HIGHER COORDINATE CYANIDE AND ISOCYANIDE COMPLEXES .8. SYNTHESIS AND STRUCTURE OF DIIODODICARBONYLTRIS(TERT-BUTYL ISOCYANIDE)TUNGSTEN(II), AN EXAMPLE OF THE 4-3 PIANO STOOL 7-COORDINATE GEOMETRY

The synthesis of diiododicarbonyltris (tert-butyl isocyanide)tungsten(II) from (t-C4H9NC)3W(CO)3 and elemental iodine is described. The compound crystallizes in polymorphic forms, depending upon the choice of solvent. The structure of an orthorhombic modification, space group Pbca, was revealed in a single-crystal X-ray diffraction study. The crystal parameters are a = 18.297 (5) Å, b = 20.632 (6) Å, and c = 13.550 (4) Å. With eight molecules per unit cell the calculated density is 1.930 g/cm3, comparable to the observed value of 1.92 (3) g/cm3. The structure was solved and refined on F to a final value of 0.045 for the discrepancy index R1 by using 2832 unique observed reflections. The tungsten atom is coordinated to two iodine atoms with W—I bond lengths of 2.863 (1) and 2.865 (1) Å, two carbonyl groups, W—C = 1.997 (13) and 1.959 (15) Å, and three isocyanide ligands, W—C = 2.093 (13), 2.100 (13), and 2.145 (13) Å. A detailed analysis of the geometry reveals the coordination polyhedron of the tungsten to be that of a 4: 3 square base-trigonal cap piano stool. Criteria for choosing this structure are discussed. © 1979, American Chemical Society. All rights reserved.