Predicting new, simple inorganic species by quantum chemical calculations: some successes.

A combination of ab initio calculations with the isoelectronic principle and chemical intuition is a useful way to predict new species. Some experimentally verified examples are (1) the transition-metal hydrides, MH(n) (n = 4-12), (2) new members of the multiply-bonded 2nd- or 3rd-period species A≡B, A=B=C, A=B=C=D or A≡B-C≡D, and A=B=C=D=E classes, the last-mentioned class including the cations N and OCNCO(+), (3) new members of the uranyl isoelectronic series, (4) actinyls where one of the oxygens is replaced by a 5d transition-metal (TM), (5) certain systems with noble-gas-noble-metal bonds, (6) the first argon compound HArF, (7) the cluster series of WAu(12), (8) TM-centred polyazide anions, (9) covalent molecules with a central -Zn-Zn- bond, (10) tetrahedral clusters of zinc and cadmium, (11) model systems for otherwise missing multiple bonds and (12) certain endohedral A@B systems. Further series of hypothetical species were used as a tool for developing recent sets of covalent radii, for studying the endohedral intermolecular interactions in A@B systems, or for finding examples of a 32-electron rule, corresponding to the well-known 8e- and 18e-rules. For obvious reasons, much of the molecular chemistry of the superheavy elements is based on studies of hypothetical model systems.