Michael Koop

Surfactant -Encapsulated Clusters (SECs): (DODA)20(NH4)[H3Mo57V6(NO)6O183(H2O)18], a Case Study

We present a comprehensive study of the partially reduced polyoxomolybdate [H3-Mo57V6(NO)6O183(H2O)18]21-encapsulated in a shell of dimethyldioctadecylammonium (DODA) surfacmolecules. Treatment of an aqueous solution of (NH4)21[H3Mo57V6-(NO)6O183(H2O)18] . 65H2O (1a) with a trichloromethane solution of the surfactant leads to instant transfer of the encapsulated complex anion into the organic phase. Results from vibrational spectroscopy. analytical ultracentrifugation, small-angle X-ray scattering, transmission electron microscopy, elemental analysis, and Langmuir compression isotherms are consistent with a single polyoxometalate core encapsulated within a shell of 20 DODA molecules. The molar mass of the supramolecular assembly is 20249 gmol(-1) and the diameter is 3.5 nm. A material with the empirical formula (DODA)20(NH4)[H3-Mo57V6NO)6O183(H2O)18] (2) was isolated as a dark violet solid, which readily dissolves in organic solvents. Slow evaporation of solutions of 2 on solid substrates forces the hydrophobic particles to aggregate into a cubic lattice. Annealing these so-formed films at elevated temperature causes de-wetting with terrace formation similar to liquid crystals and block copolymers. Compound 2 forms a stable Langmuir monolayer at the air-water interface; Langmuir-Blodgett multilayers are readily prepared by repeated transfer of monolayers on solid substrates. The films were characterized by optical ellipsometry, Brewster angle microscopy, transmission electron microscopy, and X-ray reflectance.

Unusual Stepwise Assembly and Molecular Growth: [H14Mo37O112]14− and [H3Mo57V6(NO)6O189(H2O)12(MoO)6]21−

The understanding of the formation of complex molecular systems from simple building blocks by conservative self-assembly processes is still a challenge. We report the synthesis and structural characterization of the large reduced polyoxometallate compounds (NH4)(14)[H14Mo37O112]. 35 H2O (1), (NH4)(21)[H3Mo57V6(NO)(6)O-183(H2O)(18)]. 55H(2)O (2) (by an improved synthesis) and Na-3(NH4)(18)[H3Mo63V6(NO)(6)O-195(H2O)(12)]. 41H(2)O (3). The cluster systems are formed by a stepwise growth process. This implies the appearance, during the cluster formation, of ephemeral polyoxometallate intermediates (some of which we were able to isolate). The negative charge and therefore the nucleophilicity of the intermediate cluster fragments increase when they are reduced, resulting in further attraction of electrophiles and thus in growth of molecular systems. IN the case of the cluster anion of 3 we observed, correspondingly, the loss of an [MoO](4+) oxometallate fragment by air oxidation; this implies that aits uptake and release are controlled by th degree of reduction of the cluster. correspondingly, intermediates between the anions of 2 and 3 of the {Mo57+xV6} type could be isolated. The unusual anion of 1 is formed by symmetry breaking processed.

Facile and Optimized Syntheses and Structures of Crystalline Molybdenum Blue Compounds Including one with an Interesting High Degree of Defects: Na26[Mo142O432(H2O)58H14] · ca. 300 H2O and Na16[(MoO3)176(H2O)63(CH3OH)17H16] · ca. 600 H2O · ca. 6 CH3OH

The syntheses and structures of the two mixedvalence crystalline molybdenum blue compounds Na26[Mo142O432(H2O)58H14] · ca. 300 H2O (1) (containing the maximal number of well defined defects which influence the overall structure and the reactivity of the anionic cluster) and Na16[(MoO3)176(H2O)63(CH3OH)17H16] · ca. 600 H2O · ca. 6 CH3OH (2) (obtained in an optimized high-yield synthesis) are reported with reference to the critical conditions required for the isolation of corresponding crystalline materials.

Exchanged ligands on the surface of a giant cluster: [(MoO3)176(H2O)63(CH3OH)17Hn](32 – n)–

The synthesis of 1a·(32 – n)Na+·ca. 600 H2O·ca. 30 CH3OH 1 containing the ring-shaped, mixed-valence (MoV/MoVI) cluster [(MoO3)176(H2O)63(CH3OH)17Hn](32 – n)– 1a as a discrete unit in the crystal lattice is reported, which for the first time yields a compound of this type via a facile synthetic method and without amorphous reaction products; remarkably, H2O ligands can be replaced by CH3OH on the surface of a giant metal-oxide based cluster which has a nanometer sized cavity and, in contrast to zeolites, reducing properties.

Building blocks as disposition in solution: [{MoVIO3(H2O)}10{VIVO(H2O)}20{(MoVI/MoVI5O21)(H2O)3}10({MoVIO2(H2O)2}5/2)2 ({NaSO4}5)2]20–, a giant spherical cluster with unusual structural features of interest for supramolecula

The unique polyoxometalate compound Na20[{MoVIO3- (H2O)}10{VIVO(H2O)}20{(MoVI/MoVI5O21)(H2O)3}10({MoVI- O2(H2O)2}5/2)2 ({NaSO4}5)2]·xH2O 1 (x ≈ 170) shows remarkable structural features: e.g. (i) {MoVI/MoVI5}-type pentagons as building blocks (being present in the relevant reaction medium as disposition), (ii) a ‘magnetic ring-shaped band’ built up by ten linked {VIV3} triangles having common corners and (iii) two {NaSO4}5 rings encapsulated inside the cavity of an icosidodecahedron formed by twenty triangular and twelve pentagonal faces built up by ten MoVI and twenty VIV centres, respectively.

[{MoVI8VIV4O36(VVO4)(VIVO)2}n]7n-: cappedα-Keggin fragments linked to a chain

The synthesis and single-crystal X-ray structure analysis of the unusual Mo/V polyoxometalate compound Na 0.5 K 6.5 [Mo VI 8 V IV 4 O 36 (V V O 4 )(V IV O) 2 ]·12.5H 2 O which contains capped α-Keggin fragments linked to a chain is reported; this chain is an interesting object for magnetochemists and can be considered to consist of an assembly of electron storage units.

Infinite octamolybdate chains cross-linked by paramagnetic iron (II) centers

The paper presents a new polymeric polyoxomolybdate cluster with infinite octamolybdate chains cross-linked by iron (II) centers. The layer-type substance contains sodium cations sandwiched between the [Fe(H2O)4Mo8O27]∞ layers. The structure was determined by single crystal X-ray diffraction analysis. Magnetic properties, due to the presence of paramagnetic iron (II) centers, are presented and discussed.