Spectroscopy of Multiply Charged Metal Ions: IR Study of Mn 2+ (18-crown-6 ether)(MeOH) 1-3 Jason D. Rodriguez and James M. Lisy Department of Chemistry, University of Illinois Urbana- Champaign

Ionophores Complex ions in solution selectively –Useful for ion extraction in industrial and environmental processes The balance of various non-covalent effects determine selectivity –ion-ionophore –solvent-ionophore –ion-solvent –solvent-solvent A common example: Crown Ethers 18-crown-6 ether

Why is It Important to Study Multiply Charged Metal Ions? Most gas-phase studies on metal ion solvation have been predominantly on the singly charged state. PROBLEM: Many metal ions of chemical and biological interest have common formal charges that are higher than +1. If these studies are to be good models for the condensed phase or biological systems, metal ions must be studied in their common oxidation state. But it is hard to generate multiply charged metal cluster ions by traditional sources………………………………

Generating Ions Via Electrospray Developed by J.B. Fenn (Nobel Prize 1992) Used by P. Kebarle in early 1990s for mass spectrometric studies of multiply charged metal ion solvation Advantage –“Soft” technique—noncovalent interactions present in solution are preserved in the transfer to the gas phase Disadvantage –Ions must be present in solution—solute must be dissolvable by solvent

Experimental Apparatus Continuum Surelite II-10 Hz Nd 3+ :YAG (1064 nm) Tunable LaserVision OPO/A Source Chamber Detector Chamber Ion Selecting Quadrupole Ion Guiding Quadrupole Ion Analyzing Quadrupole Octapole Ion guide ESI Needle Syringe Pump Heated Capillary Skimmer Electrostatic Lenses Mn 2+ (18-crown-6 ether)(MeOH) n + hvMn 2+ (18-crown-6 ether)(MeOH) n-1 + MeOH

n=0 n=1 n=2 n=3 n=4

n=3 n=2 n=1

n=3 n=2 n=1 No hydrogen bonding features observed Hydrogen bonded feature centered at ~3180 cm -1 Free O—H band of methanol located at 3645 cm -1 Broad hydrogen bonded feature centered at ~3150 cm -1 A doublet appears in the Free O—H region, 3645 and 3663 cm -1 Only one feature present in Free O—H region, 3663 cm -1 Ref :Lisy et al. JCP, 95, 1991, 3924.

n=3 n=2 n=1

Features increase in intensity as solvation increases. Intensity of these features does not vary much with increase in solvation. Gas-phase neutral C—H stretches: MeOH a ( 2844,2970, 2999 cm -1 ) 18-crown-6 b (2870, 2942 cm -1 ) a: Serrallach, A. J.Mol.Spectrosc. 1974, 52, b: NIST online Chem. WebBook n=3 n=2 n=1

n=3 n=2 n=1 Calculations done at B3LYP/6-31+G*

Summary of Results The ESI technique has been used to generate solvated Mn 2+ :18-crown-6 ether clusters The IR spectra in the Free O—H stretch region of MeOH show changes as number of MeOH solvent molecules increases For n=2 and n=3, hydrogen bonding is observed In the C—H stretch region, there are features that appear to be due to C—H stretches of both MeOH and 18-crown-6

Future Work Computational work is currently in progress to characterize these results. This study lays the foundation for further work on solvation studies of multiply charged metal ions. The versatility of the ESI will be used to study other multiply charged metal ions and ionophores of chemical and biological interest.

Acknowledgements Prof. James M. Lisy Group Members: –Ms. Dorothy Miller –Ms. Amy Nicely –Mr. Jordan Beck –Mr. Oscar Rodriguez Mrs. Fatima J. Rodriguez Funding –NSF –UIUC Graduate College Fellowship –UIUC Chem. Dept. Fellowship