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Synthesis, crystal structures and magnetic properties of linear and bent trinuclear complexes formed by hexacyanometallates and copper(ii) complexes

2002; Royal Society of Chemistry; Issue: 19 Linguagem: Inglês

10.1039/b205749m

1472-7773

R. J. Parker, Kevin D. Lu, Stuart R. Batten, Boujemaa Moubaraki, Keith S. Murray, Leone Spiccia, J.D. Cashion, A. David Rae, Anthony C. Willis,

Metal complexes synthesis and properties

The bimetallic trinuclear complexes, [{(tpa)Cu(NC)}2Fe(CN)4]ClO4·6H2O (1), [{(tren)Cu(NC)}2Fe(CN)4]ClO4·4H2O (2), [{Cu(tpa)NC}2Cr(CN)4]ClO4·8H2O (3) and [{Cu([15]aneN4)NC}2Cr(CN)4]ClO4·4H2O (4) [tpa = tris(2-pyridylmethyl)amine, tren = tris(2-aminoethyl)amine, ([15]aneN4 = 1,5,9,12-tetraazacyclopentadecane] were prepared by addition of solutions of the CuII tpa, tren and [15]aneN4 complexes to solutions of hexacyanometallate, [M(CN)6]3− (M = Fe or Cr), in a 2:1 molar ratio. For 1, an oxidant was added to prevent reduction of the FeIII centre, while for 2, the synthesis was carried out in acetonitrile. 1 Consists of quasi-linear trinuclear units of two trans-oriented [Cu(tpa)]2+ ions linked to the central FeIII core via two bridging cyano groups with the CuII centres residing in a distorted trigonal bipyramidal geometry. Use of a bis(bidentate) Cu(II) chelate, [Cu(H2LN4)2](NO3)2 (H2LN4 = 1,1′,4,4′,5,5′,6,6′-octahydro-2,2′-bipyrimidine), yielded the first example of a non-linear cis-oriented trinuclear complex, [{(H2LN4)2Cu(NC)}2Fe(CN)4]NO3·3H2O (5), in which the CuII centres have a square pyramidal geometry. Magnetic studies on complex 1 show a rapid increase in the magnetic moment below 25 K, consistent with the presence of ferromagnetic coupling between the FeIII (LS, S = ½) and CuII (S = ½) metal centres, where gCu = gFe = 2.16, J12 = 4.3 cm−1, J13 = −0.18 cm−1. The cis-complex, 5, showed close to Curie-like behaviour and gave a good fit to the trimer model using gCu = gFe = 2.31, J12 = 1.95 cm−1, J13 = −2.1 cm−1. The CuIICrIIICuII complex 4 also displayed ferromagnetic coupling across the Cr–CN–Cu bridges because of orthogonal t2g(Cr)/eg(Cu) orbital overlap. Best-fit parameters are g = 2.1, JCuCr = 1.31 cm−1, JCuCu = 0 cm−1. Complexes 2 and 3 showed related ferromagnetic behaviour but which fitted poorly to the trimer model.