Microstructure of N-picolylpolyurethane transition metal complexes

Spectroscopic methods are used to investigate coordination structure of N-p icolylpolyure thane transition metal complexes (PUPYM, M = Co2+ and Ni2+). Geometrical arrangement of ligands in first-shell coordination sphere of me tal ions is postulated to be tetrahedral CoL2Cl2 and octahedral NiL2-Cl(2)Z (2), where L is the picolyl group and Z is a hydrate. From extended X-ray a bsorption fine structure (EXAFS) analysis, bond lengths for metal-chlorine and metal-ligand of PUPYM are similar to those of small molecular weight tr ansition metal complexes. A two-phase model of PUPYM, which best describes the experimental data of DMTA and SAXS, is proposed. One microphase is the hard domain of self-segregated hard segments brought about by metal-ligand interaction, and the other phase is the matrix of soft segments. Transition metal ion-ligand moieties and their interactions dominate the macroscopic thermal behavior of PUPYM. The ligand field stabilization energy difference (Delta LFSE) between metal d-electrons in complexes with two picolyl ligan ds in the coordination sphere of metal ions and complexes maintaining one p icolyl ligand as coordination pendent group is calculated on the basis of o bserved coordination structure, and it represents the energy supplied to sp lit coordination cross-links. Delta LFSE of polyurethane nickel(II) complex is larger than that of the cobalt(II) complex. Since the mobility of hard segments is in inverse proportion to the strength of coordination cross-lin ks, a higher ct-transition temperature of PUPYNi2+ with respect to PUPYCo2 is found as expected.