Multicomponent halide templating: The effect of structure-directing agents on the assembly of molecular and extended coordination compounds

Platonic and Archimedean solids in discrete metal-containing clusters

Metal-containing clusters have attracted increasing attention over the past 2-3 decades. This intense interest can be attributed to the fact that these discrete metal aggregates, whose atomically precise structures are resolved by single-crystal X-ray diffraction (SCXRD), often possess intriguing geometrical features (high symmetry, aesthetically pleasing shapes and architectures) and fascinating physical properties, providing invaluable opportunities for the intersection of different disciplines including chemistry, physics, mathematical geometry and materials science. In this review, we attempt to reinterpret and connect these fascinating clusters from the perspective of Platonic and Archimedean solid characteristics, focusing on highly symmetrical and complex metal-containing (metal = Al, Ti, V, Mo, W, U, Mn, Fe, Co, Ni, Pd, Pt, Cu, Ag, Au, lanthanoids (Ln), and actinoids) high-nuclearity clusters, including metal-oxo/hydroxide/chalcogenide clusters and metal clusters (with metal-metal binding) protected by surface organic ligands, such as thiolate, phosphine, alkynyl, carbonyl and nitrogen/oxygen donor ligands. Furthermore, we present the symmetrical beauty of metal cluster structures and the geometrical similarity of different types of clusters and provide a large number of examples to show how to accurately describe the metal clusters from the perspective of highly symmetrical polyhedra. Finally, knowledge and further insights into the design and synthesis of unknown metal clusters are put forward by summarizing these "star" molecules.

Metalloporphyrinic metal-organic frameworks: Controlled synthesis for catalytic applications in environmental and biological media

Recently, as a new sub-family of porous coordination polymers (PCPs), porphyrinic-MOFs (Porph-MOFs) with biomimetic features have been developed using porphyrin macrocycles as ligands and/or pillared linkers. The control over the coordination of the porphyrin ligand and its derivatives however remains a challenge for engineering new tunable Porph-MOF frameworks by self-assembly methods. The key challenges exist in the following respects: (i) collapse of the large open pores of Porph-MOFs during synthesis, (ii) deactivation of unsaturated metal-sites (UMCs) by axial coordination, and (iii) the tendency of both coordinated moieties (at peripheral meso- and beta-carbon sites) and the N₄-pyridine core to coordinate with metal cations. In this respect, this review covers the advances in the design of Porph-MOFs relative to their counterpart covalent organic frameworks (Porph-COFs). The potential utility of custom-designed porphyrin/metalloporphyrins ligands is highlighted. Synthesis strategies of Porph-MOFs are also illustrated with modular design of hybrid guest@host composites (either Porph@MOFs or guest@Porph-MOFs) with exceptional topologies and stability. This review summarizes the synergistic benefits of coordinated porphyrin ligands and functional guest molecules in Porph-MOF composites for enhanced catalytic performance in various redox applications. This review shed lights on the engineering of new tunable hetero-metals open active sites within (metallo)porphyrin-MOFs as out-of-the-box platforms for enhanced catalytic processes in chemical and biological media.

Mechanistically Driven Control over Cubane Oxo Cluster Catalysts

Predictive and mechanistically driven access to polynuclear oxo clusters and related materials remains a grand challenge of inorganic chemistry. We here introduce a novel strategy for synthetic control over highly sought-after transition metal {M₄O₄} cubanes. They attract interest as molecular water oxidation catalysts that combine features of both heterogeneous oxide catalysts and nature's cuboidal {CaMn₄O₅} center of photosystem II. For the first time, we demonstrate the outstanding structure-directing effect of straightforward inorganic counteranions in solution on the self-assembly of oxo clusters. We introduce a selective counteranion toolbox for the controlled assembly of di(2-pyridyl) ketone (dpk) with M(OAc)₂ (M = Co, Ni) precursors into different cubane types. Perchlorate anions provide selective access to type 2 cubanes with the characteristic {H₂O-M₂(OR)₂-OH₂} edge-site, such as [Co₄(dpy-C{OH}O)₄(OAc)₂(H₂O)₂](ClO₄)₂. Type 1 cubanes with separated polar faces [Co₄(dpy-C{OH}O)₄(L2)₄] ⁿ⁺ (L2 = OAc, Cl, or OAc and H₂O) can be tuned with a wide range of other counteranions. The combination of these counteranion sets with Ni(OAc)₂ as precursor selectively produces type 2 Co/Ni-mixed or {Ni₄O₄} cubanes. Systematic mechanistic experiments in combination with computational studies provide strong evidence for type 2 cubane formation through reaction of the key dimeric building block [M₂(dpy-C{OH}O)₂(H₂O)₄]²⁺ with monomers, such as [Co(dpy-C{OH}O)(OAc)(H₂O)₃]. Furthermore, both experiments and DFT calculations support an energetically favorable type 1 cubane formation pathway via direct head-to-head combination of two [Co₂(dpy-C{OH}O)₂(OAc)₂(H₂O)₂] dimers. Finally, the visible-light-driven water oxidation activity of type 1 and 2 cubanes with tuned ligand environments was assessed. We pave the way to efficient design concepts in coordination chemistry through ionic control over cluster assembly pathways. Our comprehensive strategy demonstrates how retrosynthetic analyses can be implemented with readily available assembly directing counteranions to provide rapid access to tuned molecular materials.

Assembly, disassembly and reassembly: a "top-down" synthetic strategy towards hybrid, mixed-metal {Mo10Co6} POM clusters

Polyoxometalates (POMs) are commonly prepared using a "bottom-up" synthetic procedure. The alternative "top-down" approach of disassembling a pre-formed POM unit to generate new synthetic intermediates is promising, but relatively comparatively underused. In this paper, a rationale for the top-down method is provided, demonstrating that this approach can generate compounds that are fundamentally inaccessible from simple bottom-up assembly. We demonstrate this principle through the synthesis of a series of 10, new, mixed-metal, hybrid compounds with the general formula [TBA]2[MoVI10CoII6O30(RpPO3)6(RcCOO)2(L)x(H2O)6] (TBA = tetrabutylammonium, Rp = phosphonate moiety, Rc = carboxylate moiety, L = pyridyl ligand, and x = 2-4), including a one-dimensional polyoxometalate-based coordination polymer. We propose that these structures are generated from {MoxO3x-1} fragments that cannot be accessed from bottom-up assembly alone. The POM clusters are stabilised by three distinct classes of organic ligand - organophosphonate, carboxylate and pyridyl ligands - which can each be substituted independantly, thus providing a controlled route to ligand functionalisation.