New metal organic frameworks and supramolecular arrays assembled with the bent ditopic ligand 4,4-diaminodiphenylmethane

Transcription

1 PAPER CrystEngComm New metal organic frameworks and supramolecular arrays assembled with the bent ditopic ligand 4,4-diaminodiphenylmethane Lucia Carlucci, a Gianfranco Ciani,* a Davide M. Proserpio a and Francesca Porta b Received 8th May 2006, Accepted 19th July 2006 First published as an Advance Article on the web 1st August 2006 DOI: /b606482e Twelve novel coordination polymers and supramolecular architectures have been obtained using the bent ditopic ligand 4,49-diaminodiphenylmethane (dadpm) and different metal salts (chlorides and nitrates), and their structures have been elucidated by single crystal X-ray analysis. The new products include some examples of simple zigzag chains, as in [MCl 2 (dadpm)] [M 5 Co (1); M 5 Cd (2)] and [Ag(NO 3 )(dadpm)] (3). The chains are connected via weaker interactions (H-bonds or contacts with the anions) to give 2-D layers. In [Ni(H 2 O) 2 (dadpm) 2 ]Cl 2 (4) the polymeric 1-D chains consist of parallel ribbons of rings with the non-coordinated chloride anions generating a 3-D architecture via NH Cl bonds. Noteworthy, compound 5a, [Ni(H 2 O) 2 Cl 2 (dadpm) 2 ], has an identical composition but a different structure, thus representing a novel case of supramolecular isomerism: it contains mononuclear octahedral complexes, with two trans coordinated H 2 O molecules, two trans Cl anions and two trans monodentate dadpm ligands. The dangling ends of the dadpm ligands, however, form H-bonds with the H 2 O molecules coordinated on adjacent complexes, thus giving rise to double-stranded chains resembling the ribbons of rings present in 4. Compound 5b, [Mn(H 2 O) 2 Cl 2 (dadpm) 2 ], is isomorphous with 5a and also compound 6, [Ni(H 2 O) 2 (NO 3 ) 2 (dadpm) 2 ], shows a similar structure. Compounds [MCl 2 (dadpm)] [M 5 Cd (7); M 5 Mn (8)] are isostructural, but not isomorphous, and contain single 3-D networks with the ths (ThSi 2 ) topology. In compound 9, [CdCl 2 (dadpm)], complex 2-D layers of (6,3) topology are observed. The structure of [Cd 3 Cl 6 (dadpm) 2 ](10) is comprised of complex Cd/Cl chains inter-connected by double bridging dadpm ligands to give a 3-D network with the cds (CdSO 4 ) topology (or, alternatively, the cds-a augmented topology). In [Ag(dadpm) 3 ](NO 3 )(11) the Ag centres are octahedrally coordinated by six bridging dadpm ligands, resulting in a 3-D network with the pcu (a-po) topology. It is worth mentioning that three compounds (2, 7 and 9, of composition [CdCl 2 (dadpm)]) show a remarkable case of supramolecular isomerism. Introduction The rational design of coordination polymers is of great current interest both for the potential applications of these networked organic inorganic materials, 1 like gas storage, molecular selection, ion exchange and catalysis, and also for their intriguing architectures, topologies and entanglement phenomena. 2 The synthesis of such species is often based on the self-assembly of suitable building blocks to give supramolecular networks assembled by covalent and hydrogen bonds or other weaker interactions. The programmed building of these extended structures cannot yet be fully realized, though it is possible to get some control on the products by a careful choice of the metal ion, the geometry and length of the organic ligand and the orientations of the ligand donor groups. Ligands containing pyridine and other aromatic bases as donors have been widely used and were shown to produce relatively stable networks, while aromatic bridging ligands with NH 2 donor groups are less frequently employed. This is a Dipartimento di Chimica Strutturale e Stereochimica Inorganica, Università di Milano, Via G. Venezian 21, Milano, Italy b Dipartimento CIMA, Via G. Venezian 21, Milano, Italy related to a certain instability of the ligands as well as to the poorer donor ability of the amine groups towards the metal centres. On the other hand, the lability of the metal N interactions can allow for easy rearrangements in the selfassembly, that could lead to unprecedented motifs, and can also result in cases of supramolecular isomerism. The bent ditopic ligand 4,49-diaminodiphenylmethane (dadpm) was previously used to produce few monomers and cyclic oligomers 3 and some polymeric species, with 4 or without 5 the additional involvement of bridging anions. In this paper we report on the self-assembly reactions of dadpm with some metal(ii) chlorides, with Ni(NO 3 ) 2 and with AgNO 3. Complex mixtures are often obtained in these reactions and we have been able to isolate and structurally characterize twelve new products showing a variety of motifs, including simple chains, 1-D ribbons of rings, 2-D layers, and 3-D single networks with the ths (ThSi 2 ), the cda (CdSO 4 ) and the pcu (a-po) topology. The role of the anions is fundamental in most of these species, since they are directly involved in coordination to the metal centres and, acting as bridges, in the formation of the networks. As expected some examples of supramolecular isomers 6 have been observed within these products. 696 CrystEngComm, 2006, 8, This journal is ß The Royal Society of Chemistry 2006

