engleski

Magnetic behaviour of novel metal-organic low dimensional magnetic coordination polymers containing Mn, Cr, Cu and Ca metals

Coordination polymers with metal-organic frameworks and organic or inorganic functional cations offer many possibilities in constructing interesting multifunctional materials such as ferromagnetic conductors, photo and piezo switching magnets, chiral magnets and multiferroics. Especially interesting are oxalate-based compounds, where the C2O42-acts as a linker between metal centres and provides various possibilities of coordination to metal centres resulting in structures with different dimensionalities. The other useful property of oxalate ions is their ability to mediate super-exchange interaction.In this work we will present magnetic behaviour of three novel metal-organic coordination polymers synthetized by a layering technique. The investigated compounds consist of single or multi metal cations bridged by an oxalate ion. The first compound, {; ; Mn(bpy) (C2O4) ·1.5H2O }; ; n, has a 1D chain structure, where the chains are connected by πinteractions between 2, 2’ bipyridyl molecules coordinated on the manganese ions of neighbouring chains. The second compound, {; ; [CrCu(bpy)(C2O4)3] [CrCu3(bpy)3(CH3OH)(H2O) (C2O4)4]·CH2Cl2·CH3OH·H2O}; ; n , consists of two kinds of chains in which two metal ions, chromium and copper ions, are bridged by the oxalate ion. The 2, 2’-bipyridyl molecules are coordinated on the copper ions, enabling the existence of πinteraction between the chains. One chain consists of only Cu and Cr ions bridged by oxalate, while the other chain has two more Cu atoms connected to the Cr ion. The third compound, {; ; [CaCr2Cu2(phen) (C2O4)6]n·4CH3CN·2H2O}; ; n, is a two dimensional coordination polymer which consists of copper, chromium and calcium ions bridged by the oxalate bridge in the 2D network. The molecule coordinated on the copper is a 1, 10- phenanthroline. The magnetic properties of polycrystalline samples in powder form were investigated using a MPMS5 SQUID magnetometer. Temperature dependence of magnetization was measured in the temperature range 2 -400 K, measuring both zero field cooled (ZFC) and field cooled (FC) magnetization curves. The MT curve of a single metal chain compound showed a broad peak at 15K, characteristic of antiferromagnetic chains, while the other two compounds show curves similar to the paramagnetic ones, with no maximum, or saturation at low temperatures, indicating a more complex magnetic coupling. The field dependence of magnetization was measured up to 5 T. The MH curve for the first compound is almost linear with no saturation, characteristic of antiferromagnetic chains, and the value of 1.1 μB/f.u. at 5T and 2K. The second and third compound show saturation of the magnetization at the value of 8 and 7 μB/f.u. respectively, indicating ferromagnetic or ferrimagnetic coupling of Cu and Cr ions.

coordination polymers ; oxalate-bridged ; magnetic property

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