Pseudo-two-dimensional structures (HXYH)3n2H6n (XY = GaN, SiC, GeC, SiSi, or GeGe; n = 1-3): density functional characterization of structures and energetics.

Hybrid density functional calculations with effective core potential basis sets are performed for monomeric group 13/15 and group 14/14 analogues of cyclohexane, as well as for three different pseudo-two-dimensional structures that can be formed from expanding one and two concentric rings around the central one (trans-fused chairs, a rolling combination of trans- and cis-fused chairs, and cis-fused boats). Varying contributions from torsional strain, angle strain, electrostatics, and nontraditional H-H hydrogen bonding lead to different orderings and magnitudes of motif energies in the various systems: Homoatomic SiSi and GeGe systems prefer the trans-fused chair alternative and heteroatomic systems GaN, SiC, and GeC prefer the rolling chair. Decomposition of structure energies into characteristic fragment contributions indicates that pseudo-one-dimensional rods of poly(imidogallane) are thermodynamically more stable than any of the pseudo-two-dimensional structures.