Syntheses and Structures of Three Types of Hybrid Metal Dipicolinato Complexes Induced by Alkali Metal Ion and the Semiconductor Character

Three types of hybrid transition-alkali metal complexes, [MK2(pdc)2(H2O)7]n (H2pdc = 2,6-pyridinedicarboxylic acid, or so-called dipicolinic acid, M = Mn (1), Co (2), Zn (3), Mn0.5Co0.5 (4)), {[Na2(H2O)8(CH3OH)0.5][Mn2Na2(pdc)4(H2O)8]·0.25CH3OH·2H2O}n (5) and [Ni(H2O)6][Ni2K2(pdc)4(H2pdc)2(H2O)2]·2H2O (6) were self-assembled from a reaction system containing a divalent transition metal, alkali metal and H2pdc, and were isolated under different crystallization conditions. In all complexes, [M(pdc)2]^2- units were included as independent components to connect to the alkali metal chains or pdc units. Alkali metal ions act as templates for inducing the organization of the [M(pdc)2]^2- components into respective special architectures in different fashions. Complexes 1-4 are isostructural with the same space group and similar cell parameters, in which the [M(pdc)2]^2- units are bonded to the water-bridged K chains forming neutral 2D lamellar-like polymers, while 5 contains water-bridged Na chains correlated to Mn2Na2 cluster anions by hydrogen bonds, and 6 is a discrete Ni2K2 tetranuclear cluster consisting of Ni(pdc)2 and K(H2pdc) units. The infrared spectra of these complexes show a large difference between the asymmetrical and symmetrical stretching vibrations, (delta)((nu)as - (nu)s) > 200 cm^-1, for the carboxyl groups, indicating unidentate and unsymmetrical bridging coordination modes. The variable-temperature electrical conductivities of complexes 1-5 were determined to display semiconductor features, and the magnetic properties of 1, 2, 4 and 5 were also studied.