10.1 Introduction 65, 66, 67 and 68) 16)

Transcription

1 362 Chapter X Interaction of metal-free maleic and fumaric acids with alkyl diamines and metallation of chiral zwitter ions leading to the formation of some novel products Abstract: This chapter deals with the study of the interaction of maleic and fumaric acids with various Lewis bases (en and dap) in metal-free state and probe the possibility of having any cis-trans isomerization. Besides the interaction can also lead to acid:diamine adducts. Since both maleic and fumaric acids are dicarboxylic acids the diamines en and dap are expected to form 1:1 type adducts/salts even if they don t interact to give any chiral zwitterions. Interestingly, we find 2:1 type adduct for maleic acid:diamine while the fumaric acid gives the anticipated 1:1 adduct whatever may be the ratio in which we try the reaction. Detailed crystal and molecular structure features of 4 different adducts (65, 66, 67, 68) formed could be carried out which showed several interesting features. Since the zwitterions we have generated through insertion reaction are essentially amino acids we attempted to derivatize them using metal salts as they can then be relevant in bio-systems and as enzyme mimics. We were able to synthesize a Ca 2+ derivative 69 and structurally characterize it through single crystal XRD. The structure reveals some novel characteristics. We were also able to generate a novel ternary type 1D polymer 70 made up of Cu +2, zwitterion 16 and fumaric acid, the fumaric acid being generated in situ by dissociation of part of the zwitter ion used. The 1D polymer has a unique paddle-wheel type configuration in which the zwitter ions act as capping ligands and fumarate moiety as connectors. The molecular and packing features of 70 is unique and unprecedented. The structural features of all the products (65-70) are presented in detail in the chapter.

2 Introduction Having observed the unprecedented reaction of [M(Hmal) 2 (H 2 O) 4 ] with alkyl amines generating novel cyclically interconnected one-dimensional coordination polymers made up of [M(mal) 2 ] 2- motifs we have been interested in probing how these two isomeric dicarboxylic acids react in their natural form with various alkyl amines. Since these two acids are structurally and chemically different because of their cis and tras configurations we thought that they would react differently with amines forming structurally dissimilar products. We have considered only alkyl diamines because both maleic and fumaric acids are dicarboxylic acids. Further, there are a few scattered reports available on these two acids reacting with aromatic diamines like 4,4 - bipyridine. 96,114 We have confined our studies on such a perspective by taking into consideration only 1,2-diaminoethane (en) and 1,3-diaminopropane (dap) as diamines which can be considered as almost similar but having difference only in the nature of - (CH 2 )- spacer lengths. In this chapter we try to consolidate all the relevant details on the nature of reaction and also the type of products obtained through the reaction of H 2 mal and H 2 fum with both en and dap and present crystal and molecular structures of some interesting adducts formed (65, 66, 67 and 68). Since the chiral zwitterions (like 16) generated during our reactions discussed earlier (Chapters IV and V) are similar to some of the important amino acids, we have also attempted to synthesize their metal derivatives to look at their structural and conformational features. An interesting Ca complex 69 formed from 23 containing two coordinated chiral zwitter ions could be made and its structural features studied through single crystal XRD. Presented in the chapter are also some details on a novel and unprecedented metal-zwitterion derivative 70 including its unique structural features. We have made use of a wide variety of experimental techniques like CHN analysis, TG, DTA, FTIR, 1 H NMR, 13 C NMR, EPR, PXRD and single crystal X-ray diffraction

3 364 studies rather extensively for the detailed characterization of all the products obtained during the transformation reactions Experimental Materials The diamines 1,2-diaminoethane and 1,3-diaminopropane were purchased from Merck KgaA. Maleic acid and fumaric acid were E. Merck (India) Limited products. All chemicals were used as received. Analytical Methods Elemental analyses (C, H and N) were performed using an Elementar Vario EL III elemental analyzer. IR spectra ( cm -1 ) were measured on a Shimadzu FTIR- 8400S spectrophotometer, where KBr was used as the dispersal medium. Thermo gravimetric analyses were carried out on a Shimadzu DTG-60 simultaneous DAT-TG apparatus. EPR spectrum was recorded in solution state in methanol on a Varian E-112 EPR spectrometer operating in X-band using DPPH as the g marker. Single crystal X- ray diffraction data were collected at 293 ± 2K on an automated Bruker axs (Kappa apex2) CCD diffractometer. Synthesis Considering the possibility of formation of different types of adducts/compounds the reaction of diamines with both maleic and fumaric acids were carried out both in 1:1 and 2:1 (acid: diamine) molar ratios. We could see that irrespective of these two acid: diamine molar ratios we start with, the composition and nature of products obtained was seen to be always dependent on the nature of the acid (maleic or fumaric acid) we have employed. In the case of maleic acid the acid: diamine ratio in the product was always 2:1 while in the case of fumaric acid it was 1:1. Therefore we have carried out the aciddiamine reaction by maintaining the respective optimum molar ratios. The specific synthetic conditions/details for each case are given below.

