Structural and spectroscopic characterisation of bis[1-(diaminomethylene)thiouron-1-ium] fumarate.

The single crystals of bis[1-(diaminomethylene)thiouron-1-ium] fumarate were grown using a solution growth technique. The compound crystallises in the centrosymmetric P21/c space group of the monoclinic system. The conformation of the 1-(diaminomethylene)thiouron-1-ium cation is not strictly planar, but twisted. Both arms of the cation are oppositely rotated by 13.8(1)_ around the CAN bonds involving the central N atom. The fumarate(2_) anion is also non-planar, both deprotonated carboxylate groups are oppositely turned in relation to the planar carbon chain. The arrangement of oppositely charged components, i.e. 1-(diaminomethylene)thiouron-1-ium cations and fumarate(2_) anions in the crystal is mainly determined by ionic and hydrogen-bonding interactions forming three-dimensional network. The compound was also characterised by the FT-IR and Raman spectroscopy. The characteristic bands of the NH2, C=S and COO_ groups as well as of CANAC, NACAN, CACOO and C@CAC skeletal groups are discussed. The vibrational assignments have been supported by the isotropic frequency shift