Theoretical versus experimental charge and spin-density distributions in trans-[Ni(NH3)4(NO2)2]

The experimental charge and spin-density distributions for [Ni(NH3)4(NO2)2] have been compared with theory at various levels. Ab initio unrestricted Hartree 13Fock (UHF) and discrete variational X;1(DVX;1) Hartree 13Fock 13Slater molecular orbital (m.o.) calculations are reported together with cellular ligand field (c.l.f.) results. The UHF and DVX;1 approaches yield closely similar descriptions of the charge and spin densities, and qualitatively reproduce the main features of both types of experimental data, namely the Ni 13N covalence is strong, the NO2 13 ion is a better <3 donor than the NH3 molecule, and the Ni 13N <0-bonding is small. Both theories indicate quite appreciable O(NO2) participation in the bonding and antibonding m.o.s involving nickel. C.l.f. calculations which include only the Ni 13N interactions reproduce the experimental d 13d spectra and the signs of the single-crystal paramagnetic anisotropies quite well, but assign a weaker <3-donor role to the nitrite ligand relative to NH3. An extension of the model to include explicit Ni 13O interactions is more satisfactory and places the NO2 13 ion as the stronger <3 donor consistent with the other theoretical and experimental data

Basic Inorganic Chemistry

vi;ill.;28c

Introduction to ligand field

ix, 351 hlm.: il. ; 23 c

Spin and charge density in Ni(NH3)4(NO2)2 and the chemical bonding

Polarised neutron and X-ray diffraction experiments have been performed on Ni(NH3)4(NO2) 2, to study respectively the spin and charge distributions in the molecule. The results have been compared with an ab-initio M.O. calculation. 27 % of the spin is transferred to the ligand atoms by covalent interactions. A simple ligand field model, with four empirical parameters, agrees qualitatively, but not quantitatively with the combined spin and charge results. The U.H.F. ab-initio calculation results are also in broad agreement with the experiments, but correspond to a good deal less covalency in the bonding. This emphasises the need to consider configuration interaction and/or a long range "crystal field" in describing bonding in crystalline transition metal compounds

SPIN AND CHARGE DENSITY IN Ni(NH3)4(NO2)2 AND THE CHEMICAL BONDING

Des expériences de diffraction de neutrons polarisés et de rayons X par Ni(NH3)4(NO2)2 ont été réalisées pour étudier respectivement les distributions de spin et de charge dans la molécule. Les résultats sont comparés aux calculs ab-initio d'orbitales moléculaires. 27 % des spins sont transférés sur les ligands par interactions covalentes. Un modèle simple de champ de ligands, à quatre paramètres empiriques, est en accord qualitatif mais non quantitatif avec les résultats combinés de spins et de charge. Les résultats d'un calcul U.H.F. ab-initio sont en accord approximatif avec les expériences, mais correspondent à des liaisons beaucoup moins covalentes. Ceci indique la nécessité de considérer l'interaction de configuration et/ou un champ cristallin à longue portée pour décrire les liaisons dans les composés de métaux de transition.Polarised neutron and X-ray diffraction experiments have been performed on Ni(NH3)4(NO2) 2, to study respectively the spin and charge distributions in the molecule. The results have been compared with an ab-initio M.O. calculation. 27 % of the spin is transferred to the ligand atoms by covalent interactions. A simple ligand field model, with four empirical parameters, agrees qualitatively, but not quantitatively with the combined spin and charge results. The U.H.F. ab-initio calculation results are also in broad agreement with the experiments, but correspond to a good deal less covalency in the bonding. This emphasises the need to consider configuration interaction and/or a long range "crystal field" in describing bonding in crystalline transition metal compounds