Vibrational Predissociation Spectroscopy of Homoleptic Heptacoordinate Metal Carbonyl Complexes Allen M. Ricks and Michael A. Duncan Department of Chemistry University of Georgia, Athens Ga.

7-Coordinate metal carbonyl complexes Vanadium cation is s 2 d 2 7 carbonyls (2 e - each) completes 18-electron rule Predicted to be thermodynamic minima Can it be made

Experimental Evidence

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

OPO OPA 1 crystal angle tuned 4 crystals angle tuned signal (not used) idler 532 nm 1064 nm KTP oscillator KTA diff. gen. + amp of idler beam AgGaSe 2 diff. gen. Tunable  m 1 crystal angle tuned Tunable mid-IR  m LaserVision Tunable Infrared Laser System designed by Dean Guyer Tuning range: cm -1 Linewidth: ~1.0 cm -1 Pumped by pulsed, unseeded YAG e.g., Spectra Physics PRO cm cm -1 Tunable IR Spectroscopy

Typical Mass Spectra Vanadium carbonyl complexes show “magic number” at n=6, implies inherent stability of this complex Tantalum has magic number for n=7 Infrared photodissiciation spectra shown in insets shows termination of fragmentation at n=6 and n=7 respectively Indicates that these correspond to the coordination spheres of the complexes

Infrared spectra of V(CO) 7 + Infrared spectrum of V(CO) 6 + obtained by elimination of 2 CO from V(CO) 8 + Shows no evidence for 7- coordinate species Argon tagging confirms the assignment to the 6 coordinate triplet complex

Infrared Spectra of Nb(CO) 6 + and Nb(CO) 7 + Spectrum of Nb(CO) 8 + obtained by monitoring the elimination of one and two CO shows marked differences The loss of one CO channel gives spectrum primarily of the 7-coordinate Nb(CO) 7 + species Loss of two CO channel shows presence of Nb(CO) 6 + ion Appear to be trapping singlet and triplet complexes

Infrared Spectrum of Nb(CO) 7 + obtained via Ar tagging Using the argon tagging technique we see only the spectrum of Nb(CO) 7 + in the Ar loss channel Spectrum of Nb(CO) 6 + with a surface CO and Ar obtained via elimination of Ar and CO Confirms our original assignments

Different spectra obtained by monitoring different fragmentation channels The infrared spectrum of Nb(CO) 10 + changes based on the fragmentation channel monitored Evidence for two isomers present

Infrared Spectrum of Ta(CO) 7 + Infrared spectrum of Ta(CO) 7 + obtained by elimination of CO from Ta(CO) 8 + Only evidence for the 7-coordinate species Spectrum in excellent agreement with DFT calculations for a C 3v structure

Infrared Spectrum of Ta(CO) 7 + obtained by argon tagging Ta(CO) 7 + Ar shows evidence for both the six and seven coordinate species Under conditions where argon tagging is efficient (cold) we are able to trap the higher energy triplet complex

Conclusion For vanadium we see no evidence for a 7-coordinate species This is in disagreement with the previous work from the Armentrout group However we do observe evidence for 7-coordinate tantalum and niobium carbonyl complexes

Future Directions

USAFRF and DOE for funding Prof. Michael Duncan Prof. Peter Armentrout Thank Y’all fo’ Y’alls comin out here Acknowledgements