New carbide clusters in the cobalt sub-group. Part 15. Synthesis and crystallographic characterization of di-µ6-carbido-deca-µ-carbonyl-tridecacarbonyl-polyhedro-dodecarhodate(4–) as its tetrapropylammonium salt, [N(C3H7)4]4[Rh12C2(CO)23]
Abstract
The compound [N(C3H7)4]4[Rh12C2(CO)23] has been prepared by reduction with alkali-metal hydroxide in MeOH of the dianion [Rh12C2(CO)24]2–. Its molecular structure has been determined by single-crystal X-ray crystallography: monoclinic, space group P21/c, a= 21.132(4), b= 15.334(3), c= 30.093(5)Å, β= 103.07(4)°, and Z= 4. The structure has been solved from 7 589 intensities and refined to R= 0.0738. The metal-atom polyhedron is almost unchanged from that present in the dianion. It may be described as a three-layer stacking sequence of metal atoms generating two prismatic cavities occupied by two interstitial carbon atoms. The main difference between the two anions is the loss of a CO ligand and the rearrangement of the seven ligands bonded to the equatorial layer with formation of two bridges. The idealized symmetry is C2v. Relevant average distances are: Rh–Rh 2.829, Rh–C(carbide) 2.13 Å; Rh–C and C–O, 1.82, 1.17 and 2.03, 1.20 Å for terminal and bridging CO groups, respectively.
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