BEDT-TTF based molecular conductor containing the [Ni(H2O)5Br]+ magnetic cation

- New molecular metal β”-(BEDT-TTF)3[Ni(H2O)5Br]2Br4 has been prepared, TMI = 172 K.
- The octahedral cation [Ni(H2O)5Br]+ is for the first time observed in solid state.
- BEDT-TTF bond lengths distribution at 100 K indicates charge separation.
- Magnetic susceptibility of 1 is defined mainly by octahedral nickel(II) cations.
- Ferromagnetic coupling in Ni2+ chains and interchain antiferromagnetic order.

An organic conductor of a new unusual composition β″-[(BEDT-TTF)3]2+([Ni(H2O)5Br]+)2(Br‾)4 includes cations of two types: organic cations containing π conduction electrons (BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene) and inorganic cations carrying 3d localized magnetic moments. Single-crystal study reveals that the octahedral [Ni(H2O)5Br]+ cations form a network by hydrogen bonds, and the organic cations form conductive layers of a β″-type donor arrangement; the networks and the layers are separated by bromine anions. Resistivity measurements show metallic behavior with a metal-insulator transition at TMI = 172 K. Charge disproportionation between BEDT-TTF molecules have been found in the crystal structure below TMI from the BEDT-TTF intramolecular bond length distribution. Magnetic susceptibility of 1 is defined mainly by nickel(II) cations and, in combination with the structural data, allows us to assume weak ferromagnetic coupling in the Ni(II) chains and antiferromagnetic coupling between these chains. The ESR signal comes mainly from the conduction π-electrons of BEDT-TTF+.

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