The reduction of solutions of acidified molybdate leads to the formation of a family of nanostructured molybdenum blue (MB) wheels which are linked together in a series of complex reaction networks. These networks are complex because the species which define the nodes are extremely labile, unstable, and common to many different networks. Herein, we combine gel electrophoresis and electrospray ionization mass spectrometry (ESI-MS) to investigate the effect of the pH and the ratio of reactants and reducing agents, R (R = [S2O4(2-)]/[MoO4(2-)]), on the complex underlying set of equilibria that make up MBs. By mapping the reaction parameter space given by experimental variables such as pH, R, solvent medium, and type of counterion, we show that the species present range from nanostructured MB wheels (comprising ca. 154 Mo atoms) to smaller molecular capsules, [(SO3)2Mo(V)2Mo(VI)16O54](6-) ({S2Mo18}), and templated hexameric [(μ6-SO3)Mo(V)6O15(μ2-SO3)3](8-)({S4Mo6}) anions. The parallel effects of templation and reduction on the self-assembly process are discussed, taking into consideration the Lewis basicity of the template, the oxidation state of the Mo centers, and the polarity of the reaction medium. Finally, we report a new type of molecular cage (TBA)5[Na(SO3)2(PhPO3)4Mo(V)4Mo(VI)14O49]·nMeCN (1), templated by SO3(2-) anions and decorated by organic ligands. This discovery results from the exploration of the cooperative effect of two anions possessing comparable Lewis basicity, and we believe this constitutes a new synthetic approach for the design of new nanostructured molecular metal oxides and will lead to a greater understanding of the complex reaction networks underpinning the assembly of this family of nanoclusters.

Thermal migration of the sodium cation in the cavity of Preyssler-type phosphotungstate is reported here. Heating of a Preyssler-type compound-[P5W30O110Na(side)(H2O)] 14--in which a sodium cation occupies one of the two side cavities, at 300°C forms a new compound-[P5W30O110Na(center)] 14--in which the sodium cation is encapsulated in the central cavity. Characterization by single crystal X-ray structure analysis, NMR technique, elemental analysis, IR, and ESI-MS confirmed the structure of the compound. The thermal displacement ellipsoid of the central sodium, estimated by the crystallographic study, is elongated along the direction perpendicular to the equatorial plane of the Preyssler molecule. These results confirmed prediction using DFT calculation by López and Poblet (ref. 21, J. Am. Chem. Soc. 2007, 129, 12244.) that the most stable site for sodium is the central cavity with a slight shift from the center of the molecule.

Newly prepared single crystals of [Co(ii)(dabco)(NCS)2(MeOH)2]·dabco (1-pink; dabco: 1,4-diazabicyclo[2.2.2]octane) showed chromotropic behaviour in the solid state, changing from pink to blue upon heating or grinding. The complex 1-pink exhibited a two-dimensional orthogonal network structure with the coordination chain of -dabco-Co- bridged by hydrogen bonds between coordinative methanol and a second dabco molecule, where the methanol molecule was trapped by coordinative and hydrogen bonds. Chromism was demonstrated to stem from the quantitative desorption of methanol from 1-pink to produce [Co(ii)(dabco)(NCS)2]·dabco (1-blue(c)) by thermogravimetric (TG) and temperature controlled gas chromatography-mass spectrometry (GC-MS) analyses, and powder X-ray diffraction (XRD) analysis suggests that the transformation between the crystalline phases of 1-pink and 1-blue(c) occurred with similar lattice parameters. Furthermore, the desolvated species showed chemo-chromic behaviour due to the selective size- and polarity-dependent adsorption of solvent molecules.

We synthesized an Fe(II) [2 × 2] molecular grid with pyridyl-substituted bis-terdentate ligands. The molecular grid showed abrupt spin crossover between fully high-spin and fully low-spin states in a narrow temperature width of ∼10 K. The spin crossover event also included a first-order structural phase transition, in which the dielectric constant jumped atypically toward a low-spin state.

The structural phase of a metal oxide changes with temperature and pressure. During phase transitions, component ions move in multidimensional metal–oxygen networks. Such macroscopic structural events are robust to changes in particle size, even at scales of around 10 nm, and size effects limiting these transitions are particularly important in, for example, high‐density memory applications of ferroelectrics. In this study, we examined structural transitions of the molecular metal oxide [Na@(SO3)2(n‐BuPO3)4MoV4MoVI14O49]5− (Molecule 1) at approximately 2 nm by using single‐crystal X‐ray diffraction analysis. The Na+ encapsulated in the discrete metal‐oxide anion exhibited a reversible order–disorder transition with distortion of the Mo–O molecular framework induced by temperature. Similar order–disorder transitions were also triggered by chemical pressure induced by removing crystalline solvent molecules in the single‐crystal state or by substituting the countercation to change the molecular packing.