title: Systematic studies on pH-dependent transformations of dinuclear vanadium(V)-citrate complexes in aqueous solutions. A perspective relevance to aqueous vanadium(V)-citrate speciation.
abstract: Vanadium(V) involvement in interactions with physiological ligands in biological media prompted us to delve into the systematic pH-dependent synthesis, spectroscopic characterization, and perusal of chemical properties of arising aqueous vanadium(V)-citrate species in the requisite system. To this end, facile reactions led to dinuclear complexes (NH(4))(4)[V(2)O(4)(C(6)H(5)O(7))(2)].4H(2)O (1) and (NH(4))(6)[V(2)O(4)(C(6)H(4)O(7))(2)].6H(2)O (2). Complex 1 and 2 were characterized by elemental analysis, FT-IR and X-ray crystallography. Complex 1 crystallizes in the monoclinic space group C2/c with a=16.998(5) A, b=16.768(5) A, c=9.546(3) A, beta=105.22(1) degrees, V=2625(1) A(3), and Z=4. Complex 2 crystallizes in the triclinic space group P1;, with a=9.795(4) A, b=9.942(4) A, c=9.126(3) A, alpha=90.32(1) degrees, beta=111.69(1) degrees, gamma=108.67(1) degrees, V=774.5(5) A(3), and Z=1. The structures of 1 and 2 were consistent with the presence of a V(V)(2)O(2) core, to which citrate ligands of differing protonation state were bound in a coordination mode consistent with past observations. Ultimately, the aqueous pH dependent transformations of a series of three dinuclear complexes, 1, 2 and (NH(4))(2)[V(2)O(4)(C(6)H(6)O(7))(2)].2H(2)O (3), all isolated at pH values from 3 to 7.5, were explored and revealed an important interconnection among all species. Collectively, pH emerged as a determining factor of structural attributes in all three complexes, with the adjoining acid-base chemistry unfolding around the stable V(V)(2)O(2) core. The results point to the participation of all three species in aqueous vanadium(V)-citrate speciation, and may relate the site-specific protonations-deprotonations on the dinuclear complexes to potential biological processes involving vanadium(V) and physiological ligand targets.
authors.affiliation: Department of Chemistry, University of Crete, 71409 Heraklion, Greece.
authors.forename: M
authors.initials: M
authors.lastname: Kaliva
authors.forename: C P
authors.initials: CP
authors.lastname: Raptopoulou
authors.forename: A
authors.initials: A
authors.lastname: Terzis
authors.forename: A
authors.initials: A
authors.lastname: Salifoglou
mesh_terms: D002951:Citrates / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D012996:Solutions; D017550:Spectroscopy, Fourier Transform Infrared; D014639:Vanadium / Q000737:chemistry*
chemical_list: D002951:Citrates; D012996:Solutions; D014639:Vanadium