Crystallographic and thermal investigations of organic ammonium tetrathiomolybdates

The organic ammonium tetrathiomolybdates N-methylethylenediammonium tetrathiomolybdate (N-Me-enH2)[MoS4] (1), N-(3-aminopropyl)propane-1,3-diaminium tetrathiomolybdate (dipnH2)[MoS4] (2), 4-(2-ammonioethyl)piperazin-1-ium tetrathiomolybdate hemihydrate (2-pipH-1-EtNH3)[MoS4] · 1/2H2O (3) and 2,2′-iminodiethanaminium tetrathiomolybdate (dienH2)[MoS4] (4), were synthesized by an aqueous reaction of ammonium tetrathiomolybdate with the organic amines N-methylethylenediamine (N-Me-en), bis(3-aminopropyl)amine (dipn), 2-piperazin-1-ylethanamine (2-pip-1-EtNH2) and bis(2-aminoethyl)amine (dien), respectively. All compounds were characterized by elemental analysis, 1H NMR, IR, Raman and UV–Vis spectra, and the crystal structures of compounds 1–3 were determined. The structures of 1–3 consist of diprotonated organic cations, which are linked to the tetrahedral [MoS4]2− anions with the aid of several weak H-bonding interactions. The MoS4 tetrahedron in all compounds is slightly distorted with one or more Mo–S bonds being elongated, which can be attributed to the H-bonding interactions. The difference Δ between the longest and the shortest Mo–S bond lengths for 1–3 are 0.0379, 0.0186 and 0.0302 Å, respectively. Unlike 1 and 2, which are anhydrous, compound 3 is a hemihydrate. The water molecule in 3 occupies the pores between alternating layers of the cations and anions in the crystallographic bc-plane. Compound 3 exhibits four types of weak H-bonding interactions namely N–H⋯S, N–H⋯O, O–H⋯S and C–H⋯S. All four tetrathiomolybdates decompose endothermically forming amorphous disulfides containing C and N. A comparative structural description of 28 tetrathiomolybdates is presented.

Graphical abstractThe structures of N-methylethylenediammonium tetrathiomolybdate, N-(3-aminopropyl)propane-1,3-diaminium tetrathiomolybdate, 4-(2-ammonioethyl)piperazin-1-ium tetrathiomolybdate hemihydrate consist of tetrahedral tetrathiomolybdate anions which are linked to the organic ammonium cations with the aid of weak hydrogen bonding interactions. A comparative study of the structural features of 28 tetrathiomolybdates is described.Figure optionsDownload full-size imageDownload as PowerPoint slide