Formation and structural chemistry of the unusual cyanide-bridged dinuclear species [Ru 2( NN) 2(CN) 7] 3− ( NN = 2,2′-bipyridine or 1,10-phenanthroline)

Abstract

Crystallisation of simple cyanoruthenate complex anions [Ru( NN)(CN) 4] 2− ( NN = 2,2′-bipyridine or 1,10-phenanthroline) in the presence of Lewis-acidic cations such as Ln(III) or guanidinium cations results, in addition to the expected [Ru( NN)(CN) 4] 2− salts, in the formation of small amounts of salts of the dinuclear species [Ru 2( NN) 2(CN) 7] 3−. These cyanide-bridged anions have arisen from the combination of two monomer units [Ru( NN)(CN) 4] 2− following the loss of one cyanide, presumably as HCN. The crystal structures of [Nd(H 2O) 5.5][Ru 2(bipy) 2(CN) 7] · 11H 2O and [Pr(H 2O) 6][Ru 2(phen) 2(CN) 7] · 9H 2O show that the cyanoruthenate anions form Ru–CN–Ln bridges to the Ln(III) cations, resulting in infinite coordination polymers consisting of fused Ru 2Ln 2(μ-CN) 4 squares and Ru 4Ln 2(μ-CN) 6 hexagons, which alternate to form a one-dimensional chain. In [CH 6N 3] 3[Ru 2(bipy) 2(CN) 7] · 2H 2O in contrast the discrete complex anions are involved in an extensive network of hydrogen-bonding involving terminal cyanide ligands, water molecules, and guanidinium cations. In the [Ru 2( NN) 2(CN) 7] 3− anions themselves the two NN ligands are approximately eclipsed, lying on the same side of the central Ru–CN–Ru axis, such that their peripheries are in close contact. Consequently, when NN = 4,4′- t Bu 2-2,2′-bipyridine the steric bulk of the t-butyl groups prevents the formation of the dinuclear anions, and the only product is the simple salt of the monomer, [CH 6N 3] 2[Ru( t Bu 2bipy)(CN) 4] · 2H 2O. We demonstrated by electrospray mass spectrometry that the dinuclear by-product [Ru 2(phen) 2(CN) 7] 3− could be formed in significant amounts during the synthesis of monomeric [Ru(phen)(CN) 4] 2− if the reaction time was too long or the medium too acidic. In the solid state the luminescence properties of [Ru 2(bipy) 2(CN) 7] 3− (as its guanidinium salt) are comparable to those of monomeric [Ru(bipy)(CN) 4] 2−, with a 3MLCT emission at 581 nm.