Hans‐Jörg Himmel

Heats of Hydrogenation of Compounds Featuring Main Group Elements and with the Potential for Multiply Bonding

Reaction enthalpies are calculated for the hydrogenation reactions of main group hydrides with the potential for multiple bonding, and thus the unsaturated character of these species is determined. In addition to the global minimum structures, which leave in some cases no hope for even a single E-E bond (E=Group 13, 14, or 15 element), calculations are also performed for geometries with maximum potential for multiple bonding. The trends down the groups and the periods are established. Interpretations have to take several factors into account. These factors sometimes work hand in hand but also against each other. We also include in our survey the species [HGaGaH]2- as a free anion and Na2[HGaGaH] as well as their hydrogenation products [H2GaGaH2]2- and Na2[H2GaGaH2]2-. The results show that the presence of the Na+ ions has a significant impact on their chemistry, and thus suggests that they are involved to a large extent in the bonding. Our results indicate that the compounds should be described as cluster compounds.

Low valent and would-be multiply bonded derivatives of the Group 13 metals Al, Ga and In revealed through matrix isolation

Abstract Two aspects of Group 13 metal chemistry are surveyed in the light of recent matrix-isolation and quantum chemical studies. The first concerns derivatives of the metals Al, Ga and In (M) in formal oxidation states less than +3: these include the M0 derivatives MLn, where L=CO, N2, NH3 or PH3, and n=1 or 2; the MI derivatives MX, where X=H, CH3 or NH2, and M2H2; and the MII derivatives HMX, where X=H, CH3, NH2 or PH2. The second concerns derivatives in which there is the opportunity for the metal to engage in multiple bonding, as exemplified by the cases of M2H2 and H2MNH2. Experimental studies have involved thermally or photolytically excited reactions between M atoms, or sometimes M2 molecules, and an appropriate substrate, e.g. H2, CO, N2, CH4, NH3 or PH3. The reagents have been trapped in solid noble gas matrices, the IR spectra of which have been exploited to deduce the course of events and identities of the products. Confirmation of the identity and geometry of each of the products have been achieved primarily on the basis (i) of isotopic effects and (ii) of comparison of the measured spectrum with that anticipated by quantum chemical calculations. This liaison of experiments with theory has led to the characterisation not only of numerous simple molecules that are short-lived under normal conditions, but also of some of the reaction channels open to them, typically through photolytic activation. The structure, energies and reactivities of the compounds are reviewed.

Ni(N2)4 revisited: an analysis of the Ni–N2 bonding properties of this benchmark system on the basis of UV/Vis, IR and Raman spectroscopy

Matrix isolation of Ni atoms in an N2 matrix leads to the formation of Ni(N2)4. This compound, being isoelectronic with the well known Ni(CO)4, represents an important bench-mark system. It has been characterised experimentally by UV/Vis, IR and Raman spectra. The vibrational spectra give evidence for both a1 modes, three of the four t2 modes, and one of the two e modes of the Td symmetric molecule. The experimental data obtained for Ni(14N2)4 and Ni(15N2)4 were used to determine the valence force constants f(Ni-N) and f(N-N), which are compared with those derived for Ni(N2) and for the corresponding carbonyl complexes Ni(CO) and Ni(CO)4. In addition, several overtones and combination modes of Ni(N2)4 were observed for the first time, providing further valuable information about the bond properties. The data allow for the first time a direct estimate of the Ni-N2 bond energy in Ni(N2)4 (120 kJ mol(-1)), that compares with a value of 148 kJ mol(-1) determined by the same method for Ni(CO)4.

1,1,3,3-tetramethylguanidine-gallane, (Me2N)(2)CN(H)center dot GaH3: an unusually strongly bound gallane adduct

The novel adduct 1,1,3,3-tetramethylguanidine-gallane, (Me2N)2CN(H).GaH3, has been prepared by the reaction of [(Me2N)2CNH2]+Cl- with LiGaH4 in Et2O solution. Its spectroscopic properties indicate a monomeric species with an unusually strong coordinate link between the imido function and GaH3, an inference confirmed by the crystal structure at 150 K which also reveals significant secondary interactions through non-classical N-H...H-Ga bridges. Despite the intrinsic strength of the Ga-N bond, however, vaporisation at ca. 310 K occurs with partial dissociation, and decomposition via more than one pathway proceeds at temperatures >330-350 K to give a variety of products, including the free base, Me2NH, H2, and a novel gallium-nitrogen compound composed of a Ga4N4 cubane-like core bridged on three edges by -N{C(NMe2)2}GaH2- units.

On the reactivity of subvalent compounds of the Group 13 elements: exploration of the mechanism for the reactions of MCl (M = Ga or In) with dihydrogen to give H2MCl

Motivated by recent experimental results on the reactivity of the diatomic Group 13 subhalogenides GaCl and InCl in solid Ar matrices, the mechanisms for spontaneous and photoactivated reactions of these species are studied herein by means of quantum chemical methods as applied to their reactions with H2. The experimental results show that reaction with H2 in a solid Ar matrix does not occur spontaneously, but requires photoactivation, the trivalent derivatives H2MCl (M = Ga or In) being the detectable products. Furthermore, these results indicate that the photoactivated reactions proceed in a concerted fashion. Quantum chemical calculations are employed to explain the observed reactivities and provide quantitative estimates for the barriers to reaction. Calculations were performed for several electronic states and multiplicities of the GaCl/H2 and InCl/H2 systems likely to be of relevance and enable a detailed noverall analysis of the reaction mechanisms to be made. The reactions of Group 13 subhalogenides with other molecules are anticipated to follow the same pattern and, thus, the results reported herein should be of relevance to the reactivity of Group 13 subhalogenides in general.