4 365 Maleic acid-en adduct/salt, 65 An aqueous solution (10mL) of maleic acid (0.232g, 2mmol) was mixed with an aqueous solution of (10mL) 1,2-diaminoethane (0.07mL, 1mmol). The solution was warmed on a water bath and kept aside for slow evaporation. Colourless block crystals, 65 were obtained after three days. The crystals were washed with water and dried. Yield: 80% Maleic acid-dap adduct/salt, 66 The experimental procedure employed for 66 was almost the same as above. To a 10mL of aqueous solution of maleic acid (0.232g, 2mmol) a solution of 1,3- diaminopropane (0.08mL, 1mmol, 10mL water) was added, stirred and kept for slow evaporation. Colourless block crystals of 66 obtained were collected and washed with water and dried in air. Yield: 75% Fumaric acid -en adduct/salt, 67 A methanolic solution (10mL) of fumaric acid (0.116g, 1mmol) was mixed with an aqueous solution (10mL) of 1,2-diaminoethane (0.07mL, 1mmol) under mild stirring and heating. The clear solution yielded colourless block crystals after a three days. Yield: 85% Fumaric acid - dap adduct/salt, 68 The experimental procedure was similar to the above one. In this case a methanolic solution (10mL) of fumaric acid (0.116g, 1mmol) was mixed with 10mL of aqueous solution of 1,3-diaminopropane (0.08mL, 1mmol) under heating. Colourless block crystals of 68 obtained were collected, washed with water and dried. Yield: 80% [Ca(3-pic.zwitterion) 2 (H 2 O) 2 ].4H 2 O, 69 The 3-picolinium succinate zwitterion, 23 (0.209g, 1mmol) which was obtained as a clear product through the reaction mentioned in Section was dissolved in water

5 366 by continous heating and stirring. To this aqueous solution CaCO 3 was added slowly. Brisk effervescence was seen observed in the initial stages of addition indicating that the Ca salt is reacting with the zwitterionic acid. Addition of CaCO 3 was continued till there was no effervescence. The solution was filtered and kept for crystallisation. Colourless block crystals of 69 were formed after two days. Yield: 80% [Cu 2 (fum)(zwitterion) 2 (H 2 O) 2], 70 To an aqueous solution (20mL) of pyridinium succinate zwitterion, 16 (0.195g, 1mmol) obtained as a pure product from the reaction discussed in Section 4.3.1, solid CuCO 3 was added slowly with heating and stirring till there was no evolution of effervescence. Heating was continued for half an hour and the resultant blue solution was filtered and kept for slow evaporation. Tiny prismatic blue crystals of 70 were formed after four days which were collected and washed with water and dried. Yield: 35% 10.3 Results and Discussion Since the studies covered in this chapter belong to two different aspects the results and discussion are presented under the following two main headings: (1) maleic /fumaric acid: aliphatic amine adducts/salts and (2) metal derivatives of chiral zwitterions Maleic /fumaric acid:aliphatic diamine adducts/salts We have considered the reaction of maleic acid and fumaric acids with two alkyl diamines, 1,2-diaminoethane (en) and 1,3-diaminopropane (dap) having varying lengths of -(CH 2 )- spacer moieties between the NH 2 ends to look at the nature of products formed. We wanted to probe whether there is any chance of NH 2 moiety getting inserted in the -HC=CH- double bond to form a chiral amino acid or if the diamine acts only as a base the nature and structure of the adducts formed. There could be significant difference in the nature of salt/adduct formed with maleic and fumaric acids by these diamines because of their wide structural difference. As mentioned in the preparative

6 367 section the composition of the acid-diamine products formed was dependent on the type of acid used. So we have carried out synthesis using the optimum composition needed in each case. Given in Table 10.1 are the analytical data of each of the product obtained which agree with the composition indicated. It is seen that maleic acid forms 2:1 adducts with both en and dap (65 and 66) while the composition of the fumaric acid: diamine products have 1:1 composition for both en and dap (67 and 68). Table10.1 Elemental analytical data of the maleic/fumaric acid: aliphatic amine adducts Compound (Emp.formula) Formula weight Elemental content (%) Found (Calcd.) C H N Colour and nature (solubility in water) maleic acid-en salt, 65 (Hmal -1 ) 2 (enh 2 2+ ). H 2 O (C 10 H 18 N 2 O 9 ) colourless crystals (soluble) maleic acid-dap salt, 66 (Hmal -1 ) 6 (daph 2+ 2 ). 3 H 2 O C 33 H 56 N 6 O (42.26) 6.49 (5.97) 9.00 (8.96) colourless crystals (soluble) fumaric acid-en salt, 67 (fum -2 ) (enh 2+ 2 ) C 6 H 12 N 2 O (40.86) 6.72 (6.81) (15.89) colourless crystals (soluble) fumaric acid - dap salt, 68 (fum -2 ) (daph 2 2+ ) C 7 H 14 N 2 O (44.16) 7.42 (7.36) (14.72) colourless crystals (soluble)

