Magneto-structural studies on heterobimetallic malonate-bridged MIIReIV complexes (M = Mn, Co, Ni and Cu)

The mononuclear Re(IV) compound of formula (PPh4)(2)[ReBr4(mal)] (1) was used as a ligand to obtain the heterobimetallic species [ReBr4(mu-mal)Co(dmphen)(2)]center dot MeCN (2), [ReBr4(mu-mal)Ni(dmphen)(2)] (3), [ReBr4(mu-mal)Mn(dmphen)(2)] (4a), [ReBr4(mu-mal)Mn(dmphen)(H2O)(2)]center dot dmphen center dot MeCN center dot H2O (4b), [ReBr4(mu-mal)Cu(phen)(2)]center dot 1/4H(2)O (5) and [ReBr4(mu-mal)Cu(bipy)(2)] (6) (mal = malonate dianion, dmphen = 2,9-dimethyl-1,10-phenanthroline, phen = 1,10-phenanthroline and bipy = 2,2'-bipyridine). The structures of 2 and 5 (single-crystal X-ray diffraction) are made up of neutral [ReBr4(mu-mal)M(AA)] dinuclear units [AA = dmphen with M = Co (2) and AA = phen with M = Cu (5)] where the metal ions are connected through a malonate ligand which exhibits simultaneously the bidentate [at the Re(IV)] and monodentate [at the M(II)] coordination modes. The carboxylate-malonate group in them adopts the anti-syn conformation with intramolecular Re center dot center dot center dot M separation of 5.098(8) (2) and 4.947(2) angstrom (5). The magnetic properties of 1-6 were investigated in the temperature range 1.9-295 K. The magnetic behaviour of 1 is the expected for a magnetically isolated Re(IV) complex with a large value of the zero-field splitting (2D ca. -70 cm(-1)) whereas weak antiferromagnetic interactions between Re(IV) and M(II) are observed in the heterobimetallic compounds 2 (J = -0.63 cm(-1)), 3 (J = -1.37 cm(-1)), 4a (J = -1.29 cm(-1)), 5 (J = -1.83 cm(-1)) and 6 (J = -0.26 cm(-1)). Remarkably, 4b behaves as a ferrimagnetic chain with regular alternating Re(IV) and Mn(II) cations (J = -2.64 cm(-1)).