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4 Bulletin of the Polish Academy of Sciences. Chemistry

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From simple linkable building blocks to structures with increasing size and complexity

100%

Müller A. , Kögerler P.

1998

tom Vol. 46, No. 3

207-219

Polyoxometalates provide excellent models for the understanding of basic aspects of molecular growth processes: Using the same reaction, i.e., the acidification of the aqueous solution of oxoanions, the resulting products span three important areas of matter, from the micro-, through the meso- to the macro"cosmos", the latter of which is characterized by crystallinity or respectively, translational invariance. Upon different types of linking of well-defined building units an overwhelming variety of different species can be formed. Novel types of molecular growth processes (including those based on a type of induced cascade) are described leading to different ring-shaped, electron-rich, mixed-valence, giant polyoxomolybdates with nano-sized cavities. The recent synthesis of various large ring-cluster systems has, furthermore, opened new perspectives for a novel supramolecular chemistry in nano-scale dimensions.

Introducing heterometal centers into a [XW9O33]9- - type building block: a first step for related derivatives

80%

Botar B. , Bögge H. , Müller A.

2002

tom Vol. 50, No. 2

139-144

For the first time it was possible to introduce heterometals (V(IV)) into the important [XW(9)O(33)](9-)(III) and Bi(III) building block thereby offering new pathways for related chemistry. By reaction of a VOSO(4)-5H(2)O solution in high excess with [(SbW(9)O(33))(2)(WO(2))4(OH(2)](12)- (molar ratio of 12:1) in acetic buffer solution, a compound containing the basic-typeanionslike[(SbW(8)VO(33)(2)(VO(2)(H(2)O)(4)(WO2)(2)](14-) which in principle could be protonated with different degrees, can be obtained. This opens new perspectives for magnetochemistry and reactivity studies of these types of compounds.

The reaction of giant wheel polyoxomolybdate clusters with ethanol

61%

Bielański A. , Małecka-Lubańska A. , Poźniczek J. , Müller A. , Krickemeyer E. , Diemann E.

2001

tom Vol. 49, No. 1

85-99

The conversion of ethanol at 100-280° C was used in order to characterise the redox and acid centres present in Na15{0.5[Mo(152)O(457)H14(H(2)O)68] • 0.5[Mo(154)O(462)H(2)14 (H(2)O)(70]}-ca. 400 H(2)O (1). It is concluded that Mo(VI)/Mo pairs at the external surface of the rings, of which the structure of 1 is composed, are the redox centres active in ethanol dehydrogenation to acetaldehyde. Simultaneous ethanol dehydration to diethyl ether or ethylene is a typical reaction occurring on acid centres. It is suggested that OH groups situated in (u3-0)(2)0(2) tetrahedrons inside the ring structure play such role. The formation of ethane predominating at highest temperatures is attributed to secondary reactions of primary ethylene.

Thermal properties of the molybdenum - oxide based {Mo154} giant wheel type cluster with methanol ligands bonded to its surface

61%

Bielański A. , Małecka-Lubańska A. , Krickemeyer E. , Bögge H. , Schmidtmann M. , Müller A.

2001

tom Vol. 49, No. 3

245-254

The thermal behaviour of the giant molybdenum ring cluster compound formula - containing H2O ligands partly substituted by methanol molecules - was studied using TG, DTG and DTA analyses simultaneously, and mass spectromet-ric analysis of the decomposition products. Methanol is released from the sample quite rapidly even at room temperature (and even before the experiments start) but small traces of methanol are still present which we tried to use for characterising the different stages of giant ring transformation. The initial rapid loss of mass of the sample was accompanied by the DTA and DTG peak at 75°C. A small DTA endothermic peak at 165°C was assigned to an MS maximum indicating the increased emission of methanol and formaldehyde. Double exothermic peaks at 352 and 366° C corresponded to the loss of water formed from the abundant OH groups. Simultaneously, peaks indicating trace emission of formaldehyde, methanol, carbon dioxide as well as traces of hydrocarbons containing 2-4 carbon atoms per molecule were registered mass spectrometrically. The exothermic effect was attributed to a kind of "recrystallisation" process of the completely dehydrated product.