Structure and dynamics of iron pentacarbonyl

The dynamics of CO ligand scrambling in Fe(CO)5 has been investigated by linear infrared spectroscopy in supercritical xenon solution. The activation barrier for the Berry pseudorotation in Fe(CO)5 was determined experimentally to be Ea = 2.5 ± 0.4 kcal mol–1 by quantitative analysis of the temperature-dependent spectral line shape. This compares well with the range of Ea/(kcal mol–1) = 2.0 to 2.3 calculated by various DFT methods and the value of 1.6 ± 0.3 previously obtained from 2D IR measurements by Harris et al. ( Science 2008, 319, 1820). The involvement of Fe(CO)5···Xe interactions in the ligand scrambling process was tested computationally at the BP86-D3/AE2 level and found to be negligible

Synthesis of six-coordinate mono-, bis-, and tris(tetrazolato) complexes via [3 + 2] cycloadditions of nitriles to silicon-bound azido ligands

A convenient synthetic route to poly(tetrazolato) silicon complexes is described based on the four reactive centres of the N-rich, highly endothermic tetraazides of the type Si(N3)4(L2). Hypercoordinate azido(tetrazolato) silicon complexes Si(N3)2(N4C-R)2(L2), R = CH3, C6H5, 4-C6H4CH3 (4a, 5, 6, 7) and Si(N3)2(N4C-L)2 (9, L = 2-C5H4N), L2 = 2,2'-bipyridine, 1,10-phenanthroline, with SiN6 skeletons were synthesised via multiple [3 + 2] dipolar cycloaddition reactions starting from Si(N3)4(L2) and a nitrile. The isolated new complexes were characterised by standard analytical methods, single crystal X-ray diffraction and differential scanning calorimetry (4a,b). Tetrazolato ligand linkage isomerism was observed for complex 4a. The crystallographically characterised methyl tetrazolato complexes and plausible configurational and linkage isomers were evaluated by DFT calculations at the B3LYP/6-311G(d,p) level

Homoleptic Low-Valent Polyazides of Group 14 Elements

First examples of coordinatively unsaturated, homoleptic azido complexes of low-valent group 14 elements are reported. A simple strategy uses low-valent precursors, ionic azide transfer reagents and bulky cations to obtain salt-like compounds containing E(N3)3- of Ge(II)/Sn(II) which are fully characterised, including XRD. Remarkably, these compounds are kinetically stable at r.t. and isolable in sub-gram quantities

Tuning energetic properties through co-crystallisation - a high-pressure experimental and computational study of nitrotriazolone:4,4′-bipyridine

We report the preparation of a co-crystal formed between the energetic molecule 3-nitro-1,2,4-triazol-5-one (NTO) and 4,4′-bipyridine (BIPY), that has been structurally characterised by high-pressure single crystal and neutron powder diffraction data up to 5.93 GPa. No phase transitions or proton transfer were observed up to this pressure. At higher pressures the crystal quality degraded and the X-ray diffraction patterns showed severe twinning, with the appearance of multiple crystalline domains. Computational modelling indicates that the colour changes observed on application of pressure can be attributed to compression of the unit cell that cause heightened band dispersion and band gap narrowing that coincides with a shortening of the BIPY π⋯π stacking distance. Modelling also suggests that the application of pressure induces proton migration along an N-H⋯N intermolecular hydrogen bond. Impact-sensitivity measurements show that the co-crystal is less sensitive to initiation than NTO, whereas computational modelling suggests that the impact sensitivities of NTO and the co-crystal are broadly similar.</p

Homoleptic Poly(nitrato) Complexes of Group 14 Stable at Ambient Conditions

Using a novel approach in homoleptic nitrate chemistry, Sn(NO3)62− (3c) as well as the previously unknown hexanitrato complexes Si(NO3)62− (1c), Ge(NO3)62− (2c) were synthesized from the element tetranitrates as salt-like compounds which were isolated and characterized using 1H, 14N, and 29Si NMR and IR spectroscopies, elemental and thermal analyses, and single-crystal XRD. All hexanitrates are moderately air-sensitive at 298 K and possess greater thermal stability toward NO2 elimination than their charge-neutral tetranitrato congeners as solids and in solution. The complexes possess distorted octahedral coordination skeletons and adopt geometries that are highly symmetric (3c) or deformed (1c, 2c) depending on the degree of steric congestion of the ligand sphere. As opposed to the κ2O,O′ coordination mode reported for Sn(NO3)4 previously,1 all nitrato ligands of 3c coordinate in κ1O mode. Six geometric isomers of E(NO3)62− were identified as minima on the PES using DFT calculations at the B3LYP/6-311+G(d,p) level of which two were observed experimentally

Tuning energetic properties through co-crystallisation – a high-pressure experimental and computational study of nitrotriazolone:4,4’-bipyridine

We report the preparation of a co-crystal formed between the energetic molecule 3-nitro-1,2,4-triazol-5-one (NTO) and 4,4’-bipyridine (BIPY), that has been structurally characterised by high-pressure single crystal and neutron powder diffraction data up to 5.93 GPa. No phase transitions or proton transfer were observed up to this pressure. At higher pressures the crystal quality degraded and the X-ray diffraction patterns showed severe twinning, with the appearance of multiple crystalline domains. Computational modelling indicates that the colour changes observed on application of pressure can be attributed to compression of the unit cell that cause heightened band dispersion and band gap narrowing that coincides with a shortening of the BIPY π…π stacking distance. Modelling also suggests that the application of pressure induces proton migration along an N-H…N intermolecular hydrogen bond. Impact-sensitivity measurements show that the co-crystal is less sensitive to initiation than NTO, whereas computational modelling suggests that the impact sensitivities of NTO and the co-crystal are broadly similar

Simulating the Pyrolysis of Polyazides: a Mechanistic Case Study of the [P(N₃)₆]⁻ Anion

Pyrolysis of the homoleptic azido complex [P­(N₃)₆]⁻ was simulated using density functional theory based molecular dynamics and analyzed further using electronic-structure calculations in atom-centered basis sets to calculate the geometries and electronic structures. Simulations at 600 and 1200 K predict a thermally induced and, on the simulation time scale, irreversible dissociation of an azido anion. The ligand loss is accompanied by a barrierless (free-energy) transition of the geometry of the complex coordination sphere from octahedral to trigonal bipyramidal. [P­(N₃)₅] is fluxional and engages in pseudorotation via a Berry mechanism