THEORETICAL PREDICTION OF A POLYCYCLIC MODIFICATION OF POLYTHIAZYL - A NEW MOLECULAR SUPERCONDUCTOR

MNDO and AM1 calculations indicate that polythiazyl, (SN)x, could, und er high pressure, undergo exothermic formation of a polycyclic (SNNS)x . The methods give satisfactory geometries for the known S3N3-, S3N2Cl +, S3N2, and S4N2 and a heat of formation in reasonable agreement with the ''experimental'' value for S4N4(g). In (SNNS)x the nearest-neighb or S-S distances and the S to N charge transfer are reduced relative t o (SN)x, and the S atoms are linearly disposed. Studies of three model compounds suggest that decomposition of the polymer would be initiate d by scission of N-S bonds and that its kinetic stability would be com parable with that of polythiazyl. Although no specific mechanism for s uperconductivity in these materials is introduced here, an analysis of the high-pressure behavior of (SN)x suggests the possibility that bec ause (SNNS)x would have a more rigid chain, a shorter S-S intrachain d istance, and a lesser charge transfer from S to N than (SN)x, the supe rconducting T(c) of a sufficiently long structure for (SNNS)x could ex ceed that for compressed semimetallic (SN)x which, at present, is the only empirically known, undoped polymer which becomes superconducting.