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

journal contribution
posted on 2013-12-15, 00:00 authored by Madeleine SchultzMadeleine Schultz, Philipp-Nikolaus Plessow, Frank Rominger, Laura Weigel
The complex [1,2-bis(di-tert-butylphosphanyl)ethane-κ(2)P,P']diiodidonickel(II), [NiI2(C18H40P2] or (dtbpe-κ(2)P)NiI2, [dtbpe is 1,2-bis(di-tert-butylphosphanyl)ethane], is bright blue-green 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-κ(2)P,P']dichloridonickel(II), [NiCl2(C18H40P2] or (dtbpe-κ(2)P)NiCl2, is very close to square planar and very weakly paramagnetic in the solid state and in solution, while the maroon [1,2-bis(di-tert-butylphosphanyl)ethane-κ(2)P,P']dibromidonickel(II), [NiBr2(C18H40P2] or (dtbpe-κ(2)P)NiBr2, 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.

History

Journal

Acta crystallographica section c: structural chemistry

Volume

69

Pagination

1437-1447

Location

Chester, Eng.

ISSN

2053-2296

eISSN

1600-5759

Language

eng

Publication classification

C Journal article, C1.1 Refereed article in a scholarly journal

Copyright notice

2013, International Union of Crystallography

Publisher

International Union of Crystallography