Synthesis, crystal and electronic structures of two novel tunnel bismuth oxychlorides Bi18O22Cl8.5(BO3)0.5 and Bi18O22Cl8Se

Single crystals of two new quaternary bismuth oxychlorides, Bi18O22Cl8.5(BO3)0.5 (1) and Bi18O22Cl8Se (2), have been serendipitously produced in syntheses starting from bismuth borate or oxyselenide and oxychloride. The crystal structure of 1 represents a high symmetry analog of the PbBi17O22Cl9 type structure, formed by double aliovalent (Pb2+ -> Bi3+, 0.5Cl- -> 0.5BO33-) substitution at the two respective cationic and anionic sites, while 2 is a full structural analog of PbBi17O22Cl9. Overall, their structures can be described as sequences of thick (16 & Aring;) slabs (2D "host" structure) comprised of litharge-like layers and ribbons formed by edge-sharing oxocentered OBin, polyhedra (n = 4 and 5). The chloride anions fill the 7.6 & Aring; channels with the triangular cross-section inside the slabs as well as the interlayer space wherein they are partially substituted by disordered BO33- groups or Se2- anions. Compound 1 is just the second example of a mixed halide-borate occupancy among bismuth compounds while 2 illustrates much broader perspectives of mixed oxyhalide-oxychalcogenide approach to construction of novel complex bismuth compounds. Both compounds make new contributions to the family of tunnel structures of anion-centered tetrahedra featuring wide trigonal channels filled by halide anions or more complex metal- -halide "salt inclusions".