When co chemisorbs on metal surfaces (1)5o orbital interacts strongly with the metallic electronic states, and the electron density of the 5o orbital is donated to the metal and new hybrid electronic states are formed(donation), these are predominately localized about the carbon end of the molecule (2)The 2" accepts electron density from the metal from a process known as back donation new hybrid electronic states are constructed which are primarily localized about the Co molecule The overlap of the 5o orbital with the metal states is most favorable if the molecule is oriented with the carbon end toward the surface and the overlap of 2T" orbital with the metal states is most favored by a linear geometry. Thus it can be predicted that the Co molecule should chemisorb carbon end down with its axis along the normal to the surface This expectation is confirmed by experiments
When CO chemisorbs on metal surfaces, (1)5 orbital interacts strongly with the metallic electronic states, and the electron density of the 5 orbital is donated to the metal and new hybrid electronic states are formed (donation), these are predominately localized about the carbon end of the molecule; (2) The 2* accepts electron density from the metal from a process known as back donation, new hybrid electronic states are constructed which are primarily localized about the CO molecule. The overlap of the 5 orbital with the metal states is most favorable if the molecule is oriented with the carbon end toward the surface; and the overlap of 2* orbital with the metal states is most favored by a linear geometry. Thus it can be predicted that the CO molecule should chemisorb carbon end down with its axis along the normal to the surface. This expectation is confirmed by experiments
The 5o orbital is nonbonding in co. therefore modification of this orbital does not have a strong influence on the intramolecular C-o bond the 2T* orbital is antibonding with respect to the c-o bond, thece, the increased occupation of the 2n engendered by back donation leads to a weakening of the C-o bond. That s the reason for the observed change of the c-o stretch vibration frequency of Co upon chemisorption on metal surfaces Gas phase >on-top twofold bridge fourfold hollow(fcc(100 )surface) The above blyholder model, the use of frontier orbitals and analogies to coordination chemistry have been successful in explaining the qualitative trends observed in the chemisorption of small molecules. But to understand quantitatively the bonding in an adsorbate/substrate system, it may be necessary to consider other orbitals beyond the frontier orbitals
The 5 orbital is nonbonding in CO. Therefore, modification of this orbital does not have a strong influence on the intramolecular C-O bond; the 2* orbital is antibonding with respect to the C-O bond, thece, the increased occupation of the 2* engendered by back donation leads to a weakening of the C-O bond. That’s the reason for the observed change of the C-O stretch vibration frequency of CO upon chemisorption on metal surfaces: Gas phase > on-top > twofold bridge > fourfold hollow (fcc(100) surface). The above Blyholder model, the use of frontier orbitals and analogies to coordination chemistry have been successful in explaining the qualitative trends observed in the chemisorption of small molecules. But to understand quantitatively the bonding in an adsorbate/substrate system, it may be necessary to consider other orbitals beyond the frontier orbitals
Transition from T-Bonded to Di-o Metallacyclic Propene on O-Modified Ag(111) W.X. Huang and J M. White* a-e 16041610 15601600 3 1234 oyrncoerr(w 8七 05 0.433 0291 0086 0.1% 0.1% 02% 800 1000 120012001400160018002800 3000 Temperature(K) Wavenumber(cm) TDS RAIRS
TDS RAIRS
a-b a-b 200K 05%100K 0.1% 0.05% 120012001400160018002800290030003100 Wavelength (cm) Model RAIRS In summary, our results show that the thermal de sorption barrier and the strength of the C=C bond vary smoothly as a function of atomic oxygen coverage, Bo, for propene adsorbed on Ag(111). Moreover, as Bo increases, there is an increased propensity to form di-o-bonded rather than JT-bonded, propene, an observation that likel influences the catalytic activity on Ag(111)facets of polycrystalline silver catalysts
RAIRS Model 100K 200K
4、金属与配体的成键,要求相互作用的轨道具有相同的对称 性。由于金属的配体环境不同,金属将采用不同的轨道(dxy2 或d)形成σ/π键。如配体环境为八面体或平面四边形,金属 可采用dx2y2形成键;而配体环境为四面体时,金属则要用dy 形成σ键。 5、参与成键的轨道的能级差决定着形成金属-配体化学键的强 度。一般,分离原子的轨道能级差越大,所形成的化学键强度 越低。当金属与配体间形成双键时,相互作用的最高占据轨道 与最低未占据轨道的能级差取决于金属与配体的Ferm能级
4、金属与配体的成键，要求相互作用的轨道具有相同的对称 性。由于金属的配体环境不同，金属将采用不同的轨道（dx2-y2 或dxy）形成/ 键。如配体环境为八面体或平面四边形，金属 可采用dx2-y2形成键；而配体环境为四面体时，金属则要用dxy 形成键。 5、参与成键的轨道的能级差决定着形成金属-配体化学键的强 度。一般，分离原子的轨道能级差越大，所形成的化学键强度 越低。当金属与配体间形成双键时，相互作用的最高占据轨道 与最低未占据轨道的能级差取决于金属与配体的Fermi能级