Magnetic and Electrical Behaviors of the Homo- and Heterometallic 1D and 3D Coordination Polymers Based on the Partial Decomposition of the [Cr(C2O4)(3)](3-) Building Block

One-dimensional (1D) oxalate-bridged homometallic {[Mn(bpy)(C2O4)]center dot 1.5H(2)O}(n) (1) (bpy = 2,2'-bipyridine) and heterodimetallic {[CrCu3(bpy)(3)(CH3OH)(H2O)(C2O4)(4)][Cu(bpy)Cr(C2O4)(3)]center dot CH2Cl2 center dot CH3OH center dot H2O}(n) (2) coordination polymers, as well as the three-dimensional (3D) heterotrimetallic {[CaCr2Cu2(phen)(4)(C2O4)(6)]center dot 4CH(3)CN center dot 2H(2)O}(n) (3) (1,10-phenanthroline) network, have been synthesized by a building block approach using a layering technique, and characterized by single-crystal X-ray diffraction, infrared (IR) and impedance spectroscopies and magnetization measurements. During the crystallization process partial decomposition of the tris(oxalato)chromate(III) happened and 1D polymers 1 and 2 were formed. The antiferromagnetic interactions between the manganese(II) ions were mediated by oxalate ligands in the chain [Mn(bpy)(C2O4)](n) of 1, with intra-chain super-exchange interaction = (-3.134 +/- 0.004) K; magnetic interaction between neighbouring chains is negligible making this system closer than other known Mn-chains to the ideal 1D Heisenberg antiferromagnet. Compound 2 comprises a 1D coordination anion [Cu(bpy)Cr(C2O4)(3)](n)(n)(-) (Cr2-Cu4) with alternating [Cr(C2O4)(3)](3)(-) and [Cu(bpy)](2+) units mutually bridged through the oxalate group. Another chain (Cr1-Cu3) is similar, but involves a homodinuclear unit [Cu(bpy)(H2O)(mu-C2O4)Cu(bpy)(CH3OH)](2+) (Cu1-Cu2) coordinated as a pendant group to a terminal oxalate oxygen. Magnetic measurements showed that the Cu1-Cu2 cationic unit is a strongly coupled antiferromagnetic dimer, independent from the other magnetic ions within ferromagnetic chains Cr1-Cu3 and Cr2-Cu4. A 3D polymer {[CaCr2Cu2(phen)(4)(C2O4)(6)]center dot 4CH(3)CN center dot 2H(2)O}(n) (3) comprising three different metal centers (Ca2+, Cr3+ and Cu2+) oxalate-bridged, contains Ca2+ atoms as nodes connected with four Cr3+ atoms through oxalate ligands. The network thus formed can be reduced to an underlying graph of diamondoid (dia) or (6(6)) topology. Magnetization of 3 shows the ferromagnetic oxalate-bridged dimers [(CuCrIII)-Cr-II], whose mutual interaction could possibly originate through the spin polarization of Ca2+ orbitals. Compounds 1 and 3 exhibit lower electrical conductivity at room temperature (RT) in comparison to compound 2.