Cu(II) and Ni(II) complexes of n (2 hydroxybenzyl) amino acid ligands synthesis, structures, properties and catecholase activity 3

Chapter Cu(II) and Ni(II) Complexes of reduced Schiff base Ligands containing Additional Functional Groups in the Amino Acid side chain 175 Chapter 3-1. Introduction Having a simple amino acid side chain in the reduced Schiff base ligand made this to be an effective tridentate ligand and the carbonyl oxygen is able to bind intermolecularly to the neighboring metal ions to produce interesting coordination polymeric structures.1a Presence of additional reactive functional groups on the amino acid side chain of the ligand that are available to bind metal ions intermolecularly will be more interesting. Indeed, Cu(II) complexes of the H2Shis ligand form cyclic trimer. Two such trimers form molecular capsule hosting pyridine molecules.1b Hence, we wish to investigate the Cu(II) and Ni(II) complexes of the ligand system having additional donor atoms available to coordinate neighboring metal ions or otherwise, these functional groups can also be used to form interesting hydrogen bonded structures in the solid state. For this purpose, naturally occurring amino acids such as L-aspartic acid and L-glutamic acid having additional carboxylate donor group, Lmethionine having –SCH3, and L-aspargine with –CONH2 in their side arms have been utilized to synthesize the corresponding ligands- H3Sas (N -(2-hydroxybenzyl)L-aspartic acid), H3Sglu (N -(2-hydroxybenzyl)-L-glutamic acid), H3MeSglu (N-(2hydroxy-5-methylbenzyl)-L-glutamic acid), H2Smet (N -(2-hydroxybenzyl)-L- methionine) and H2Sapg (N -(2-hydroxybenzyl)-L-aspargine). These ligands (Figure 3-1) have been successfully employed for complexation with Cu(II) and Ni(II) ions and the complexes [Cu(HSas)(H2O)].2H2O, III-1; [Cu(HSglu)(H2O)].H2O, III-2; [Cu(HMeSglu)(H2O)].2H2O, III-3; [Cu2(Smet)2], III-4; [Ni(HSas)(H2O)], III-5; [Ni2(Smet)2(H2O)2], III-6 and [Ni(HSapg)2], III-7 have been obtained. This chapter presents the synthesis and characterization of III-1 to III-7, structural studies showing 1D and/or 2D hydrogen bonded supramolecular structures in III-2, III-3, III-5, III-6 and 3D hydrogen bonded supramolecular structure in III-7. 176 Chapter Figure 3-1. Ligands employed for complexation. 3-2. Results and discussion The ligands H3Sas, H3Sglu, H3MeSglu, H2Smet and H2Sapg and their complexes III-1 to III-7 have been synthesized and isolated, following the procedures described in the experimental section, in moderate to good yields ranging from 60-82%. Single crystals were grown during the synthesis of the complexes by diffusion method. The solid state structures of III-2, III-3, III-5, III-6 and III-7 were determined by the single crystal X-ray crystallographic studies. The structural characterization indicated III-2, III-3 and III-5 are 1D coordination polymers while III-7 has hydrogen bonded 2D structure comprising mononuclear building blocks. However, the ligand H2Smet generated dinuclear copper(II) and nickel(II) complexes, III-4 and III-6 respectively. Our attempts to get suitable single crystals of III-1 and III-4 (structure refinement in III-4 was not satisfactory, see Appendix) were unsuccessful. All the ligands and complexes were characterized by the elemental analysis and other physicochemical 177 Chapter techniques. While attempting to synthesize the ligands with substitution at the 5th position of phenyl ring by using various -para substituted salicylaldehydes, only the methyl substituted H3MeSglu ligand has been successfully isolated and its copper(II) complex III-3 was obtained. But, the attempts to isolate corresponding Ni(II) complex either in the form of bulk or single crystals were also not successful. Our attempts to obtain 1:1 complex of Cu(II) and Ni(II) with H2Sapg were not successful. Nevertheless, the complexation of the ligand H2Sapg with nickel in 1:1 stiochiometry has furnished III-7 having 2:1 (ligand: metal) stiochiometry. 