Dimorphs of [1,2-bis(diphenylphosphino)ethane]dichloronickel(II)

Abstract

The two known forms, A and B, of [1,2-bis(diphenylphosphino) ethane] dichloronickel(II), [Ni(dppe)Cl2], were synthesised and identified by IR spectroscopy. The spectra showed that form A had a lower symmetry than form B. The forms were also found to differ by solid-state 31P NMR spectroscopy and powder X-ray diffraction, but the solution properties were identical. The IR spectrum of the dichloromethane solvate of [Ni(dppe)Cl2] was the same as that of form B but with a strong additional band due to CH2Cl2. The X-ray diffraction pattern from this sample matched that calculated for a previously published crystal structure of [Ni(dppe)Cl2]·Ch2Cl2, thus identifying the form used in that work. Crystals of form A obtained from acetone were used for a single-crystal X-ray structure determination. Comparison of the molecular structures showed that both forms have the same chelate-ring conformation (δ) but differ in the orientations of the phenyl rings. There is a non-crystallographic two-fold axis in form B which is absent from A, explaining the additional bands present in the IR spectrum of the latter, Solid-state 31P NMR was better than IR spectroscopy at distinguishing the two forms from each other and from mixtures.