2 Results and discussion The reactions of the dadpm ligand with many metal salts were carried out in polar solvents using different metal to ligand ratios. A variety of products, as crystalline materials, were obtained by slow evaporation of the reaction mixtures (see the list in Table 1). The bulk precipitates in some cases contain more than one species, as evidenced by the analysis of the X-ray powder diffraction (XRPD) patterns compared with the single crystal data, indicating that the formation of a specific product is driven by subtle factors and some competitive paths leading to different species (with a different or the same stoichiometry) are often possible. This is particularly true for the reactions of dadpm with Ni(II) chloride and Cd(II) chloride (hydrated salts). By slightly changing the reaction conditions different species (some unidentified) have been observed in the former case by XRPD on the bulk precipitates. Single crystals of compounds 4 and 5a have been isolated from samples obtained by slow diffusion of an ethanolic solution of the metal salt into a CHCl 3 solution of the ligand with a reagent ratio of 1 : 2. Ni(II) nitrate hydrated, reacted with dadpm in the ratio 1 : 2, gives a bulk precipitate containing a mixture of compound 6 and of the previously reported species trans [Ni(H 2 O) 2 - (dadpm) 4 ](NO 3 ) 2?2H 2 O, 3a as evidenced by XRPD. The reactions of Cd(II) chloride with dadpm were previously attempted unsuccessfully, a fact ascribed to the poor coordination ability of the ligand. 4a On the contrary we report here on four different Cd(II) products (compounds 2, 7, 9 and 10), three of which have the same composition. All four species are observed together in the XRPD pattern of the precipitate obtained by evaporating the reaction solution prepared with an excess of dadpm. We were able to find syntheses for all these products but one (compound 9). Thus we have observed that the main product obtained at room temperature in the 1 : 1 metal to ligand ratio is compound 2, while compound 7 can be recovered in good yield only at very low temperature Table 1 List of the products and their structural types No. Formula Structural motifs 1 [CoCl 2 (dadpm)] Zigzag chains linked by H-bonds into 2-D layers 2 [CdCl 2 (dadpm)] Zigzag chains linked by anions into 2-D layers 3 [Ag(NO 3 )(dadpm)] Zigzag chains linked by anions into 2-D layers 4 [Ni(H 2 O) 2 (dadpm) 2 ]Cl 2 Ribbons of rings 5a [Ni(H 2 O) 2 Cl 2 (dadpm) 2 ] Monomers joined by H-bonds into ribbons of rings 5b [Mn(H 2 O) 2 Cl 2 (dadpm) 2 ] Monomers joined by H-bonds into ribbons of rings 6 [Ni(H 2 O) 2 (NO 3 ) 2 (dadpm) 2 ] Monomers joined by H-bonds into ribbons of rings 7 [CdCl 2 (dadpm)] Single 3-D network with the ths topology 8 [MnCl 2 (dadpm)] Single 3-D network with the ths topology 9 [CdCl 2 (dadpm)] 2-D layers of (6,3) topology 10 [Cd 3 Cl 6 (dadpm) 2 ] 3-D network with the cds (or the cds-a) topology 11 [Ag(dadpm) 3 ](NO 3 ) Single 3-D network with the pcu topology (see Experimental). Compound 10 is obtained in essentially pure form on using the correct metal to ligand 3 : 2 ratio. Few crystals of 9 were serendipitously observed, together with all the other cadmium species, in a precipitate obtained on drying the reaction mixture prepared using a 1 : 6 metal to ligand ratio in methanol/chloroform. The reaction of AgNO 3 with dadpm in the ratio 1 : 1 affords [Ag(NO 3 )(dadpm)] (3) while the use of a high excess of the ligand gives the 3-D network [Ag(dadpm) 3 ](NO 3 )(11). Description of the structures All the isolated single crystal species are stable in the air and have been charaterized by X-ray analysis (see Table 2). Selected bond distances and angles are given in Table 3. Simple 1-D chains and their supramolecular interactions in compounds 1 3. Some of the products, of composition [MCl 2 - (dadpm)] [M 5 Co (1); M 5 Cd (2)] and [Ag(NO 3 )(dadpm)] (3), contain simple 1-D parallel chains, with the metal atoms connected by single dadpm ligands. In 1 (see Fig. 1, top) the metal atoms display a slightly flattened tetrahedral coordination [Co N 2.052(3), Co Cl 2.249(1) Å; N Co N 117.2(2), Cl Co Cl 115.1(1), N Co Cl (1)u]. The chains have a period corresponding to the dadpm bridged Co Co contact ( Å, the a axis). Noteworthy the bent ligands (having rigorous C 2v symmetry) in all the chains are disposed by the same side, thus creating a polar axis (the b axis) in the crystal, belonging to the non-centrosymmetric space group Im2m. The chains are close packed along the b axis direction [4.425(1) Å] due to the formation of hydrogen bonds involving the Cl atoms of one chain and the NH 2 groups of an adjacent chain (Cl N 3.36 Å). Thus 2-D layers are formed (see Fig. 2) that are stacked along the c axis with an ABAB sequence. The structure is similar to that previously reported for [CdI 2 (dadpm)], 4a that crystallizes in the same space group. The 1-D chains in 2 are similar (Fig. 1), looking moderately winding when viewed from the top (see the comparison of 2 vs, 1 in Fig. 3), due to a somewhat different ligand conformation (C 2 symmetry). The chain period is somewhat longer than in 1 and equal to the dadpm bridged Cd Cd contact (13.39 Å, coincident with the a axis). The lengthening is mainly related to the increased metal dimensions [see e.g. Cd N 2.272(2) Å] but also to the different coordination geometry of the Cd atoms. In this case the two chlorides bound to a metal atom of one chain show additional weaker interactions with a metal atom of an adjacent chain (semi-bridging interactions, Cd Cl (5) Å vs. Cd Cl (6) Å, thus originating a 2-D layer similar to that observed in 1 but with a shorter interchain metal metal distance of vs Å (see Fig. 2). The Cd atoms display a distorted octahedral coordination geometry, as evidenced by the bond angles: N Cd N (8)u, Cl Cd Cl 89.94(3)u, Cl Cd Cl 71.20(2)u, N Cd Cl (5)u, N Cd Cl 75.46(4) 76.04(5)u, Cl Cd Cl 99.43(2)u, Cl Cd Cl (2)u. Asymmetric halogen bridges were found also in [CdI 2 (dadpm)], 4a Cd I 2.794(3) and Cd I Å (ratio long/short contact 1.28 vs in 2). Curiously the crystal structure of 2, in spite of the chemical similarity, differs from that of [CdI 2 (dadpm)] (as well as from This journal is ß The Royal Society of Chemistry 2006 CrystEngComm, 2006, 8,