3-2-1. Description of crystal structures 3-2-1-1. [Cu(HSglu)(H2O)].H2O, III-2 The asymmetric unit of III-2 contains a copper(II) center with slightly distorted square pyramidal geometry (τ = 0.033)2 as shown in Figure 3-2. Coordination of copper with secondary amine nitrogen atom (Cu(1)-N(1), 1.978(2) Å ), α carboxylate oxygen atom (Cu(I)-O(2), 1.970(2) Å), oxygen atom of aqua ligand (Cu(1)-O(6), 1.964(2) Å) and the carboxylate oxygen atom of neighboring molecule (Cu(1)-O(4), 1.921(2) Å) completes the basal plane of the square pyramid. Interestingly, the axial position of square pyramid is occupied by the phenolic oxygen atom (Cu(1)-O(1), 2.345(2) Å) which is protonated. Selected bond lengths and bond angles are given in Table 3-1. Very few structural evidences exist for such phenolic group coordinating axially to the Cu(II) ions without deprotonation in different mononuclear,3-4 dinuclear5-7 and ternary copper(II) complexes.8 The Cu-OH(phenol) bond distances observed in these reports lie in the range of 2.432(4)-2.601(4) Å which is still within the range of 2.2-2.9 Å known for the common axial Cu-O bond lengths.9 178 Chapter Figure 3-2. Perspective view of the repeating unit in III-2 The connectivity of each Cu(HSglu) unit by the carboxylate oxygen atom of the neighboring molecule generated 1D zigzag coordination polymeric structure along c axis in III-2 as shown in Figure 3-3. Figure 3-3. A segment of 1D polymeric structure propagating along c axis in III-3 (C-H Hydrogen atoms omitted). 179 Chapter Table 3-1. Selected bond lengths and bond angles in III-2 Cu(1)-O(4)a 1.921(2) Cu(1)-O(6) 1.964(2) Cu(1)-O(2) 1.969(2) Cu(1)-N(1) 1.978(2) Cu(1)-O(1) 2.345(2) O(1)-C(1) 1.371(3) C(7)-N(1) 1.486(4) N(1)-C(8) 1.477(3) O(4)-Cu(1)b 1.921(2) O(4)a-Cu(1)-O(6) 89.14(9) O(4)a-Cu(1)-O(2) 92.69(8) O(6)-Cu(1)-O(2) 173.65(1) O(4)a-Cu(1)-N(1) 175.64(9) O(6)-Cu(1)-N(1) 93.68(9) O(2)-Cu(1)-N(1) 84.15(8) O(4) -Cu(1)-O(1) 91.49(8) O(6)-Cu(1)-O(1) 95.35(1) O(2)-Cu(1)-O(1) 90.68(9) N(1)-Cu(1)-O(1) 91.56(8) C(12)-O(4)-Cu(1)b 112.7(2) C(8)-N(1)-Cu(1) 106.11(1) a Symmetry transformations used to generate equivalent atoms: a: -x+1, y+1/2,-z+2 b: -x+1,y-1/2,-z+2. These 1D coordination polymeric chains are stacked together into 2D sheets (Figure 3-4) supported by the intermolecular hydrogen bonds involving aqua ligand, amine hydrogen, and lattice water molecule and carboxylate oxygen atoms. Aqua ligand is involved in hydrogen bonding with the α-carboxylate oxygen atom (O(6)H6(1)···O(2)) of the neighboring molecule and lattice water molecule (O(6)H6(2)···O(7)). The other oxygen atom of the neighboring carboxylate involved in hydrogen bonding with phenolate hydrogen atom (O(1)-H(1)···O(5)), and as well as with lattice water (O(7)-H7(1)···O(5)). COO···H(1A)-N(1) hydrogen bonds are generated by amine hydrogen atom with the free α-carboxylate oxygen atom of the adjacent monomeric unit. Hydrogen bond parameters are given in Table 3-2. 180 Chapter Figure 3-4. View of the portion of 2D hydrogen bonded sheets along c axis in III-2 (The C-H hydrogen bonds are omitted for clarity). Table 3-2. Hydrogen bond lengths (Å) and bond angles (º) in III-2 D-H d(D-H) d(H···A) d(D···A) ∠D-H···A A Symmetry O1-H1 0.72(4) 1.94(4) 2.648(3) 167(4) O5 x, y+1, z N1-H1A 0.80(4) 2.09(4) 2.862(3) 164(4) O3 x+1, y, z O6-H6(1) 0.81(3) 2.00(3) 2.754(3) 156(3) O2 x+1, y, z O6-H6(2) 0.78(2) 1.85(2) 2.616(5) 168(4) O7 x+1, y+1,z O7-H7(1) 0.83(3) 2.09(3) 2.816(4) 147(3) O5 3-2-1-2. [Cu(HMeSglu)(H2O)].2H2O, III-3 The asymmetric unit of the Cu(II) complex III-3 containing HMeSglu ligand contains the mononuclear square pyramidal copper(II) building blocks (Figure 3-5), with two lattice water molecules (O(7) and O(8)). The geometry around copper ion is distorted square pyramidal (τ = 0.105),2 and similar to that present in III-2. Selected bond lengths and bond angles are given in Table 3-3. 181 Chapter Figure 3-5. Perspective view of the building block III-3. The connectivity of the copper center by the coordination of neighboring carboxylate oxygen atom (Cu(1)-O(4A)) generated a zigzag 1D coordination polymer (Figure 3-6) along c axis in III-3 as observed in III-2 But the molecular packing is slightly different from III-2 due to the presence of methyl group and additional water molecule. Figure 3-6. Portion of 1D polymeric structure propagating along c axis in III-3 (C-H Hydrogen atoms omitted). 