Pa. Reynolds et al., COVALENCE AND SPIN POLARIZATION IN TETRAPHENYLARSONIUM TETRACHLORONITRIDOTECHNETATE(VI) STUDIED BY POLARIZED NEUTRON-DIFFRACTION, Journal of the Chemical Society. Dalton transactions, (8), 1997, pp. 1447-1453
Polarised neutron diffraction from two orientations of tetragonal sing
le crystals of [AsPh4][TcNCl4] at 1.5 K and a magnetic field of 4.6 T
gave a combined data set of 116 magnetic structure factors. These were
fitted by a 26-parameter model which includes proton nuclear-spin ori
entation to give a spin-density model for the formally 4d(1) [TcNCl4](
-) ion. This model revealed substantial anisotropic pi bonding between
Tc and Cl resulting in 29(2)% of the spin being delocalised onto the
chlorine in-plane 3p(pi) orbitals, - 15(1)% onto the nitrogen as a res
ult of spin-polarising the short Tc-N bond, and substantial spin polar
isation on the technetium site of 4d and more diffuse density. Three u
nconstrained Hartree-Fock and density functional calculations with goo
d basis sets failed to reproduce these observations adequately, but an
unconstrained density functional calculation with gradient correction
s and a relativistic treatment of the core gave encouraging agreement
with experiment.