3 Table 2 Crystallographic data for compounds a 5b Formula C 13 H 14 Cl 2 - C 13 H 14 - C 13 H 14 - C 26 H 32 Cl 2 - C 26 H 32 Cl 2 - C 26 H 32 Cl 2 - C 26 H 32 - C 13 H 14 - C 13 H 14 - C 13 H 14 - C 26 H 28 Cd 3 - C 39 H 30 - CoN 2 CdCl 2 N 2 AgN 3 O 3 N 4 NiO 2 N 4 NiO 2 MnN 4 O 2 N 6 NiO 8 CdCl 2 N 2 Cl 2 MnN 2 CdCl 2 N 2 Cl 6 N 4 AgN 7 O 3 M System Orthorhombic Monoclinic Orthorhombic Monoclinic Triclinic Triclinic Triclinic Triclinic Monoclinic Triclinic Monoclinic Rhombohedric Space group Im2m (44) P2/c (13) Pcca (54) P21/c (14) P1 (2) P1 (2) P1 (2) P1 (2) C2/c (15) P1 (2) C2/c (15) R3 c (167) a/å (1) (1) (3) (3) 5.660(1) 5.691(1) 5.837(3) 8.678(2) (1) 6.444(1) (2) (1) b/å 4.425(1) 4.293(1) 4.453(1) (3) 9.323(3) 9.500(1) 9.424(5) (3) 8.767(1) (2) 8.101(1) (1) c/å (1) (1) (1) 9.153(2) (4) (2) (5) (3) (1) (2) (1) (1) a/u (2) (1) (4) 85.50(1) (1) b/u (1) (1) 93.39(2) 92.72(1) 98.08(4) 77.33(1) 91.22(1) 95.87(1) 99.46(1) 90 c/u (2) (1) (4) 82.58(1) (1) U/Å (7) (8) (3) (6) 632.3(3) (14) 660.9(5) (6) (2) 764.0(2) (4) (3) Z Density/g cm m(mo Ka)/mm Reflections collected Indep. refls, R(int) 622, , , , , , , , , , Observed [Fo. 4s(Fo)] R1 [Fo. 4s(Fo)] wr2 (all data) that of 1) in that it is centrosymmetric. The three structures contain similar polar 2-D layers, but in 2 adjacent layers show opposite polarity and exhibit also inter-layer Cl H N bridges (Cl N 3.61 Å, see Fig. 3, bottom). The structure of compound 3 consists of zigzag chains of Ag atoms bridged by dadpm ligands (Ag Ag Å) with a period of Å (equal to the a axis); m-nitrate-k 2 O anions bridge adjacent chains (Ag Ag Å, see Fig. 4) giving 2-D layers of (4,4) topology, that stack along c with an AAA sequence. Both the Ag atoms and the dadpm ligands lie on two-fold crystallographic axes. The metal coordination geometry is distorted linear [Ag N 2.197(7) Å, N Ag N 155.1(4)u], showing two additional weak contacts with oxygen atoms of the nitrates [Ag O 2.669(8) Å]. Hydrogen bond bridges of the type N H O(nitrate) are present in the above 2-D layers and also join the layers into a 3-D architecture. Double-stranded chains: supramolecular isomerism for compounds 4 and 5a. The structure of compound 4, [Ni(H 2 O) 2 - (dadpm) 2 ]Cl 2, consists of double-stranded chains all running along the a direction, that can be described as ribbons of rings (see Fig. 5, top). The adjacent metal centres are linked by two dadpm ligands and exhibit Ni Ni contacts of Å (coincident with the length of the a axis). The Ni atoms, lying on inversion centres, show octahedral coordination geometry, with four equatorial links to NH 2 groups of dadpm ligands [Ni N 2.144(4) 2.201(4) Å] and two axial water molecules [Ni O 2.066(4) Å]. The chloride anions are uncoordinated but form H-bond bridges (the shortest ones involving the coordinated water molecules and other ones the NH 2 groups of the dadpm ligands) that join the chains into a 3-D array (see Fig. 6). Within the coordination polymers assembled with the dadpm ligand these 1-D independent chains are unique, though they were previously observed in the species [Cd(dadpm) 2 X](dca) (X 5 Cl, Br; dca 5 dicyanamide anion) 4a linked by the halides into 2-D layers via Cd X Cd linear bridges. However the ribbons of rings represent a rather common type of coordination polymer. Therefore the main interest for 4 does not consist in its topology but rather in that it is a supramolecular isomer of compound 5a, [Ni(H 2 O) 2 Cl 2 (dadpm) 2 ], illustrated in Fig. 5, bottom. Compound 5a is a mononuclear octahedral complex and the Ni atom, lying on an inversion centre, is bound to two trans monodentate dadpm ligands [Ni N 2.103(5) Å], two trans water molecules [Ni O 2.062(4) Å] and two trans chlorides [Ni Cl 2.457(2) Å]. The isomorphous species 5b, [Mn(H 2 O) 2 Cl 2 (dadpm) 2 ], is the manganese analogue of 5a, and exhibits somewhat longer bond distances [Mn N 2.292(2), Mn O 2.180(2), Mn Cl 2.543(1) Å]. A similar complex, [Cd(H 2 O) 2 (CH 3 COO) 2 (dadpm) 2 ], was previously reported. 3c In 5a the uncoordinated NH 2 groups of the two dadpm ligands form hydrogen bond bridges with the water molecules coordinated on adjacent complexes (N O Å), thus generating 1-D parallel ribbons of rings (Fig. 5) sustained both by coordinative and H-bonds, all running along the [111] direction. The rings are enlarged with respect to 4 and the adjacent metals exhibit longer Ni Ni contacts ( Å). The 698 CrystEngComm, 2006, 8, This journal is ß The Royal Society of Chemistry 2006

4 Table 3 Selected bond distances (Å) and angles (u) for compounds 1 11 Compound 1 Co N (3) Co Cl (12) N1 Co N (2) Cl Co Cl (7) N1 Co Cl (5) Compound 2 Cd N (15) Cd Cl (5) Cd C l (6) N1 Cd N (8) Cl Cd Cl 71.20(2) Cl Cd Cl 89.94(3) N1 Cd C (5) N1 Cd Cl (5) N1 Cd Cl (4) Cl Cd Cl (16) Cl Cd Cl (16) Compound 3 Ag N (7) Ag O (8) N1 Ag N (4) O12 Ag O (4) N1 Ag O (3) N1 Ag O (3) Compound 4 Ni O (4) Ni N (4) Ni N (4) N1 Ni N N2 Ni N O Ni O O Ni N (16) O Ni N (16) O Ni N (16) O Ni N (16) N2 Ni N (16) N2 Ni N (16) Compound 5a Ni OW (4) Ni N (5) Ni Cl (17) N1 Ni N O1W Ni O1W Cl Ni Cl O1W Ni N (19) O1W Ni N (19) O1W Ni Cl (13) O1W Ni Cl (13) N1 Ni Cl (15) N1 Ni Cl (15) Compound 5b Mn O1W (19) Mn N (2) Mn Cl (7) Cl Mn Cl O1W Mn O1W N1 Mn N O1W Mn N (8) O1W Mn N (8) O1W Mn Cl (6) O1W Mn Cl (6) N1 Mn Cl (6) N1 Mn Cl (6) Compound 6 Ni O1W (3) Ni N (3) Ni O (3) O1W Ni O1W N1 Ni N O33 Ni O O1W Ni N (11) O1W Ni N (11) O1W Ni O (11) O1W Ni O (10) N1 Ni O (12) N1 Ni O (12) Compound 7 Cd1 N (16) Cd1 N (16) Cd1 Cl (6) Cd1 Cl (7) Cd1 Cl (6) Cd1 Cl (8) Cd2 N (16) Cd2 