New members of the family of In-Sb-S compounds: Different roles of organic amines

Reported here are the syntheses, structures, and characterizations of four novel In-Sb-S compounds containing organic amines, namely, [PAH]₃[In₃Sb₂S₉] (PA = n-propylamine) (1), [Fe(en)₃][In₂Sb₂S₇] (en = ethylenediamine) (2), [Mg(dien)₂][In₂Sb₂S₇]·0.5H₂O (dien = diethylenetriamine) (3), and In₂(N,N-dmen)₂Sb₂S₆ (N,N-dmen = N,N-dimethylethylenediamine) (4). Compound 1 features a [In₃Sb₂S₉]_n^3n- layer assembled by the alternating linkage of the {In₂Sb₂S₈}_n ribbons and the {In₄Sb₂S₁₂}_n double-ribbons. Both compounds 2 and 3 possess layered anionic parts with the same stoichiometry of [In₂Sb₂S₇]_n^2n- but distinct linkage modes between the subunits of {In₂S₇} groups and Sb³⁺ ions. Notably, the {In₂Sb₂S₉} heterometallic cluster observed in 3 is initially regarded as the secondary building unit (SBU) for the construction of the [In₂Sb₂S₇]_n^2n- layer. Compound 4 features a novel discrete inorganic-organic hybrid molecule of In₂(N,N-dmen)₂Sb₂S₆. Through the structural analyses on 1-4, the organic amines applied played three different roles on the formation of the final crystalline products. For 1, the protonated n-propylamines arrange in the space around the anionic network and balance the negative charge. For 2 and 3, the chelating polyamines coordinate to central metal ions to form metal complexes, which then act as space-filling and charge-balancing agents. For 4, two N,N-dimethylethylenediamines chelate to two In³⁺ ions of the inorganic segment through coordination bonds, leading to the formation of a rare inorganic-organic hybrid cluster. At last, we gave a systematic discussion about the characteristics and roles of organic amines in all related In-Sb-S compounds. In one word, the work presented here enriches the structural chemistry of the main-group heterometallic chalcogenidometalates, providing more chances for researchers to work out the rules in their composition- or structure-function relationship.