182 Chapter Table 3-3. Selected bond lengths and bond angles in III-3 Cu(1)-O(4)a 1.937(2) Cu(1)-O(2) 1.944(2) Cu(1)-O(6) 1.963(3) Cu(1)-N(1) 1.985(3) Cu(1)-O(1) 2.361(3) O(4)-Cu(1)b 1.937(2) O(4)a-Cu(1)-O(2) 93.2(1) O(4)a-Cu(1)-O(6) 87.6(1) O(2)-Cu(1)-O(6) 170.2(1) O(4)a-Cu(1)-N(1) 176.5(1) O(2)-Cu(1)-N(1) 84.3(1) O(6)-Cu(1)-N(1) 95.2(1) O(4)a-Cu(1)-O(1) 87.5(1) O(2)-Cu(1)-O(1) 95.8(1) C(1)-O(1)-Cu(1) 109.2(2) C(12)-O(4)-Cu(1)b 118.1(2) Symmetry transformations to generate equivalent atoms: a: -x+2,y-1/2,-z+1; b: -x+2,y+1/2,z+1 The intermolecular N-H···O hydrogen bonds are generated between amine hydrogen atoms and free α-carboxylate oxygen atom (N(1)-H(1)···O(3)), and O-H···O hydrogen bonds formed between the α-coordinated carboxylate atom and aqua ligand (O(6)-H(6A)···O(2)) to form a 2D hydrogen bonded sheet structures along c axis as shown in Figure 3-7. These 2D sheet structures are further sustained by O(6)H(6B)···O(8) hydrogen bonds formed between aqua ligand (O(6)) and lattice water molecule (O(8)). In addition to these interactions, intermolecular hydrogen bonds are also observed between two lattice water molecules (O(8)-H(8A)···O(7)) and the other carboxylate oxygen atoms (O(7)-H(7C)···(O5), O(7)-H(7D)···O(4), O(8)- H(8B)···O(5)). The intermolecular connectivity between 1D strands via aqua ligands, N-H hydrogen atoms and lattice water molecules is clearly shown in Figure 3-8. The hydrogen bond parameters are summarized Table 3-4. 183 Chapter Figure 3-7. Packing of III-3 along c axis showing H-bonding. Figure 3-8. Packing diagram of III-3 along b axis. 184 Chapter oxygen atom (N(2)-H(2A)···O(7) and N(4)-H(4B)···O(7)) from the adjacent molecules (Figure 3-17). The hydrogen bond parameters are given in Table 3-10. Figure 3-17. (Top) Hydrogen bonded 3D network structure in III-7 viewed from b axis. (Bottom) A segment of hydrogen bonded 3D network showing the connectivity via hydrogen bonding by –CONH2 hydrogens in III-7. 194 Chapter Table 3-10. Hydrogen bond lengths (Å) and bond angles (º) in III-7 D-H d (D-H) d(H···A) d(D···A) ∠D-H···A A O1-H1 1.10(7) 1.66(7) 2.724(3) 163(7) O2 Symmetry equivalent operator x-1, y, z N2-H2A 0.83(3) 2.08(4) 2.882(5) 163(3) O7 x-2, y-1/2, z-1 N2-H2B 0.70(5) 2.33(5) 2.945(5) 149(5) O3 x-2, y-1/2, z-2 N4-H4A 0.79(5) 2.12(4) 2.886(4) 162(4) O3 x-2, y+1/2, z-2 N4-H4B 0.98(6) 1.98(6) 2.931(4) 161(5) O7 x-2, y+1/2, z-1 O5-H5 1.26(6) 1.54(6) 2.729(3) 155(6) O6 x-1, y, z C5-H5A 0.94 2.59 3.490(5) 160 O3 x-2, y+1/2, z-2 C16-H16 0.94 2.60 3.495(5) 160 O7 x-2, y-1/2, z-1 3-3. Physico-chemical studies 3-3-1. Infrared spectra Selected IR bands for the complexes are presented in Table 3-11. A broad band at ca. 3400 cm-1 indicates the presence of water molecules, except in III-4 and III-7, in the structure. 16a The bands observed at ca. 3100 and 1260 cm-1 correspond to the υ(NH) and υ(phenolic C-O) respectively. The asymmetric [νasCOO-] and symmetric [νsCOO-] bands of the carboxylate group respectively were observed in the region of 1560-1640 cm-1 and 1360-1400 cm-1. 16b The Δν value of ca. 210 cm-1 observed in III-2 and 222 cm-1 in III-3 suggests the monodentate coordination mode of carboxylate 16c and the same has been confirmed by the X-ray crystal structures. The observed Δν of ca. 186 cm-1 in III-5 suggests the bridging carboxylate 16c generating the octahedral Ni(II) center and same has been reflected in the X-ray crystal structure. The assigned IR stretching frequencies in III-1 – III-7 are in agreement with the available literature for the related Ni(II) 11b, 17 and Cu(II) 13b, 18-19, 22 complexes. 