7 368 FTIR spectral data of 65, 66, 67 and 68 Given in Table 10.2 are some of the important IR absorption peaks of the four phase pure forms of acid-amine adducts obtained. In both 65 and 66 we could observe the presence of strong bands around 1701cm -1 indiacting the presence of free COOH groups in the maleic acid adducts. In contrast we could not find any such peaks for the fumaric acid adducts. Besides the COOH peaks in 65 and 66 the strong absorptions due to ν as (COO - ) and ν s (COO - ) were seen with a Δν value of around 200 cm -1 indicating the presence of ionic type COO - moiety. 82 In the case of fumaric acid adducts with both en and dap we could notice ν as (COO - ) and ν s (COO - ) specific vibrations around 1600 and 1400 cm -1 with a Δν value around 200 cm - 1 which also suggests the ionic nature of COO - moieties. We were able to notice ν(nh 3 + ) specific vibration peaks as a broad band below 3100 cm -1. No peaks characteristic to NH 2 group are seen in all the samples indicating that all the NH 2 moieties are in the protonated form. The broad nature and low value of 3100 cm -1 indicates that the NH + 3 groups are involved in strong H-bonding. The simultaneous presence of the characteristic peak of free COOH group at 1701cm -1 and the characteristic peaks for ν as (COO - ) and ν s (COO-) show that only one carboxyl group is deprotonated in the maleic acid salts/adducts 65 and 66. This is also clear from the molecular structures (Fig.10.1 and 10.3).This accounts for the fact that the maleic acid :diamine composition is always 2:1. In the case of fumaric acid salts (67 and 68) we could not see any COOH specific peaks which suggests that both of the carboxylate moieties are in the deprotonated form. Consequently the fumaric acid: diamine composition expected is 1:1 which is what we find from the analytical data of both 67 and 68. Further, we find ν OH (H 2 O) peaks only for the maleic acid salts (65 and 66) which are due to the H 2 O molecules present in them.

8 369 Table 10.2 IR spectral data of the acid: amine adducts (in cm -1 ) ν OH(H 2 O) ν (COOH) ν as (COO) ν s (COO) Δν ν(n-h) Thermal decomposition features ν(c-h) aliphatic TGA show that only the maleic acid salts/adducts (65 and 66) have water of crystallization while the adducts of fumaric acid with both en and dap (67 and 68) are water free. In the first thermal stage guest water is lost by about 63 C. The remaining portion of the thermograms is similar for all the four salts. The next stage is a strong endothermic loss of the amine. It is observed that the heat of loss of amine is higher for en salts (3.5 and 3.6kJ/g for 65 and 67) compared to that of dap salts (2.57 and 2.58kJ/g for 66 and 68) which shows that en may be more strongly hydrogen bonded. The last step is the decomposition of the acid which begins at about 250 C and ends at around 600 C with a broad exothermic peak in the DTA curve, with a heat of decomposition of about 20 kj/g. Structural details of the amine adducts Regardless of whether the reacting molar ratios of acid to diamine are 1:1 or 2:1, maleic acid adducts always crystallize with a 2:1 ratio of acid to diamine (for both en and dap) in the final product. However, the fumaric acid adducts have a 1:1 stoichiometry for both en and dap. We could carry out the single crystal XRD studies of all the four maleic/fumaric acid: amine salts. Discussed below are the crystal structure details in brief in

9 370 each case. Crystallographic data and details of structure refinements of the salts 65, 66, 67 and 68 are consolidated in Table Maleic acid-en salt, (Hmal - ) 2 (enh 2+ 2 ) H 2 O, 65 The colorless needle like crystals of 65 is seen to be crystallising in monoclinic form with space group Pc. The crystal data and refinement parameters are presented in Table ORTEP plot of compound 65 is given in Fig which clearly shows that only one of the carboxyl groups of the maleic acid is deprotoaned while the other remains in the COOH form itself. The packing features of monodeprotonated maleic acid (Hmal) and the relative orientations of successive Hmal moieties in the crystal are interesting which are depicted in Fig The C1-O1 bond length is shorter than C1- O2 bond length showing that the former is a double bond and hence one carboxyl group of the maleate anion is not deprotonated. C4-O3 bond is longer than C4-O4 because O3 is involved in intra-molecular hydrogen bond with O2-H. The H(1A)-N(1)-H(1C) bond angle of shows that the ammonium N is sp 3 hybridised as expected. There exist extensive H-bonding interactions among the carboxylate O, -NH + 3 and H 2 O molecules which is clear from Fig Selected bond lengths and bond angles are given in Table The extensive H-bonds are evident from Table 10.5.

10 371 Fig ORTEP view of 65 with the atom-labeling scheme (30% thermal ellipsoids). Fig H-bonding interactions involving anionic maleate, enh 2 2+ and H 2 O resulting in three-dimensionally extended network in the salt 65.

11 372 Table 10.3 Crystallographic data and structure refinements for 65, 66, 67 and Formula C10 H18 N2 O9 C33 H56 N6 O25 C6 H12 N2 O4 C7 H14 N2 O4 Mr Temperature (K) 293(2) K 293(2) K 293(2) K 293(2) K Wavelength Ǻ Ǻ Ǻ Ǻ Crystal system Monoclinic Monoclinic Triclinic Monoclinic Space group Pc P21/c P1 p21/a a (Å) (5) (3) (2) 8.011(4) b (Å) (3) (6) (2) (4) c (Å) (4) (10) (3) (19) ( ) (2) 90 β ( ) (2) (10) (2) (3) γ ( ) (2) 90 V (Å 3 ) (8) (12) (13) 957.8(5) Z dcalc Mg/m (mm -1 ) F(000) Crystal size (mm) 0.30 x 0.30 x x 0.30 x x 0.20 x x 0.2 x 0.2 range 1.53 to deg. 2.3 to to to Reflections collected Unique reflections Rint Absorption correction Max. and min. transmission Data / restraints / parameters Final R indices (I>2 (I)) Final R indices (all data) Semi-empirical from equivalents and Multi-scan and Semi-empirical from equivalents Multi-scan and and / 8 / / 3 / / 6 / 143 R1 = , wr2 = R1 = , wr2 = R1 = , wr2 = R1 = , wr2 = R1 = , wr2 = Largest diff. peak and hole (eå -3 ) and e.a^ and and GOF on F

