QUASI-RELATIVISTIC PSEUDOPOTENTIAL STUDY OF SPECIES ISOELECTRONIC TO URANYL AND THE EQUATORIAL COORDINATION OF URANYL

The calculated trends of geometries and vibrational frequencies of several uranyl isoelectronic species, like the known NUN and CUO,and the unknown CUN-, NUO+, and NUF2+, are reported. The NUN and CUO results support the matrix spectroscopic assignments. The simplest example of equatorial coordination to uranyl is the C-2 nu species UO3. Its calculated vibrational frequencies also support matrix spectroscopic ones. We earlier suggested that the large range of uranyl bond lengths in UO66--type systems could be interpreted in terms of a ''frozen, soft e(g) vibrational mode''. Further studies on UF6, U(OH)(6), [(OUO)(F-eq)(n)]((n-2)-), [(OUO)(NO3)(3)](-), and [(OUO)(CO3)(3)](4-) show only small variation of R(ax) as function of R(eq). Thus, the all-oxide case is a special one, where all ligands are capable of single and multiple bonding.