Ionothermal Approach to Homo- and Heteroleptic Alkylation of Tellurido Mercurate Clusters for Assembly in Lamellar Crystal Structures.

Abstract

The selective methylation and butylation of chalcogenido metalate clusters by utilizing imidazolium-based ionic liquids turned out to be not only a comparably mild but at the same time also the only known method for postsynthetic alkylation of such species in order to increase their solubility. For additional impact on the crystal structures, selective alkylation with longer alkyl chains was addressed by utilizing the ionic liquid (C10C1Im)[BF4] (C10 = decyl group at position 1 and C1 = methyl group at position 3 of the cation's Im = imidazolium ring) for ionothermal syntheses of functionalized tellurido mercurate clusters. Herein, we report three novel compounds, two of which comprise cluster anions that exhibit a selective organic functionalization of their terminal telluride ligands upon in situ alkylation with the ionic liquid: [Hg6Te6(Te2)2(TeDec)2]6- (in 1; Dec = decyl) represents the first decylated chalcogenido metalate cluster. A unique heteroleptic functionalization, combining methylation and decylation, was achieved for the second cluster, [Hg6Te6(Te2)2(TeDec)(TeMe)]6- (in 2; Me = methyl). The third cluster is purely inorganic, but based on the same cluster core architecture: [Hg4Te2(Te2)2(Te3)2]4- (in 3) comprises a tritelluride unit instead of two HgTeR groups (R = Me, Dec). As a consequence of the long alkyl chains, both at the cluster and at the charge-compensating cations, all three crystal structures are characterized by lamellar assemblies of cations and anions. For further comparison of the properties of the organometallic versus purely inorganic compounds, vibrational and optical properties of crystalline samples of the compounds comprising clusters 1 and 3 were studied by means of infrared, Raman, and UV-visible spectroscopy. The results clearly show the effect of the presence of an organic decoration (in 1) relative to its absence (in 3), reflected by a red shift of the band gap energy (1 → 3) and a replacement of the Te-C bands (in 1) with bands for tritelluride units (in 3).