N (16) Cd2 Cl (6) Cd2 Cl (6) Cd2 Cl (7) Cd2 Cl (7) N2 Cd1 N (6) N2 Cd1 Cl (5) N1 Cd1 Cl (4) N2 Cd1 Cl (4) N1 Cd1 Cl (5) Cl2 Cd1 Cl (2) N2 Cd1 Cl (5) N1 Cd1 Cl (4) Cl2 Cd1 Cl (14) Cl1 Cd1 Cl (2) N2 Cd1 Cl (4) N1 Cd1 Cl (4) Cl2 Cd1 Cl (19) Cl1 Cd1 Cl (17) Cl3 Cd1 Cl (19) N3 Cd2 N (6) N3 Cd2 Cl (4) N4 Cd2 Cl (5) N3 Cd2 Cl (5) N4 Cd2 Cl (4) Cl4 Cd2 Cl (2) N3 Cd2 Cl (4) N4 Cd2 Cl (5) Cl4 Cd2 Cl (15) Cl1 Cd2 Cl (2) N3 Cd2 Cl (4) N4 Cd2 Cl (4) Cl4 Cd2 Cl (17) Cl1 Cd2 Cl (2) Cl3 Cd2 Cl (17) Compound 8 Mn N (15) Mn N (15) Mn Cl (5) Mn Cl (5) Mn Cl (5) Mn Cl (5) N2 Mn N (6) N2 Mn Cl (4) N1 Mn Cl (4) N2 Mn Cl (4) N1 Mn Cl (4) Cl1 Mn Cl (18) N2 Mn Cl (4) N1 Mn Cl (4) Cl1 Mn Cl (16) Cl3 Mn Cl (17) N2 Mn Cl (4) N1 Mn Cl (4) Cl1 Mn Cl (16) Cl3 Mn Cl (13) Cl2 Mn Cl (13) Compound 9 Cd N (3) Cd N (3) Cd Cl (8) Cd Cl (9) Cd Cl (9) Cd Cl (8) N2 Cd N (10) N2 Cd Cl (7) N1 Cd Cl (7) N2 Cd Cl (8) N1 Cd Cl (7) Cl1 Cd Cl (3) N2 Cd Cl (7) N1 Cd Cl (7) Cl1 Cd Cl (3) Cl2 Cd Cl (3) N2 Cd Cl (7) N1 Cd Cl (7) Cl1 Cd Cl (2) Cl2 Cd Cl (3) Cl1 Cd Cl (3) Compound 10 Cd1 N (3) Cd1 N (3) Cd1 Cl (8) Cd1 Cl (8) Cd1 Cl (8) Cd1 Cl (9) Cd2 Cl (8) Cd2 Cl (8) Cd2 Cl (9) N2 Cd1 N (11) N2 Cd1 Cl (8) N1 Cd1 Cl (7) N2 Cd1 Cl (8) N1 Cd1 Cl (7) Cl2 Cd1 Cl (3) N2 Cd1 Cl (8) N1 Cd1 Cl (8) Cl2 Cd1 Cl (3) Cl3 Cd1 Cl (3) N2 Cd1 Cl (8) N1 Cd1 Cl (8) Cl2 Cd1 Cl (3) Cl3 Cd1 Cl (3) Cl1 Cd1 Cl (3) Cl3 Cd2 Cl (4) Cl1 Cd2 Cl (4) Cl2 Cd2 Cl (4) Cl3 Cd2 Cl (3) Cl3 Cd2 Cl (3) Cl3 Cd2 Cl (3) Cl2 Cd2 Cl (3) Cl2 Cd2 Cl (2) Cl3 Cd2 Cl (2) Compound 11 Ag N (2) N1 Ag N1 90, 180 chains are linked into 2-D layers by hydrogen bond bridges of the type Cl HO(water) (Cl O Å), illustrated in Fig. 7. Compounds 4 and 5a have the same formula and can be considered supramolecular isomers, though the chlorides play a varied role in the two species. Supramolecular isomerism was observed in many examples within coordination polymers and different classes have been previously envisaged. 6 In this case, by analogy with the isomeric complexes of the inner and outer coordination sphere, we could define these compounds as supramolecular constitutional isomers. This journal is ß The Royal Society of Chemistry 2006 CrystEngComm, 2006, 8,

5 Fig. 1 The polymeric single chain observed in compounds 1 (top) and 2 (bottom). Fig. 4 The 2-D layers in compound 3, evidencing the bridging nitrates. Fig. 5 The double-stranded chains in compounds 4 (sustained exclusively by coordinative bonds) and 5a (based both on coordinative and hydrogen bonds). The different role of the Cl anions is also shown. Fig. 2 Two views of the 2-D layers in compounds 1 and 2 formed by weak supramolecular interactions joining the chains. Fig. 6 The packing of the 1-D motifs in compound 4. The Cl H N hydrogen bond bridges connect the ribbons into a 3-D architecture. Fig. 3 Top views of the 1-D chains in 1 and 2. H-bond contacts are depicted as broken lines. The related mononuclear species trans [M(H 2 O) 2 (dadpm) 4 ] (NO 3 ) 2?2H 2 O (M 5 Ni, 3a Co, 3b and Cd 3c ) contain four equatorial monodentate dadpm ligands instead of the two in 5a, and give rise via hydrogen bond interactions to 3-D architectures. In order to ascertain the effects of the variation of the anion we have also prepared and characterized compound 6, [Ni(H 2 O) 2 (NO 3 ) 2 (dadpm) 2 ], that exhibits a structure very Fig. 7 The packing of the ribbons of rings in compound 5a. similar to that of 5a (see Fig. 8). Along the chains the Ni Ni contacts are Å. The chains form again 2-D layers via H-bond bridges of the type (nitrate)o HO(water) (O O Å). 700 CrystEngComm, 2006, 8, This journal is ß The Royal Society of Chemistry 2006

6 Fig. 8 A single ribbon of rings showing the terminally bonded nitrates (top) and the packing of the ribbons (bottom) in compound 6. Single 3-D networks with the ths (ThSi 2 ) topology in compounds 7 and 8. Compounds [CdCl 2 (dadpm)] (7) and [MnCl 2 (dadpm)] (8) are isostructural, but not isomorphous. There are small structural variations that seem mainly related to the different metal ion radii (see Table 3) and those give rise to different crystallographic parameters (see Table 2). We will discuss here in detail only the structure of the cadmium species 7. The structure contains [Cd(m-Cl) 2 ] n chains (see Fig. 9) all running parallel, in the direction of the b axis. The metal atoms [Cd(1) and Cd(2)] show very similar distorted octahedral environments, each interacting with four m-bridging chlorides [Cd Cl bonds in the range (6) (8) Å] and two cis m-dadpm ligands [Cd N bonds in the range 2.373(2) 2.388(2) Å]. The [Cd(m-Cl) 2 ] n chains are laterally connected via Cd(m-dadpm) 2 Cd double bridges (see Fig. 9), thus generating a 3-D single network. Assuming as nodes the Cd atoms and as edges both the longer Cd(m-dadpm) 2 Cd [Cd(1) Cd(1) , Cd(2) Cd(2) Å] and the markedly shorter Cd(m-Cl) 2 Cd interactions [Cd Cd in the range Å) the network shows the ths topology (Schläfli symbol 10 3, Vertex symbol ), 7 schematically illustrated in Fig. 10. Fig. 10 Schematic picture of the ths network in 7. A cage is evidenced in red and one [Cd(m-Cl) 2 ] n chain in blue. If compared with the ideal network in its highest symmetry, this net is drastically distorted so that no channels or free voids are left. The use of the program TOPOS 2e,f,8 not only provides the correct topology but also gives structural information on the nature of the circuits (10-membered rings). There are four distinct types of 10-gons, implying different numbers of long (L) dadpm bridged and short (S) Cl-bridged edges and different numbers of Cd(1) and Cd(2) atoms: 10a (LSLSSLSLSS) with 6 Cd(1) and 4 Cd(2), 10b (LSSSSLSSSS) with 6 Cd(1) and 4 Cd(2), 10c (same sequence as 10b) with 