Copper(II) complexes of mono-anionic glutamate: anionic influence in the variations of molecular and supramolecular
Chaitali Biswas1, Michael G B Drew, Marta Estrader
1Department of Chemistry, University of Calcutta, Kolkata, India.
Abstract:
Three new polynuclear copper(II) complexes of singly deprotonated L-glutamic acid (L-glu), {[Cu(bipy)2][Cu(bipy)(L-glu)H2O]2(BF4)4 x (H2O)3}n (1), {[Cu(bipy)(L-glu)H2O][Cu(bipy)(L-glu)(ClO4)](ClO4) x (H2O)2}n (2) and [Cu(phen)(L-glu)H2O]2(NO3)2 x (H2O)4 (3) (bipy = 2,2-bipyridine, phen = 1,10-phenanthroline), were synthesized in acidic pH (ca. 2.5) and characterized structurally. In all the complexes, L-glutamic acid acts as a bidentate chelating ligand, leaving the protonated carboxylic acid free. Both in 1 and 2, two different types of species [Cu(bipy)2](BF4)2 and [Cu(bipy)(L-glu)H2O]BF4 for 1 and [Cu(bipy)(L-glu)H2O]ClO4 and [Cu(bipy)(L-glu)(ClO4)] for 2 coexist in the solid state. In complex 1, the [Cu(bipy)(L-glu)H2O]+ units are joined together by syn-anti carboxylate bridges to form an enantiopure (M) helical chain and the [Cu(bipy)2]2+ presents a very rare example of the four-coordinate distorted tetrahedral geometry of Cu(II). In complex 2, the [Cu(bipy)(L-glu)(ClO4)] units are joined together by weakly coordinating perchlorate ions to form a 1D polymeric chain while the [Cu(bipy)(L-glu)H2O]+ units remain as mononuclear species. The different coordinating ability of the two counter anions along with their involvement in the H-bonding network seems likely to be responsible for the difference in the final polymeric structures in the two compounds. Variable-temperature (2-300 K) magnetic susceptibility measurements show negligible coupling for both the complexes. The structure of 3 consists of two independent monomeric [Cu(phen)(L-glu)H2O]+ cations, two nitrate anions and four water molecules. The copper atom occupies a five-coordinate square pyramidal environment with a water molecule in the axial position.
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