195 Chapter Table 3-11. Selected IR absorption bands (cm-1) in III-1 to III-7 Complex υ(OH) υ(NH) υas(COO-) υs(COO-) υ (CO) Δυ phenolic III-1 3513 3124 1603 1376 1262 227 III-2 3429 3118 1572 1362 1262 210 III- 3428 2985 1570 1348 1268 222 III-4 ---- 3131 1602 1374 1260 228 III-5 3445 3146 1591 1405 1261 186 III-6 3452 3151 1606 1380 1263 226 III-7 ---- 3176 1627 1371 256 1274 3-3-2. Electronic spectra Electronic spectral absorption bands of III-1 to III-7 recorded in Nujol mull are tabulated in Table 3-12. The electronic spectra of the copper complexes III-1 - III-4 showed the d-d transition bands in the range of 670-720 nm and the ligand to metal CT bands in the range of 376-406 nm. In general, the d-d transitions and charge transfer transitions occur in the range of 650-730 nm and 360-420 nm respectively for the reduced Schiff base and related copper(II) complexes with square pyramidal geometry.18-19, 22 For the Ni(II) complexes III-5 - III-7 the absorption bands observed in range of 646-653 nm and 725-740 nm can be assigned to d-d transitions and the bands found in the range of 362-372 nm are due to ligand to metal CT transitions. Generally, for the Ni(II) complexes, the d-d transitions at ca. 650 nm can be assignable to the spin allowed 3A2g (F) Æ 3T1g transitions where as the shoulder at around 740 nm will be attributed to the spin forbidden 3A2g Æ 1Eg transitions that are frequently observed in Ni(II) octahedral complexes. The electronic absorption bands observed in Ni(II) 196 Chapter complexes are well in agreement with the available octahedral Ni(II) complexes obtained with the related ligands.17, 21 Table 3-12. Electronic absorption bands of III-1 to III-7 III-1 Absorption bandsa (nm) CT d-d 720 406 III-2 673 376 III-3 678 382 III-4 685 392 III-5 646, 725 372 III-6 653, 740 366 III-7 648, 734 362 Complex [a]: nujol mull 3-3-3. Thermogravimetric studies Thermo gravimetric results for III-1 to III-7 are shown in Table 3-13. The TG of III-1 and III-3 displayed the weight loss of 14.8% (calculated, 15.2%) and 15.8% (calculated, 14.2%) respectively corresponding to the loss of three water molecules. The TG of III-2 showed a two step weight loss of 10.8% (calculated, 10.4%) corresponding to one lattice water and one aqua ligand. TG of III-4 and III-7 did not show any weight loss for water molecules indicating the absence of water in the structures as reflected by IR, elemental analysis as well as crystal structure data (see Appendix for the structure data of III-4). The TG of III-5 and III-6 displayed the weight loss of 5.4% (calculated, 5.8%) and 5.6% (calculated, 5.4%) for the loss of three water molecules respectively. Thus, besides the IR and elemental analysis data, 197 Chapter the TG results also suggest that the single crystal structures in III-2 - III-7 represent the bulk in terms of water. Table 3-13. Thermo gravimetric data of III-1 to III-7 Complex No. of Dehydration Wt. Decomp. a H2O temp.(ºC) loss (%) Temp.(ºC) III-1 35 - 171 14.8 (15.2) 285 III-2 55-166 10.8 (10.4) 205 III-3 36-180 15.5 (14.2) 208 III-4 -- -- -- 220 III-5 137-197 5.4 (5.7) 240 III-6 80-235 5.6 (5.4) 280 III-7 -- -- -- 282 [a]: calculated % weight loss 3-4. Summary Several reduced Schiff base ligands containing the amino acid side arms with reactive functional groups –COO-, SCH3 and –CONH2 have been isolated and their Cu(II) and Ni(II) complexes have been synthesized and characterized. The crystal structures of the complexes III-2, III-3, III-5, III-6 and III-7 have been determined by single crystal X-ray crystallographic techniques. The copper complexes III-2 and III-3 displayed square pyramidal Cu(II) centers while the nickel complexes III-5, III6 and III-7 are characterized by octahedral Ni(II) cores. 1D coordination polymeric structures in III-2, III-3, and III-5 have generated 2D hydrogen bonded sheet like structures via intermolecular hydrogen bonding. All the discrete dinickel(II) molecules in III-6 interconnected via COO···H-N and COO···H2O intermolecular hydrogen bonds generating 1D hydrogen bonded polymeric strands which in turn are further connected by C-H···S interactions resulting a 2D hydrogen bonded sheet 198 Chapter structure. Intermolecular hydrogen bonds generated by these phenolic protons and CONH2 hydrogen atoms from the side chain of the ligand generated 3D hydrogen bonded network in III-7. Thus, by incorporating the reactive functional groups in the side arm of the amino