Preparation and Characterization of the Halogen-Bonding Motif in the Isolated Cl–·IOH Complex with Cryogenic Ion Vibrational Spectroscopy

• DOI: 10.1021/acs.jpclett.2c00218
• Publication Date: 2022-03-22T13:19:51Z
• Authors: Santino J. Stropoli; Thien Khuu; Joseph P. Messinger; Natalia V. Karimova; Mark A. Boyer; Itai Zakai; Sayoni Mitra; Anton L. Lachowicz; Nan Yang; Sean C. Edington; R. Benny Gerber; Anne B. McCoy; Mark A. Johnson
• Keywords: Halogens; Spectrum Analysis; Hydrogen Bonding; Vibration; 01 natural sciences; Hydrogen; 0104 chemical sciences

In the presence of a halide ion, hypohalous acids can adopt two binding motifs upon formation of the ion-molecule complexes [XHOY]- (X, Y = Cl, Br, I): a hydrogen (HB) bond to the acid OH group and a halogen (XB) bond between the anion and the acid halogen. Here we isolate the X-bonded Cl-·IOH ion-molecule complex by collisions of I-·(H2O)n clusters with HOCl vapor and measure its vibrational spectrum by IR photodissociation of the H2-tagged complex. Anharmonic analysis of its vibrational band pattern reveals that formation of the XB complex results in dramatic lowering of the HOI bending fundamental frequency and elongation of the O-I bond (by 168 cm-1 and 0.13 Å, respectively, relative to isolated HOI). The frequency of the O-I stretch (estimated 436 cm-1) is also encoded in the spectrum by the weak v = 0 → 2 overtone transition at 872 cm-1.