Crystalline adducts, Ph2Hg·2L (L = 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, and 2,4,7,9-tetramethyl-1,10-phenanthroline), have been prepared by reaction of diphenylmercury and the appropriate ligands in hexane, but derivatives of the mercurial with a range of ligands having nitrogen, phosphorus, arsenic and oxygen donor atoms could not be prepared. No definite evidence for coordination of the phenanthroline ligands in the solid adducts could be obtained by infrared or ultraviolet spectroscopy. Molecular weights of the adducts in benzene or chloroform showed them to be completely dissociated in solution. Similar measurements for mixtures of the mercurial and a range of ligands in benzene showed no evidence for complex formation. Thus, any acceptor properties of diphenylmercury appear to be very weak.