Formation and structural chemistry of the unusual cyanide-bridged dinuclear species [Ru2(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 2 O) 5.5 ][Ru 2 (bipy) 2 (CN) 7 ] · 11H 2 O and [Pr(H 2 O) 6 ][Ru 2 (phen) 2 (CN) 7 ] · 9H 2 O show that the cyanoruthenate anions form Ru–CN–Ln bridges to the Ln(III) cations, resulting in infinite coordination polymers consisting of fused Ru 2 Ln 2 (μ-CN) 4 squares and Ru 4 Ln 2 (μ-CN) 6 hexagons, which alternate to form a one-dimensional chain. In [CH 6 N 3 ] 3 [Ru 2 (bipy) 2 (CN) 7 ] · 2H 2 O 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 6 N 3 ] 2 [Ru( t Bu 2 bipy)(CN) 4 ] · 2H 2 O. 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 3 MLCT emission at 581 nm.