This Account reports recent progress in the study of some approximately 20 heterometal derivatives of [Mo3S4(H2O)9]4+ with reference also to W and Se analogues. Single cubes (3:1) and corner-shared double cubes (6:1), as well as dimers of the 3:1 single cubes, are considered. A classification of the heterometals as subtypes A, B, and C is introduced.

Cuboidal cluster complexes having M 4 Q 4 cores made up of transition and main group metals (M), and non-metallic e.g. chalcogenide elements (Q), constitute a rapidly expanding area of inorganic chemistry. Extensive preparation, structural and reactivity studies have been carried out on the Group 6 metals (M ‫؍‬ Mo, W) and chalcogenide (Q ‫؍‬ S, Se, Te) clusters, and are the main focus of this perspective. The aqueous solution chemistry provides an important reference point in considering redox and other relevant properties.

6 ·26H 2 O (7) were obtained in high yield by reaction of cucurbituril with aqueous solutions of lanthanide(III) species. The crystal structures of the compounds show a packing of 1:1, 2:2, and 2:3 in the (cucurbituril)lanthanide [a]

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The trinuclear MoIV 3 incomplete cuboidal cluster [Mo3S4(H2O)9]4+ in 2 M HCl reacts rapidly (green to intense blue-green color change) with AsO2 - or HAsO4 2- in the presence of H3PO2 as reductant to give the new air-sensitive corner-shared double cube [Mo6AsS8(H2O)18]8+. Purification by Dowex 50W-X2 cation-exchange chromatography requires 4 M H(pts) (pts = p-toluenesulfonic acid) for elution, consistent with a high charge. The X-ray structure has been determined for crystals obtained from 4 M H(pts) solution, full formula [Mo6AsS8(H2O)18](pts)8·28H2O. The Mo6AsS8 core structure was confirmed from ICP elemental analysis for Mo, As, and S (6:1:8) and the 8+ charge from the 3:1 stoichiometries with [Co(dipic)2]- and [Fe(H2O)6]3+ as oxidant. Rate constants for the oxidation of [Mo6AsS8(H2O)18]8+ with [Co(dipic)2]- have been determined and indicate strong reduction properties as compared to other heteroatom clusters. The existence of short (bonding) Mo−Mo separations, 2.716 Å average, and long (nonbonding) Mo−As separations at 3.554 A, together with similar features for other heteroatom clusters, has led to a classification of the clusters into different categories. The nine 8+ double cubes, most of which contain a main group heteroatom M, are classified as (Mo3S4 4+)2 M0, with retention of two metal−metal bonded Mo3S4 4+ units. The single cubes, on the other hand, can be classified as Mo3S4 4+M0, with M a transition metal, or Mo3S4 4+M x , with M a main group element (x depends on group involved).