12 373 Table 10.4 Selected bond lengths [Å] and angles [ ] for compound 65 C(1)-O(1) 1.257(9) O(4)-C(4)-O(3) 121.2(6) C(1)-O(2) 1.299(10) O(1)-C(1)-C(2) 119.6(8) C(4)-O(3) 1.319(9) N(1)-C(17)-C(18) 110.9(4) C(4)-O(4) 1.230(6) N(1)-C(17)-H(17A) O(1)-C(1)-O(2) 118.2(9) C(17)-N(1)-H(1A) H(1A)-N(1)-H(1C) H(1B)-N(1)-H(1C) Table 10.5 Selected H-Bonds [Å] and angles [ ] for compound 66 D-H...A d(d-h) d(h...a) d(d...a) <(DHA) N(1)-H(1A)...O(9)# (8) N(1)-H(1B)...O(11)# (9) N(1)-H(1C)...O(18)# (9) N(2)-H(2A)...O(14)# (8) N(2)-H(2B)...O(17) (9) N(2)-H(2C)...O(16)# (9) N(3)-H(3A)...O(4)# (8) N(3)-H(3B)...O(2) (9) N(3)-H(3C)...O(17) (8) N(4)-H(4A)...O(8)# (8) N(4)-H(4B)...O(18) (9) O(2)-H(2O)...O(3) (9) O(6)-H(6O)...O(7) (8) O(10)-H(10O)...O(12) (8) O(18)-H(18C)...O(9) 0.855(10) 1.95(2) 2.767(8) 159(5) O(17)-H(17D)...O(14)# (10) 1.97(3) 2.740(8) 151(5) O(17)-H(17C)...O(4)# (10) 2.06(3) 2.850(8) 154(5) O(18)-H(18D)...O(8)# (10) 2.06(2) 2.836(8) 153(4) O(15)-H(13O)...O(13) 0.76(3) 1.68(4) 2.416(9) 164(4) Symmetry transformations used to generate equivalent atoms: #1 x-1,-y+1,z-1/2 #2 x-1,-y+2,z-1/2 #3 x-1,y,z #4 x-1,y-1,z #5 x,-y+2,z-1/2 #6 x,y-1,z Maleic acid-dap salt, (Hmal -1 ) 6 (daph 2 2+ ) 3. H 2 O, 66

13 374 Just as 65 the maleic acid: dap adduct 66 also crystallize in monoclinic form but with a different space group P21/c. The crystal data are presented in Table 10.3 along with that of other derivatives. Both the maleic acid salts (65 and 66) have four molecular units per unit cell but the cell volume of 66 is about three times that of 65. This is evident because one molecular unit of 66 has six Hmal - moieties where as that of 65 has only two Hmal - ions (as clear from the chemical composition). Given in Fig is the ORTEP of compound 66 with atom label. The mono-deprotonated form of the maleic acid in 66 is also clear from the molecular plot. C11-C12 bond length of 1.330(3)Ǻ is shorter than C10-C11 bond length of 1.476(3)Ǻ because the former is the double bond of the maleate ion. C13-O4 of 1.231(3)Ǻ is shorter than C12-C13 of 1.473(3)Ǻ because the former is a double bond while latter is a single bond, which indicates that one of the carboxyl groups in the maleate ion is not deprotonated. O3- H3 of 1.13(4)Ǻ shows strong intra-molecular hydrogen bond. C1 - N1 - H1A bond angle of shows that the NH 2 is protonated and the N atom is converted to sp 3 hybridised. As in the case of compound 65 there exist extensive H-bonding interactions in 66 which are depicted in Fig Relevant bond lengths and angles are given in Table The extensive H-bonds are clear from Table 10.7.

14 375 Fig.10.3 ORTEP view of 66 with the atom-labeling scheme (30% thermal ellipsoids). Fig H-bonding interactions involving anionic maleate, daph 2+ 2 resulting in three-dimensionally extended network in the salt 66 and H 2 O

15 376 Table 10.6 Selected bond lengths [Å] and angles [ ] for compound 66 C1 N (3) N1 H1B C1 C (3) N1 H1C C2 C (3) O25 H25A 0.90(2) C3 N (3) O25 H25B 0.90(3) C10 O (2) O1 H3 1.31(4) C10 O (3) O3 H3 1.13(4) C10 C (3) N1 C1 C (2) C11 C (3) C3 C2 C (2) C12 C (3) C1 N1 H1A C13 O (3) C1 N1 H1B C13 O (3) H1A N1 H1B N1 H1A C1 N1 H1C Table 10.7 Selected H-Bonds [Å] and angles [ ] for compound 66 D-H...A d(d-h) d(h...a) d(d...a) <(DHA) N1 H1C O (3) N1 H1C O (3) N2 H2A O (2) O3 H3 O1 1.13(4) 1.31(4) 2.433(2) 171(4) O5 H7 O7 1.04(5) 1.38(5) 2.415(3) 174(4) O11 H11 O9 0.96(3) 1.49(3) 2.443(3) 170(3) N1 H1A O (2) N1 H1B O (2) N2 H2C O (2) N3 H3A O (3) O25 H25A O9 0.90(2) 1.841(8) 2.726(3) 167(3)4 O25 H25B O6 0.90(3) 2.041(4) 2.939(3) 176(3)4 Fumaric acid - en salt, (fum -2 ) (enh 2 2+ ), 67

