First Ni-II-Ln(III) coordination polymers constructed by using [Ni(bpea)(2)] as a building block [Hbpca = bis(2-pyridylcarbonyl)amine]: Synthesis, crystal structures and magnetic properties

Three new heterobimetallic 1D coordination polymers have been obtained by assembling the [Ni(bpca)(2)] complex, as a building block, with lanthanide cations: [{Ln(O2NO)(H2O)(3)}{Ni(bpca)(2)}](NO3)(2)center dot 3H(2)O (Ln Gd 1; Tb 2; Dy 3). The three compounds are isostructural and their structure consists of infinite cationic chains with Ln(III). ions connected by [Ni(bpca)21 complexes acting as bridging bis-bidentate ligands. The charge of the chains is counterbalanced by uncoordinated nitrate ions. The Ln(III). ions display a coordination number of nine: four oxygen atoms from the carbonyl groups of the bpca ligands belonging to two {Ni(bpca)(2)} moieties, two oxygen atoms from a chelating nitrato ion and three water molecules. The magnetic investigation of the gadolinium derivative I revealed very weak intrachain Ni-II-Gd-III-ferromagnetic interactions (theta = +0.15 K). The weak intrachain-exchange interactions, as well as the bad magnetic isolation of the chains in the crystals, preclude the single-chain magnet behaviour of compounds 2 and 3. The out-of-phase, chi '', signal observed with compounds 2 and 3 can be ascribed to the magnetic slow relaxation of the lanthanide ions (Tb-III, Dy-III).