Copper (II) complexes of mono-anionic glutamate: anionic influence in the variations of molecular and supramolecular structures

Biswas, Chaitali ; Drew, Michael G. B. ; Estrader, Marta ; Ghosh, Ashutosh (2009) Copper (II) complexes of mono-anionic glutamate: anionic influence in the variations of molecular and supramolecular structures Dalton Transactions (25). pp. 5015-5022. ISSN 1477-9226

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Official URL: http://pubs.rsc.org/en/content/articlelanding/2009...

Related URL: http://dx.doi.org/10.1039/B906015D

Abstract

Three new polynuclear copper (II) complexes of singly deprotonated L-glutamic acid (L-glu), {[Cu(bipy)2][Cu(bipy)(L-glu)H)2O] )2 (BF4)4•(H)2O)3}n (1), {[Cu(bipy)(L-glu)H)2O][Cu(bipy)(L-glu)(ClO4)](ClO4)•(H)2O) )2}n (2) and [Cu(phen)(L-glu)H)2O] )2 (NO3))2•(H)2O)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)H)2O]BF)4 for 1 and [Cu(bipy)(L-glu)H)2O]ClO)4 and [Cu(bipy)(L-glu)(ClO)4)] for 2 coexist in the solid state. In complex 1, the [Cu(bipy)(L-glu)H)2O]+ 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)(ClO)4)] units are joined together by weakly coordinating perchlorate ions to form a 1D polymeric chain while the [Cu(bipy)(L-glu)H)2O]+ 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)H)2O]+ 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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