Effects of Compression on the Local Iodine Environment in Dipotassium Zinc Tetraiodate(V) Dihydrate K2Zn(IO3)4.2H2O

TL;DR

This study combines experimental and computational methods to investigate how pressure alters the bonding, structure, and electronic properties of K2Zn(IO3)4.2H2O, revealing significant changes in covalent bonds, hypercoordination, and band-gap energy.

Contribution

It provides detailed insights into pressure-induced structural and electronic transformations in K2Zn(IO3)4.2H2O, including the formation of multicenter bonds and a high compressibility.

Findings

Pressure causes a transition from covalent to multicenter bonds in K2Zn(IO3)4.2H2O.

The material exhibits a high compressibility with a bulk modulus of 22 GPa.

Band-gap energy decreases from 4.2 eV to 3.4 eV under 20 GPa pressure.

Abstract

Combining X-ray diffraction with density-functional theory and electron topology calculations we found that pressure substantially modifies the bonding in K2Zn(IO3)4.2H2O. We discovered that under compression there is a progressive change from primary covalent I-O bonds and secondary halogen I-O interactions towards O-I-O electron-deficient multicenter bonds. Because of this, iodine hypercoordination converts IO3 trigonal pyramids towards IO6 units. The formation of these IO6 units breaks the typical isolation of iodate molecules forming an infinite two-dimensional iodate network. Hypercoordination influences the hydrogen atoms too, such that multicenter O-H-O bonds are also promoted with increasing pressure. We have determined that K2Zn(IO3)4.2H2O is one of the most compressible iodates studied to date, with a bulk modulus of 22(3) GPa. The pressure-induced structural changes strongly modify the electronic structure as shown by optical-absorption measurements and band-structure calculations. The band-gap energy closes from 4.2(1) eV at ambient pressure to 3.4(1) eV at 20 GPa.