New Ni-Rh carbonyl clusters with unprecedented structural and electronic features: synthesis and X-ray structure of [NEt4](3)[Ni10Rh(CO)(19)]center dot C2H5CN, [NMe3CH2Ph](3)[Ni6Rh3(CO)(17)] and [NEt4](3)[Ni9Rh3(CO)(22)]

The reaction of the [Ni-6(CO)(12)](2-) dianion with [Rh(COD)Cl](2) (COD=cyc looctadiene) affords in sequence the new [Ni10Rh(CO)(19)](3-) (1) and [Ni9R h3(CO)(22)](3-) (2) trianionic clusters with good selectivity. The related [Ni6Rh3(CO)(17)](3-) (3) trianionic cluster has been initially isolated amo ng the degradation products of [Ni9Rh3(CO)(22)](3-) (2) under carbon monoxi de and has been more conveniently synthesized by condensation of [Rh(CO)(4) ](-) with Ni(CO)(4) in excess. All these new bimetallic Ni-Rh carbonyl clus ters have been isolated in the solid state as tetrasubstituted ammonium sal ts and were characterized by elemental analysis, spectroscopy and X-ray dif fraction studies. The structure of [Ni10Rh(CO)(19)](3-) (1) consists of a d istorted and incomplete Rh-centered Ni-9(mu (9)-Rh) icosahedral moiety, cap ped by the tenth Ni atom on one of the interlayer triangular faces. The [Ni 10Rh(CO)(19)](3-) (1) trianion is moderately stable to oxidation and, as in ferable from IR monitoring of the resulting reaction mixture, is irreversib ly degraded upon exposure to an atmosphere of carbon monoxide to a mixture of Wi(CO),, [Rh(CO),I- and [Ni-5(CO)(12)](2-). The [Ni9Rh3(CO)(22)](3-) (2) trianion displays a three layer metal frame identical to that previously f ound in the [H4-xNi9Pt3(CO)(21)](x-) (x=2-4) dusters. However, it features two less valence electrons. The structure of [Ni6Rh3(CO)(17)](3-) (3) is cl osely related to that of [Ni9Rh3(CO)(22)](3-) (2) and may be formally deriv ed from that of the latter by substitution of a Ni-3(CO)(3)(mu -CO)(3) moie ty with st face bridging carbonyI group. Notably, [Ni9Rh3(CO)(22)](3-) (3) is isoelectronic but not isostructural with the known [Ni6Ir3(CO)(17)](3-) congener. Both [Ni6Rh3(CO)(17)](3-) (3) and [Ni9Rh3(CO)(22)](3-) (2) are re adily degraded by carbon monoxide at atmospheric pressure to colourless sol utions containing Ni(CO), and [Rh(CO),I- mixtures. Their reaction with [Rh( COD)Cl](2) leads to the previously reported [Ni6Rh5(CO)(21)](3-) trianion a nd other yet uncharacterised Ni-Rh carbonyl clusters. All above Ni-Rh clust ers do not display protonation-deprotonation behaviour and chemically rever sible redox propensity; electrochemical experiments failed in all cases to show the occurrence of electrochemically reversible redox changes. (C) 2000 published by Elsevier Science B.V. All rights reserved.