Cobalt(III) complexes with ()-1,3-pentanediamine-N,N,N',N'-tetraacetate. The influence of nature of alkali and alkaline earth metal counter cations on the supramolecular association of the complex

The coordination of hexadentate (+/-)-1,3-pentanediamine-N,N,N',N'-tetraacetate (1,3-pndta) ligand with Co(III) has been investigated. Four octahedral [Co(1,3-pndta)](-) complexes containing different counter cations, Li[Co(1,3-pndta)]& sdot;4H(2)O (1a), Li[Co(1,3-pndta)]& sdot;2H(2)O (1b), K[Co(1,3-pndta)]& sdot;H2O (1c) and Ca[Co(1,3-pndta)](2)& sdot;5H(2)O (1d), were synthesized and structurally characterized. Single-crystal X-ray diffraction analysis, IR, NMR (H-1 and C-13) and electronic absorption spectroscopy were used for characterization of 1a - d. The influence of the ethyl substituent of 1,3-propanediamine chain in 1,3-pndta and the nature of metal counter cation on the structural modalities of carboxylate bridging groups in 1a - d were established by comparing with the analogous [M(1,3-pdta)](n-) (1,3-pdta = 1,3-propanediamine-N,N,N',N'-tetraacetate) and [M(1,3-pndta)](n-) complexes (M = Co(III), Cr(III) and Ni(II)). Our studies have shown that the supramolecular association of the complexes is primarily governed by the size of the alkali or alkaline earth metal counter cation and its templating ability, while ethyl substituents, in most cases, prevent the formation of 3D polymeric frameworks.