Synthesis, crystal structures and properties of three new tetrathiomolybdates with organic ammonium cations

Abstract

Three new tetrathiomolybdates (pipH(2))[MoS4] (1), (trenH(2))[MoS4]. H2O (2) and [(prop)(4)N](2)[MoS4] (3) (pip = piperazine, tren = tris(2-aminoethyl)amine and prop = n-propyl) were synthesized and characterized by elemental analysis, infrared spectroscopy, single crystal X-ray crystallography, and thermoanalysis. All compounds were prepared by the base promoted cation exchange method i.e. by the reaction of the ammonium salt of [MoS4](2-) with the corresponding organic amine or organic ammonium hydroxide. In the compounds 1 and 2 the organic amines pip and tren are diprotonated and they are linked to the tetrahedral [MoS4](2-) dianions through weak hydrogen bonding, interactions. The strength and number of these hydrogen bonds affect the Mo-S bond lengths an a relatively long Mo-S bond of 2.2114(8) Angstrom is observed in 1 while the longest Mo-S bond in 2 is 2.1951(5) Angstrom. In compound 3 no (SH)-H-.-N interactions are possible and the Mo-S bond lengths scatter in a more narrow range compared to those in compounds 1 and 2. The thermal behavior was investigated using differential thermal analysis and thermogravimetry. On heating compound 1 decomposes in two closely related steps while 2 loses first the crystal water followed by the decomposition of the tetrathiomolybdate. The final products are amorphous molybdenum sulfides. The decomposition of compound 3 yields a very porous material with sponge-like morphology.