“…A number of kinetic and structural studies in the past few years have indicated that the isoelectronic [MX(H 2 O)-(CN) 4 ] nÀ complexes (M = Mo IV , W IV , Tc V , Re V and Os VI , and X = O 2À and N 3À ) are all relatively labile towards monodentate substitution reactions (Leipoldt et al, 1993;Damoense et al, 1994;van der Westhuizen et al, 2002;Mtshali et al, 2006). Our literature search (Cambridge Structural Database;November 2005, Version 5.27;Allen, 2002) revealed two isostructural systems for Re V and Tc V with tetraphenylarsonium as counter-ions and X = N 3À (Purcell et al, 1992, Britten et al, 1993Baldas et al, 1990). We report here the rhenium cyano structure but with tetraphenylphosphonium as the counter-ion.…”