Thermal properties of [Ni(5,5´-dmbpy)3](TCNQ)2 complex. Crystal structure of KTCNQ at 200 ºC.

From methanolic solutions of Ni(NO3)2, 5,5ˈ-dimethyl-2,2ˈ-bipyridine and LiTCNQ (TCNQ = 7,7,8,8-tetracyanidoquinodimethane), complex [Ni(5,5ˈ-dmbpy)3](TCNQ)2 was isolated and its thermal properties were studied. The complex is stable in air atmosphere up to 208 ºC. The thermal decomposition consists in 3 consecutive steps in the temperature ranges 208-274 ºC (weight loss of 10.0 %), 274-401 ºC (17.5 %) and 401-495 ºC (64.2 %). The weight of the solid residue (8.3 %) corresponds to formation of NiO (calc. 7.3 %).KTCNQ was prepared reacting boiling acetonitrile solutions of TCNQ and KI. It is thermally stable up to 300 ºC. Its crystal structure at 200 ºC was determined. KTCNQ consists of one crystallographically independent TCNQ- anion and one potassium cation K+. Each K+ cation is octa-coordinated by eight nitrogen atoms from cyanide groups of TCNQ- anions. This crystal structure corresponds to the high-temperature phase of KTCNQ. As expected, the cell volume is by 1.5 % larger than the reported value measured at 140 ºC.