X-ray structure and spectroscopic characterization of divalent dinuclear cobalt complexes containing carboxylate- and phosphodiester- auxiliary bridges

Two dinuclear spin-coupled divalent cobalt complexes, [Co-2(P1-O)(mu(2)-OAc)](ClO4)(2), (1) and [Co-2(P1-O)( mu(2)-BNPP)](ClO4)(2), (2) containing mu-1,3 acetate (OAc) and bis(4-nitrophenyl) phosphate (BNPP) auxiliary bridges, respectively, were synthesized by the reaction of a classic dinucleating ligand, P1-OH with cobalt(II) perchlorate in presence of acetic acid/bis(4-nitrophenyl) phosphate. They were characterized by single crystal X-ray diffraction, to show a trigonal bipyramidal geometry around each cobalt center and the intervening bridging atoms that are responsible for spin-transfer between the two divalent cobalt centers; the alkoxo oxygen donor occupies an equatorial position, and the auxiliary ligand oxygens (OAc/BNPP) occupy the axial positions. Solution state magnetic moment measurement together with UV-Vis/NIR spectra revealed a high-spin ground state (S = 3/2) for Co(II) in these compounds. Complexes 1 and 2 show interesting H-1 NMR spectral features of resonances with relatively narrower linewidths in conjunction with a sizable chemical shift dispersion of -5 and 265 ppm. Complex 2 containing the bis(4-nitrophenyl) phosphate auxiliary bridge showed narrower spectral window than complex 1 that has the acetate auxiliary bridge. (C) 2009 Elsevier B.V. All rights reserved.