixture of 4, 5 and 7. As in the previous case, the excess of phen, rather than the excess of H 2 mal, plays the predominant role since it facilitates the isolation of phen-rich complexes (see molecular structures of 4, and 5). Similarly, we increased the molar ratios of Cu II and phen with respect to H 2 mal using the 1.5:1:2.5 Cu II /H 2 mal/phen molar ratio (not shown in Scheme 1), based on the stoichiometry of 4 (see synthesis of 4, method C). By keeping the same reaction conditions (i.e. respective H 2 mal/lioh H 2 O molar ratio, solvent, crystallization method) that led to the isolation of 4, we have simultaneously isolated compounds 2 5 and 7. The simultaneous excess of Cu II (previously leading to the isolation of 3 and probably 7) and phen (previously leading to the isolation of 4, 5, 7) in the reaction mixture is in agreement with the isolation of a mixture of complexes. In all cases above, the 1:2 H 2 mal/lioh H 2 O molar ratio was used to ensure the full deprotonation of H 2 mal. This is in agreement with the presence of the mal 2 anion in the crystal structures of compounds 1 4, whereas the presence of Hmal in the [Cu (phen) 2 (Hmal)] + species found in 6 was not anticipated. We have thus wondered whether the isolation of a compound containing exclusively the Hmal anion would be possible, and we have employed the 1:1 H 2 mal/lioh H 2 O molar ratio while keeping the overall Cu II /H 2 mal/phen molar ratio to 1:1:2 (see Section 2, Method B). However, regardless of the crystallization method, the only product isolated was compound 6, leading us to conclude that both mal 2 and Hmal anions coexist in the reaction mixtures and their subsequent coordination is impeded by complicated and yet unknown reaction mechanisms and conditions. Conclusively, our results from the investigation of the parameter space of the CuCl 2 /H 2 mal/phen reaction system in MeOH can be summarized as follows: (i) the reaction mixtures examined have afforded seven different products either in pure form or as mixtures; (ii) the complexes have been isolated based on their different solubilities; (iii) the excess of Cu II in the reaction mixture leads to the isolation of 3 and probably 5 or 7 as green powder; (iv) the excess of H 2 mal in the reaction mixture leads to the isolation of pure 2 despite the 1:1:1 stoichiometry found in its molecular structure; (v) the excess of phen seems to play the predominant role leading to the isolation of the phen-rich complexes 4, 5, 6 and 7 along with the equimolar complexes 2 and 3; (vi) each of the 1:1:1, 1:1:2, 1:2:2 and 1.5:1:2.5 Cu II /H 2 mal/phen reaction mixtures has afforded several products, some of which resulted from two different mixtures, and some of which were afforded by only one (Scheme 1); and (vii) other species coexisting in the reaction mixture cannot be excluded. Thus, we may conclude that each of these mixtures behaves like a Dynamic Combinatorial Library (DCL), containing many different species in equilibrium. These species can be selectively isolated, by means of crystallization in different solvent systems. It is also of interest, that these DCLs exhibit overlaps, as many isolated species are common to more than one of those DCLs. The fact that solutions of transition-metal ions and one or more ligands form complicated mixtures of products in equilibrium, due to the labile nature of the metal ligand and other non-covalent bonds that may eventually form (H-bonds, p p stacking, etc.) is not new, and this is one of the attributes that make this chemistry so difficult to control. From this multitude of products in equilibrium it is often possible to isolate one or more products by their selective precipitation and subsequent crystallization, although it

