Oligo-nuclear silver thiocyanate complexes with monodentate tertiary phosphine ligands ligands, including novel ‘cubane’ and ‘step’ tetramer forms of AgSCN : PR3 (1 : 1)4

Adducts of a number of tertiary pnicogen ligands ER3 (triphenyl-phosphine and -arsine (PPh3,AsPh3), diphenyl,2-pyridylphosphine (PPh2py), tris(4-fluorophenyl)phosphine (P(C6H4-4F)3), tris(2-tolyl)phosphine (P(o-tol)3), tris(cyclohexyl)phosphine (PCy3)), with silver(I) thiocyanate, AgSCN are structurally and spectroscopically characterized. The 1 : 3 AgSCN : ER3 complexes structurally defined (for PPh3,AsPh3 (diversely solvated)) take the form [(R3E)3AgX], the thiocyanate X = NCS being N-bound, thus [(Ph3E)Ag(NCS)]. A 1 : 2 complex with PPh2py, takes the binuclear form [(pyPh2P)2Ag(SCN NCS)Ag(PPh2py)2] with an eight-membered cyclic core. 1 : 1 complexes are defined with PPh2py, P(o-tol)3 and PCy3; binuclear forms [(R3P)Ag- (SCN NCS)Ag(PR3)] are obtained with P(o-tol)3 (two polymorphs), while novel isomeric tetranuclear forms, which may be envisaged as dimers of dimers, are obtained with PPh2py, and, as further polymorphs, with PCy3; these latter may be considered as extensions of the ‘cubane’ and ‘step’ forms previously described for [(R3E)AgX]4 (X = halide) complexes. Solvent-assisted mechanochemical or solvent-assisted solid-state synthesis methods were employed in some cases, where complexes could not be obtained by conventional solution methods, or where such methods yielded a mixture of polymorphs unsuitable for solid-state spectroscopy. The wavenumbers of the ν(CN) bands in the IR spectra are in broad agreement with the empirical rule that distinguishes bridging from terminal bonding, but exceptions occur for compounds that have a double SCN bridged dimeric structure, and replacement of PPh3 with PPh2py apparently causes a significant decrease in ν(CN) to well below the range expected for bridging SCN in these structures. 31P CP MAS NMR spectra yield additional parameters that allow a correlation between the structures and spectra.