Abstract
The trans-[Cr(NH 3) 4(CN)X] + ions, where X = NCS, F and Cl, have been prepared by reaction in methanol suspension of either trans-[Cr(NH 3) 4(H 2O)(CN)] 2+ with NCS − and F −, or trans-[Cr(NH 3) 4(Me 2SO)Cl] 2+ with CN −. Their perchlorate salts have been characterized by analysis, ion-exchange, conductance, absorption spectra, phosphorescence in room-temperature solution and aqueous chemistry. The solvent dependence of the ligand-field spectrum for X = F is ascribed to hydrogen bonding that affects the CrF interaction. Both π(X) → e g *(Cr) and t 2g (Cr) → π*(CN) charge-transfer transitions are observed, consistent with the π-donor and π-acceptor nature of the two axial ligands. All these complexes undergo acid-catalysed CN − aquation. When X = Cl this competes with pH-independent loss of X. The aquation products, fully stereoretentive, confirm the trans isomerism of the new species. The anation and aquation behaviours reveal trans effects of the CN − ligand.
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