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Pyramidal Dicationic Ge(II) Complexes with Homoleptic Neutral Pnictine Coordination: A Combined Experimental and Density Functional Theory Study
journal contribution
posted on 2021-07-28, 13:03 authored by Rhys P. King, Victoria K. Greenacre, William Levason, John M. Dyke, Gillian ReidAn unusual series of Ge(II) dicationic
species with homoleptic
phosphine and arsine coordination, [Ge(L)][OTf]2, L = 3
× PMe3, triphos (MeC(CH2PPh2)3), triars (MeC(CH2AsMe2)3), or κ3-tetraphos (P(CH2CH2PPh2)3) (OTf– = O3SCF3–) have been prepared by reaction
of [GeCl2(dioxane)] with L and 2 mol equiv of Me3SiOTf in anhydrous CH2Cl2 (or MeCN for L =
triars, triphos). X-ray crystal structures are reported for [Ge(PMe3)3][OTf]2, [Ge(triars)][OTf]2, and [Ge(κ3-tetraphos)][OTf]2, confirming
homoleptic P3- or As3-coordination at Ge(II)
in each case and with the discrete OTf– anions providing
a charge balance. The Ge–P/As bond lengths are significantly
shorter than those in neutral germanium(II) dihalide complexes with
diphosphine or diarsine coordination. Solution NMR spectroscopic data
indicate that the complexes are labile in solution. Using excess AsMe3 and [GeCl2(dioxane)] gives only the neutral product,
[Ge(AsMe2)2(OTf)2], the crystal structure
of which shows four coordination at Ge(II), via two As donor atoms
and an O atom from two κ1-OTf– ligands;
further weak, long-range intermolecular interactions give a chain
polymer. The electronic structure of the [Ge(PMe3)3]2+ dication has been investigated using density
functional theory (DFT) calculations. The computed geometrical parameters
for this dication are in good agreement with the experimental X-ray
crystallographic values in [Ge(PMe3)3][OTf]2. The results also indicate that the pyramidal arrangement
of the [Ge(PMe3)3]2+ (computed P–Ge–P
angle 96.8° at the B3LYP-D3 level) arises from a balance between
electronic energy (Eelec) contributions,
which favor a lower P–Ge–P angle, and nuclear–nuclear
contributions (Enn), which favor a higher
P–Ge–P angle, to the total energy (ETOT). An Atoms in Molecules (AIM) analysis reveals that
one reason why Eelec decreases as the
P–Ge–P angle decreases is because of C···H
and H···H interactions between atoms on different CH3 groups. The stability of the [Ge(PMe3)3]2+ dication is enhanced by the distribution of a significant
part of the positive charge on Ge2+ to the atomic centers
of the PMe3 ligands. Similar results were obtained for
[Ge(AsMe3)3][OTf]2, showing the tris-AsMe3 complex to be less stable compared to the PMe3 analogue. Related calculations were also performed for the neutral
[Ge(PMe3)2(OTf)2] and [Ge(AsMe3)2(OTf)2] complexes.