6 2320 C. Gkioni et al. / Polyhedron 27 (2008) still remains a challenge to isolate different species from a DCL, and more so to structurally characterize them [21]. In other cases, structures were not available [22], or of marginal quality [23], but the products were identified spectroscopically. In most cases, the molecular recognition of the DCL member with small molecules or ions has been served as the selection process. Very elegant examples of this work include metallosupramolecular tetrahedral [24], cubes and open books [25], tetra-, hexa- and octanuclear ferric wheels [26], linear and circular helicates [27], tetra- and hexanuclear helicates [28], bowls and capsules [29], porphyrin cages [30], tetrahedra and helicates [31], various metallacryptates [32] and Borromean Rings and Solomon Knots [33] which have been identified as members of DCLs, and in some cases isolated. The particularity of the present system is that the isolation of specific species is not based on supramolecular recognition, but on their solubility in a given solvent system. What is also noteworthy is that a large number of such species has been structurally characterized Description of structures The crystallographic characterization of 1 and 2 revealed the presence of mononuclear species [Cu(L)(phen)(mal)] (L = H 2 O(1), MeOH (2)). The structure of 1 has been reported previously [5a]. An ORTEP plot of 2 is given in Fig. 1, selected bond distances and angles for both structures are given as Supplementary data (Table S1). The coordination geometry around the Cu II ion in both 1 and 2 is square-pyramidal; the basal positions are occupied by the nitrogen atoms of the phen and the oxygen atoms (O(1) and O(3)) of the bidentate chelating mal 2 ligand, whereas the apical position is occupied by the monodentate ligand. In the structure of 2, two centrosymmetrically related mononuclear species are hydrogen bonded and form dimers [Om(1)O(4) ( x, y, 1 z) = Å, HOm(1)O(4) = Å, Om(1) HOm(1)O(4) = ] (Fig. S1). An ORTEP plot of the structure of 3 is given in Fig. 2, selected bond distances and angles are listed in Table S2. The structure of 3 consists of neutral heterometallic tetranuclear Cu II 2Li I 2 units held together by two bidentate [chelating] + bis(unidentate) mal 2 ligands (Scheme 2). The coordination geometry around the two Cu II ions is square-pyramidal, (s = 0.19). The basal positions of the square pyramid are occupied by the nitrogen atoms of the phen and the oxygen atoms O(1) and O(3) of the mal 2 ligand. The apical position is occupied by a chloride atom at 2.502(2) Å. The Cu N and Cu O bond lengths are ca and 1.95 Å, respectively. The coordination Fig. 1. Partially labeled ORTEP plot of 2 with ellipsoids drawn at the 30% probability level (Hydrogen atoms have been omitted for clarity). Fig. 2. Partially labeled ORTEP plot of 3 with ellipsoids drawn at the 30% probability level (Hydrogen atoms have been omitted for clarity). Primed atoms are generated by symmetry ( 0 = x, y, 1 z). Scheme 2. The coordination modes of the malonato ligand in 1 4. geometry around the two Li I ions is tetrahedral comprised by two oxygen atoms O(2) and O(4 0 ) belonging to two centrosymmetrically related mal 2 ligands and two coordinated methanol molecules. The bond distances around Li I range from 1.901(5) to 1.956(5) Å. The neutral heterometallic tetranuclear molecules of 3 are hydrogen bonded [Om(1)O(4) ( 1+x, y, z) = Å, HOm(1)O(4) = Å, Om(1) HOm(1)O(4) = ; Om(2) Cl(1) (x, 1+y, z) = Å, HOm(2)Cl(1) = Å, Om(2) HOm(2)Cl(1) = ] and form layers that extend parallel to the ab plane (Fig. S2). The molecular structure of 4 consists of the complex cation [Cu 2 (phen) 4 (mal)] 2+, the complex anion [CuCl(phen)(mal)], one hydroxide anion, as well as methanol