4 Cd(1) and 6 Cd(2), 10d (same sequence as 10a) with 4 Cd(1) and 6 Cd(2) (see Fig. 11). These, obviously, are structural and not topological differences. The complex 2-D (6,3) framework of [CdCl 2 (dadpm)] (9). Compound 9 consists of 2-D layers containing Cd ions as nodes. The metal coordination is distorted octahedrally, with four Cd Cl bonds [range 2.570(1) 2.694(1) Å] and two cis Cd N bonds [2.360(3) 2.392(3) Å]. The chloride anions are bridging and give rise to zizag chains [Cd(m-Cl) 2 ] n (see Fig. 12, bottom), with Cd Cd contacts of and Å and Cd Cd Cd angles of 121.7u. Fig. 9 A view showing one [Cd(m-Cl) 2 ] n chain, connected through double dadpm bridges to four adjacent chains in compound 7. Cd1 and Cd2 are related to Cd1* and Cd2* by inversion centres. Fig. 11 Two of the four distinct 10-membered rings observed in the ths network of 7 (see text). This journal is ß The Royal Society of Chemistry 2006 CrystEngComm, 2006, 8,

7 Table 4 Compound Selected structural parameters for the Cd/dadpm species M M dadpm bridged/å N N/Å [N C N/u] M N N M torsions/u (single bridge) 9.27 [107.6] [120.8] [114.3] [114.2] [121.3] Fig. 12 Comparison of the [Cd(m-Cl) 2 ] n chains in compounds 2, 7 and 9. At right the metal chains are schematically depicted approximatelly along the direction of propagation. Fig. 13 Top and side views of a (6,3) layer in compound 9. The chains are side linked by double dadpm bridges (Cd Cd contacts Å), thus resulting in 2-D layers with the (6,3) topology (see Fig. 13). The six membered rings contain four (m-cl) 2 edges and two (m-dadpm) 2 edges. The layers stack along the [0 21 1] direction with an ABAB sequence. The free voids, located in the channels running in the direction of the c axis (see Fig. 13, bottom) represent 8.5% of the cell volume. It is worth comparing in more detail the structure of 9 with that of compounds 2 and 7, since the three polymeric species have the same formula [CdCl 2 (dadpm)] but show different structures with different network topologies. Thus they can be considered true supramolecular topological isomers. All contain parallel [Cd(m-Cl) 2 ] n chains that show variated structures, with the Cd atoms disposed on a line in 2, ina zigzag fashion in 9 but in a more complex way (i.e. tracing a figure of eight ) in 7 (see Fig. 12, right). The flexibility of the dadpm ligand can account for this structural variety. In Table 4 some structural parameters for the cadmium species here reported are compared. Since, as stated previously, the reactions of CdCl 2 with dadpm usually give mixtures of the products many attempts were carried out in order to drive the process towards a specific compound, as well as to interconvert them by thermal activation. Thus we have observed that on heating a methanolic solution of compound 7 at 60 uc for 2 h leads to a progressive transformation into compound 2 (as confirmed by XRPD). No reverse transformation (from 2 to 7) is observed on lowering the temperature. TGA monitoring of compound 2 in the range uc shows a weight loss of ca. 17% (attributed to 1/3 of the ligands) in the range uc, followed by a second weight loss of ca. 35% (due to the remaining 2/3 of the ligands) in the range uc to produce pure CdCl 2. The XRPD spectra recorded after the first loss clearly show the formation of compound 10, described below. The 3-D networked structure of [Cd 3 Cl 6 (dadpm) 2 ] (10) with a cds related topology. The structure of compound 10 is again comprised of parallel Cd/Cl chains, all running in the direction of the c axis, but in this case the chain stoichiometry is different. They are formed by fused centrosymmetric clusters, illustrated in Fig. 14, containing two types of Cd atoms, in distorted octahedral coordinations. One type, Cd(1), is bound to two (m-cl) [2.5309(8), (8) Å], two (m 3 -Cl) [2.6785(8), (9) Å] and two (m-dadpm) ligands [2.350(3), 2.351(3) Å], the latter ones in cis position, while the other metal atom, Cd(2) (lying on a twofold crystallographic axis), is exclusively bound to chloride ions, namely four (m-cl) [2.5586(8), (8) Å] and two (m 3 -Cl) [2.7079(9) Å]. The two types of metals are present in the ratio 2 : 1. Similar M 4 Cl 6 clusters were observed previously in some molecular species and also as subunits of polymeric chains. 9,10 As already suggested for the tetranuclear cluster, 10 considered as a fragment of a layered structure of the CdCl 2 type, we could also recognize the entire chain of 10 as a portion of such a layer ideally extracted from the solid by the dadpm ligands (see Fig. 15). Fig. 14 The Cd/Cl chains of clusters (top) and a single cluster (bottom) in compound 10. Cd1 and Cd2 are related to Cd1* and Cd2* by inversion centres. 702 CrystEngComm, 2006, 8, This journal is ß The Royal Society of Chemistry 2006

8 Fig. 15 A layer of the CdCl 2 structure type with a chain like that in 10 evidenced in yellow. Fig. 16 The side bridges connecting the chains in compound 10. The chains are linked to adjacent chains by double (m-dadpm) bridges, as illustrated in Fig. 16. The subtended Cd Cd contacts are Å long. These interchain links generate a single 3-D network that can be described in different ways according to the different choice of the nodes. Using as nodes the barycentres of the clusters we obtain a net with the cds (CdSO 4 type) topology (see Fig. 17, top). Otherwise, selecting as nodes the Cd(1) atoms and the triple bridging Cl(1) atoms we obtain a 3-connected network of the cds-a topology (augmented CdSO 4 ), shown in Fig. 17 (middle), that can be compared with the ideal net in its highest symmetry illustrated in Fig. 17 (bottom). The pcu (a-po) structure of [Ag(dadpm) 3 ](NO 3 ) (11). Within the