High-pressure synchrotron X-ray diffraction studies of cobalt iodate, Co­(IO3)2, reveal a counterintuitive pressure-induced expansion along certain crystallographic directions. High-pressure Raman and infrared spectroscopy, combined with density-functional theory calculations, reveal that with increasing pressure, it becomes energetically favorable for certain I–O bonds to increase in length over the full range of pressure studied up to 28 GPa. This phenomenon is driven by the high-pressure behavior of iodate ion lone electron pairs. Two pressure-induced isosymmetric monoclinic–monoclinic phase transitions are observed at around 3.0 and 9.0 GPa, which are characterized by increasing oxygen coordination of the iodine atoms and the probable formation of pressure-induced metavalent bonds. Pressure–volume equations of state are presented, as well as a detailed discussion of the pressure dependences of the observed Raman- and infrared-active modes, which clarifies previous inconsistencies in the literature.

The investigation of CdCl 2 -HIO 3 system, in aqueous and HNO 3 solutions, revealed that anhydrous cadmium iodate presents a marked polymorphism. No less than four new Cd(IO 3 ) 2 polymorphs have been isolated and characterized, two of which showing second harmonic generation activity. Single crystals of ε-Cd(IO 3 ) 2 are obtained by slowly evaporating, at 60°C, a saturated solution of γ-Cd(IO 3 ) 2 in 30 % nitric acid. This compound crystallizes in the orthorhombic space group Pca2 1 [a ϭ 17.581(2), b ϭ 5.495 (2), Å ]. The basic structural unit can be described as the connection of two cadmium polyhedrons with a short metal Ϫ metal distance of 3.88 Å . These units are further linked through two other iodate bridges resulting in layers parallel to the (100) plane. The 3D linkage is ensured by short bonds of the fourth iodate group.

We report a characterization of the high-pressure behavior of zinc iodate, Zn(IO 3 ) 2 . By the combination of x-ray diffraction, Raman spectroscopy, and first-principles calculations we have found evidence of two subtle isosymmetric structural phase transitions. We present arguments relating these transitions to a nonlinear behavior of phonons and changes induced by pressure on the coordination sphere of the iodine atoms. This fact is explained as a consequence of the formation of metavalent bonding at high pressure which is favored by the lone-electron pairs of iodine. In addition, the pressure dependence of unit-cell parameters, volume, and bond distances is reported. An equation of state to describe the pressure dependence of the volume is presented, indicating that Zn(IO 3 ) 2 is the most compressible iodate among those studied up to now. Finally, phonon frequencies are reported together with their symmetry assignment and pressure dependence.

Synthesis and characterization of anhydrous LiZn(IO3)3 powders prepared from an aqueous solution are reported. Morphological and compositional analyses were carried out by using scanning electron microscopy and energy-dispersive X-ray measurements. The synthesized powders exhibited a needle-like morphology after annealing at 400 °C. A crystal structure for the synthesized compound was proposed from powder X-ray diffraction and density-functional theory calculations. Rietveld refinements led to a monoclinic structure, which can be described with space group P21, number 4, and unit-cell parameters a = 21.874(9) Å, b = 5.171(2) Å, c = 5.433(2) Å, and  = 120.93(4)°. Density-functional theory calculations supported the same crystal structure. Infrared spectra were also collected, and the vibrations associated with the different modes were discussed. The non-centrosymmetric space group determined for this new polymorph of LiZn(IO3)3, the characteristics of its infrared absorption spectrum, and the observed second-harmonic generation suggest it is a promising infrared non-linear optical material.

The structural and vibrational behavior of Mg(IO 3 ) 2 under compression has been investigated via a combination of high-pressure (HP) synchrotron x-ray diffraction (XRD), Raman scattering, and infrared spectroscopy experiments as well as first-principles ab initio calculations. In this paper, we reveal that Mg(IO 3 ) 2 undergoes a pressure-induced phase transition between 7.5 and 9.7 GPa at ambient temperature from a monoclinic (space group P2 1 ) to a trigonal (space group P3) structure. Mg(IO 3 ) 2 also exhibits the gradual formation of additional bonds between iodine and oxygen atoms in neighboring IO − 3 units with increasing pressure, thereby increasing the oxygen-iodine coordination from 3 to 6. The bond formation under compression is a consequence of the existence of lone electron pairs on the iodine cation. To accommodate the additional bonds, the I-O bonds within the original [IO 3 ]trigonal pyramids increase in length under increasing compression. The appearance of additional Raman modes at 7.7 GPa and infrared modes at 9.6 GPa supports the phase transition observed in XRD experiments. Interestingly, the lengthening of I-O bonds causes a softening of several Raman modes under compression. We provide the crystal structure of the HP phase, the pressure-volume equations of state for both low-and HP phases, and the symmetry assignment of the Raman-and infrared-active modes of both phases.