ELECTRONIC AND GEOMETRIC STRUCTURES OF SEVERAL STATES OF DIATOMIC SCANDIUM NITRIDE

The electronic and geometric structures of 15 scandium nitride species with formal σ,π,π triple σ,π, double π,π double, σ single, and π single two-electron bonds have been studied by ab initio MCSCF and multireference Cl techniques. All 15 species are bound relative to the ground-state atoms. Although Sc has a2D4s23d1 ground state, the ground-state ScN is the triply bonded1Σ+ with a 3d3 configuration dominant in situ. The π,π doubly bonded3Σ+and the σ,π, doubly bonded 3 are only 7.4 and 12.1 kcal/mol higher in energy, respectively. Thus, we expect that the bond in the triply bonded species will readily be broken by singly bonded R-R’ species resulting in species with a linear RScNR’ framework with, doubly bonded Sc-N and singly bonded Sc-R and N-R’. Indeed, our MCSCF calculations suggest that linear ‘+ HScNH is at least 53.6 kcal/mol more stable than ground-state ScN and H2. A Mulliken population analysis suggests the following: there is a substantial ionic character in these bonds; regardless of the number of formal covalent bonds between N and Sc, the gross Sc to N charge transfer is relatively constant for the 14 species with an in situ 4s’3d2,4s13d14p1, or 3d3 excited-state Sc configuration dominant at equilibrium and is smaller for the one state with an in situ 4s23d1. The term symbol, calculated bond length (Req,Å), vibrational frequency (ωe,cm-1), gross Sc to N charge transfer, the absolute bond energy relative to the ground-state fragments (De, kcal/mol), and the dipole moment (μ, Debye, with polarity Sc+N-) are as follows: Triply bonded species:1Σ+,1.768, 726, 0.59, 62.7, 5.34. σ,π, -Doubly bonded species:3II, 1.839, 802, 0.62, 50.6, 3.79;1II, 1.845, 789.0. 62, 49.8, 3.56;3B1 2.061, 566,0.60,17.8, 2.23. π,π Doubly bonded species:3Σ+, 1.769, 861,0.56, 55.3, 2.46;3Δ, 1.830, 790, 0.63, 11.7, 9.38;1Δ, 1.843, 785, 0.62,10.5, 9.22. σ Singly bonded species:3Σ-, 2.058, 577, 0.48, 27.3, 1.75;5Σ-, 2.250, 400.0. 60, 5.6, 2.36;5II, 2.231,438,0.64,10.3, 3.78;5Δ, 2.173,489, 0.65, 21.1, 3.67;3Δ, 2.178, 491,0.66, 18.9, 3.59;1Δ, 2.179, 496, 0. 67, 17.3, 3.62. π Singly bonded species:5Σ+, 2.102, 530,0.58, 2.4, 2.26;5B1, 2.059, 576,0.60, 13.7, 2.34. The structure of the calculations that we have been using for transition-metal-containing species is discussed with an emphasis on the effect of the interatomic spin couplings on the electronic structures. © 1990, American Chemical Society. All rights reserved.