127I Solid-State NMR Spectroscopy of Organic Periodates Featuring Halogen Bonded IO4̶ … IO4̶ Adducts.

Abstract

Hydroxyanions and oxyanions can overcome electrostatic repulsion between like charges to form supramolecular architectures whose formation is driven by non-covalent interactions such as hydrogen bonds and halogen bonds (HaB).  We report here a 127I solid-state nuclear magnetic resonance (SSNMR) study of a series of six organic periodates including compounds which feature I…O HaB between pairs of IO4- anions and control samples which do not feature HaB.  127I SSNMR spectra of powdered samples acquired under stationary conditions at 9.4, 11.75, and 21.1 T are simulated using an exact diagonalization of the Zeeman-quadrupolar Hamiltonian to provide the isotropic chemical shift, 127I nuclear quadrupolar coupling constant (CQ), and quadrupolar asymmetry parameter for each compound. One of the HaB compounds, 4-(pyrrolidin-1-yl)pyridinium periodate, is characterized by the largest CQ(127I) value measured to date for a periodate anion, 52.70 MHz.  Control organic periodates which do not have HaBs have CQ(127I) values that are much lower than those seen in the halogen-bonded systems, thereby easily differentiating between these two sets of compounds.  The CQ(127I) values for those compounds featuring only halogen-bonded periodate anions correlate with the shear strain of the anion, which may be attributed to the influence of the HaB on the local geometry.