16 377 Crystal data and structure refinement parameters of 67 are consolidated in Table It is seen that while the two maleic acid adducts (65 and 66) crystallise in monoclinic system the fumaric acid-en salt is formed in triclinic system with P1 space group. It is also interesting to see that this compound has the smallest cell volume compared to the other three acid: amine salts. This is because only one molecular unit is present per unit cell. Contrary to the maleic acid salts, the fumaric acid salt has an acid: amine ratio 1:1 which is clear from the ORTEP of 67 as given in Fig This is expected because in the salts of fumaric acid both carboxyl groups can be deprotonated since there is no intra-molecular hydrogen bond due to the transconfiguration. The en entity adopts a trans configuration in order to facilitate H-bonding interactions with the fumarate dianion, which is also clear from the ORTEP. The difference in the C-O bond lengths is due to the difference in the number of hydrogen bonds attached to the O atoms of the carboxyl groups. H-bonds are represented in Fig C2-C3 distance of 1.32Ǻ is the characteristic double bond length. All the ammonium hydrogens are equivalent. H(1A)-N(1)-H(1C) bond angle of is consistent with the tetrahedral geometry of the -NH 3 group. Relevant bond lenghts and angles are given in Table 10.8 and H-bonds are presented in Table Packing features of 67 are illustrated in Figs. 10.7, 10.8 and 10.9.

17 378 Fig.10.5 ORTEP view of 67 with the atom-labeling scheme (30% thermal ellipsoids). Fig.10.6 H-bonding interactions involving anionic fumarate, and (enh 2 2+ ), resulting in the three-dimensionally extended network in 67.

18 379 Fig Linear chain of fumarate units and the sandwiched ethylene diamonium cations. (view along c axis). Fig.10.8 Network of H-bonds. (only some H-bonded cites are shown for clarity). View along a axis.

19 380 Fig The 3D network due to H-bonding interactions in 67 Table 10.8 Bond lengths [Ǻ] and angles [ ] for 67. C(1)-O(2) 1.251(3) N(1)-H(1B) C(1)-O(1) 1.258(3) N(1)-H(1C) C(4)-O(4) 1.234(3) O(2)-C(1)-O(1) 123.0(3) C(4)-O(3) 1.275(2) C(2)-C(3)-C(4) (12) C(1)-C(2) 1.496(3) O(4)-C(4)-O(3) 124.4(3) C(2)-C(3) (11) N(1)-H(1A) N(1)-C(5)-H(5A) N(1)-C(5)-C(6) (16) H(1A)-N(1)-H(1C) 109.5

20 381 Table 10.9 H-bonds for 67 [Ǻ and deg.] D-H...A d(d-h) d(h...a) d(d...a) <(DHA) N(1)-H(1A)...O(3)# (3) N(1)-H(1B)...O(3)# (3) N(1)-H(1C)...O(4)# (3) N(2)-H(2A)...O(1)# (3) N(2)-H(2B)...O(2)# (3) N(2)-H(2C)...O(2)# (3) Symmetry transformations used to generate equivalent atoms: #1 x,y,z-1 #2 x-1,y,z-1 #3 x-1,y-1,z-1 #4 x+1,y,z #5 x+1,y-1,z #6 x,y-1,z Fumaric acid:dap salt, (fum -2 ) ((daph 2+ 2 ), 68 Eventhough the en salt of fumaric acid (67) crystallises in triclinic system the dap salt of fumaric acid (68) is formed in monoclinic system as in the case of the two maleic acid: amine salts. One unit cell of 68 contains four molecules and the space group is p21/a. The crystal data and structure refinement parameters have been presented in Table As in the case of fumaric acid:en salt, the molar ratio of fumaric acid:dap salt is also 1:1 which is clear from the molecular picture in Fig The dideprotonated nature of fumaric acid and the protonated form of the NH 2 groups also are clear in the ORTEP. The sp 3 hybridised nature of N in NH 3 is evident from the tetrahedral bond angles, the slight distortions are due to H-bonds. The H-bonding interactions and packing features are given in Fig a and b. Bond lengths and angles are presented in Table

21 382 Fig ORTEP view of 68 with the atom-labeling scheme (30% thermal ellipsoids). a Fig (a) and (b) H-bonding interactions involving anionic fumarate, and daph 2 2+ resulting in the 3D extended network in salt 68. b

22 383 Table Bond lengths [Ǻ] and angles [deg] for 68 C(1)-N(1) 1.480(2) N(2)-H(4N) (11) C(1)-C(2) 1.506(2) C(4)#1-C(4)-C(5) (19) C(4)-C(4)# (3) O(2)-C(5)-C(4) (15) C(4)-C(5) 1.495(2) H(1N)-N(1)-H(2N) 108(2) C(5)-O(2) 1.243(2) H(1N)-N(1)-H(3N) 112(2) C(5)-O(1) 1.272(2) H(2N)-N(1)-H(3N) 107(2) Symmetry transformations used to generate equivalent atoms: #1 -x+3,-y,-z+2 #2 -x+3,-y,-z Metal derivatives of zwitterions As mentioned in Chapter IV and V the pyridinium zwitterions, which contain an active COOH, can be utilized for coordination to metal centers to generate MOCNs or coordination compounds. Since the zwitterions are essentially amino acids their metallated forms can be of relevance in biological context and also as useful biomimics. Even though we have tried to synthesise the metal derivatives of the three zwitterions (16, 23 and 25) with various metals like Mn, Co, Ni, Cu and Zn we could not get totally phase pure form of the derivative through conventional route. However we were successful to get one of the Ca derivatives (69) in phase pure form and as good quality crystals. Similarly yet another ternary type zwitterion product 70 incorporating a chiral zwitterion and fumarate ion coordinated to Cu ion could be successfully synthesized. Given below are the synthetic and structural details of the compounds including their crystal and molecular structures. [Ca(3-pic zwitterion) 2 (H 2 O) 2 ]. 4H 2 O, 69 The preparative details of the compound are discussed already. While the zwitterion itself and its other metal derivatives are not easy to crystallize we were able

