Molecular squares of NiII and CuII: ferromagnetic exchange interaction mediated by syn–anti carboxylate-bridging

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Abstract

The synthesis of four discrete tetranuclear complexes {[Ni(II)(L(2))][ClO(4)]}(4).MeCN (1), {[Cu(II)(L(1))(O(3)SCF(3))]}(4).H(2)O (), {[Cu(II)(L(3))(OClO(3))]}(4).MeCN () and {[Cu(II)(L(4))][ClO(4)]}(4).3MeCN.4H(2)O (4), supported by a closely similar group of carboxylate-appended (2-pyridyl)alkylamine ligands [L(1)(-): 3-[N-methyl-{2-(pyridin-2-yl)ethyl}amino]propionate; L(2)(-): 3-[(2-(pyridin-2-yl)ethyl){2-(pyridin-2-yl)methyl}amino]propionate; L(3)(-): 3-[N-isopropyl-{2-(pyridin-2-yl)methyl}amino]propionate and L(4)(2-): 3-[N-{2-(pyridin-2-yl)methyl}amino]-bis(propionate)] is described. Structural characterization reveals that each Ni(II) centre in 1 has square-pyramidal Ni(II)N(3)O(2) coordination and each Cu(II) centre in 2-4 has distorted square-pyramidal Cu(II)N(2)O(3) coordination, utilizing three N and one carboxylate O in 1 and two N and carboxylate O (one in 2 and 3; two in 4) of the ligand and the fifth/fourth coordination is provided by an oxygen atom belonging to the carboxylate group of an adjacent molecule. A CF(3)SO(3)(-) or a ClO(4)(-) ion provides an O coordination in 2 and 3, respectively. Temperature-dependent magnetic studies reveal the existence of ferromagnetic exchange interaction in each case, due to the presence of equatorial-equatorial syn-anti carboxylate bridge between M(II) centres.

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