Structural studies on tris(2-cyanoethyl)phosphine complexes of Cu(I): The sensitivity of the secondary nitrile coordination to the nature of the anion

Tris(2-cyanoethyl)phosphine (tcep) reacts with the copper(I) compounds, CuX (X = Cl, Br, I and SCN), in a 1:1 ratio to give 1:1 complexes, CuX(tcep), whereas it reacts with CuY (Y = PF 6 , ClO 4 , NO 3 , BH 4 , CN and CF 3 COO) in a 2:1 ratio to give the 2:1 complexes, CuY(tcep) 2 . Single crystal X-ray structures show that for the anions X = Br and SCN, the complexes are coordination polymers, [CuX(tcep)] n , with the Cu centres being bridged by the anion, and as well, one nitrile arm per tcep ligand coordinates intermolecularly to the Cu to give tetrahedral ‘PBr 2 N’ and ‘PSN 2 ’ coordination spheres respectively. The 2:1 compounds exhibit a variety of structures. For Y = ClO 4 , CN and CF 3 COO polymeric structures are formed except for Y = BH 4 where the compound is a discrete monomer, [Cu(BH 4 )(tcep) 2 ], with a chelating anion and two monodentate P-bound tcep ligands. Both the compounds obtained with Y = CN and CF 3 COO also contain coordinated anions and are formulated as [Cu(CN)(tcep) 2 ] n and [Cu(CF 3 COO)(tcep) 2 ] n respectively. In the case of Y = CN the anion is bridging and the tcep ligands are only P-bound giving a ‘P 2 NC’ coordination sphere. In contrast, for Y = CF 3 COO, the anion is an O-bound monodentate and the tcep ligands bridge to give a ‘P 2 NO’ environment for the copper. In the case of Y = ClO 4 , the anion is not coordinated but a polymeric structure, [Cu(tcep) 2 ] n (ClO 4 ) n , is formed via bridging tcep ligands linking Cu centres intermolecularly resulting in a ‘P 2 N 2 ’ coordination sphere.