Tetraberyllium-η4-oxo-hexa(arylcarboxylates)

Raphael J.F. Berger, Michael A. Schmidt, Jonas Jusélius, Dage Sundholm, Peter Sirsch, Hubert Schmidbaur

Research output: Contribution to journalArticlepeer-review

33 Scopus citations

Abstract

Tetraberyllium-oxo-hexabenzoate and -hexa(mesitylcarboxylate) were prepared from benzoic / mesitylcarboxylic acid and freshly precipitated beryllium hydroxide in a tetrahydrofuran / water two-phase system. The crystal structure of the benzoate was determined from Be4O(OCOPh)6(C6H6)3, and that of the mesitylcarboxylate from the phase Be4O(OCOMes)6(CCl4). The two clusters have the μ4-oxo cage structure also detected for the acetate and nitrate complexes, and for the related hexacarbonato hexaanion. The high symmetry of the cluster allows the observation of 9Be and 17O signals in the solution NMR spectra. The terminal atoms of the rigid carboxylate groups may be expected to lie at the vertices of large octahedra enclosing the cluster molecules. The axes of the six aryl groups would thus coincide with the axes of the cartesian coordinates with the μ4 oxygen atom at the origin. This disposition suggests a connectivity suitable for cubic lattices if p-difunctional arene-dicarboxylate anions are employed instead of aryl-monocarboxylate anions. However, the new results show that significant deviations of the OBe2O2C-Ar six-membered rings from planarity cause major deviations from octahedral symmetry and therefore no connectivity in cubic symmetry is to be expected. Fragmentation of the Be4O(OCOR)6 clusters upon ionization in a mass spectrometer leads predominantly to cations [Be3O(OCOR)3]+ which can be assigned a planar, highly symmetrical tricyclic core structure of D3h symmetry. Quantum chemical calculations confirm discrete energy minima for these cations and show that their stability is largely due to the favourable arrangement of alternating charges of neighbouring core atoms. The high polarity of Be-O bonds rules out any significant contributions from aromaticity. The reactions of Be(OH)2 with 4-HS-C6H4-COOH and HS(CH2)2COOH give the corresponding cluster compounds Be4O(OCORSH)6, [R = C6H4, (CH2)2] with six terminal mercapto functions.

Original languageEnglish
Pages (from-to)979-989
Number of pages11
JournalZeitschrift fur Naturforschung - Section B Journal of Chemical Sciences
Volume56
Issue number10
DOIs
StatePublished - Oct 2001
Externally publishedYes

Keywords

  • Beryllium carboxylates
  • Beryllium chemistry
  • Quantum chemical calculations

Fingerprint

Dive into the research topics of 'Tetraberyllium-η4-oxo-hexa(arylcarboxylates)'. Together they form a unique fingerprint.

Cite this