Stability, properties and electronic g-tensors of H 2CO − as stabilized in H 2CO·Na complexes

Abstract

Using HF and MP methods with high-level basis sets, the geometries, frequencies, electric dipole moments, electric field gradients, Fermi contact terms and other properties were calculated for three isomers of the H 2CO·Na complex. Isomers I and II are ion-pair complexes of type H 2CO −Na +, whereas III is of van der Waals type. The H 2CO − moiety in isomers I and II is confirmed to be nonplanar. Isomer III is the most stable one, although energy differences between the isomers are very small (some less than 1 kcal/mol). The electron-spin magnetic moments ( g-tensors) were calculated both by ROHF and multireference CI methods. Various basis sets and several gauge origins were used. The gauge dependence is small. At the ROHF level, Δ g av in ppm (Δ g= g− g e) is about 1300 for I, 800 for II, and −200 for III. Correlated values are expected to ∼400 ppm higher for isomer I and ∼250 ppm for isomer II. The large second-order contributions to Δ g of I and II result mainly from the σ→π * and n→π * states, which are highly excited states of the complexes. Experimental studies on H 2CO − in aqueous solution find Δ g av=1400–1600 ppm, in good agreement with our results.