Coordinatively unsaturated cobalt ion in Co+(H2O)n (n = 4–6) probed with infrared photodissociation spectroscopy

Abstract The hydrated cobalt ions, Co + (H 2 O) n ( n =  4–6), are studied with the infrared (IR) photodissociation spectroscopy in the OH-stretch region and density functional theory calculations. The calculations predict a T-shaped coordination structure for Co + (H 2 O) 3 , which exposes empty coordination sites for additional H 2 O ligands. Nevertheless, the IR spectrum of Co + (H 2 O) 4 indicates that the fourth H 2 O prefers to occupy the second shell through H-bonding rather than coordinate directly to Co + . A comparison between the experimental and theoretical IR spectra suggests that the T-shaped coordination remains intact in the n =  4–6 ions, leaving the direct coordination sites unoccupied.