Nuclear magnetic resonance spectroscopic characterisation and the crystal and molecular structures of Ph3PS·AlCl3 and Ph3PSe·AlCl3: a classification of the co-ordinative bonding modes of the phosphine chalcogenides. - Burford, Neil; Royan, Bruce W.; Spence, Rupert E. v. H. (Journal of the Chemical Society, Dalton Transactions, 1990)