compounds described here compound 11 shows the highest ligand to metal ratio (3 : 1). Each silver ion (placed on a 3 special position) exhibits an unusual octahedral coordination, 11 being bound to six dadpm ligands with a propeller disposition and Ag N bond lengths of 2.555(2) Å (see Fig. 18, top). A 3-D 6-connected network is thus formed that has the pcu topology. The network is not interpenetrated since the cages are strongly compressed along the 3-fold crystallographic axis of the rhombohedral cell: so the structural type results in a highly distorted a-po cage, with cage angles changed from 90 to 111.8u and 68.1u. A single molecular cage, exhibiting edges of Å and body diagonals of (one) vs Å (three), is shown in Fig. 18, middle. A schematic view of the network is illustrated in Fig. 18, bottom; disordered nitrate anions, lying on 32 special positions (a of Wykoff), are located in the centers of the cages. Conclusions The twelve coordination compounds here described include different structural motifs with variated dimensionality and topology. This variety seems related to a certain flexibility of the dadpm ligands which display a wide range of different relative orientations of the NH 2 donor groups. The lability of the metal N interactions and the easy rearrangements that can Fig. 17 The schematic network with the cds (CdSO 4 ) topology in compound 10 (top), the alternative topological description, namely cds-a, i.e. augmented CdSO 4 topology (middle) and the ideal cds-a net in its highest symmetry (bottom). occur around the metal centres favour the formation of supramolecular isomers. In particular, the finding of three polymeric species with the same composition, namely [CdCl 2 (dadpm)] (compounds 2, 7 and 9), but quite different structural motifs is particularly notewhorthy. The topological analysis of the ths networks of 7 and 8 shows that computeraided approaches (like the use of TOPOS) can be also useful in revealing structural details that are otherwise overlooked. The anions play an important role in determining the whole architecture in many of these species. Moreover, it is worth mentioning the intriguing topology observed in compound 10 and the unusual 6-coordination for silver atoms in compound 11. The structural features observed within these products can, therefore, contribute to increase our knowledge about the interactions of metal centres with polytopic amine-donor ligands in the crystal engineering of extended architectures. Experimental General procedures and materials All reagents and solvents employed were commercially available, high-grade purity materials (Aldrich or Fluka), used This journal is ß The Royal Society of Chemistry 2006 CrystEngComm, 2006, 8,

9 [CdCl 2 (dadpm)] (2). dadpm (17.2 mg; mmol) dissolved in methanol (4 ml) was added to a suspension of CdCl 2.5/2H 2 O (20.2 mg; mmol) in methanol (2 ml). The reaction mixture was refluxed at 60 uc for about 2 h, then cooled at room temperature and filtered in air. The collected white solid was washed with methanol and dried under vacuum. (Yield: 96%). Single crystals of 2 were obtained by slow diffusion of a dichloromethane solution of the ligand into a methanolic solution of the metal salt in the molar ratio 1 : 1. Calc. for C 13 H 14 CdCl 2 N 2 : C 40.92; H 3.70; N 7.34%; Found: C 41.03; H 3.92; N 7.35%. [Ag(NO 3 )(dadpm)] (3). An ethanolic solution (6 ml) of dadpm (93,1 mg, mmol) was added under stirring to an aqueous solution (5 ml) of AgNO 3 (79.8 mg; mmol). A white precipitate formed immediately. After stirring for several hours the mixture was filtered in air, and the collected white microcrystalline solid was washed with ethanol and dried under vacuum. (Yield: 95%). Single crystals of 3 were obtained, together with single crystals of 11, by the slow diffusion method from an aqueous solution of the metal salt and an ethanolic solution of the ligand in the 1 : 3 molar ratio. Calc. for C 13 H 14 AgN 2 O 3 : C 42.41; H 3.83; N 11.41%; Found: C 42.78; H 3.94; N 11.67%. Fig. 18 The silver coordination environment (top), a single molecular cage of the network (middle) and the schematic pcu net (bottom) in compound 11. as supplied, without further purification. Elemental analyses were carried out at the Microanalytical Laboratory of the University of Milan. The purity of the bulk microcrystalline materials obtained from the syntheses was checked by XRPD analyses. All the powder patterns were collected on a Philips PW1820 diffractometer in the range 5 35u of 2h. Thermal analyses were carried out on a Perkin-Elmer DSC 7 and TGA 7 under nitrogen flux with an heating rate of 10 uc min 21. Synthesis of the complexes [CoCl 2 (dadpm)] (1). The dadpm ligand (25.3 mg; mmol) dissolved in 3 ml of a methanolic solution was added under stirring to 3 ml of a solution of the same solvent of CoCl 2?6H 2 O (30.2 mg; mmol). Almost immediately a blue precipitate was formed. The mixture was left to react for 2 h more, and then the microcrystalline blue solid was collected by filtration in the air, washed with methanol, chloroform and dried under vacuum. (Yield: 87%). Single crystals were obtained by the slow diffusion method from a chloroform solution of the ligand and an ethanolic solution of the metal salt in the 1 : 1 ratio. Calc. for C 13 H 14 Cl 2 CoN 2 : C 47.59; H 4.30; N 8.54%; Found: C 48.40; H 4.53; N 8.45%. [Ni(H 2 O) 2 (dadpm) 2 ]Cl 2 (4) and [Ni(H 2 O) 2 Cl 2 (dadpm) 2 ] (5a). Many attempts have been performed to obtain compounds 4 and 5a as bulk pure materials but always without success. The solvent system, concentration and temperature were changed while using always the same 1 : 2 metal to ligand ratio. Different unidentified