Crystal and molecular structures of 1,1′-di-tert-butylnickelocene (η5-C5H4C4H9t)2Ni in the temperature range 143-243 K:: Thermal motion in the crystal

The crystal structure of 1,1'-di-tert-butylnickelocene is studied by the X-ray diffraction technique in the temperature range 143-243 K. The crystals are monoclinic, space group P2(1)/n, Z = 2. The molecule is centrosymmetric. The cyclic ligands are parallel and adopt a staggered conformation. At 143 K, the mean bond lengths are as follows: Ni-C, 2.194(6); C-C (in the ring), 1.421(6); and C-C (Me), 1.538(2) Angstrom. Analysis of the thermal motion of the molecule is performed within the single-parameter model, which allows for the independent motion of the cyclopentadienyl ring with the tert-butyl group as a whole and the motion of the tert-butyl group. It is shown that the molecule is structurally nonrigid and the tert-butyl group executes librational motion. The B-5 heights of the rotation barriers are estimated from the rms libration amplitudes: < phi2 > are equal to 40(5) and 34(4) kJ/mol at 143 and 243 K, respectively. (C) 2001 MAIK "Nauka/Interperiodica".