acids the different molecular connectivity can be achieved resulting mainly in monomeric units to generate different hydrogen bonded polymeric structures. Compared to our earlier reports18-19 on the dinuclear Cu(II) and Zn(II) complexes, the coordination mode of the current set of ligands has been found to be different from the binucleating nature while forming the mononuclear complexes. Further, it is worthwhile mentioning the axial Cu-OHphenol bonds (with protonated phenolic oxygen) observed in III-2 and III-3 which will provide more insight into the Cu(II)-phenolic substrate interactions,3, the knowledge of which is reasonably required for understanding the enzymatic hydroxylation catalyzed by tyrosinase. These results will further enhance the transition metal coordination chemistry of reduced Schiff bases containing natural amino acids while improving the structural insights in terms of hydrogen bonding tendencies of the amino acid components. 3-5. Experimental 3-5-1. Synthesis of ligands N -(2-hydroxybenzyl)-L-aspartic acid, H3Sas To the clear solution of L-aspartic acid (0.62 g, 4.7 mmol) and NaOH (0.37 g, 9.4 mmol) in a solvent mixture of water (10 mL) and methanol (10 mL), was added salicylaldehyde (0.5 mL, 4.7 mmol) and the resulting yellow solution was stirred for 45 min. After cooling the mixture in an ice bath for 30 min, it is reduced with a slight excess of NaBH4 (0.19 g, 5.2 mmol). The yellow color slowly discharged after 20-30 and the pH of the mixture was maintained 5-6 by the addition of acetic acid. After h the solvent was completely removed and finally an insoluble product 199 Chapter obtained after adding excess of methanol was filtered, washed with Et2O and then dried under vacuum. Yield: 0.82 g (73%). m. p. 221-223 ºC. 1H NMR (d2, D2O) : δ 2.02 (m, 2H, CH2), 2.34 (t, 2H, CH2), 3.46 (t, 1H, CH), 3.92 (m, 2H, benzylic), 6.547.04 (m, 4H, Ar). 13 C NMR: δ 42.02 (-CH2), 57.33 (-CH), 63.42 (benzylic), 118.83, 126.21, 129.65, 141.58, 148.63 and 159.16 (aromatic), 181.55 (-COOH), 180.36 (COOH). Anal. Calcd. for C11H13NO5: C, 55.2; H, 5.5; N, 5.8. Found: C, 55.0; H, 5.3; N, 5.6. IR (KBr, cm-1): υ (OH) 3460; υ (NH) 2960; υas (COO-) 1618; υs (COO-) 1388; υphenolic (CO) 1276. EI-MS: [M+H], 239.3. N -(2-hydroxybenzyl)-L-glutamic acid, H3Sglu H3Sglu was prepared following the same procedure as H3Sas but the sticky mass, obtained after completely removing the solvent by rotary evaporator, was treated with ethanol (25 mL) to precipitate H3Sglu. Yield: 0.85 g (71%). m.p. 247-248°C (decomp); 1H NMR (d2, D2O) : δ 2.04 (m, 2H, CH2), 2.24 (t, 2H, CH2), 3.55 (t, 1H, CH), 3.82 (m, 2H, CH2), 6.78 - 7.27 (m, 4H, Ar). 13C NMR: δ 42.12 (-CH2), 47.66 (CH2) 56.43 (-CH), 63.42 (benzylic), 117.73, 127.51, 128.64, 142.58, 148.36 and 156.16 (aromatic), 181.41 (-COOH), 182.36 (-COOH). Anal. Calcd for C12H15NO5: C 56.9, H 5.9, N 5.5; found: C 56.4, H, 5.8, N, 5.6. IR (KBr): υ (OH) 3460, υ (NH) 2960, υas (COO-) 1590, υs (COO-) 1381, υ(phenolic CO) 1276. N-(2-hydroxy-5-methylbenzyl)-L-glutamic acid, H3MeSglu H3MeSglu was prepared following the same procedure as H3Sglu by using 5methyl salicylaldehyde. Yield: 0.95 g (78%). m.p. 236-238 ºC. 1H NMR (d2, D2O): δ 2.0 – 2.02 (m, J = 6.4 Hz, 2H, CH2), 2.16 – 2.27 (t, 2H, CH2), 2.37 (m, 3H, Ar-CH3), 6.64-7.27 (m, 4H, Ar), 3.92 - 4.12 (m, 2H, CH2), 3.26 (t, 1H, CH). 13C NMR: δ 21.6 (Ar-CH3), 42.01 (-CH2), 48.22 (-CH2) 55.43 (-CH), 62.32 (benzylic), 116.73, 126.51, 200 Chapter 129.64, 141.58, 148.66 and 157.66 (aromatic), 181.45 (-COOH), 180.36 (-COOH). Anal. Calcd for C13H17NO5: C, 58.4; H, 6.4; N, 5.2. Found: C, 58.1; H, 6.2; N, 5.3. IR (KBr, cm-1): IR (KBr, cm-1): υ (OH) 3428, υ (NH) 2985, υas (COO-) 1590, υs (COO-) 1398, υ (phenolic CO) 1268. N-(2-hydroxybenzyl)-L-methionine, H2Smet H2Smet was prepared by the same procedure as described for H2Scp11 in Part A in Chapter (Page 96) by using salicylaldehyde and L-methionine. Yield: 0.74 g (62%). m.p. 227-229 ºC. 1H NMR (d4-CD3OD): δ 1.89 (m, 2H, CH2), 2.03 (s, 3H, -CH3), 2.62 (m, 2H, CH2) 2.78 (m, 1H, -CH), 3.93 (m, 2H, benzylic CH2), 6.42-7.08 (m, 4H, Ar-H). 