ROD-BASED SULFOSALT STRUCTURES DERIVED FROM THE SNS AND PBS ARCHETYPES

In the present review on the rod-based sulphosalt structures we descri be the fundamental features of their large- to medium-scale crystal ch emistry. The principal, lozenge-shaped rods in these structures repres ent portions based on the SnS or PbS archetype, with their surfaces be ing alternatively of the pseudotetragonal or pseudohexagonal (often sh eared) type. The formation of the rod-based sulphosalt structures can then be understood as a recombination of these rods into a structure b y means of non-commensurate Q:H interfaces. All of these structures sh ow distinct accumulation of Sb and Bi in rod interiors (that represent the lone electron pair micelles) and of Pb (and other large cations) on the pseudotetragonal surfaces of the lozenge-shaped rod. Detailed a nalysis is given of the first largest category of rod-based sulphosalt structures, those based on rods interconnected into layers. Twelve di fferent types of such layers have been recognized, based primarily on the mode of interconnection of the rods into layers; further subdivisi on in each category reflects the characteristic dimensions of their lo zenge-shaped cross-sections. All these derivations result in character istic geometry and stoichiometry of these structures, treated here in some detail. A survey of matches and combinations of different rod-lay er types observed or envisageable during the structure-recombination p rocess concludes the part on rod-layer based structures. The second pa rt of the review starts with a survey of pure (i.e. not layer-like) ro d-based sulphosalt structures and proceeds to lay out classification p rinciples for the three fundamental categories of rod-based structures : (1) the layer-, (2) the chess-board, and (3) the cyclic category, wi th the suggestions for their further subdivision. The present review d eals with the most important Pb-Sb, Sn-Sb, Pb-Bi-Sb as well as the sel ected Pb-Bi, Ba-Bi and other sulphosalts, eventually with minor conten ts of Cu or Fe.