One-Dimensional CoII and CuII Coordination Polymers and a Discrete Cu4II Complex of Carboxylate-Appended (2-Pyridyl)alkylamine Ligands: Spin-Canting and Anti-/Ferromagnetic Coupling

Structural characterization of the newly synthesized complexes [M-II((LOO)-O-1)(xH(2)O)][ClO4]center dot 2H(2)O [M = Co, x = 1 (1); M = Cu, x = 0 (2); (LOO-)-O-1 = 3-[(2-(pyridin-2-yl)ethyl){2-(pyridin-2-yl)methyl}amino]propionate] reveals that 1 and 2 are 1D chainlike coordination polymers. A tridentate variety of this ligand afforded a discrete tetranuclear complex {[Cu-II((LOO)-O-2)(OClO3)]}(4)center dot MeCN (3) [(LOO-)-O-2 = 3-[N-methyl-{2-(pyridine-2-yl)ethyl}amino]propionate]. Analysis of the crystal packing diagrams reveals extensive pi-pi stacking in 1 and C-H...O hydrogen bonding interactions in 3, leading to the formation of network structures. For these complexes, absorption spectral properties have been investigated. All three complexes exhibit exchange interaction between the M-II ions through a syn-anti bridging carboxylate pathway. Magnetic studies on 1 show spontaneous magnetization below 5 K, which corresponds to the presence of spin-canted antiferromagnetism. At T = 2 K, the values of coercive field (H-c) and remnant magnetization (M-r) are 200 G and 0.019 mu(B), respectively. Analysis of the magnetic data through spin Hamiltonians in the form (H) over cap = Sigma(n)(Kj) -Jij (S) over cap (i)(S) over cap (j) (J is positive for a ferromagnetic interaction and negative for an antiferromagnetic interaction) leads to the following set of best-fit parameters: J = -2.65(2), -0.66(1), and +12.2(2) cm(-1) for 1, 2, and 3, respectively. An attempt has been made to rationalize the observed magnetic behavior.