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.

Fecht's acid revisited: a spirocyclic dicarboxylate for non-aromatic MOFs

The first of a new class of spiroalkane-derived MOF linkers shows aromaticity is not a prerequisite for ligand design in porous materials.

Formation of a robust, double-walled LiMOF from an L-shaped di-substituted N-heterocyclic adamantane-based ligand

The properties of adamantane render it an attractive building block towards the synthesis of robust frameworks. This work describes the synthesis of the L-shaped 1,3-bis(3'-carboxypyridine)adamantane (L1) ligand and the corresponding Li(i), Zn(ii) and Cu(ii) frameworks. Three topologically analogous Li(i) frameworks LiMOF12, LiMOF30 and LiMOF50 are reported, with calculated solvent accessible void volumes of 46, 43 and 36%, respectively. The reaction between the carboxylate groups of L1 and the Li(i) cations resulted in the formation of Li-carboxylate rods. The Li-carboxylate rods contributed to the formation of a double-walled MOF with large, open one dimensional channels. The synergistic effect of the double wall, lithium-carboxylate rods and the adamantane core itself, resulted in the formation of a robust network stable up to temperatures of 300-350 °C and a minimum of three months stability in air. Furthermore, complexation of L1 with Cu(BF4)2·H2O and Zn(CF3SO3)2 provided a 2D → 3D interpenetrated network containing a classic dimeric copper paddle-wheel SBU, and an infinite 1D chain which extended into a 3D structure facilitated by hydrogen-bonding interactions, respectively.

Templating metastable Pd2 carboxylate aggregates

Evaluation of the potential for metal-metal (M-M) cooperation to enable catalysis requires access to specific polynuclear aggregates that display appropriate geometry and size. In many cases, exerting synthetic control over the aggregation of simple metal salts is a challenge. For example, Pd(ii) acetate self assembles as a trimer (i.e. Pd3(OAc)6) both in the solid state and in solution and does not feature close Pd-Pd interactions. Related carboxylate-supported Pd2 aggregates (i.e. Pd2(OAc)4), which would feature close Pd-Pd interactions, are thermodynamically metastable in solution phase and thus largely unavailable. Here we demonstrate ion metathesis within pre-formed metal-organic frameworks (MOFs) to prepare metastable Pd2 tetracarboxylates sites. The newly synthesized materials are characterized by elemental analysis, PXRD, SCXRD, EXAFS, XANES, and gas adsorption analysis. In addition, the critical role of network solvation on the kinetics of ion metathesis was revealed by coupled TGA-MS and ICP-MS experiments. The demonstration of templated ion metathesis to generate specific metastable coordination sites that are inaccessible in solution phase chemistry represents a new opportunity to interrogate the chemistry of specific polynuclear metal aggregates.

Non-interpenetrated Cu-based MOF constructed from a rediscovered tetrahedral ligand

A stable non-interpenetrated MOF, UOF-1 (UOF = University of Otago framework), was made by combining the rigid tetrahedral tetrakis(4-carboxyphenyl)adamantane (L) ligand and copper(ii) paddle-wheel SBU. This low-density open framework displayed excellent selectivity for CO₂ over N₂ at practical operating conditions.

Zinc and cadmium complexes based on bis-(1H-tetrazol-5-ylmethyl/ylethyl)-amine ligands: structures and photoluminescence properties

Nine zinc and cadmium coordination compounds with bis-(1H-tetrazol-5-ylmethyl/ylethyl)-amine were synthesized and structurally characterized, and the fluorescent emission and fluorescence lifetime of complexes 1–9 have been investigated and discussed.

Guest-induced single-crystal-to-single-crystal transformations of a new 4-connected 3D cadmium(ii) metal–organic framework

A unique 4-connected network [Cd(pic)(H₂O)]·H₂O (1) with wheel-type hexa-nuclear SBU has been synthesized. Guest-induced single-crystal-to-single-crystal reversible transformations occurred between 1 and the desolvated crystal [Cd(pic)] (1a).

Structural diversity of five new bitriazole-based complexes: luminescence, sorption, and magnetic properties

Employing a new bitriazole ligand, five complexes were assembled that display diverse structures, selective CO₂/CH₄ adsorption, luminescent sensing, and antiferromagnetic properties.