Vibrational Predissociation Spectroscopy of Metal Carbonyl Complexes 1: Co(CO)n+ (n=1-10) Allen M. Ricks and Michael A. Duncan Department of Chemistry University of Georgia, Athens Ga. *(2 will be on Thursday RA08)

Fe(CO)5, Co(CO)5+ and the 18-electron rule Iron pentacarbonyl, Fe(CO)5 is a known stable compound Fe is d6 so Fe(CO)5 satisfies the 18-electron rule Has a known D3h structure So popular it even has its own wikipedia page Co+ is isoelectronic to Fe Presumably Co(CO)5+ would have the same structure as Fe(CO)5

Mass selection of cations by time-of-flight. full mass spectrum activate mass gate; select one cluster mass. excite at turning point. Production of cold cations and complexes with laser vaporization in a supersonic expansion. Mass selection of cations by time-of-flight. Tunable laser photodissociation with IR OPO; measure fragment intensity versus wavelength. photofragments parent ion depletion

Tunable IR Spectroscopy LaserVision Tunable Infrared Laser System designed by Dean Guyer Tuning range: 700-4300 cm-1 Linewidth: ~1.0 cm-1 2000-4300 cm-1 Tunable mid-IR 2.3-5.0 m 700-2200 cm-1 Tunable 4.5-14.3 m OPO OPA idler KTP oscillator KTA diff. gen. + amp of idler beam AgGaSe2 diff. gen. 532 nm signal (not used) 1 crystal angle tuned 4 crystals angle tuned 1 crystal angle tuned 1064 nm Pumped by pulsed, unseeded YAG e.g., Spectra Physics PRO-230.

Typical Mass spectrum observed in this experiment Addition of water is necessary to facilitate ion formation The peak corresponding to Co(CO)5+ is dominant over other cluster sizes Indicates inherent stability of this complex This is the 18-electron species

Infrared photofragmentation breakdown spectra Infrared photodissociation breakdown spectra show termination at n=5, again indicating the stability of this complex We were able to fragment the n=5 complex, however it is inefficient and we believe it to due to multiphoton absorption

Infrared Spectra of Co(CO)n+ (n=5-9) measured via elimination of CO Dashed line shows νco stretch at 2143 cm-1 The band at ~2166 cm-1 is due to “surface” carbonyls, those beyond the coordination sphere This corresponds to a 23 cm-1 shift to the blue from the gas phase CO value Is due to the electrostatic interaction of the carbonyls with the core ion Bands at ~2140 and ~2150 assigned to Co(CO)5+ core ion Spectrum of n=5 featureless, supporting our assumption that fragmentation of this complex is caused by multiphoton absorption

Infrared spectra of Co(CO)n+ complexes obtained via rare gas tagging Spectrum of Co(CO)5+ obtained via rare gas tagging shows structure not observed in previous spectrum Appears to be a 15 cm -1 frequency shift between Co(CO)4+ and Co(CO)5+ Spectrum of Co(CO)3+ shows one CO stretch consistent with a D3h structure Single peak in Co(CO)2+ spectrum indicates a D∞h structure Doubly argon tagging required for Co(CO)1+ due to high binding energy

Comparison of experimental and theoretical spectra of larger argon tagged cobalt carbonyl complexes Theoretical calculations help us elucidate the multiplicity of the complexes being studied There is a spin change between n=4 and n=5 Singlet Co(CO)5+ is isoelectronic to the 18-electron Fe(CO)5 complex

Comparison of experimental and theoretical spectra of smaller argon tagged cobalt carbonyl complexes Spectrum of Co(CO)5+ obtained via rare gas tagging shows structure not observed in previous spectrum Appears to be a 15 cm -1 frequency shift between Co(CO)4+ and Co(CO)5+ Spectrum of Co(CO)3+ shows one CO stretch consistent with a D3h structure Single peak in Co(CO)2+ spectrum indicates a D∞h structure Doubly argon tagging required for Co(CO)1+ due to high binding energy

Structures of small cobalt carbonyl and argon tagged cobalt carbonyl complexes Structures of Co(CO)5+ complexes Argon shows large structural perturbation? Actually due to basis set superposition error Usage of larger basis set on metal ion alleviates this problem

Current work in other systems Current work on vanadium carbonyl complexes Have achieved efficient Ne tagging! Spectrum of the dimer shows two peaks when neon and argon tagging Must be due to different spin states present

Acknowledgements USAFRF and DOE for funding Prof. Michael Duncan Prof. Peter Armentrout