The crystal structures of the ammonium, 1, lithium, 2, potassium, 3, and cesium, 4, salts of a new nitrogen oxy anion, N3O4 -, have been determined. In 1 there are two interpenetrating three-dimensional lattices linked by strong hydrogen-bonding interactions between all four ammonium protons and three of the four dinitramide oxygen atoms. Even though 2−4 have similar formula units each has a completely different structure characterized by differing coordination numbers and geometries. The structure of 2 is unique in that it is the only one containing a dinitramide ion in the C 2 conformation predicted by ab initio studies to be the minimum energy conformation. There is good agreement between the predicted and experimental metrical parameters for the C 2 conformer of the dinitramide anion.

Single-crystal X-ray studies show that the strength of the Se´´´N interactions depends on the relative electronegativity of the group attached to the selenium and the nature of the heteroatom. These interactions lengthen the SeÀX (X Se, Cl, Br, I, CH 2 À ) bond trans to the N´´´Se bond and increase the possibility of nucleophilic attack on the selenium. In addition to the Se´´´N intramolecular interaction, Se´´´X (X Cl, Br, I) intermolecular interactions were observed in [2-(4,4-dimethyl-2-oxazolinyl)phenyl]-selenenyl chloride (4), bromide (5), and iodide (6), indicative of the hypervalent (pseudo-high-valent) nature of the selenium. The strength of the Se´´´N intramolecular interaction decreases in the order RSeCl, RSeBr, RSeI, whereas the Se´´´X intermolecular interaction increases in the same order. The aryl benzylic compounds [2-(4,4-dimethyl-2-oxazolinyl)phenyl]benzyl selenide (7), (9), and 1,3,5-tri[2-(4,4-dimethyl-2-oxazolinyl)phenylselenenyl]-2,4,6-trimethylbenzene (10)

Reaction of GeH 4 and GeH 3 Ph with the agostic complex Mo(CO)(dppe) 2 (dppe ) Ph 2 PC 2 H 4 -PPh 2 ) provides germane σ complexes Mo(CO)(η 2 -GeH 4-n Ph n )(dppe) 2 (n ) 0, 1). The coordination in these complexes has been assigned as (η 2 -Ge-H) on the basis of NMR and IR spectroscopy and by comparison to the analogous complexes of silanes. When the more electron-rich phosphine depe (depe ) Et 2 PC 2 H 4 PEt 2 ) is used, oxidative addition (OA) products MoH(GeH 3 )(CO)(depe) 2 and MoH(GeH 2 Ph)(CO)(depe) 2 are isolated (NMR and X-ray evidence). However, when the secondary organogermane GeH 2 Ph 2 is used in the depe system, the η 2 -complex Mo(CO)(η 2 -GeH 2 Ph 2 )(depe) 2 is obtained. This complex was characterized by X-ray crystallography and NMR and IR spectroscopy. The Mo(CO)(η 2 -GeH 3 Ph)(dppe) 2 and Mo(CO)(η 2 -GeH 2 Ph 2 )(depe) 2 complexes were found to be in tautomeric equilibrium with their OA products in solution. Structure and bonding comparisons are made to the analogous silane complexes, e.g., Mo(CO)(η 2 -SiH 2 Ph 2 )(depe) 2 , the X-ray structure for which is also reported. The Ge-H bonds undergo OA much more easily than Si-H, and to obtain further insight into the activation processes, ab initio DFT calculations have been performed on Mo(CO)(EH 4-n vin n )(dhpe) 2 model complexes (E ) Si, Ge; n ) 0-3; dhpe ) H 2 PCH 2 CH 2 PH 2 ; vin ) CHdCH 2 ) and also the analogous H 2 complex. Because the ease of the whole OA process is a balance between the E-H bonding energy and Mo-E bonding energy, it can be concluded that the factor that makes OA of the Ge-H bond easier than that for Si-H is the relative weakness of the Ge-H bond, despite the fact that the Mo-Ge bond is also weaker. This competition between both factors is also seen for OA of H 2 , for which although the Mo-H bonding energy is much higher than Mo-Si and Mo-Ge bonding energies, the H-H bond is also significantly stronger than the Si-H and Ge-H bonds. In general, the ease of OA of molecular hydrogen is between that of germanes and silanes. Calculations show that for alkanes the OA is much more difficult because the loss of the high C-H bond energy (comparable to or greater than that for H-H) is not as well compensated for by the energy of formation of the Mo-C bond due to the weakness of the Mo-C bond.

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