Conformational polymorphism in a mononuclear phosphanegold(I) thiocarbamato species, Cy₃PAu[SC(OEt)=N(C₆H₄Cl-3)]

Abstract Two polymorphs of Cy 3 PAu[SC(OEt)=N(C 6 H 4 Cl-3)], that is a triclinic form ( P <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <m:mrow> <m:mover accent="true"> <m:mn>1</m:mn> <m:mo>‾</m:mo> </m:mover> </m:mrow> </m:math> $\overline{1}$ with Z ′ = 1; the α -form) and a monoclinic form ( P 2 1 / c ; Z ′ = 1; the β -form) have been characterised. The molecular structures feature linear P–Au–S coordination geometries with close intramolecular Au⋯O(ethoxy) contacts of 3.1552(17) and 3.097(2) Å for the α - and β -forms, respectively. The major conformational differences between the polymorphs relates to the relative orientations of the thiocarbamato anions and of the cyclohexylphosphane ligands. Computational chemistry shows the molecular structures to be isoenergetic (single-point calculations) and to have practically a zero barrier to interconversion. An analysis of the molecular packing highlights the importance of cyclohexyl-C–H···S(thiolate) and methyl-C–H···π(chlorophenyl) contacts in the crystal of the α -form, and methyl-C–H···π(chlorophenyl) and π(chlorophenyl)···π(chlorophenyl) contacts in the packing of the β -form. While similarities are apparent in the solid-state luminescence spectra, different electronic transitions are responsible for the spectroscopic observations.