and water solvate molecules. An ORTEP plot of the complex cation and anion is given in Fig. 3, and selected bond distances and angles are listed in Table S3. Each Cu II ion in the cation of 4 presents an O 2 N 4 distorted octahedral coordination geometry comprised by the nitrogen atoms of two phen molecules and two carboxylato oxygen atoms of the mal 2 ligand. Each carboxylato group of the mal 2 ligand is asymmetrically coordinated to the Cu II ions (Cu(1) O(1) = 1.955(5), Cu(1) O(2) = 2.884(5), Cu(2) O(3) = 1.970(6), Cu(2) O(4) = 2.770(6) Å), presenting the novel bis(bidentate) [bridging] coordination mode (Scheme 2). The Cu N bond distances fall in the range 1.990(7) 2.207(10) Å. The coordination geometry around the Cu II ion in the anion of 4 is square-pyramidal (s = 0.16) comprised of the nitrogen atoms of the phen and the oxygen atoms of the bidentate chelating mal 2 ligand (Scheme 2) in the basal positions and a chloride atom at the apex at 2.567(6) Å. The Cu N and Cu O bond distances are ca and 1.92 Å, respectively. The overall coordination environment around

7 C. Gkioni et al. / Polyhedron 27 (2008) Fig. 3. Partially labeled ORTEP plot of the cation and anion of 4 with ellipsoids drawn at the 30% probability level (hydrogen atoms have been omitted for clarity). Fig. 4. Partially labelled ORTEP plot of the new cationic species [Cu(phen) 2 (Hmal)] + found in the structure of 6 with ellipsoids drawn at the 30% probability level (hydrogen atoms have been omitted for clarity). Cu(3) is quite similar to that found around Cu(1) and its centrosymmetric equivalent in the structure of 3. The structural characterization of 5 revealed the presence of [CuCl(phen) 2 ]Cl, whose structure has been previously reported [34]. The coordination geometry around the Cu II ion is distorted trigonal bipyramidal (s = 0.58) comprised of two phen ligands and a chloride atom. The structural characterization of 6 revealed the presence of three mononuclear species, the cation [CuCl(phen) 2 ] + also found in 5, the anion [CuCl(phen)(mal)] also found in 4, and the new cationic species [Cu(phen) 2 (Hmal)] + whose structure is shown in Fig. 4. Selected bond distances and angles are given as Supplementary data (Table S4). The coordination geometry around the Cu II ion in [Cu(phen) 2 (Hmal)] + resembles that of Cu(1) and Cu(2) in the cation of 4. Two phen molecules and an oxygen atom from the Hmal ligand are coordinated to the metal in a square-pyramidal geometry (s = 0.17). Three nitrogen atoms and the unidentate Hmal ligand occupy the basal positions of the square pyramid, whereas the forth nitrogen atom is directed at the apex. The presence of the monoanion Hmal has not been encountered in the other structurally characterized species isolated from this reaction system. The Cu N bond lengths fall in the range 1.988(11) 2.177(11) Å, the Cu(3) O(11) bond distance is 2.035(2) Å whereas O(12) is Å away of the metal ion. Fig. 5. Mass spectra from methanolic solutions of Mass spectrometry For the elucidation of the solution chemistry of the system, the complexes that could be obtained in pure form were studied. Mass spectra of complexes 2 4 and 6 recorded in 50% aqueous methanolic solutions are given in Figs. 5 8, respectively. Characteristic peaks and their interpretation are listed in Table 3 and summarized in Scheme 3. The main characteristic of all spectra is the absence of the parent ion peak leading to the conclusion that all complexes spontaneously decompose in solution, thus the peaks observed correspond to various molecular fragments, some of which are common in all spectra. In the spectra of 2 4 and 6 the basic peak (with relative abundance 100%) appears at M/z 302 Fig. 6. Mass spectra from methanolic solutions of 3.

