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Magnetic and electrical features of 1D and 3D oxalate-bridged coordination polymers

The design and synthesis of new materials with targeted physical properties represents an operative area of research for materials scientists. The combination of magnetic oxalate- based coordination polymers with organic/inorganic functional cations provides a suitable approach for designing hybrid magnetic materials exhibiting multifunctional properties. The oxalate moiety, C2O4 2−, acts as a linker between metal centers, with various possibilities of coordination to metal centers yielding open structures with dimensionalities ranging from 0 to 3. A property of oxalate ions that has been of specific interest is their ability to mediate electronic effects between paramagnetic metal ions. Proton conductivity is a new performance of the coordination polymers since they could provide required proton-conducting pathways, mostly by introducing (i) the guest molecules and counterions or acids into the voids, creating complicated hydrogen-bonded networks ; (ii) other functional groups which can improve the acidity and hydrophilicity of the organic ligands and thus form an efficient proton transport pathway. Three novel oxalate-bridged coordination polymers have been synthesized using [Cr(C2O4)3] 3− as building block: 1D 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), as well as 3D heterotrimetallic {; ; ; ; [CaCr2Cu2(phen)4(C2O4)6]·4CH3CN·2H2O}; ; ; ; n (3) (1, 10- phenanthroline), and their structural diversity is reflected on magnetic and electrical properties which have been studied. The Mn-chains of 1 are antiferromagnetic ; 2 shows the existence of antiferromagnetic oxalate-bridged Cu2+ dimers, which are independent from the oxalate- bridged Cu2+ and Cr3+ ions interacting ferromagnetically ; 3 displays dimeric behavior, with Cu2+ and Cr3+ ions coupled ferromagnetically. Further, polymers 1 and 3 exhibit lower electrical conductivity at RT in comparison to compound 2.

coordination polymers ; oxalate-bridged ; crystal structure ; electrical property ; magnetic property

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