13C NMR (d4-CD3OD): δ 16.82 (-SCH3), 31.90 (-CH2), 34.74 (-CH2) 50.11 (CH), 64.78 (benzylic), 114.58, 120.25, 125.48, 128.98, 166.69 and 171.31 (aromatic), 182.19 (-COOH). Anal. Calcd. for C12H17NO3S: C, 56.4; H, 6.7; N, 5.5; S, 12.6. Found: C, 56.4; H, 6.8; N, 5.5; S, 12.5. IR (KBr, cm-1): υ (OH) 3457; υ (NH) 3154; υas (COO-) 1621, υs (COO-) 1396; υ (phenolic CO) 1263. N-(2-hydroxybenzyl)-L-aspargine, H2Sapg H2Sapg was prepared by the same procedure as H3Sglu. After the solvent was removed to a minimum volume of 2-3 mL, an insoluble product was precipitated by adding excess of diethyl ether and then dried under vacuum. Yield: 0.87 g (77%). m. p. 237-239 ºC. 1H NMR (d4-CD3OD): δ 1.68 (s, 2H, -CH2), 2.78 (m, 1H, -CH), 3.93 (m, 2H, benzylic CH2), 6.56-6.84 (m, 4H, Ar-H). 13 C NMR (d4-CD3OD): δ 24.41 (- CH2), 50.67 (-CH), 61.50 (benzylic), 118.44, 125.57, 128.24, 130.68, 157.88 and 161.61 (aromatic), 177.28 (-CONH2), 180.69 (-COOH). Anal. Calcd for C11H14N2O4: 201 Chapter C, 55.4; H, 5.9; N, 11.8. Found: C, 55.2; H, 5.6; N, 11.6. (KBr, cm-1): υ (OH) 3412; υ (NH) 3089; υas (COO-) 1648, υs (COO-) 1397; υ (phenolic CO) 1264. 3-5-2. Synthesis of complexes [Cu(HSas)(H2O)].2H2O, III-1 A clear aqueous solution (2.5 mL) of copper nitrate trihydrate (0.12 g, 0.5 mmol) was slowly diffused into the aqueous solution (2.5 mL) of H3Sas (0.12 g, 0.5 mmol). This reaction mixture furnished rod like bluish single crystals after 3-4 days. Yield: 0.11 g (63%). Anal. Calcd. for C11H17NO6Cu: C, 37.2; H, 4.8; N, 4.0; H2O, 15.2. Found: C, 37.6; H, 4.9; N, 4.2; H2O 14.8 (from TG). [Cu(HSglu)(H2O)].H2O, III-2 A clear solution of H3Sglu (0.25 g, 1.0 mmol) in water (2.5 mL) was allowed to diffuse slowly into a clear solution of copper nitrate trihydrate (0.24 g, 1.0 mmol) in water (2.5 mL). The dark blue blocks of single crystals suitable for X-ray diffraction were obtained in the next day. Yield: 0.26 g (74%) Anal. Calcd. for C12H17NO7Cu: C, 41.1; H, 4.9; N, 4.0; H2O, 10.4. Found: C, 41.0; H, 4.8; N, 4.2; H2O 10.8 (from TG). [Cu(HMeSglu)(H2O)].2H2O, III-3 A clear solution of H3Sglu (0.25 g, 1.0 mmol) in water (7.5 mL) was allowed to diffuse slowly into an aqueous solution (5 mL) of copper nitrate trihydrate (0.24 g, 1.0 mmol). The dark blue blocks of single crystals suitable for X-ray diffraction were obtained after one day. Yield: 0.26 g (78%). Anal. Calcd. for C13H20NO8Cu: C, 40.8; H, 5.2; N, 3.7; H2O, 14.2. Found: C, 40.5; H, 5.1; N, 3.6; H2O, 15.8 (from TG). 202 Chapter [Cu2(Smet)2], III-4 To a clear solution containing H2Smet (0.13 g, 0.5 mmol) and NaOH (0.04 g, 1.0 mmol) in a solvent mixture containing water (10 mL) and acetonitrile (10 mL) was added copper nitrate trihydrate (0.12 g, 0.5 mmol) and stirred for 30 min. The resulting dark green clear solution was filtered and the filtrate was allowed for slow evaporation. Dark green single crystals obtained after two days were dried in air. Yield: 0.25 g (78%). Anal. Calcd. for C24H30N2O6S2Cu2: C, 45.5; H, 4.8; N, 4.4; S, 10.1. Found: C, 45.3; H, 4.7; N, 4.5; S, 10.1. [Ni(HSas)(H2O)], III-5 A clear solution of H3Sas (0.24 g, 1.0 mmol) in water (4 mL) was allowed to slowly diffuse into the aqueous solution (4 mL) of nickel chloride hexahydrate (0.24 g, 1.0 mmol). Light greenish rod like single crystals suitable for X-ray diffraction studies were obtained after one week. Yield: 0.21 g (67%). Anal.Calcd for C11H13NO6Ni: C, 42.1; H, 4.2; N, 4.5; H2O, 5.7. Found: C, 42.0; H, 4.2; N, 4.6; H2O, 5.4 (from TG). Ni2(Smet)2(H2O)2], III-6 A clear solution of H2Smet (0.06 g, 0.25 mmol) and KOH (0.03g, 0.5 mmol) in water (2.5 mL) was slowly diffused into a clear ethanolic solution (4 mL) of nickel perchlorate hexahydrate. After one week, light greenish rod shaped crystals suitable for X-ray diffraction studies were obtained. Yield: 0.05 g (60%). Anal. Calcd for C24H34N2O8S2Ni2: C, 43.6; H, 5.2; N, 4.2; S, 9.7; H2O, 5.4. Found: C, 43.1; H, 5.1; N, 4.3; S, 9.1; H2O, 5.6 (from TG). 