Metal discrete molecular systems

Which levels on the metal surface are responsible for these interactions In discrete molecular systems we know that the important contributions to bonding are forward donation, 31a, from the carbonyl lone pair 5o to some appropriate hybrid on a partner metal fragment, and back donation, 31b, involving the 2x of CO and a dx orbital xz, yz of the metal. We would suspect that similar interactions are operative on the surface. 

An interesting combined use of discrete molecular and continuum techniques was demonstrated by Floris et al.181,182 They used the PCM to develop effective pair potentials and then applied these to molecular dynamics simulations of metal ion hydration. Another approach to such systems is to do an ab initio cluster calculation for the first hydration shell, which would typically involve four to eight water molecules, and then to depict the remainder of the solvent as a continuum. This was done by Sanchez Marcos et al. for a group of five cations 183 the continuum model was that developed by Rivail, Rinaldi et al.14,108-112 (Section III.2.ii). Their results are compared in Table 14 with those of Floris et al.,139 who used a similar procedure but PCM-based. In... 

Photochemical behaviour of coordination compounds described in previous chapters results mainly from electronic interactions between the central metal atom or ion and ligands in the hrst coordination sphere. An increased size of molecular systems to clusters and nanosized crystals expands the possibility of photoinduced electron transfer between the discrete electronic states to excitation within bands. Furthermore, interactions of nanoparticles with molecules yield unique materials, combining structural versatility of molecular species with collective properties of solids. 

Owing to the enormous range of what can now be described as supramolecular chemistry, the present work will chiefly focus on discrete molecular assemblies. In particular, no attempt has been made to discuss the burgeoning field d of crystal engineering . Similarly, unless of particular relevance to the topic under discussion, higher oligomeric and polymeric systems, including most metal cluster and related compounds, have also been excluded from the discussion. 

Inorganic Molecules.— The crystal structure of the technetium(vii) oxide, Tca07, comprises discrete molecular units. The oxygen atoms form a tetrahedron around each metal atom, and two such tetrahedra are linked through a linear Tc-O-Tc system to form a dinuclear, centrosymmetric molecule. The Tc-O(bridging) and the average Tc-O(terminal) distances are 1.840(1) and 1.672 A, respectively. 

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