23 384 to get the Ca product 69 as good quality colorless needle like crystals rather easily. Elemental analytical data of 69 are consistent with a composition [Ca(3-pic zwitterion) 2 (H 2 O) 2 ]. 4H 2 O. The CHN data and the nature of the metal-zwitterion derivative 69 is given in Table Table Elemental analytical data of 69 and 70 Compound (Emp. formula) Formula weight Elemental content (%) Found (calcd.) C H N Colour and nature (solubility in water) [Ca(3-piczwitterion) 2 (H 2 O) 2 ]. 4H 2 O, 69 (Ca C 20 H 32 N 2 O 14 ) (42.51) 5.43 (5.67) 4.21 (4.25) colourless crystals (soluble) [Cu 2 (fum)(zwitterion) 2 (H 2 O) 2 ], 70 (Cu 2 C 22 H 22 N 2 O 14 ) blue crystals (sparingly soluble) FTIR spectral data of 69 and 70 Given in Table are the IR stretching vibrations seen for various characteristic groups in 69. The Ca derivative has its ν as (COO - ), ν s (COO - ) and Δν values 1566, 1380, 186 cm -1 respectively which suggests the mono-dentate coordination mode of the carboxylate group of both of its zwitterion moieties. There are also H 2 O specific vibrations seen for the compound at 3232 and 3402 cm -1 indicating the presence of both coordinated and guest type H 2 O molecules. This could be confirmed from both TGA and also crystal structure studies.

24 385 Table10.12 FTIR spectral data of the metal derivatives of the zwitterions, 69 and 70 compounds νoh(h2o) νas(coo) νs(coo) Δν ν(m-o) ν(c-h) aromatic ν(c-h) aliphatic ν(c-c), ν(c-n) ring stretch Ring deformation of pyridine Structural characterization of [Ca(3-pic zwitterion) 2 (H 2 O) 2 ]. 4H 2 O, 69 Structural details: Compound 69 has the composition [Ca(3-pic zwitterion) 2 (H 2 O) 2 ]. 4H 2 O. The compound crystallizes in monoclinic form with space group P2/n. The crystal data along with structural refinement details are given in Table Given in Fig is the ORTEP plot of 69 which clearly shows the η 1 mode of the carboxylate groups of the zwitterion to the Ca 2+ ion. Interestingly the Ca 2+ ion is seen in CaO 6 octahedral environment. A closer look at the coordinating moieties on the Ca 2+ ion (Fig 10.13a) shows that there are in fact four carboxylate moieties coordinated to a single metal ion along with two H 2 O molecules. Further, all the four carboxylate moieties coordinated to a single metal uion come from for different zwitterions. The resulting geometry of CaO 6 is distorted octahedron. The two oxygens situated in the opposite corners of the

25 386 Table Crystallographic data and structure refinements for 69 and Empirical formula Ca C 20 H 32 N 2 O 14 Cu 2 C 22 H 22 N 2 O 14 Formula weight Temperature 293(2) K 293(2) K Wavelength Ǻ Ǻ Crystal system Monoclinic Triclinic space group P2/n P-1 a (Å) (4) (5) b (Å) (4) (6) c (Å) (5) (6) ( ) (4) β ( ) (2) (3) γ ( ) (3) Volume (9) (7) A^3 Z 2 1 Calculated density Mg/m^ Mg/m^3 Absorption coefficient mm^-1 F(000) 338 Theta range for data collection 2.18 to deg. Reflections collected unique R(int) Absorption correction Semi-empirical from equivalents Max. and min. transmission and Refinement method Full-matrix leastsquares on F^2 Data / restraints / parameters 7282 / 12 / 373 Goodness-of-fit on F^ Final R indices [I>2sigma(I)] R1 = , wr2 = R indices (all data) R1 = , wr2 = Largest diff. peak and hole R1 = , wr2 = R1 = , wr2 = and e.a^-3

26 387 octahedron are from two coordinated water molecules (Fig and 10.13a). Even though there are four carboxylate groups coordinated to a Ca 2+ ion the overall charge appears to be compensated because one of the COO- moieties of the zwitterions 23 is always with a -1 charge (which is internally charge compensated by +1 charge on the pyridinium moiety) and it is this COO- moiety which is coordinated to the Ca 2+ ion along with the deprotonated COOH group. Thus there are two deprotonated COOH and two originally present COO- moieties coordinated to each Ca 2+ ion along with two H 2 O molecules. Because four different zwitter ionic moieties are coordinated to Ca 2+ ion the bonding and crystal packing is such that they form neatly arranged 2D layers (Fig 10.13b). There are four lattice water molecules also per molecule of 69 which participate in inter-chain hydrogen bonding interactions through both coordinated and lattice H 2 O molecules or between the water and the carboxylate ions (Fig a). The Ca-O bond distances in 69 are in the range (9) (11)Å. Crystal parameters, selected bond lengths and bond angles are listed in Table 10.13, and respectively. Fig ORTEP of 69 with atom label.

