Metals framework rearrangement

However, only one hydrido ligand resonance is observed in the 1H NMR spectrum of each cluster at temperatures low enough to prevent the metal framework rearrangement process from operating, although for the... 

A novel metal framework rearrangement occurs for the Hg-bridged Fe—Rh carbonyl cluster In solution the Hg atom migrates around the Fe2Rh... 

Reaction of Osg(CO)ig with (SPPh2)2NH at low temperature results in a metal framework rearrangement to give the spiked-bridged-tetrahedral hydrido complex 39 ... 

Molecular Dynamics of H FeR CCO)-] and Related Mixed-Metal Clusters. Metal clusters have been shown to undergo a wide variety of fluxional processes in which carbonyls, hydrides, and even the metals themselves undergo rearrangement (25). Mixed-metal clusters are ideally suited for studies of fluxional processes because of the low symmetry which is inherent within their metal framework. In such clusters, the majority of... 

Some polynuclear anions change the structure of their metal cores on protonation. For example, the dianion [OSj(CO),J " has O, symmetry the first proton bridges an O, face, and the second causes the metal framework to rearrange to a monocapped square pyramid in which the exact location of the hydrogen ligands is not clear ... 

The synthesis of [HFe4(CO),3] from [Fe4(CO),3]2 (186,187) is interesting because of the major structural rearrangement that occurs following protonation (184). The parent dianion has a tetrahedral metal framework (Section II,C,4) (153) which undergoes metal-metal bond scission and formation of the II —CO upon protonation. The metal core geometry for [HFe4(CO)13] is butterfly shaped, and the proper 62-electron count for a butterfly metal cluster is achieved if the II —CO is assumed to be a 4-electron donor. 

As stated in the previous section, dynamic behaviour involving intramolecular rearrangements of the metal skeletons of Group 11 metal heteronuclear clusters is relatively common, in marked contrast to the situation observed for almost all other transition metal clusters, which have metal frameworks that are stereochemically rigid in solution. The mechanisms of these metal core rearrangements are, therefore, of considerable interest. 

In our own work there have been two main strands - the determination of solution-phase structures of heteronuclear clusters and the study of cluster reactions in which the metal framework is assembled or rearranges. In this work we have sought to obtain enhanced structural data as a result of the presence of more than one X-ray absorbing element (metal) in the cluster framework. Furthermore the presence of platinum or palladium in many of these systems leads to much structural variability. 

Although very many carboxylate and amine-based hybrid frameworks have been prepared, solid state NMR has not been used as a characterisation tool in the same way as it has for inorganic zeolitic frameworks. This is probably because they are commonly prepared as crystals suitable for single crystal diffraction, and often with paramagnetic metals. It is likely, however, that NMR will reveal important structural details as these materials are studied more carefully, particularly in monitoring interactions and framework rearrangements upon adsorption of molecules.Studies of framework and sorbate motion by deuterium NMR are also highly relevant here (Chapter 7). 

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