Ionothermal Synthesis, Structure, and Bonding of the Catena-Heteropolycation 1∞[Sb2Se2]+

The reaction of antimony and selenium in the Lewis-acidic ionic liquid 1-butyl-3-methyl-imidazolium tetrachloridoaluminate, [BMIm]Cl center dot 4.7AlCl(3), yielded dark-red crystals of [Sb2Se2]AlCl4. The formation starts above 160 degrees C; at about 190 degrees C, irreversible decomposition takes place. The compound crystallizes in the triclinic space group P (1) over bar with a = 919.39(2) pm, b = 1137.92(3) pm, c = 1152.30(3) pm, alpha = 68.047(1)degrees, beta = 78.115(1)degrees, gamma = 72.530(1)degrees, and Z = 4. The structure is similar to that of [Sb2Te2] AlCl4 but has only half the number of crystallographically independent atoms. Polycationic chains (1)(infinity)[Sb2Se2](+) form a pseudo-hexagonal arrangement along [01 (1) over bar], which is interlaced by tetrahedral AlCl(4)(-)groups. The catena-heteropolycation (1)(infinity)[Sb2Se2](+) is a sequence of three different four-membered [Sb2Se2] rings. The chemical bonding scheme, established from the topological analysis of the real-space bonding indicator ELI-D, includes significantly polar covalent bonding in four-member rings withinthepolycation. Theringsareconnectedintoaninfinitechainbyhomonuclear non-polar Sb-Sb bonds and highly polar Sb-Se bonds. Half of the selenium atoms are three-bonded.