One-dimensional Co^II and Cu^II coordination polymers and a discrete Cu^II₄ complex of carboxylate-appended (2-Pyridyl)alkylamine ligands: spin-canting and anti-/ferromagnetic coupling

Abstract

Structural characterization of the newly synthesized complexes [M^II(L¹OO)(xH₂O)][ClO₄]·2H₂O [M = Co, x = 1 (1); M = Cu, x = 0 (2); L¹OO- = 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(L²OO)(OClO₃)]}₄·MeCN (3) [L²OO^- = 3-[N-methyl-{2-(pyridine-2-yl)ethyl}amino]propionate]. Analysis of the crystal packing diagrams reveals extensive π-π 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 μ_B, respectively. Analysis of the magnetic data through spin Hamiltonians in the form H = ∑_i<jⁿ -J_ijSiSj (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.