Similarities and Differences on the Electronic Structure and Chemical Bonding of Isoelectronic Molecules: X 2 NH and HNX 2 NH, where X = N and C –

High Resolution Image Download MS PowerPoint Slide Identifying similarities and differences among isoelectronic moieties is crucial for understanding chemical bonding, stability, and reactivity. Here, the molecular and electronic structures, chemical bonding, and binding energies of the N 2 NH, HNN 2 NH, [C 2 NH] −/2–, and [HNC 2 NH] −/2– moieties are calculated via DFT, CCSD(T), QCISD(T), and MRCISD(+Q) methodologies. Although N 2 and [C 2 ] 2– are isoelectronic and both exhibit triple bonds in their ground X 1 Σ g + state and double bonds in their first excited A 3 Σ u + state, their binding energies and stabilities differ. These variations, along with the metastable nature of [C 2 ] 2–, affect the bonding and energetics of the studied species. Thus, the N 3 H and N 4 H 2 molecules have singlet ground states, while the [C 2 NH] 2– and [C 2 N 2 H 2 ] 2– anions present triplet ground states. The N≡N–NH is formed via a dative bond from N 2 ( X 1 Σ g + ) to NH( a 1 Δ), while adding another NH, the bonding changes to HN═N–N═NH; their CCSD(T) formation energies are −2.59 eV (N 2 NH) and −11.93 eV (HNN 2 NH). On the contrary, in both [C 2 NH] 2– and [HNC 2 NH] 2– anions, electron charge is transferred to NH, i.e., the in situ diatomic moieties are excited states of [C 2 ] − and C 2 + NH – (X 2 Π). Their formation energies are −1.14 eV ([C 2 NH] 2– ) and −8.57 eV ([HNC 2 NH] 2– ). Electron transfer from metastable [C 2 ] 2– to one or two NH stabilizes both [C 2 NH] 2– and [HNC 2 NH] 2–, suggesting their possible experimental detection.