title: Molecular squares of Ni(II) and Cu(II): ferromagnetic exchange interaction mediated by syn-anti carboxylate-bridging.
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.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208 016, India.
authors.forename: Himanshu
authors.initials: H
authors.lastname: Arora
authors.forename: Francesc
authors.initials: F
authors.lastname: Lloret
authors.forename: Rabindranath
authors.initials: R
authors.lastname: Mukherjee