Using thickness-dependent first-principles electronic structure calculations, we predict that hydrogenated ultra-thin films of tin harbor a new class of twodimensional (2D) topological insulators (TIs). A single bilayer (BL) tin film assumes a 2D-TI phase, but it transforms into a trivial insulator after hydrogenation. In contrast, tin films with 2 and 3 BLs are found to be trivial insulators, but hydrogenation of 2 to 4 BL films results in a non-trivial TI phase. For 1 to 3 BLs, H-passivation converts the films from being metallic to insulating. Moreover, we examined iodine-terminated tin films up to 3 BLs, and found these to be non-trivial, with the films becoming semi-metallic beyond 1 BL. In particular, the large band gap of 340 meV in an iodine-terminated tin BL is not sustained in the iodine-terminated 2 BL and 3 BL tin films.

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Methods for processing the electronic spectra of tetragonal chromium(II1) complexes are briefly reviewed. New criteria for assigning the spectra of these complexes are introduced and the data processed to yield a series of crystal field and molecular orbital parameters. The validity of these are discussed with particular reference to the apparent x bond contribution in the chromium ligand bonds.It is concluded that the bonding is better described in ionic rather than covalent terms.

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In Table 3, the parameter set for Cren,(OH), ' The correction does not materially alter the was incorrectly calculated.