Abstract
One-dimensional (1D) oxalate-bridged homometallic {[Mn(bpy)(C2O4)]·1.5H2O}n (1) (bpy = 2,2’-bipyridine) and heterodimetallic {[CrCu3(bpy)3(CH3OH)(H2O)(C2O4)4][Cu(bpy)Cr(C2O4)3]·CH2Cl2·CH3OH·H2O}n (2) coordination polymers, as well as the three-dimensional (3D) heterotrimetallic {[CaCr2Cu2(phen)4(C2O4)6]·4CH3CN·2H2O}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 𝐽 = (−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]nn− (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)(µ-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]·4CH3CN·2H2O}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 (66) topology. Magnetization of 3 shows the ferromagnetic oxalate-bridged dimers [CuIICrIII], 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.
Highlights
The design and synthesis of new materials with targeted physical properties represents an operative area of research for materials scientists, chemists and physicists
As a continuation of our magneto-structural studies about the oxalate-bridged polymers prepared by a building block approach [23,24,25,26,27], we report crystal structures, electrical and magnetic properties of novel oxalate-bridged coordination compounds: one-dimensional (1D) homometallic {[Mn(bpy)(C2 O4 )]·1.5H2 O}n (1) and heterodimetallic
Thermal properties were investigated from room temperature (RT) to 1000 ◦ C in a nitrogen atmosphere with a Shimadzu DTG-60H analyzer
Summary
The design and synthesis of new materials with targeted physical properties represents an operative area of research for materials scientists, chemists and physicists. Its various possibilities of coordination to the metal centres and the ability to mediate magnetic interactions between paramagnetic metal ions has enabled synthesis and characterization of a large number of oxalate-based transition-metal species of different nuclearity and dimensionality, many of them having tunable magnetic frameworks [4]. An appropriate approach for creating hybrid magnetic materials including multifunctional properties is the combination of magnetic oxalate-based coordination polymers with organic/inorganic functional cations. Most of the oxalate-based molecular magnets described so far have been obtained by the “complex-as-ligand approach” [5]. This means that the tris(oxalato)metalate [MIII (C2 O4 )3 ]3− anion (MIII = Cr, Mn, Fe, Ru, Rh, or V) is used as a molecular building block, as a ligand towards another metal cations.
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