Structure, magnetism and colour in simple bis(phosphine)nickel(II) dihalide complexes: an experimental and theoretical investigation

Abstract

The complex [1,2-bis(di-tert-butylphosphanyl)ethane-2 P,P 0 ]-diiodidonickel(II), [NiI 2 (C 18 H 40 P 2 ] or (dtbpe-2 P)NiI 2 , [dtbpe is 1,2-bis(di-tert-butylphosphanyl)ethane], is bright bluegreen in the solid state and in solution, but, contrary to the structure predicted for a blue or green nickel(II) bis(phosphine) complex, it is found to be close to square planar in the solid state. The solution structure is deduced to be similar, because the optical spectra measured in solution and in the solid state contain similar absorptions. In solution at room temperature, no 31 P{ 1 H} NMR resonance is observed, but the very small solid-state magnetic moment at temperatures down to 4 K indicates that the weak paramagnetism of this nickel(II) complex can be ascribed to temperature independent paramagnetism, and that the complex has no unpaired electrons. The red [1,2-bis(di-tert-butylphosphanyl)ethane-2 P,P 0 ]dichloridonickel(II), [NiCl 2 (C 18 H 40 P 2 ] or (dtbpe-2 P)NiCl 2 , is very close to square planar and very weakly paramagnetic in the solid state and in solution, while the maroon [1,2-bis(ditert-butylphosphanyl)ethane-2 P,P 0 ]dibromidonickel(II), [NiBr 2 (C 18 H 40 P 2 ] or (dtbpe-2 P)NiBr 2 , is isostructural with the diiodide in the solid state, and displays paramagnetism intermediate between that of the dichloride and the diiodide in the solid state and in solution. Density functional calculations demonstrate that distortion from an ideal square plane for these complexes occurs on a flat potential energy surface. The calculations reproduce the observed structures and colours, and explain the trends observed for these and similar complexes. Although theoretical investigation identified magnetic-dipole-allowed excitations that are characteristic for temperature-independent paramagnetism (TIP), theory predicts the molecules to be diamagnetic.

The Importance of Ligand‐Induced Backdonation in the Stabilization of Square Planar d10 Nickel π‐Complexes

“…DFT calculations were performed on each of the species in Table using simplified diphosphine ligands (see Figure SI 07 for details, Supporting Information). Molecular structures derived from B3LYP/def2‐TZVP calculations of the dtbpe complexes, as well as those using a simplified diphosphine ligand (dmpe=1,2‐bis(dimethylphosphino) ethane), yield good agreement with solid‐state molecular structures of 1 – 12 . The effect of decreasing the steric bulk and electron donation in the supporting diphosphine ligand does not affect the general structural trends and conclusions, which are consistent with those observed in the experimental data.…”

“…Molecular structures derived from B3LYP/def2-TZVP calculations of the dtbpe complexes, as well as those using as implified diphosphine ligand (dmpe = 1,2-bis(dimethylphosphino) ethane), 1 yield good agreement with solid-state molecular structures of 1-12. [10,11,22,57,102,103] The effect of decreasing the steric bulk and electron donation in the supporting diphosphine ligand does not affect the generals tructural trendsa nd conclusions, which are consistent with those observed in the experimental data. Furthermore, the spectroscopic features observed in the Ni Kedge XASd ata are well-reproduced using time-dependent (TD) DFT analysis.…”

The importance of ligand-induced backdonation in the stabilization of square planar d10 nickel π-complexes

“…Molecular structures derived from B3LYP/def2-TZVP calculations of the dtbpe complexes, as well as those using a simplified diphosphine ligand (dmpe = 1,2-bis(dimethylphosphino) ethane), A yield good agreement with solid-state molecular structures of 1-12. [10,11,22,57,100,101] The effect of decreasing the steric bulk and electron donation in the supporting diphosphine ligand does not affect the general structural trends and conclusions, which are consistent with those observed in the experimental data. Furthermore, the spectroscopic features observed in the Ni Kedge XAS data are well reproduced using TD-DFT analysis.…”

Probing the Dichotomy of Square Planar d¹⁰ Complexes: Geometric and Electronic Structure of Nickel π-Complexes

“…solid-state molecular structures of 1-12. 10,11,21,56,96,97 The effect of decreasing the steric bulk and electron donation in the supporting diphosphine ligand does not affect the general structural trends and conclusions, which are consistent with those observed in the experimental data. Furthermore, the spectroscopic features observed in the Ni K-edge XAS data are well reproduced using TD-DFT analysis.…”