27Al NMR Study of the Metal Cluster Compound Al50C120H180

Abstract

We present an 27 Al NMR study of the metal cluster compound Al 50 Cp* 12 which is composed of (identical) Al 50 clusters, each surrounded by a Cp* ligand shell, and arranged in a crystalline 3D array (here Cp* = pentamethylcyclopentadienyl = C 5 (CH 3 ) 5 ). The compound is found to be non-conducting, the nuclear spin-lattice relaxation in the temperature range 100-300 K being predominantly due to reorientational motions of the Cp* rings. These lead to a pronounced maximum in the relaxation rate at T $ 170 K, corresponding to an activation energy of about 850 K. Data for the related compound Al 4 Cp* 4 , containing very much smaller Al 4 clusters are also presented. A comparison is drawn with the quadrupolar relaxation recently observed for the non-conducting fraction of Ga 84 molecules in the metal cluster compound Ga 84 [N(SiMe 3 ) 2 ] 20 -Li 6 Br 2 (thf) 20 AE2toluene.

The Mackay‐Type Cluster [Cu43Al12](Cp*)12: Open‐Shell 67‐Electron Superatom with Emerging Metal‐Like Electronic Structure

“…The 1 HMAS NMR spectrum shows one broad singlet at 1.72 ppm, assigned to the methyl groups of the 12 Cp* ligands,i n accordance with the icosahedral symmetry.T he additional signal at 6.95 ppm arises from co-crystallization of benzene (see Supporting Information for the corresponding 13 CM AS NMR data). [33] IR spectroscopic analysis reveals the characteristic set of bands for Cp* ligands, being the n C-H and n C-C vibrational modes at 2872 and 2818 cm À1 ,a nd 1412 and 1358 cm À1 .A na dditional very strong absorption is observed at 391 cm À1 which is assigned to the Al-Cp* vibration. [33] IR spectroscopic analysis reveals the characteristic set of bands for Cp* ligands, being the n C-H and n C-C vibrational modes at 2872 and 2818 cm À1 ,a nd 1412 and 1358 cm À1 .A na dditional very strong absorption is observed at 391 cm À1 which is assigned to the Al-Cp* vibration.…”

Experimentally Based DFT Calculations on the Hindered Disproportionation of [Al4Cp*4]: Formation of Metalloid Clusters as Intermediates on the Way to Solid Al Prevents the Decomposition of a Textbook Molecule

“…[12] The stability of 1 has been investigated, mainly as tetrameric entities in solution [3] and in the solid state. [13,14] The dissociation of the tetramers to monomeric units in solution [3,15] and in the gas phase [16] at 100 8C (the temperature of the classical synthesis) has also been investigated. However, the fact that the disproportionation of 1 is hindered, even above 100 8C, has never been discussed, which is surprising because the unsubstituted analogue [Al 4 Cp 4 ] (Cp= C 5 H 5 ) (2) spontaneously decomposes to metallic aluminum and Al III species even when it is warmed to temperatures above À30 8C.…”

Theory and X-ray Absorption Spectroscopy for Aluminum Coordination Complexes – Al K-Edge Studies of Charge and Bonding in (BDI)Al, (BDI)AlR2, and (BDI)AlX2 Complexes

“…However, Al K-edge XANES spectroscopy could become a powerful complement to 27 Al NMR, which is also sensitive to a range of factors including formal charge and the nature of bonding ligands, their geometry, and coordination number. [21][22][23]124,125 Studies on a wider range of aluminum molecules and extended solids are needed to explore possible correlations between observables provided by the two techniques.…”