Crystal and molecular structures of the tetrakis(diphenylketimine) derivatives of silicon, germanium, and tin

Abstract

The crystal and molecular structures of the title compounds [M(NCPh₂)₄; (1) M = Si, (2) M = Ge, (3) M = Sn] have been determined from diffractometer data. Crystal parameters are as follows: (1), triclinic, space group P, a= 12.342(6), b= 18.100(8), c= 19.586(15)Å, α= 86.89(5), β= 82.72(5), γ= 84.06(4)°, Z= 4, 2 524 observed reflections, R 0.067; (2), monoclinic, space group C2/c, a= 24.050(2), b= 11.971(1), c= 18.839(3)Å, β= 130.44(8)°, Z= 4, 2 189 observed reflections, R 0.058; (3), tetragonal, space group I4₁/a, a= 18.142(5), c= 14.461 (3)Å, Z= 4, 1 329 observed reflections, R 0.118. All the crystals contain discrete molecules, and the principal differences lie in the M–NC angles [134.7, 139.5 for (1), 127.0 for (2), 121.3° for (3)]. The deviation of this angle from 120° and its change is attributed to the presence of pπ→dπ bonding, decreasing from Si to Sn. The structures of (2) and (3) were determined by the heavy-atom method, and of (1) by direct methods.