Magnesium systems
We carried out essentially the same modes of analysis for theD 3h[MgH3Mg]+ and
[HeMgH3MgHe]+ cations as we have
described for the beryllium systems. Again we found, without the
imposition of any symmetry relations amongst the active orbitals, that
the converged SCGVB(6) solutions for the ‘bare’D 3h[MgH3Mg]+ cation features two sets
of three symmetry-related orbitals, with each ‘pair’ being primarily
associated with a particular Mg−H−Mg linkage (see first two images in
the top row of Figure 3). The orbital overlap\(\left\langle\phi_{1}\middle|\phi_{2}\right\rangle\) is 0.825 and
the total active space spin function, \(\Theta_{0,0}^{6},\) is again
dominated by the perfect-pairing mode: this system features three
symmetry-equivalent highly polar 3c‑2e Mg−H−Mg bonding units, albeit
SCGVB orbital \(\phi_{1}\) appears to have a larger relative
contribution from H than was the case for the various beryllium species.
The dominant valence LNOs for the D 3h[MgH3Mg]+ cation consist of three
almost doubly-occupied symmetry-equivalent orbitals that are consistent
with notions of 3c‑2e character (see the third image in the top row of
Figure 3). Except again for a larger relative contribution from H, there
are obvious similarities to the bonding situation that we found for the
beryllium species.