27 388 Table Selected bond lengths [Å] and angles [ ] for 69 C(1)-O(2) (16) C(8)-C(9) (19) C(1)-O(1) (15) C(8)-C(10) 1.500(2) C(1)-C(2) (16) C(9)-N(1) (17) C(2)-N(1) (15) O(1)-Ca(1) (9) C(2)-C(3) (18) O(1W)-Ca(1) (11) C(3)-C(4) (17) O(3)-Ca(1)# (9) C(4)-O(3) (16) Ca(1)-O(1)# (9) C(4)-O(4) (17) Ca(1)-O(3)# (9) C(5)-N(1) (16) Ca(1)-O(3)# (9) C(5)-C(6) 1.375(2) Ca(1)-O(1W)# (11) C(7)-C(8) 1.391(2) O(2)-C(1)-C(2) (11) O(1)-Ca(1)-O(1)# (5) O(1)-C(1)-C(2) (11) O(1)-Ca(1)-O(3)# (4) N(1)-C(2)-C(3) (10) O(1)#2-Ca(1)-O(3)# (4) N(1)-C(2)-C(1) (10) O(1)-Ca(1)-O(3)# (4) C(3)-C(2)-C(1) (10) O(1)#2-Ca(1)-O(3)# (4) C(4)-C(3)-C(2) (11) O(3)#3-Ca(1)-O(3)# (6) O(3)-C(4)-O(4) (12) O(1)-Ca(1)-O(1W)# (5) C(5)-N(1)-C(2) (10) O(1)#2-Ca(1)-O(1W)# (4) C(9)-N(1)-C(2) (10) O(3)#3-Ca(1)-O(1W)# (4) C(1)-O(1)-Ca(1) (9) O(3)#1-Ca(1)-O(1W)# (4) C(4)-O(3)-Ca(1)# (9) O(1)-Ca(1)-O(1W) 98.91(4) Symmetry transformations used to generate equivalent atoms: #1 -x+2,-y,-z+1 #2 -x+3/2,y,-z+1/2 #3 x-1/2,-y,z-1/2

28 389 Fig a (a) Coordination environment of Ca ion and H-bonds and (b) bridging of Ca ions by the COO - groups of 23 to form 1D chains in 69. b Table Hydrogen bonds [Å] and angles [ ] for 69 D-H...A d(d-h) d(h...a) d(d...a) <(DHA) O(2W)-H(2A)...O(4) 0.893(9) 1.853(11) (17) 168(2) O(2W)-H(2B)...O(2W)# (10) 1.99(4) 2.787(2) 148(6) O(3W)-H(3D)...O(2) 0.895(10) 1.865(10) (19) 177(3) O(1W)-H(1A)...O(2W)# (9) 1.922(10) (16) 172.5(19) O(1W)-H(1B)...O(4)# (9) 1.878(10) (16) 161.9(19) Symmetry transformations used to generate equivalent atoms: #1 -x+2,-y,-z+1 #2 -x+3/2,y,-z+1/2 #3 x-1/2,-y,z-1/2 #4 -x+5/2,y,-z+1/2

29 Structural characterization of [Cu 2 (fum)(zwitterion) 2 (H 2 O) 2, 70 It is interesting to note that even though we carried out reactions of Cu 2+ salt (CuCO 3 ) with zwitter ion 16 in hot aqueous condition in almost 1:2 ratio both analytical, spectral and crystal structure data clearly indicated the ternary nature of the compound with fumarate ion as an additional and surprising constituent. The analytical data (Table ) and FTIR spectra clearly showed the presence of the fumarate moiety along with the zwitterions in the compound. The ν as (COO - ), ν s (COO - ) and Δν values of the compound also indicated that carboxylate moieties are acting as bridging bidentate moieties characteristic of paddle-wheel type structure for the compound. 19 The important vibrations are listed in Table We were able to get good quality blue needle like single crystals for the compound 70 which is seen crsyallising in triclinic form with P-1 space group. Crystal data and structure refinement parameters are given in Table Given in Fig is the ORTEP plot of the compound which shows the presence of both zwitter ion and fumarate moiety. The copper atoms have a five-coordinate square pyramidal environment (Fig ). The basal plane is defined by four oxygen atoms from two distinct fumarate carboxylato groups and two pyridinium succinate zwitterions. The apical position is occupied by H 2 O molecule. The coordination environment consists of tetracarboxylate-bridged dimetallic paddle-wheel secondary building units (SBUs). The asymmetric unit consists of one copper atom, one pyridinium succinate zwitterion, half of fumarate ligand and one water molecule. The copper atom is in a distorted square pyramidal environment [Cu1-O 1.950(6)-2.095(6)Ǻ, Cu Cu (4)Ǻ]. The fumarate ligands bridge the copper ions to form a 1D chain (Fig.10.15). These chains are connected by hydrogen bonds between the coordinated water molecules and the free carboxylate groups of the zwitterions to form a 3D network (Fig ). Bond lengths and angles are given in Table Selected H-bonds are summarized in Table