203 Chapter [Ni(HSapg)2], III-7 A clear saturated aqueous solution (2 mL) of nickel nitrate hexahydrate (0.14 g, 0.5 mmol) was allowed to slowly diffuse into the clear saturated aqueous solution (3 mL) of H2Sapg (0.12 g, 0.5 mmol). Light bluish prismatic single crystals suitable for X-ray diffraction analysis were obtained after a week. Yield: 0.22 g, (82%). Anal. Calcd. for C22H26N4O8Ni: C, 49.6; H, 4.9; N, 10.5. Found: C, 49.3; H, 4.2; N, 10.2. 3-5-3. X-ray crystallography The solid-state structures of III-2, III-3, III-5, III-6, and III-7 have been determined by X-ray crystallographic techniques. The details of crystal data and refinement parameters are given in Table 3-14. 204 Chapter Table 3-14. Crystallographic data and structure refinement details Complex III-2 III-3 III-5 III-6 III-7 Formula C12H17CuNO7 C13H20CuNO8 C11H13NNiO6 C12H17NNiO4S C22H26N4NiO8 f.w. 350.81 381.84 313.93 330.04 533.18 T/K 223(2) 223(2) 223(2) 223(2) 223(2) λ/Å 0.71073 Å 0.71073 0.71073 0.71073 0.71073 Crystal system Monoclinic Monoclinic Orthorhombic Orthorhombic Monoclinic Space group P21 P21 P212121 P212121 P21 a/Å 5.9362(2) 5.9048(4) 5.8913(6) 13.0323(8) 8.3072(7) b/Å 10.1204(4) 11.0358(8) 8.8699(9) 16.8654(10) 11.8460(10) c/Å 11.9417(4) 12.4823(9) 22.926(2) 6.2158(4) 11.5356(10) β/o 94.3770 91.137(1)° 90° 90° 90.017(2) V/Å / Z 715.33(4)/ 813.24(10)/ 1198.0(2)/ 1366.2(2)/ 1135.2(2)/ Dcalcd /g.cm-3 1.629 1.559 1.741 1.605 1.560 μ/mm-1 1.559 1.383 1.643 1.581 0.912 Reflns col. 4989 5001 6839 9767 6461 Ind. Reflns/ Rint 3009/0.0207 2267/0.0211 2104/0.0428 3129/0.0393 3431/0.0276 GooF 1.053 1.121 1.134 1.010 1.053 Flack parameter 0.026(13) 0.022(16) 0.06(3) 0.007(13) 0.022(14) 0.0272/0.0775 0.0498/0.1194 0.0322/0.0675 0.0322/0.0813 Final R[I>2σ], R1a / wR2b 0.0288/0.0763 a R1 = Σ||Fo| - |Fc||/Σ|Fo|. b wR2 = [Σw(Fo2 - Fc2)2/Σw(Fo2)2]1/2 205 Chapter 3-6. References 1. a) Koh, L. L.; Ranford, J. D.; Robinson, W.; Stevenson, J. O.; Tan, A. L. C.; Wu, D. Inorg. Chem. 1996, 35, 6466 and references therein; b) Alan, M. A.; Nethaji, M.; Ray, M. Angew. Chem. Int. Ed. Engl. 2003, 42, 1940. 2. (a) Addison, A. W.; Rao, T. N.; Reedijk, J. J.; Rijn, V.; Verschoor, G. C. J. Chem. Soc., Dalton Trans. 1984, 1349; (b) Murphy, G.; Sullivan, C. O.; Murphy, B.; Hathaway, B. Inorg. Chem. 1998, 37, 240; (c) Marlin, D. S.; Olmstead, M. M.; Mascharak, P. K. Inorg. Chem. 2001, 40, 7003; (d) Yang, C. T.; Vittal, J. J. Inorg. Chim. Acta 2002, 1, and references therein. 3. Masuda, H.; Odani, A.; Yamauchi, O. Inorg. 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Chem. 2005, 44, 1205; b) Adams, H.; Clunas, S.; Fenton, D. E.; McHugh, P. E.; Spey, S. E.; Inorg. Chem. Acta 2003, 346, 239; c) Bavla, S. R.; Zhiquiang, X, Patriz, B. O.; Rettig, S. J.; pink, M.; Thompson, R. C.; Orvig, C. Inorg. Chem. 2003, 42, 1576. 13. a) Allen, F.H.; Bird, C. M.; Rowland, R.S., Raithby, P. R. Acta. Crystallogr. Sect B53, 1997, 696; b) Bond, A. D.; Jones, W.; J. Chem. Soc., Dalton Trans. 2001, 3045 and references therein. 14. Zhou, H. P.; Zhu.Y. M.; Chen, J. J.; Hu, Z. J.; Wu, J. Y.; Xie, Y.; Jiang, M. H.; Tao. X. T.; Tian, Y. P. Inorg. Chem. Commun. 2006, 9, 90; b) Lewis, G. R.; Dance, I. J. Chem. Soc., Dalton Trans. 2000, 3176. 15. a) Ueno, T.; Inohara, M., Ueyama, N.; Nakamura, A. Bull. Chem. Soc. Jpn. 1997, 70, 1077; b) Sun, W.-Y.; Shi, X.-F.; Zhang, L.; Hu, J. Wei, J.-H. J. 207 Chapter Inorg. Biochem. 1999, 76, 259; b) Ren, X.; Xie, J.; Chena, Y.; Kremer, R.; K. J. Mol. Struct. 2003, 660, 139. 16. a) Ferraro, J. R. 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Acta 1977, 22, 1. 209 [...]... coordination chemistry of reduced Schiff bases containing natural amino acids while improving the structural insights in terms of hydrogen bonding tendencies of the amino acid components 3- 5 Experimental 3- 5-1 Synthesis of ligands N -(2- hydroxybenzyl)- L-aspartic acid, H3Sas To the clear solution of L-aspartic acid (0.62 g, 4.7 mmol) and NaOH (0 .37 g, 9.4 mmol) in a solvent mixture of water (10 mL) and methanol... given in Table 3- 14 204 Chapter 3 Table 3- 14 Crystallographic data and structure refinement details Complex III-2 III -3 III-5 III-6 III-7 Formula C12H17CuNO7 C13H20CuNO8 C11H13NNiO6 C12H17NNiO4S C22H2 6N4 NiO8 f.w 35 0.81 38 1.84 31 3. 