Autori: M. Menelaou, M. Daskalakis, A. Mateescu, C.P. Raptopoulou, A. Terzis, C. Mateescu, V. Tangoulis, T. Jakusch, T. Kiss, A. Salifoglou

Editorial: G. Christou, C.E. Housecroft., Elsevier, Polyhedron, 30(2) , p.427-437, 2011.

Rezumat:

Cobalt is an abundant metal ion present in the abiotic and biological world. The chemical reactivity of Co(II) is exemplified through complex interactions with variable molecular mass ligands, including amino acids, peptides, variable nature organic ligands, and/or phospho(nate)-derivatives thereof. Poised to gain
insight into the chemical reactivity of Co(II) toward the family of mixed (carboxy)phosphonate-containing
ligands, pH-specific aqueous reactions were carried out between Co(II) and N,N-bis(phosphonomethyl)-glycine (NTA2P), leading to a new pH-structural variant species (NH4)3[Co(C4H6O8NP2)(H2O)2]4H2O (1) at pH 8. Compound 1 was characterized analytically, spectroscopically (FT-IR, UV–Vis, EPR), and magnetically.
X-ray crystallography reveals a mononuclear complex of Co(II) in an NO5 octahedral environment. The solid state magnetic and EPR data on 1 suggest the presence of a high-spin Co(II) in a distorted octahedral geometry, with a ground state of an effective spin S = 1/2. The solution UV–Vis and EPR data suggest retention of the integrity of 1, consistent with the magnetization measurements.
Detailed aqueous speciation studies on binary Co(II)–carboxylate (NTA) and all Co(II)–(carboxy)phosphonate
(NTAxP; x = 1–3) systems reveal the aqueous distributions of all species involved in the respective systems and project a mononuclear species not unlike that of 1 in the Co(II)–NTA2P system. The structural and chemical attributes of the title complex reflect the (a) pH-dependent chemical reactivity in the binary Co(II)–NTA2P system, and (b) structure–activity correlations in the aqueous media linking both high and low pH-structural variants. To this end, fundamental structural properties influence the reactivity of Co(II) toward phosphonate and mixed carboxyphosphonate ligands and are ultimately exemplified as a function of phosphonate-containing moieties in NTA derivatives. The variably configured species in such binary Co(II)–ligand systems define the pH dependence and nature of interactions
between the two reagents, and could serve further as precursors in the design and discovery of new Co(II)–organophosphonate materials of specific structural lattice, spectroscopic, and magnetic properties

Cuvinte cheie: Cobalt(II), (Carboxy)phosphonic acids, Aqueous speciation studies, Magnetic properties, Structure–reactivity

URL: http://www.elsevier.com/locate/poly