Ammonia orbital energies

Cations [Cr(NH3)4X2]+ have as and trans geometrical isomers (see Coordination Organometallic Chemistry Principles). The higher syrmnetry of the trans form makes its d d spectrum easier to analyze. We assume NH3 to be a pure a donor (see Ammonia N-donor Ligands). Hence e (NH3) is zero. The axial hgands are n donors (e r > 0). The AOM orbital energies E are given in equations (27-30). 

E2.32 The molecular orbital energy diagram for ammonia is shown in Figure 2.30. The interpretation given in the text was that the 2a) molecular orbital is almost nonbonding, so the electron configuration Iai le 2ai results in only three bonds ((2 + 4)/2 = 3). Since there are three N-H bonds, the average N-H bond order is I (3/3 = 1). 

Figure 5.17 shows a molecular orbital energy-level diagram for ammonia. Label the molecular orbitals as bonding, non-bonding or antibonding. What is the total bond order ... 

Molecular orbital energy-level diagram for ammonia, NH3. 

In molecules such as ammonia the energy of the 2 p orbital of nitrogen is similar to that of the hydrogen 1 s orbital but the 2 i orbital is considerably more stable (by ca. 10.00 ev). A first-order correction [24, 25] to the wave functions arising from a change in Coulomb integral from a to a + 6a is given by ... 

The tetramethylammonium salt [Me4N][NSO] is obtained by cation exchange between M[NSO] (M = Rb, Cs) and tetramethylammonium chloride in liquid ammonia. An X-ray structural determination reveals approximately equal bond lengths of 1.43 and 1.44 A for the S-N and S-O bonds, respectively, and a bond angle characteristic bands in the IR spectrum at ca. 1270-1280, 985-1000 and 505-530 cm , corresponding to o(S-N), o(S-O) and (5(NSO), respectively. Ab initio molecular orbital calculations, including a correlation energy correction, indicate that the [NSO] anion is more stable than the isomer [SNO] by at least 9.1 kcal mol . ... 

Both the LUMO and LUMO + 1 energy levels of the nitronaphthyridines and the values of the coefficients at the carbon and ring nitrogen in the LUMO and LUMO -f 1 orbitals were determined. Using homo = -11.9 eV for ammonia, the values of the stabilization energy AE) for each position of the nitronaphthyridines were calculated. Tire results of the cal-... 

The reader will find far more elegant drawings of these orbitals in Section III, for instance by referring to the orbitals (II1.0) of the pyramidal methyl radical. Similar orbitals exist, of course, for ammonia (II 1.8). Again, as in the CH2 case, the energy ordering is... 

Water has two lone pairs of electrons. Once one of these is used to form the cr-bond to the metal ion, the second may be used to form a iT-bond. This causes the f2g set of orbitals to move up in energy, making A() smaller therefore, water is a weak-field ligand. Ammonia does not have this extra lone pair of electrons and consequently cannot function as a tt-donor ligand. 

In this case, the product is the fac isomer, in which all NH3 ligands are trans to the CO molecules. Ammonia does not form ty bonds to metals because it has no orbitals of suitable energy to accept electron density. Thus, the back donation from Cr in Cr(NH3)3(CO)3 goes to only three CO molecules, and the bond order is reduced even more than it is in Cr(CO)s, where back donation occurs equally to six CO molecules. There is, of course, an increase in Cr-C bond order and stretching frequency in Cr(NH3)3(CO)3 compared to Cr(CO)s. Based on the study of many mixed carbonyl complexes, it is possible to compare the ability of various ligands to accept back donation. When this is done, it is found that the ability to accept back donation decreases in the order... 

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