Preparation of nano Arsenic(III) sulfide from arsenic(III)-dithiocarbamate precursors: Synthesis, spectral, single crystal X-ray structural, BVS and CSM analysis of tris(disubstituteddithiocarbamato)arsenic(III) complexes

Nano As2S3 was prepared solvothermally from three dithiocarbamte precursor complexes [As(chmdtc)3] (1), [As(chedtc)3] (2) and [As(dchdtc)3] (3) (where chmdtc = cyclohexylmethyldithiocarbamate, chedtc = cyclohexylethyldithiocarbamate and dchdtc = dicyclohexyldithiocarbamate). The nano arsenic trisulfide was characterized by PXRD, SEM-EDX, HRTEM-SAED techniques. The arsenic(III) complexes, (1), (2) and (3) were prepared and characterized by electronic, IR, TG/DTA and NMR (1H and 13C) spectra and single crystal X-ray diffraction. Electronic spectra of the complexes show signature bands in the range: 446–451 nm due to charge transfer transitions. Thioureide νC−N bands observed at 1444, 1468 and 1470 cm−1 for (1), (2) and (3) respectively indicate the partial double bonded nature. NMR spectra show that the immediate environment around thioureide nitrogen was largely affected by complex formation. 13C NMR confirmed the presence of thioureide carbon as a weak signal in the range: 197.63–198.32 ppm. The single crystal X-ray structures of [As(chmdtc)3] (1) [As(chedtc)3] (2) and [As(dchdtc)3] (3) indicate that the central atom is in a highly distorted octahedral environment of sulfur atoms due to the presence of lone pair of electrons. Continuous Shape measures of AsS6 cores in the three complexes are 7.5752, 6.2013 and 8.2473 for (1), (2) and (3) respectively confirm the proximate geometry to be octahedral. Complex (3) deviates to the largest extent from the octahedral geometry than the other two because of the largest steric demand of the two cyclohexyl rings. Two sets of As-S distances, shorter ones are in the range: 2.3164(7)–2.3438(8) Å and the longer ones are in the range: 2.841(2)–2.913(2) Å resulting in heteroleptic bonding. As a contrast to [As(chmdtc)3] (1), ethylcyclo- and dicyclo-analogues show non-covalent S—H, C—H and H—H short contacts, which results in supramolecular interactions. BVS calculations with structural data confirmed the formal oxidation state of arsenic as 3.0.