Adamantane-type clusters: compounds with a ubiquitous architecture but a wide variety of compositions and unexpected materials properties

The research into adamantane-type compounds has gained momentum in recent years, yielding remarkable new applications for this class of materials. In particular, organic adamantane derivatives (AdR4) or inorganic adamantane-type compounds of the general formula [(RT)4E6] (R: organic substituent; T: group 14 atom C, Si, Ge, Sn; E: chalcogenide atom S, Se, Te, or CH2) were shown to exhibit strong nonlinear optical (NLO) properties, either second-harmonic generation (SHG) or an unprecedented type of highly-directed white-light generation (WLG) - depending on their respective crystalline or amorphous nature. The (missing) crystallinity, as well as the maximum wavelengths of the optical transitions, are controlled by the clusters' elemental composition and by the nature of the organic groups R. Very recently, it has been additionally shown that cluster cores with increased inhomogeneity, like the one in compounds [RSi{CH2Sn(E)R'}3], not only affect the chemical properties, such as increased robustness and reversible melting behaviour, but that such 'cluster glasses' form a conceptually new basis for their use in light conversion devices. These findings are likely only the tip of the iceberg, as beside elemental combinations including group 14 and group 16 elements, many more adamantane-type clusters (on the one hand) and related architectures representing extensions of adamantane-type clusters (on the other hand) are known, but have not yet been addressed in terms of their opto-electronic properties. In this review, we therefore present a survey of all known classes of adanmantane-type compounds and their respective synthetic access as well as their optical properties, if reported.

Structure of a Fe4O6-Heteraadamantane-Type Hexacation Stabilized by Chelating Organophosphine Oxide Ligands

Metal-containing heteraadamantanes are compounds of interest due to their spectroscopic and magnetic properties, which make them promising materials for non-linear optics and semiconductors. Herein we report the comprehensive structural characterization of a new coordination compound of the formula [(µ-OH′)₂(µ-OH″)₄(O = P(Ph₂)CH₂CH₂(Ph₂)P = O)₄{Fe(t-BuOH)}₄](PF₆)₄(Cl)₂ with the chelating ligand Ph₂P(O)-CH₂CH₂-P(O)Ph₂. The compound crystallizes as a polynuclear metal complex with the adamantane-like core [Fe₄O₆] in the space group I-43d of a cubic system. The single-crystal XRD analysis showed that the crystal contains one symmetrically independent octahedrally coordinated Fe atom in the oxidation state +3. The adamantine-like scaffold of the Fe complex is formed by hydroxy bridging oxygen atoms only. Hirshfeld surface analysis of the bridging oxygen atoms revealed two types of µ-OH groups, which differ in the degree of exposure and participation in long-range interactions. Additionally, the Hirshfeld surface analysis supported by the enrichment ratio calculations demonstrated the high propensity of the title complex to form C-H^…Cl, C-H^…F and C-H^…O interactions.