30 391 It has been very surprising matter for us how a fumarate moiety was incorporated in 70 in addition to 16 while we carried out reaction of Cu 2+ salt with only chiral zwitterion 16. In fact we carried out the complexation reaction in hot aqueous condition. Since fumarate moiety in 70 can come only from the zwitterions, we heated a suspension of zwitter ion 16 in aqueous condition for a few hours and checked whether the zwitter ion remains still stable. Analysis of the product obtained after heating in aqueous condition showed that the compound obtained after heating has turned to a product mixture containing the original zwitter ion ad fumaric acid. We could also notice the evolution of pyridine during the reaction. This clearly indicates the partial instability of the zwitter ion in hot aqueous condition. Since the zwitter ion can be considered as a product formed by the insertion of pyridine in either fumaric acid or maleic acid, heating it in aqueous condition may be causing the reverse reaction thereby generating fumaric acid in solution. Therefore we believe that fumarate moiety which is contained in 70 must have been generated through pyridine expulsion from part of the zwitterions taken for the reaction. In any case we believe that compound 70 is very novel and unprecedented ternary type paddle-wheel type compound the design of which has not been done or reported so far.

31 392 Fig ORTEP view of 70 with the atom-labeling scheme (30% thermal ellipsoids). a Fig b (a) and (b) The 1D chain of 70 showing the paddle wheel arrangement of the ligating atoms.

32 393 a Fig (a) and (b) The 3D network of hydrogen bonds in 70 b Table Bond lengths [Ǻ] and angles [deg] for 70 Cu(1)-Cu(2) (4) O(9)-Cu(1)-O(3) 167.5(3) O(9)-Cu(1) 1.970(7) O(11)-Cu(1)-O(5) 96.2(3) O(3)-Cu(1) 1.985(6) O(12)-Cu(2)-O(6) 99.8(3) O(10)-Cu(2) 1.965(6) O(10)-C(18)-O(9) 126.9(8) O(4)-Cu(2) 1.963(6) O(3)-C(9)-O(4) 124.7(7) O(5)-Cu(1) 2.095(6) O(13)#2-Cu(1)-O(11) 167.6(3) O(6)-Cu(2) 2.145(7) O(13)#2-Cu(1)-O(9) 91.9(3) O(11)-Cu(1) 1.950(6) O(5)-Cu(1)-Cu(2) (16) O(12)-Cu(2) 1.950(7) O(12)-Cu(2)-O(14)# (3) O(4)-Cu(2)-O(10) 166.8(3) O(12)-Cu(2)-Cu(1) 83.7(2) Symmetry transformations used to generate equivalent atoms: #1 x,y-1,z #2 x,y+1,z

33 394 Table H-bonds for 70 [Ǻ and deg.]. D-H...A d(d-h) d(h...a) d(d...a) <(DHA) O(5)-H(5A)...O(2)# (9) 2.14(2) 2.924(10) 153(3) O(5)-H(5B)...O(7)# (9) 2.039(15) 2.871(9) 168(4) O(6)-H(6A)...O(7)# (10) 2.16(6) 2.808(9) 133(6) O(6)-H(6B)...O(2)# (10) 1.84(4) 2.595(9) 146(7) O(6)-H(6B)...O(14)# (10) 2.796(18) 2.993(10) 94.9(11) Symmetry transformations used to generate equivalent atoms: #1 x,y-1,z #2 x,y+1,z #3 x+1,y,z-1 #4 x-1,y,z #5 x-1,y,z+1 #6 x+1,y,z EPR spectrum of [Cu 2 (fum)(zwitterion) 2 (H 2 O) 2, 70 We have made some attempt to look at the bonding features of 70 by measuring EPR spectrum in methanolic solution at liquid nitrogen temperature. The spectrum shows four aniosotropic hyperfine splittings which is characteristic of Cu 2+ ion (Fig ). The EPR spin-hamiltonian parameters of the compound are evaluated assuming axial symmetry and using DPPH as the g markerthe. The values are :A = 9mT, H = 309.5mT, A = 5.66mT, H = 320.7mT, g = 2.14, g = 2.06, g iso = 2.08, G=2.38, α 2 = The low A value of 9mT shows that Cu is not octahedrally coordinated by the ligands. g > g > 2 indicates tetragonally elongated Cu(II) complex and also indicates that the unpaired electron resides in the d 2 2 x - y orbital. The fact that g < 2.3 indicates the covalent nature of the complex. G value less than 4, indicates a strong ligand field. Similarly the low value (0.4524) of inplane σ covalency parameter α 2 shows that the metal- ligand bond has a high covalent character.

34 Intensity GAUSS Fig X-band EPR spectrum of a methanolic solution of 70 in LNT. Summary and conclusion Relevant details on the nature of reaction and also the type of products obtained through the reaction of maleic acid and fumaric acid with both en and dap have been presented. Crystal and molecular structures of some interesting adducts also have been discussed. An interesting Ca complex formed from 3-picoline zwitterion containing two coordinated chiral zwitter ions could be made and its structural features studied through single crystal XRD. Presented in the chapter are also some details on a novel and unprecedented metal-zwitterion derivative 70 including its unique structural features. We have made use of a wide variety of experimental techniques like CHN analysis, TG, DTA, FTIR, 1 H NMR, 13 C NMR, EPR, PXRD and single crystal X-ray diffraction studies rather extensively for the detailed characterization of all the products obtained during the transformation reactions.