James J. Turner

The Structure of [Fe(CO)4]—An Important New Chapter in a Long‐Running Story

The structure of the singlet state (1 A1 ) of [Fe(CO)4 ] in the gas phase has been determined by a combination of laser photochemistry of [Fe(CO)5 ] and electron diffraction imaging. The ground state of [Fe(CO)4 ] is known to be a triplet species (3 B2 ), and this is the species detected in picosecond time-resolved IR experiments with [Fe(CO)5 ] in solution. This is an appropriate moment to survey the state of knowledge on [Fe(CO)4 ], beginning from the first low-temperature matrix experiments.

Nanosecond time-resolved infrared spectroscopy: a comparative view of spectrometers and their applications in organometallic chemistry

Three time-resolved infrared (TRIR) spectrometers are described. These instruments are based on (i) a line-tunable CO laser (2000–1550 cm–1), (ii) a continuously tunable semiconductor diode laser (approximately 2250–1900 cm–1) and (iii) a modified and adapted dispersive IR spectrometer with Nernst glower (or globar) which, in principle, could cover all of the mid-IR region. The spectrometers differ in their inherent signal-to-noise ratio and their response. Although the ultimate performance can be achieved with the CO laser, the instruments are complementary, each with its own advantages. The performances of the three TRIR spectrometers were compared in a number of applications in organometallic photochemistry, including the IR detection of molecules in electronically excited states, the kinetic behaviour of intermediates in the reaction of (η5-C5H5)M(CO)4 compounds (M = V, Nb and Ta), an IR study of the photochemical reaction of CpMn(CO)3 within polyethylene film and solvent interactions in supercritical xenon solution and the detection of W(CO)5Xe.

Excited states of transition metal complexes studied by time-resolved infrared spectroscopy

Abstract This article describes the application of time-resolved infrared spectroscopy (TRIR) to probe structure and reactivity of excited states of transition metal complexes.

Cyclopentadienylidene. A matrix isolation study exploiting photolysis with unpolarized and plane-polarized light.

Diazocyclopentadiene (1) was photolyzed in N(2), CO, and other low-temperature matrices. The resulting carbene, cyclopentadienylidene (2), was characterized by its UV and IR spectra, and its thermal dimerization and reaction with CO were observed. Photolysis of 1 with plane-polarized light gave matrices exhibiting linear dichroism. Comparison of dichroic IR and UV spectra revealed that the photolysis proceeds via an excited A(l) state of the diazo compound. Plane-polarized irradiation of the corresponding ketene (4) in CO matrices resulted in photoreorientation of the molecules of 4 without significant loss.

Matrix photochemistry of metal carbonyls

This lecture presents a summary of detailed photochemical studies on metal carbonyls isolated in low-temperature matrices and shows how such studies are of relevance to conventional solution photochemical studies at room-temperature.

Excited-state properties and reactivity of [ReCL(CO)3(2,2′-bipy)](2,2′-bipy = 2,2′-bipyridyl) studied by time-resolved infrared spectroscopy

Fast time-resolved infrared spectroscopy shows that the v(CO) bands of the important CO2-reducing complex, [ReCl(CO)3(2,2′-bipy)]1(2,2′-bipyridyl), shift up in frequency in the metal to ligand charge-transfer excited state and that the anion 1–, generated by reaction of the excited state with triethylamine, shows a lowering in frequency of the v(CO) bands significantly different from those of related but non-reducing complexes.

Time-resolved infrared spectroscopy of excited states of transition metal species

Abstract This article describes examples of the application of time-resolved infrared Spectroscopy (TRIR) to the probing of the excited states of transition metal species. Other “direct” methods for excited states include time-resolved absorption Spectroscopy, and, more importantly, time-resolved resonance Raman Spectroscopy (TR 3 ). Both of these techniques have limitations and hence TRIR is of value in complementing them. The common “indirect” methods are absorption, emission, and excitation spectroscopies, to which has been more recently added, resonance Raman, particularly in the time-dependent formulation. The relevance of these methods is also discussed.

Vibrational spectrum of HCCIF2 in liquid argon

Abstract The IR spectrum of HCClF 2 , obtained in liquid argon at 110 K, shows great detail and when combined with Raman polarization data from liquid HCClF 2 allows the assignment of all the fundamentals and in particular, resolves the confusion concerning the C-F stretching modes. An interesting example of Fermi resonance is observed and an assignment of a number of overtone and combination bands is made.

Fast time-resolved infrared spectroscopy of organometallic intermediates; detection of [(η5-C5H5)Fe(CO)2] and [(η5-C5H5)Fe(µ-CO)3Fe(η5-C5H5)] in room-temperature solution

A line-tunable CO laser has been use as a fast (1 µs) i.r. monitor to obtain spectra (2012–1710 cm–1) and lifetimes of [CpFe(CO)2](Cp =η5-C5H5) and [CpFe(µ-CO)3FeCp], formed during u.v.–visible flash photolysis of [CpFe(CO)2]2 in cyclohexane solution.

Photochemistry of an ozone-bromine complex; the IR spectrum of matrix isolated Br2O

Abstract Cocondensation of O3/Ar and Br2/Ar mixtures gives IR evidence for a weak O3/Br2 complex which is shown by 18O substitution to have an asymmetric structure. As in previous work photolysis leads to new species one of which has two IR bands; detailed comparisons suggest these are the ν3 (weak, 623.4 cm−1) and ν1 (strong, 526.1 cm−1) bands of a perturbed BrOBr molecule.