Behaviour of the one-dimensional, inorganic polymer 1∞[MPS4]- anions (M = Ni, Pd) in organic solutions

The behaviour of the KMPS4 (M = Ni, Pd) sails and some solid-solution phases, KNixPd1-xPS4, when dissolved in dimethylformamide (DMF) have been studied. For KNiPS4-DMF the novel re-arranged molecular bowl-like [Ni3P3S12](3-) trianion can be formed from solutions that have been heated at 323 K for 2 days and K+ exchanged by larger organic cations such as PPh4+ (tetraphenylphosphonium),TMA(+) (tetramethylammonium), TEA(+) ( tetraethylammonium), and MEM+ (methylethylmorpholinium). This remarkable dispersion/auto-fragmentation/re-arrangement sequence extends the concept of mere excision in solution of monomeric molecular motifs from low-dimensional inorganic solids. Investigations by electrospray mass spectrometry (ESMS), P-31 solution-state NMR and optical microscopy under polarized light of KNiPS4 in DMF have shown that chains of (1)(infinity)[MPS4](-) exist intact in freshly prepared solutions. These solutions show transient birefringence under stress. ESMS and NMR studies of KNIPS4 solutions show that the (1)(infinity)[NiPS4](-) chains are quickly broken down at ambient temperature and that cyclic [Ni3P3S12](3-) trianions are formed. By contrast, the (1)(infinity)[PdPS4](-) chain remains intact at temperatures up to 323 K. This behavioural difference can be understood in terms of the Ni-S and Pd-S bond strengths. ESMS spectra of aged KNixPd1-xPS4/DMF solutions indicate that mixed metal trianions are formed, such as [Ni2PdS12](3-), [NiPd2P3S12](3-) and [Ni3P3S12](3-), but no [Pd3P3S12](3-) species have yet been observed.