Hydrogen-bonded molecular clusters

Keywords Noncovalent interactions Cation-n n-n stacking Hydrogen bonding Molecular clusters Cooperativity Biological relevance of metal ion interactions... 

The interaction model described above has been extensively tested and successfully used in many calculations on weak van der Waals as well as hydrogen bonded molecular clusters (see Hydrogen Bonding I and Hydrogen Bonding 2). It also forms the kernel of many solute/solvent potentials that are used in the various approaches to the modeling of solvation. 

S. Re and Y. Osamura, Size-dependent hydrogen bonds of cluster ions between phenol cation radicals and water molecules a molecular orbital study, J. Phys. Chem. A, 102 (1998) 3798-3812. 

A microwave pulse from a tunable oscillator is injected into the cavity by an anteima, and creates a coherent superposition of rotational states. In the absence of collisions, this superposition emits a free-mduction decay signal, which is detected with an anteima-coupled microwave mixer similar to those used in molecular astrophysics. The data are collected in the time domain and Fourier transfomied to yield the spectrum whose bandwidth is detemimed by the quality factor of the cavity. Hence, such instruments are called Fourier transfomi microwave (FTMW) spectrometers (or Flygare-Balle spectrometers, after the inventors). FTMW instruments are extraordinarily sensitive, and can be used to examine a wide range of stable molecules as well as highly transient or reactive species such as hydrogen-bonded or refractory clusters [29, 30]. 

Hydrogen-bonded clusters are an important class of molecular clusters, among which small water clusters have received a considerable amount of attention [148, 149]. Solvated cluster ions have also been produced and studied [150, 151]. These solvated clusters provide ideal model systems to obtain microscopic infonnation about solvation effect and its influence on chemical reactions. 

A metal cluster can be considered as a polynuclear compound which contains at least one metal-metal bond. A better definition of cluster catalysis is a reaction in which at least one site of the cluster molecule is mechanistically necessary. Theoretically, homogeneous clusters should be capable of multiple-site catalysis. Many heterogeneous catalytic reactions require multiple-site catalysis and for these reasons discrete molecular metal clusters are often proposed as models of metal surfaces in the processes of chemisorption and catalysis. The use of carbonyl clusters as catalysts for hydrogenation reactions has been the subject of a number of papers, an important question actually being whether the cluster itself is the species responsible for the hydrogenation. Often the cluster is recovered from the catalytic reaction, or is the only species spectroscopically observed under catalytic conditions. These data have been taken as evidence for cluster catalysis. 

These may include atomic and molecular hydrogen, as well as hydrogen bonded at oxygen-related clusters. Passivation of the 450°C thermal donors has also been investigated as a function of cluster size by Johnson and Hahn (1986) and Johnson et al. (1986). 

---