The shapes and geometries of the molecular transition-metal halides have interested and intrigued experimental and computational chemists for a long time. The majority of such halides are high-temperature vapor-phase species, which makes them challenging to study by structural and spectroscopic techniques. They are also a challenge to theoretical/ computational chemists. The vapor composition is often complex, and spectral interpretation and assignment are not always straightforward.

HgF(2) and Hg have been trapped in dilute F(2)/Ar and neat F(2) matrices, subjected to UV-Vis and vac-UV photolysis and annealing, with the products identified by FTIR, UV-Vis-NIR and Hg L(3)-edge XAFS spectroscopic techniques. Whilst there was no convincing evidence for the formation of HgF(4) under our argon matrix isolation conditions, a new Hg...F(2) complex was identified and subsequent photolysis yielded HgF(2) very cleanly. Hg L(3)-edge EXAFS has provided the first experimental value of 1.94(2) A for the Hg-F bond length in HgF(2), which is in excellent agreement with the computational values incorporating relativistic effects.

The hitherto elusive silaisocyanoacetylene molecule (HCCNSi)-a member of the silaisocyanide family-has been synthesized for the first time through the reaction of the silicon nitride radical (SiN) with acetylene (C(2)H(2)) in the gas phase under single collision conditions. Compared to the isoelectronic reaction of the cyano radical (CN) with acetylene, the replacement of the carbon atom in the cyano group by an isovalent silicon atom has a pronounced effect on the reactivity. Whereas the silicon nitride radical was found to pass an entrance barrier and adds with the nitrogen atom to the acetylene molecule, the cyano radical adds barrierlessly with the carbon atom forming the HCCH(NSi) and HCCH(CN) intermediates, respectively. These structures undergo hydrogen loss to form the linear silaisocyanoacetylene (HCCNSi) and cyanoacetylene molecules (HCCCN), respectively. Therefore, the isovalency of the silicon atom was found to bear little resemblance with the carbon atom having a dramatic effect not only on the reactivity, but also on the reaction mechanism, thermochemistry, and chemical bonding of the isoelectronic silaisocyanoacetylene and cyanoacetylene products, effectively reversing the thermodynamical stability of the nitrile versus isonitrile and silanitrile versus isosilanitrile isomer pairs.

The atom-radical reaction of ground state carbon atoms (C((3)P)) with the vinyl radical (C(2)H(3)(X(2)A')) was conducted under single collision conditions at a collision energy of 32.3 ± 2.9 kJ mol(-1). The reaction dynamics were found to involve a complex forming reaction mechanism, which is initiated by the barrier-less addition of atomic carbon to the carbon-carbon-double bond of the vinyl radical forming a cyclic C(3)H(3) radical intermediate. The latter has a lifetime of at least 1.5 times its rotational period and decomposes via a tight exit transition state located about 45 kJ mol(-1) above the separated products through atomic hydrogen loss to the cyclopropenylidene isomer (c-C(3)H(2)) as detected toward cold molecular clouds and in star forming regions.

Palladium atoms generated by thermal evaporation and laser ablation were reacted with and trapped in F2/Ar, F2/Ne, and neat F2 matrices. The products were characterized by electronic absorption and infrared spectroscopy, together with relativistic density functional theory calculations as well as coupled cluster calculations. Vibrational modes at 540 and 617 cm(-1) in argon matrices were assigned to molecular PdF and PdF2, and a band at 692 cm(-1) was assigned to molecular PdF4. A band at 624 cm(-1) can be assigned to either PdF3 or PdF6, with the former preferred from experimental considerations. Although calculations might support the latter assignment, our conclusion is that in these detailed experiments there is no convincing evidence for PdF6.