8 2322 C. Gkioni et al. / Polyhedron 27 (2008) Fig. 7. Mass spectra from methanolic solutions of 4. Fig. 8. Mass spectra from methanolic solutions of 6. Table 3 Mass spectra from 50% aqueous methanolic solutions of compounds 2 4 and 6 Fragment (calc. M/z) Obs. M/ z(%) Obs. M/z (%) Obs. M/z (%) Obs. M/z (%) [Cu(phen) 2 (malh)] (526.5) (3.5) (3.5) (3) (3) [CuCl(phen) 2 ] (459) (12) (45) (45) [CuCl(phen)(CH 3 COOH)] (339) (3) (8) (10) [Cu(OH)(phen)(CH 3 COOH)] (319.5) (3) (5) (25) (25) [Cu(phen)(CH 3 COOH)] (100) (100) (100) (100) Abstraction of OH from [Cu(phen)(CH 3 COO)] + (25) (20) (10) (10) (284.5) [CuCl(MeOH)(malH)] (235) (5) (85) (80) [phenh] (181) (15) (12) and it is attributed to the molecular fragment [Cu(phen)(CH 3- COO)] + (theoretical M/z = 302.5) generated by decarboxylation of the malonato ligand. Further abstraction of OH from the above fragment, also common during the decomposition of organic acids, is recorded at in the spectra of the four complexes. In the spectra of [Cu 2 Li 2 Cl 2 (phen) 2 (mal) 2 (MeOH) 4 ] (3) the peak at M/ z = is assigned to the fragment [CuCl(phen) 2 ] + (theoretical M/z = 459). In the spectra of [Cu 2 (phen) 4 (mal)][cucl(phen)- (mal)](oh) (4) the two peaks at M/z and are assigned to the cationic fragments [CuCl(phen) 2 ] + (theoretical M/z = 459) and [CuCl(MeOH)(Hmal)] + (theoretical M/z = 233). A peak at M/ z = with relative abundance 15% corresponds to the cation [phenh] + (theoretical M/z = 181). Finally, in the spectra of [CuCl (phen)(mal)][cucl(phen) 2 ][Cu(phen) 2 (malh)]cl (6), a set of peaks at and with relative abundance 80% and 25%, respectively, are assigned to the cationic fragment [CuCl(MeOH)(Hmal)] + (theoretical M/z = 233) as in the case of 4, and to [Cu(OH) (phen)(ch 3 COO)] + (theoretical M/z = 319.5). The peak at M/z = with relative abundance 45% is attributed to the presence of the cationic fragment [CuCl(phen) 2 ] +, one of the cations found in the crystal structure of 6, as well as in the structure of 5. The molecular ion of [phenh] + also appears in the spectra of 6 at M/z = Another common feature in the mass spectra of the four complexes is the presence of peaks with relative abundance less than 15% at M/z 526 and 338. In particular, the peak at M/z 526 corresponds well to the theoretical value of calculated for the cationic species [Cu(phen) 2 (Hmal)] +, one of the cations found in the crystal structure of 6. The peak at M/z 338, may be attributed to the cation [CuCl(phen)(CH 3 COOH)] + with theoretical M/z value 339. Careful inspection of the mass spectra leads to the following conclusions: (i) the cationic fragment [Cu(phen) 2 (Hmal)] + present in the methanolic solutions of the four compounds is present in the solid state only in 6; (ii) the cationic fragment [CuCl(phen) 2 ] + present in the methanolic solutions of 3, 4 and 6 is present in the solid state in 5 and 6; (iii) the cationic fragment [Cu(phen)(CH 3- COO)] + in the methanolic solutions of the four compounds originates from the species [CuX(phen)(mal)] z, which in the solid state are present in 2 (z = 0, X = MeOH) and in 4 and 6 (z = 1, X = Cl); and (iv) the cationic fragment [CuCl(phen)(CH 3 COOH)] + in the methanolic solutions of 3, 4 and 6 originates from the anionic species [CuCl(phen)(mal)] which in the solid state is present in 4 and 6. Thus the methanolic solutions of 2 4 and 6 contain fragments of the complexes that have been previously isolated from the various CuCl 2 /H 2 mal/phen reaction systems, and the most important is that these fragments are not present in the solid state structure of the complex under examination. It is thus evident that compounds 2 4 and 6 decompose in solution followed by rearrangement/reorganization to species isolated in complexes 1 6, confirming the dynamic character of the system. Thus mass spectrometry supports indirectly our consideration that the various CuCl 2 /H 2 mal/phen reaction mixtures examined constitute a set of overlapping Dynamic Combinatorial Libraries whose members are complexes of the various ligands to the metal ions in solution Magnetic susceptibility studies Complexes 3 and 4 were chosen for a magnetic study since their structures suggested the possibility of magnetic exchange. The v M T products for 3 and 4 at 300 K are 0.77 and 1.41 cm 3 mol 1 K (Fig. 9). These are close to the values expected for two and three non-interacting S = 1/2 spins (0.83 and 1.24 cm 3 mol 1 K, respectively, g = 2.1). For 3, the slightly lower value than theoretically predicted indicates antiferromagnetic interactions. This is confirmed by the drop of v M T upon cooling, which is more abrupt below 50 K, falling to 0.75 cm 3 mol 1 K at 5 K. For 4, on the other hand, v M T increases upon cooling to a broad maximum of

