The structure and energetics of singlet, closed-shell [B, C, F, H2]: Simplicity resulting in diversity

The structure and energetics of triplet [B, C, F, H2]

“…The structurally related carbene H 2 B-C-F with the boron and carbon transposed is plausibly a ground state triplet as we recognize this species to be a substituted derivative of the parent carbene, CH 2 . Indeed this isomer was quite dominant in earlier literature discussions of [B, C, F, H 2 ] [3,4], even though our more exact calculations failed to confirm it to be a minimum on the singlet potential energy surface [1]. Any of our earlier hydrogen bridged or hydrogen bonded complexes containing CH 2 , CHF or BH, might also be expected to have triplet counterparts as all of these fragments have energetically low lying states with unpaired electrons [5][6][7].…”

“…We have chosen semi-systematic designations for our minima, realizing that proper names are often cumbersome and not designed for most of our species. As with the singlets [1], no cyclic triplet compounds are at minima. Unlike the singlets, no fluorine-bridged triplet compounds are at minima.…”

“…The only other singlettriplet hydrogen-bonded pairs are S4, 7 and S5, 8 [1]. It must be noted that AIM analysis [37] finds no bond path linked to boron in S11, despite a shorter C-B distance in this molecule than in S12 and most of the triplet molecules (Table 1).…”

“…Three of the covalently bound structures are the partially bond-ruptured excited ketene-and diazomethane-like 1 H 2 C -B -F, analogous to S1 H 2 C5 5B-F on the singlet PES, and the related partially bond-ruptured 5 t-H(F)C -B -H and 6 c-H(F)C -B -H, analogous to S2 H(F)C5 5B-H. (Note: in this article species denoted without a letter prefix are triplet minima. Singlet minima [1] will be denoted with the prefix ''S'' to distinguish them from the triplet species.) Isomer 11 H(F)CBH is an oddly shaped molecule with the same connectivity as 5 and 6 but a linear HCB angle (Table 1 and Fig.…”

“…They are the simplest such species for which the question of spin state naturally emerges [1]. The formally doubly bonded H 2 C5 5B-F is logically a closed-shell singlet, analogous to the isoelectronic diazomethane and ketene.…”