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

Abstract

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=PF6, ClO4, NO3, BH4, CN and CF3COO) 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 ‘PBr2N’ and ‘PSN2’ coordination spheres respectively. The 2:1 compounds exhibit a variety of structures. For Y=ClO4, CN and CF3COO polymeric structures are formed except for Y=BH4 where the compound is a discrete monomer, [Cu(BH4)(tcep)2], with a chelating anion and two monodentate P-bound tcep ligands. Both the compounds obtained with Y=CN and CF3COO also contain coordinated anions and are formulated as [Cu(CN)(tcep)2]n and [Cu(CF3COO)(tcep)2]n respectively. In the case of Y=CN the anion is bridging and the tcep ligands are only P-bound giving a ‘P2NC’ coordination sphere. In contrast, for Y=CF3COO, the anion is an O-bound monodentate and the tcep ligands bridge to give a ‘P2NO’ environment for the copper. In the case of Y=ClO4, the anion is not coordinated but a polymeric structure, [Cu(tcep)2]n(ClO4)n, is formed via bridging tcep ligands linking Cu centres intermolecularly resulting in a ‘P2N2’ coordination sphere.