9 C. Gkioni et al. / Polyhedron 27 (2008) Scheme 3. Species that form upon dissolution of 2 4 and 6 in MeOH. Species II V are directly observed by ESI-MS data, while the presence of I and VI is inferred by the presence of the decarboxylated fragments [Cu(phen)(CH 3 COO)] + and [CuCl(phen)(CH 3 COOH)] +, respectively. Dissolved species, present in certain complexes (e.g. II in 6) may have formed from transformation of complexes that did not initially contain them in the solid state (e.g. II from 2), confirming the dynamic character of the reaction system. considered for the interpretation of the magnetic susceptibility data of 3. The corresponding Hamiltonian was bh ¼ 2J b S 1 b S2 ð1þ Fig. 9. v M vs. T and v M T vs. T experimental data for complexes 3 and 4, and theoretical curves based on the Hamiltonians of Eqs. (1) and (2), respectively cm 3 mol 1 Kat70 K, before falling abruptly to a value of 0.99 cm 3 mol 1 K at 5 K. This overall behaviour indicates the interplay of ferro- and antiferromagnetic interactions. The close CuCu distances between neighboring molecules ( Å), which are comparable to the intramolecular intermetallic separation (9.818 Å), suggest the possible existence of both intra- and intermolecular magnetic interactions. However, in order not to overparametrize our problem, a simple dimer model was Fitting of the data according to this model yielded best-fit parameters J = 0.19 cm 1, g = with R = This very weak coupling agrees with the structural parameters of 3, in which Cu(1) and Cu(1 0 ) are separated by a distance of 9.82 Å, and magnetic exchange must be transmitted through a series of seven diamagnetic atoms. For the interpretation of the magnetic susceptibility data of 4, certain assumptions were made. Given its structure, a relatively strong interaction was expected between Cu(1) and Cu(2) via the malonato bridge. Initial attempts to fit the data considering only this interaction failed to reproduce the data. Thus, it was considered that Cu(3) might also be involved in magnetic exchange. Inspection of the molecular structure of 4, led us to assume that Cu(3) should mainly interact with Cu(1) through a p p stacking interaction. Thus, inclusion of a second exchange coupling brought about a remarkable improvement to the fits. The Hamiltonian used was bh ¼ 2ðJ 1 b S1 b S2 þ J 2 b S1 b S3 Þ Fitting according to that model yielded best-fit parameters J 1 = 80.0 cm 1, J 2 = 3.4 cm 1, g = with R = J 1 corresponds to the magnetic exchange mediated through the malonato bridge, which is expected to be stronger than the one mediated through the p p interaction and more ferromagnetic, given the propensity of malonates to promote ferromagnetic couplings in various coordination modes [35]. ð2þ

10 2324 C. Gkioni et al. / Polyhedron 27 (2008) Another point of interest concerns the malonato-mediated exchange coupling, which is strongly ferromagnetic. Qualitatively we could rationalize this by the relatively large intermetallic separation, in combination with the fact that the malonato bridge is coordinated to the equatorial positions of the copper atoms. Due to the first situation, the direct orbital overlap of the copper atoms is expected to be negligible, thus suppressing the antiferromagnetic component of the magnetic exchange. Due to the second situation, the malonate occupies the magnetic orbitals of the copper atoms (mainly of d x 2 y character), thus strong interactions can be 2 expected, which should be of ferromagnetic character. We should stress, however, that complex 4 is the first copper(ii) complex to our knowledge to exhibit the syn syn bridging mode of the malonate through two different carboxylate functions. Thus, it is not a simple task to propose a mechanism for the magnetic exchange, and theoretical studies should be pursued toward that direction. These, however, are beyond the scope of this work EPR spectroscopy X-band EPR spectra from powdered samples of 3 and 4 were recorded in the K temperature range. For both complexes no significant variation with temperature was observed. The 4.2 K spectra are shown in Fig. 