Improved syntheses of the hexanuclear clusters [Ru 6 (CO) 18 ] 2– , [HRu 6 -(CO) 18 ] – , and H 2 Ru 6 (CO) 18 . The X-ray analysis of [HRu 6 (CO) 18 ] – , a polynuclear carbonyl containing an interstitial hydrogen ligand

The X-ray analyses of two crystalline modifications, (I) and (II), of [N(PPh3)2][HRu6(CO)18] are reported, together with improved synthetic routes to this and the related clusters [Ru6(CO)18]2– and H2Ru6(CO)18. Crystals of (I) are triclinic, space group P1–, with a= 18.083(4), b= 19.101(4), c= 19.238(5)Å, α= 117.70(4), β= 78.13(2), γ= 97.05(2)°, and Z= 4. Crystals of (II) are monoclinic, space group P21/n, with a= 33.82(8), b= 52.55(10), c= 9.832(2)Å;, β= 92.66(2)°, and Z= 12. Least-squares refinement using diffractometer data (Mo-Kα) has given an R of 0.068 1 for 9 165 reflections for (I) and an R of 0.23 (Ru only) for 1 485 reflections for (II). The unit cell in (I) contains two independent molecules of [HRu6(CO)18]–, cluster (1) which is ordered and cluster (2) which is disordered between two sites (2A) and (2B) that are related by a non-crystallographic two-fold axis. The combined evidence of the X-ray analyses, 1H n.m.r. studies, i.r. [v(CO)] spectra, and variable-temperature 13C n.m.r. is only consistent with the hydrogen ligand lying inside the Ru6 octahedron.