species have been evidenced by XRPD analysis. Compound 4 was observed together with unidentified species in a reaction carried out by adding to a methanolic solution (20 ml) of NiCl 2.6(H 2 O) 2 (24.16 mg; mmol) 20.3 mg (0.203 mmol) of dadpm. On mixing the two reagents the reaction mixture remained clear and was left to stand at room temperature for several days. After slow solvent evaporation a pale-green precipitate was observed containing a small amount of 4 as evidenced by XRPD analysis. Single crystals of compounds 4 and 5a were obtained by a slow diffusion method of an ethanolic solution of the metal in a solution of the ligand in chloroform in the ratio 1 : 2. [Mn(H 2 O) 2 Cl 2 (dadpm) 2 ] (5b). A methanolic solution (3 ml) of dadpm (117.5 mg; mmol) was added to 3 ml of a methanolic solution of MnCl 2?4H 2 O (58.6 mg; mmol). The reaction mixture remained clear on mixing and was stirred for several hours. The solvent was allowed to evaporate in the air almost to dryness leaving a brown precipitate which was almost completely re-dissolved by dichloromethane. The solution was separated from the solid residue by filtration and the clear filtrate was slowly evaporated in the air obtaining a yellow brown microcrystalline material which was recovered on a Buckner washed with small amounts of methanol and dried under vacuum. The nature of the bulk material as pure 5b was checked by XRPD. (Yield: 78%). Single crystals were obtained by slow evaporation of a methanolic solution of the ligand and the metal salt in the 2:1 molar ratio. Calc. for 704 CrystEngComm, 2006, 8, This journal is ß The Royal Society of Chemistry 2006

10 C 26 H 32 Cl 2 MnN 4 O 2 : C 55.92; H 5.78; N 10.03%; Found: C 56.09; H 5.99; N 10.93% [Ni(H 2 O) 2 (NO 3 ) 2 (dadpm) 2 ] (6). A methanolic solution (3 ml) of dadpm (167.6; mmol) was added under stirring to Ni(NO 3 ) 2?H 2 O (122.9 mg; mmol) dissolved in 2 ml of methanol. The reaction colour became green-blue and in 2 3 h a green precipitate separated from the reaction mixture. The reaction mixture was filtered in the air and the clear filtrate was left to stand. After solvent evaporation a green solid was formed which was collected on a Buchner and washed with a small portion of methanol and dried under vacuum. XRPD analysis reveals that this solid is a mixture of 6 and the already known compound [Ni(H 2 O) 2 (dadpm) 4 ] (NO 3 ) 2 (H 2 O) 2 4a in about 60/40% ratio. A mixture of single crystals of the two above species was obtained by slow diffusion of a methanolic solution of the metal salt into a chloroform solution of the ligand in the 1 : 2 molar ratio. [CdCl 2 (dadpm)] (7). This compound was obtained at 230 uc utilizing a bath of dry ice and acetone. To a cold suspension of CdCl 2?5/2H 2 O (100.2 mg; mmol) in methanol (8 ml) dadpm (87.1 mg; mmol) dissolved in methanol (3 ml) was added. The suspension was left to react at 230 uc for several hours and then filtered in air. The collected white solid was washed with methanol and dried under vacuum. This solid contained single crystals of 7 suitable for X-ray diffraction. The purity of the bulk material was checked by XRPD. (Yield: 86%). Calc. for C 13 H 14 CdCl 2 N 2 : C 40.92; H 3.70; N 7.34%; Found: C 41.97; H 3.76; N 7.39%. [MnCl 2 (dadpm)] (8). dadpm (100.4 mg; mmol) dissolved in 4 ml of acetonitrile was added under stirring to a methanolic solution (2 ml) of MnCl 2?4H 2 O (100.3 mg; mmol). The mixture was left to react at room temperature for about 2 h. During this time a pale-yellow precipitate was formed which was recovered by filtration, washed with methanol, acetonitrile and dried under vacuum. The nature of this solid as compound 8 was verified by XRPD. (Yield: 84%). Single crystals were obtained by slow evaporation of the mother solution mixture at room temperature. Calc. for C 13 H 14 Cl 2 MnN 2 : C 48.18; H 4.35; N 8.64%; Found: C 48.38; H 4.49; N 8.66%. [CdCl 2 (dadpm)] (9). Single crystals suitable for diffraction analysis were obtained by the slow diffusion method of a methanolic solution (6 ml) of CdCl 2?5/2H 2 O (13.9 mg, mmol) into a dichloromethane solution (4 ml) of the ligand (75.2 mg; mmol). Despite many attempts were performed on varying the reaction conditions it was not possible to get pure microcrystalline samples of 9. [Cd 3 Cl 6 (dadpm) 2 ] (10). A solution of dadpm (16.9 mg; mmol) in CH 2 Cl 2 was added, under stirring, to a methanolic (7 ml) solution of CdCl 2?5/2H 2 O (37.3 mg; mmol). A white precipitate formed almost immediately. The reaction mixture was left to stir overnight and then filtered on a Buchner. The collected white solid was washed with small amounts of dichloromethane and dried under vacuum. XRPD analysis confirms the purity of this bulk material. (Yield: 50%). Single crystals were obtained by the slow diffusion method into a chloroform solution of the ligand of a solution (mixture of acetonitrile/methanol/water) of the metal salt in the 1 : 2 molar ratio. Calc. for C 26 H 28 Cd 3 Cl 6 N 4 : C 32.99; H 2.98; N 5.92%; Found: C 33.12; H 3.01; N 5.99%. [Ag(dadpm) 3 ](NO 3 ) (11). To an ethanolic solution (6 ml) of AgNO 3 (31.3 mg; mmol) a 12-fold excess of dadpm (437.9 mg; 2.21 mmol) dissolved in 30 ml of ethanol was added. The reaction mixture was left to react at room temperature for about 2 h. During this time compound 11 precipitated as a white solid which was recovered by filtration in air, washed with a small amount of ethanol and dried under vacuum. (Yield: 91%). Single crystals of 11 were obtained, together with single crystals of 3, by the slow diffusion method of an ethanolic solution of the ligand into an aqueous solution of the metal salt in the 3 : 1 molar ratio. Calc. for C 39 H 30 AgN 7 O 3 : C 62.24; H 4.02; N 13.03%; Found: C 62.58; H 4.53; N 12.92%. Crystallography The crystal data for all compounds are listed in Table 2. The data collections were performed at room temperature (Mo Ka l Å). Compounds 5a and 6 were collected by the v-scan method on an Enraf-Nonius CAD4 diffractometer, while all the other ones on a SMART-CCD Bruker diffractometer. Empirical absorption correction were applied to all data: y-scan for 5a and 6 and SADABS 12 for the remainder. The structures were solved by direct methods (SIR97) 13 and refined by full-matrix least-squares on F 2 (SHELX-97) 14 with WINGX interface. 