Mono- and dinuclear gold(I) thio- and selenocyanate complexes

Complexes of the type (R₃P)AuSCN and (R₃P)AuSeCN have been prepared in high yields from the corresponding chlorides (R₃P)AuCl by treatment with KSCN or KSeCN, respectively, in a two-phase water/dichloromethane system. Crystal structure determinations revealed discrete monomeric molecules for the isomorphous thiocyanate and selenocyanate compounds with R=2-MeC₆H₄. For R=ⁱPro there is only weak association into dimers via long Au-S contacts, but for R₃=Me₂PhP chain-like polymers are formed via short aurophilic interactions [Au-Au, 3.2334(2) and 3.2533(2) Å]. A monoclinic modification of (Ph₃P)AuSCN was found, which shows a standard geometry of the molecules. An orthorhombic modification published previously featured a doubtful strongly distorted molecular geometry. All compounds of the type (R₃P)AuS/SeCN can be converted into salts with dinuclear cations {[(R₃P)Au]₂S/SeCN}⁺Y^- on reaction with equimolar quantities of [(R₃P)Au]⁺Y^- (Y=BF₄, SbF₆) as confirmed by analytical and spectroscopic data. The S/SeCN units are found to be bridging the two metal atoms via the S/Se atoms. The tetrafluoroborates are less stable than the hexafluoroantimonates, and all selenocyanate complexes are markedly less stable thermally and more sensitive towards air and moisture than their sulfur counterparts.