65 th International Symposium on Molecular Spectroscopy June 21, 2010 Lindsay N. Zack Brent J. Harris Matthew P. Bucchino Ming Sun Lucy M Ziurys Department

65th International Symposium on Molecular Spectroscopy June 21, 2010

Pure Rotational Spectrum of ZnOD and the Structure

of ZnOH Lindsay N. Zack

Brent J. Harris

Matthew P. Bucchino

Ming Sun

Lucy M ZiurysDepartment of Chemistry, Department of Astronomy,

Steward Observatory, and Arizona Radio Observatory

University of Arizona

Dennis ClouthierDepartment of Chemistry, University of Kentucky


Zinc Metalloenzymes Zn important in many metalloenzymes

Lewis acid, no redox function LFSE zero, multiple geometries Hard/soft borderline (S,O,N) As co-factor or catalyst

ZnOH in carbonic anhydrase II Transport of CO2 and pH regulation via

CO2 /HCO3-

Zn function is catalytic, ligand exchange The Zn coordination sphere has received most

of the attention but what about the ZnOH unit itself


Hydroxides: Big Picture Alkali and alkaline earth hydroxides have linear or quasilinear metals out of the main group are bent.

1 2 3 4 5 6 7 8 9 10 11 12 13

HOH

LiOH BeOH

NaOH MgOH AlOH

KOH CaOH ScOH TiOH VOH CrOH MnOH FeOH CoOH NiOH CuOH ZnOH GaOH

RbOH SrOH YOH AgOH InOH

CsOH BaOH

Sc Ti V Cr Mn Fe Co Ni Cu Zn

OH 3D 4A" 5A" 6A' 7A' 6A' 3A' 2A' 1A' 2A'


ZnOH X2A’

Asymmetric top Near prolate rotor a-type transitions (DKa = 0)

Spin rotation splitting from unpaired electron Approx 190 MHz from ZnOH

Five naturally occurring zinc isotopes 64Zn (48.6%), 66Zn (27.9%), 68Zn (18.8%), 67Zn (4.1), 70Zn (0.6%)

Production H2O in Ar carrier gas, DC discharge assisted (250mA, 200V) Inconsistent production


ZnOD Experimental

D2O (2 mT) in Zn vapors and Ar (15mTorr)carrier gas, DC discharge assisted (250mA at 300V)

Instrumentation: Phase-locked Gunn oscillators and

Schottky diode multipliers (65-850 GHz)

Broida-type oven Gaussian beam optics Reaction chamber: double-pass, water-

cooled steel cell containing a Broida-type oven

InSb bolometer detector Radiation is modulated at 25 kHz and

detected at 2f


Spectra ZnOD•500MHz window

•Spin-rotation (approx 180 MHz)

•Asymmetry doubling (K=3 collapsed)

•U lines


Pattern Comparison

*Spin-rotation components not shown*K=1 flank out, other components compressed


Experimental: FTMW DALAS

0.5% CH3OH in Ar pulsed at 45psi, Zn laser ablated, DC discharge assisted (1100 V)

Instrumentation Fabry-Perot cavity, aluminum

mirrors and antennae for emitting and receiving

4-40 GHz MW synthesizer Pulsed-valve nozzle 40° to mirror

axis with ablation part 532 nm Surelite I-10 Nd:YAG

laser Frequency at 10Hz


Spectra: FTMW64ZnOH (X 2A’)

• 1.8 MHz

• 250 shots


• 8 transitions

• across 200 GHz

• 3 isotopes 64ZnOD 66ZnOD 68ZnOD

• 500 lines for fit


Constants

Heff = Hrot + Hsr + Hmhf


114 °, covalent character, significant sterics, unpaired electron on Zn

O-H bond distance (H acidity)

Zn-O increased bond length Zn radius smaller that Cu but bigger angle opposite from CuOH/AgOH (H+/ M+ repulsion) H destabilizes Zn-O bond for ligand exchange or insertion chemistry

Agreement with theory

Structure


Hyperfine Analysis

Fermi contact term• Existence of fermi contact term points to 4s character• Small fermi contact term consistent with Zn--H coupling • But why negative: supports delocalized non-bonding MOs that affect spin density at H directly

Dipolar term• Points to significant d character• sd hybridization (electron correlation among d-orbitals necessary for CuOH/AgOH calculations)


Conclusions Synthesized ZnOD using D2O for direct millimeter absorption, and

using CH3OH for FTMW DALAS Identified 64ZnOD, 66ZnOD, and 68ZnOD Determined constants ZnOD/ZnOH Determined structure for ZnOH

Bent structure (114°) Covalent bonding character

Future ZnSH, ZnCCH Trends in 3d hydroxides on to Ni, Co, Fe


Acknowledgements Professor Lucy M. Ziurys Lindsay N. Zack Matthew P. Bucchino Ming Sun Dennis Clouthier Ziurys research group Funding: NSF and NASA

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65 th International Symposium on Molecular Spectroscopy June 21, 2010 Lindsay N. Zack Brent J. Harris Matthew P. Bucchino Ming Sun Lucy M Ziurys Department