文摘
Two novel heterobimetallic complexes of formula [Cr(bpy)(ox)2Co(Me2phen)(H2O)2][Cr(bpy)(ox)2]路4H2O (1) and [Cr(phen)(ox)2Mn(phen)(H2O)2][Cr(phen)(ox)2]路H2O (2) (bpy = 2,2鈥?bipyridine, phen = 1,10-phenanthroline, and Me2phen = 2,9-dimethyl-1,10-phenanthroline) have been obtained through the 鈥渃omplex-as-ligand/complex-as-metal鈥?strategy by using Ph4P[CrL(ox)2]路H2O (L = bpy and phen) and [ML鈥?H2O)4](NO3)2 (M = Co and Mn; L鈥?= phen and Me2phen) as precursors. The X-ray crystal structures of 1 and 2 consist of bis(oxalato)chromate(III) mononuclear anions, [Crp>IIIp>L(ox)2]p>鈭?/sup>, and oxalato-bridged chromium(III)-cobalt(II) and chromium(III)-manganese(II) dinuclear cations, [Crp>IIIp>L(ox)(渭-ox)Mp>IIp>L鈥?H2O)2]p>+p>[M = Co, L = bpy, and L鈥?= Me2phen (1); M = Mn and L = L鈥?= phen (2)]. These oxalato-bridged Crp>IIIp>Mp>IIp> dinuclear cationic entities of 1 and 2 result from the coordination of a [Crp>IIIp>L(ox)2]p>鈭?/sup> unit through one of its two oxalato groups toward a [Mp>IIp>L鈥?H2O)2]p>2+p> moiety with either a trans- (M = Co) or a cis-diaqua (M = Mn) configuration. The two distinct Crp>IIIp> ions in 1 and 2 adopt a similar trigonally compressed octahedral geometry, while the high-spin Mp>IIp> ions exhibit an axially (M = Co) or trigonally compressed (M = Mn) octahedral geometry in 1 and 2, respectively. Variable temperature (2.0鈥?00 K) magnetic susceptibility and variable-field (0鈥?.0 T) magnetization measurements for 1 and 2 reveal the presence of weak intramolecular ferromagnetic interactions between the Crp>IIIp> (SCr = 3/2) ion and the high-spin Cop>IIp> (SCo = 3/2) or Mnp>IIp> (SMn = 5/2) ions across the oxalato bridge within the Crp>IIIp>Mp>IIp> dinuclear cationic entities (M = Co and Mn) [J = +2.2 (1) and +1.2 cmp>鈥?p> (2); H = 鈥?i>JSCr路SM]. Density functional electronic structure calculations for 1 and 2 support the occurrence of S = 3 Crp>IIIp>Cop>IIp> and S = 4 Crp>IIIp>Mnp>IIp> ground spin states, respectively. A simple molecular orbital analysis of the electron exchange mechanism suggests a subtle competition between individual ferro- and antiferromagnetic contributions through the 蟽- and/or 蟺-type pathways of the oxalato bridge, mainly involving the dyz(Cr)/dxy(M), dxz(Cr)/dxy(M), dxp>2p>鈥?i>yp>2p>(Cr)/dxy(M), dyz(Cr)/dxz(M), and dxz(Cr)/dyz(M) pairs of orthogonal magnetic orbitals and the dxp>2p>鈥?i>yp>2p>(Cr)/dxp>2p>鈥?i>yp>2p>(M), dxz(Cr)/dxz(M), and dyz(Cr)/dyz(M) pairs of nonorthogonal magnetic orbitals, which would be ultimately responsible for the relative magnitude of the overall ferromagnetic coupling in 1 and 2.