10. Evident is the lack of hyperfine splitting features as is frequently observed in concentrated solid samples of Cu II complexes where exchange interactions are present [36]. For 3 the spectrum consists of a relatively broad absorption at g 2.31 and a narrower derivative feature at g Present also is a much weaker signal at 1600 G. From the crystal structure of 3, the closest intramolecular CuCu distance within the heterometallic tetranuclear unit is 9.8 Å, whereas hydrogen bonding interactions lead to the formation of layers extending parallel to the ab plane (Fig. S2). The intermolecular CuCu distances within these layers range from ca. 8.3 to 14.5 Å. The magnetic measurements discussed above indicate small intramolecular exchange interactions. Weak dipolar intra- or intermolecular interactions, may affect the EPR spectra. The weak feature at 1600 G is consistent with the so-called half-field transition (Dm S = ± 2) arising from such dipolar interactions [37]. If we approximate the present situation with a dimeric model, the relative intensity between the weak feature at 1600 G (Dm S = ± 2 transition) and the much stronger signal in the g = region (Dm S = ± 1 transitions) may be used in order to estimate the CuCu distances [37]. We find that this ratio is consistent with CuCu distances of the order of 8 9 Å, in reasonable agreement with the crystallographic data. The EPR spectrum from a powdered sample of 4 consists of a broad asymmetric signal in the 3000 G region, with a zero cross point at g 2.09 (Fig. 10). No other signals are observed in spectra recorded in various temperatures. The magnetic susceptibility measurements for 4 were modeled with an exchange coupled trimer yielding an S = 3/2 ground state. The temperature behaviour of the spectra indicates that the individual spin states cannot be discriminated. The apparent anisotropy of the spectrum is lower than this anticipated for an isolated Cu II ion in a square-pyramidal geometry. Such a behaviour is observed in concentrated solid state Cu II complexes in the presence of misalignment of the local molecular axes of the copper ions [36]. Misalignment for the three copper ions is indicated from the crystal structure of 4 (Fig. 3). 4. Summary and conclusions Fig. 10. X-band EPR spectra from powdered samples of 3 and 4 at 4.2 K. EPR conditions: 3: microwave power, 0.13 mw; mod. ampl., 0.5 Gpp (Dm S = ± 1 transitions); microwave power, 2.2 mw; mod. ampl., 10 Gpp (half field transition). The half-field transition signal has been multiplied by the indicated factor; the different recording conditions have been considered. Compound 4: microwave power 0.13 mw; mod. ampl., 1.0 Gpp. Microwave frequency (9.42 GHz). The investigation of the CuCl 2 /H 2 mal/phen reaction system (H 2 mal = malonic acid) in MeOH led to the isolation of an unexpectedly large number of products. Indeed, seven complexes have been isolated, six of which have been structurally characterized, i.e. complexes [Cu(H 2 O)(phen)(mal)] (1), [Cu(MeOH)(phen)(mal)] (2), [Cu 2 Li 2 Cl 2 (phen) 2 (mal) 2 (MeOH) 4 ] (3), [Cu 2 (phen) 4 (mal)][cucl (phen)(mal)](oh) (4), [CuCl(phen) 2 ]Cl (5), and [CuCl(phen)(mal)] [CuCl(phen) 2 ][Cu(phen) 2 (Hmal)]Cl (6). Complex 7 was identified as analogous to 5 based on their superimposable IR spectra. The large variety of accessible complexes initially obtained, prompted us to study this system in greater depth and in a systematic manner. Thus, variation of the molar ratios and the crystallization methods employed, afforded compounds 1 7 either in pure form or as mixtures, indicating that all these species (and probably other, more soluble ones) exist in equilibrium in the reaction solution. Initial attempts to isolate those complexes by employing stoichiometric reactions, resulted in various mixtures of 1 7 rather than pure products. However, careful choice of stoichiometries and crystallization conditions allowed us to obtain pure products in most cases (1 4, 6). The observation that several species are present in equilibrium in solution, in ratios depending on the starting materials stoichiometries, led us to conclude that, in effect, these reaction systems constitute a set of overlapping Dynamic Combinatorial Libraries. Indeed, due to the labile nature of the metal ligand coordination bonds, complexes 1 7 should coexist in various ratios in the reaction mixtures, through a constant formation decomposition process.