Unravelling the diarsenic hydrides: Reactivity and spectroscopic properties

Abstract

Diarsenic hydrides in the ground state are among the simplest molecular systems, with an arsenic-arsenic bond. This investigation aimed to characterize the structural and electronic properties of diarsenic hydrides, as well as the relative stability between their isomers. The As2Hn (n=1-4) structures are represented by hydrogen diarsenide (As2H), the equilibrium structures of diarsene isomers (As2H2), a trihydride diarsenic species (diarsenium, As2H3), and the diarsine molecule (H2AsAsH2) and its ylide isomer (H3AsAsH). The energetic profile calculated at the CCSD(T)/CBS level indicated trans-HAsAsH as the global minimum structure among the dihydrides, and diarsine as the most stable configuration among the tetrahydrides, lying 33 kcal mol−1 below H3AsAsH. The diarsenic bonds were characterized with σ (2.362−2.490 Å) and π (2.177-2.268 Å) bond characters corroborated by natural bond orbital (NBO) and bond order index analyses. The accuracy to reproduce the experimental data was also evaluated at the DFT and MP2 levels using a training set of 8 arsenic-bearing molecules. The results showed that B97D functional showed the best performance in reproducing observable frequencies with slight differences among cc-pVnZ and aug-cc-pVnZ basis sets (n=D, T). On the other hand, B2PLYP/aug-cc-pVTZ achieve the best agreement with experimental results by using vibrational second-order perturbation theory (VPT2) to rationalize the vibrational results.