15 All hydrogen atoms were placed in geometrically calculated positions and thereafter refined using a riding model with U iso (H) 5 1.2U eq (C). Anisotropic thermal parameters were assigned to all the nonhydrogen atoms. All the diagrams were performed using the TOPOS 8 program. The accessible free voids were calculated by PLATON. 16 For compound 1 an acentric space group was found and the handedness of the crystal was determined by testing the two enantiomeric models with a final refined Flack parameters of 0.15(3). Orientationally disordered nitrate anions were found in 11 and a suitable disorder model was refined. CCDC reference numbers For crystallographic data in CIF or other electronic format see DOI: /b606482e Acknowledgements This work was supported by MIUR within the PRIN 2004 Crystal engineering of molecule-based materials and their utilization in gas absorption and solvent-free reactions. References 1 (a) N. W. Ockwig, O. Delgado-Friederichs, M. O Keeffee and O. M. Yaghi, Acc. Chem. Res., 2005, 38, 176; (b) S. Kitagawa, R. Kitaura and S. I. Noro, Angew. Chem., Int. Ed., 2004, 43, 2334; (c) C. Janiak, Dalton Trans., 2003, 2781; (d) S. L. James, Chem. Soc. Rev., 2003, 32, 276; (e) O. R. Evans and W. Lin, Acc. Chem. Res., 2002, 35, 511; (f) A. N. Khlobystov, A. J. Blake, This journal is ß The Royal Society of Chemistry 2006 CrystEngComm, 2006, 8,

11 N. R. Champness, D. A. Lemenovskii, A. G. Majouga, N. V. Zyk and M. Schröder, Coord. Chem. Rev., 2001, 222, 155; (g) A. K. Cheetham, G. Ferey and T. Loiseau, Angew. Chem., Int. Ed., 1999, 38, 3269; (h) A. J. Blake, N. R. Champness, P. Hubberstey, W. S. Li, M. A. Withersby and M. Schröder, Coord. Chem. Rev., 1999, 183, (a) S. R. Batten and R. Robson, Angew. Chem., Int. Ed., 1998, 37, 1461; (b) S. R. Batten, CrystEngComm, 2001, 3, 67; (c) L. Carlucci, G. Ciani and D. M. Proserpio, Coord. Chem. Rev., 2003, 246, 247; (d) L. Carlucci, G. Ciani and D. M. Proserpio, CrystEngComm, 2003, 5, 269; (e) V. A. Blatov, L. Carlucci, G. Ciani and D. M. Proserpio, CrystEngComm, 2004, 6, 377; (f) I. A. Baburin, V. A. Blatov, L. Carlucci, G. Ciani and D. M. Proserpio, J. Solid State Chem., 2005, 178, 2452; (g) L. Öhrström and K. Larsson, Molecule-Based Materials: The Structural Network Approach, Elsevier, Amsterdam, (a) Y. Zhang, Z. Lei, L. Jianmin, M. Nishiura and T. Imamoto, J. Mol. Struct., 2001, 559, 55; (b) K. J.Nordell, K. N. Schultz and D. Smith, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2004, 60, m857; (c) R. Wang, M. Hong, J. Weng, R. Cao, Y. Liang and Y. Zhao, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2001, 57, m344; (d) R.-H. Wang, L. Han, Z.-Z. Lin, J.-H. Luo and M.-C. Hong, Chin. J. Struct. Chem., 2004, 23, 403; (e) Z.-Z. Lin, F.-L. Jiang, L. Chen and M.-C. Hong, Chin. J. Struct. Chem., 2004, 23, 993; (f) R.-H. Wang, M.-C. Hong, J.-H. Luo, R. Cao and J.-B. Weng, Eur. J. Inorg. Chem., 2002, 3097; (g) Y. Zhang, M. Nishiura, Li Jianmin, D. Wei and T. Imamoto, Inorg. Chem., 1999, 38, 825; (h) H.-X. Zhang, Z.-N. Chen, K.-B. Yu and B.-S. Kang, Inorg. Chem. Commun., 1999, 2, (a) J. Luo, M. Hong, R. Wang, R. Cao, Q. Shi and J. Weng, Eur. J. Inorg. Chem., 2003, 1778; (b) H.-X. Zhang, B.-S. Kang, Z.-Y. Zhou, A. S. C. Chan, Z.-N. Chen and C. Ren, J. Chem. Soc., Dalton Trans., 2001, (a) X.-L. Zhi, W.-H. Zhang, Y. Zhang and J.-P. Lang, Acta Crystallogr., Sect. C: Cryst. Struct. Commun., 2004, 60, m554; (b) X.-L. Zhi, W.-H. Zhang, Y. Zhang, Y. Xu, J.-X. Chen, Z.-G. Ren and J.-P. Lang, Chin. J. Inorg. Chem., 2005, 21, B. Moulton and M. J. Zaworotko, Chem. Rev., 2001, 101, (a) O. Delgado-Friedrichs, M. D. Foster, M. O Keeffe, D. M. Proserpio, M. M. J. Treacy and O. M. Yaghi, J. Solid State Chem., 2005, 178, 2533; (b) O. Delgado-Friedrichs and M. O Keeffe, J. Solid State Chem., 2005, 178, (a) V. A. Blatov, A. P. Shevchenko and V. N. Serezhkin, J. Appl. Crystallogr., 2000, 33, 1193; (b) V. A. Blatov, Crystallogr. Rev., 2004, 10, See e.g.: C. J. Carmalt, A. C. Newport, I. P. Parkin, A. J. P. White and D. J. Williams, J. Chem. Soc., Dalton Trans., 2002, 4055; E. Babaian-Kibala and F. A. Cotton, Acta Crystallogr., Sect. C: Cryst. Struct. Commun., 1991, 47, 1716; F. A. Cotton and M. Shang, J. Am. Chem. Soc., 1988, 110, 7719; O. Fuhr and D. Fenske, Z. Anorg. Allg. Chem., 2000, 626, H. Zhao, R. Clerac, J.-S. Sun, X. Ouyang, J. M. Clemente-Juan, C. J. Gomez-Garcia, E. Coronado and K. R. Dunbar, J. Solid State Chem., 2001, 159, See e.g.: L. Carlucci, G. Ciani, D. M. Proserpio and A. Sironi, Angew. Chem., Int. Ed. Engl., 1995, 34, G. M. Sheldrick, SADABS: Siemens Area Detector Absorption Correction Software, University of Goettingen, Germany, A. Altomare, M. C. Burla, M. Camalli, G. Cascarano, C. Giacovazzo, A. Guagliardi, A. G. Moliterni, G. Polidori and R. Spagna, J. Appl. Crystallogr., 1999, 32, G. M. Sheldrick, SHELX-97, University of Goettingen, Germany, L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, A. L. Spek, J. Appl. Crystallogr., 2003, 36, CrystEngComm, 2006, 8, This journal is ß The Royal Society of Chemistry 2006