93 330 .04 533 .18 T/K 22 3( 2) 22 3( 2) 22 3( 2) 22 3( 2) 22 3( 2) λ/Å 0.710 73 Å 0.710 73 0.710 73 0.710 73 0.710 73 Crystal system Monoclinic Monoclinic Orthorhombic Orthorhombic Monoclinic... bands in the range of 37 6-406 nm In general, the d-d transitions and charge transfer transitions occur in the range of 650- 730 nm and 36 0-420 nm respectively for the reduced Schiff base and related copper(II) complexes with square pyramidal geometry.18-19, 22 For the Ni(II) complexes III-5 - III-7 the absorption bands observed in range of 646-6 53 nm and 725-740 nm can be assigned to d-d transitions... Ni(II) complexes 188 Chapter 3 obtained with similar type of ligands. 11 Similar Ni-S bond distances were observed in the earlier reports on the related nickel complexes 10a, 12 The two aqua ligands are oriented in cis fashion to each other Selected bond lengths and bond angles are given in Table 3- 7 Table 3- 7 Selected bond lengths and bond angles for III-6 Ni(1)-O(1)a 2. 03 4(2) Ni(1) -N( 1) 2.05 0(2) Ni(1)-O(2)... 2:1 Ni(II) complexes 10a containing similar type of ligands in which either phenolic oxygen or S atom of thiophenolate group participated in coordination with Ni(II) centers, the formation of III-7 is probably due to the experimental conditions employed for synthesis Table 3- 9 Selected bond lengths and bond angles in III-7 Ni(1)-O(8) 2.044 (3) Ni(1)-O(4) 2.049 (3) Ni(1)-O(6) 2.06 0(2) Ni(1)-O(2) 2.06 2(2) ... along c axis Selected bond lengths and bond angles are given in Table 3- 5 185 Chapter 3 Figure 3- 9 Perspective view of III-5 showing the connectivity between the monomers Table 3- 5 Selected bond lengths and bond angles in III-5 Ni(1)-O(5)a 2. 033 (4) O(5)-Ni(1)b 2. 033 (4) Ni(1) -N( 1) 2.041(5) Ni(1)-O(4) 2.049(4) Ni(1)-O(2) 2.054(4) Ni(1)-O(6) 2.068(5) Ni(1)-O(1) 2.092(4) O(5)a-Ni(1) -N( 1) 175. 3( 2) O(5)a-Ni(1)-O(4)... oxygen atom of the side chain (Ni(1)-O(4) = 2.049(4) Å) and the neighboring carboxylate (Ni(1)-O(5A) = 2. 033 (4) Å) as shown in Figure 3. 9 The Ni-O and Ni -N bond lengths observed in III-5 are in agreement with the available octahedral Ni(II) complexes obtained with reduced Schiff base ligands containing N2 O2 donors.10a-b The Ni-OH distance of 2.092(4) Å in III-5 has been found to be in agreement with... via intermolecular hydrogen bonds generated by the carboxylate oxygen atoms (O(2) and O (3) ) of the neighboring molecule with both NH hydrogen atoms (N( 1)-H(1)···O (3) ) and aqua ligands (O(4)-H(4A)-O(2)) These hydrogen bonding interactions resulted in the formation of 1D hydrogen bonded polymeric structure as shown in Figure 3- 13 Further connectivity of each 1D hydrogen bonded polymeric strand to the neighboring... coordination of two bridging phenolate oxygen atoms (Ni(1)-O(1), 2. 03 3( 2) Å), amine nitrogen (Ni(1 )N( 1), 2.05 0(2) Å), α-carboxylate oxygen (Ni(1)-O(2), 2.06 4(2) Å), sulfur atom from the side arm of the amino acid (Ni(1)-S(1), 2.517(8) Å) and aqua ligand (Ni(1)-O(4), 2.06 6(2) Å) as shown in Figure 3- 12 The bond distances observed are in consistent with the available few phenoxo bridged dinuclear and octahedral... in the side arm of the amino acids the different molecular connectivity can be achieved resulting mainly in monomeric units to generate different hydrogen bonded polymeric structures Compared to our earlier reports18-19 on the dinuclear Cu(II) and Zn(II) complexes, the coordination mode of the current set of ligands has been found to be different from the binucleating nature while forming the mononuclear . Chapter 3 Cu(II) and Ni(II) Complexes of reduced Schiff base Ligands containing Additional Functional Groups in the Amino Acid side chain 175 Chapter 3 3- 1. Introduction Having. L- methionine having –SCH 3 , and L-aspargine with –CONH 2 in their side arms have been utilized to synthesize the corresponding ligands- H 3 Sas (N -(2- hydroxybenzyl)- L-aspartic acid) , H 3 Sglu (N. oxygen atoms (O(2) and O (3) ) of the neighboring molecule with both N- H hydrogen atoms (N( 1)-H(1)···O (3) ) and aqua ligands (O(4)-H(4A)-O(2)). These hydrogen bonding interactions resulted in the