Reactions of the nitridocarbonyl cluster anion [Rh6N(CO)15]- with strong bases: Synthesis and crystal structure of the hydridic dianion [Rh6(μ-H)N(CO)14]2

The reaction of the nitridocarbonyl anion [Rh6N(CO)15]-, as its K+ salt, in water or alcoholic solution with alkali metal hydroxides afforded the novel hydridic species [Rh6(μ-H)N(CO)14]2-, isolated as the caesium (2a) and the bis(triphenylphosphine)iminium (2b) salts. Both species have been investigated by X-ray structural analysis. Compound 2a crystallizes in the hexagonal system, space group P63/mmc (no. 194), with a = b = 11.089(2), c = 12.308(4) Å, Z = 2. Compound 2b gives monoclinic crystals, space group C2/c (no. 15), with a = 26.896(3), b = 17.143(6), c = 20.250(2) Å, β = 118.80(1)°, Z = 4. The structures were refined on the basis of 355 (2a) and 2170 (2b) significant independent reflections to final R values of 0.0427 and 0.0491 for 2a and 2b, respectively. The anion contains a trigonal prismatic cluster centred by the nitrido ligand. The hydrido ligand bridges an interbasal Rh-Rh edge replacing a bridging CO group of the parent anion [Rh6N(CO)15]-. This substitution causes some stereochemical effects which are discussed for 2b; in 2a the anion has essentially the same stereochemistry but the interbasal ligands (two CO and one H) are disordered, due to the presence of a three-fold crystallographic axis.