Structural Modulation of Molybdenyl Iodate Architectures by Alkali Metal Cations in AMoO₃(IO₃) (A = K, Rb, Cs):  A Facile Route to New Polar Materials with Large SHG Responses

Abstract

Three new molybdenyl iodates, KMoO3(IO3) (1), RbMoO3(IO3) (2), and CsMoO3(IO3) (3), have been prepared through the hydrothermal reactions of MoO3 with AIO4 (A = K, Rb, or Cs) at 180 C. These compounds are isolated as nearly colorless, air-stable crystals. Single-crystal X-ray diffraction experiments reveal that 1 possesses a corrugated layered structure constructed from molybdenum oxide chains that are bridged by iodate anions. The puckering of the layers is caused by the alignment of bent molybdenyl (MoO2(2+)) groups along one side of the molybdenum oxide chains. The K+ cations separate these layers from one another and serve to balance charge. In contrast, compounds 2 and 3, which are isostructural, form three-dimensional structures with small cavities filled with Rb+ or Cs+ cations. The differences between the structures of 1 and those of 2 and 3 are due to rotation of the molybdenyl units as translation occurs down the molybdenum oxide chains in order to accommodate the increased size of the Rb+ and Cs+ cations. This rotation allows for the iodate anions to bridge the molybdenum oxide chains in an additional dimension, creating a three-dimensional network structure. Furthermore, while 1 crystallizes in a centrosymmetric space group, 2 and 3 crystallize in polar space groups. Second-harmonic generation measurements on 2 and 3 show large responses of 400x alpha-quartz. Differential scanning calorimetry measurements demonstrate that 2 and 3 are thermally stable to 494 and 486 C, respectively. UV-vis diffuse reflectance spectra of these compounds show a high degree of transparency from 1 to 3 eV and a band gap of 3.1 eV.

The Lone‐Pair Cation I5+ in a Hexagonal Tungsten Oxide‐Like Framework: Synthesis, Structure, and Second‐Harmonic Generating Properties of Cs2I4O11

“…This efficiency is comparable to other NCS iodates, including HIO 3 (300 SiO 2 ), [26] LiIO 3 (300 SiO 2 ), [26] NdMoO 2 (IO 3 ) 4 (OH) (350 SiO 2 ), [28] and AMoO 3 (IO 3 ) (A = Rb or Cs, 400 SiO 2 ). [29] By sieving the polycrystalline powder into various particle sizes (20-150 mm) and measuring the SHG as a function of particle size, we were able to determine that Cs 2 I 4 O 11 is non-phasematchable (Type 1). This information along with the SHG efficiency allows us to estimate hd eff i exptl , which for Cs 2 I 4 O 11 is 9.6 pm V À1 .…”

Rb2Na(NO3)3: A Congruently Melting UV-NLO Crystal with a Very Strong Second-Harmonic Generation Response

“…In order to obtain NLO materials exhibiting strong second-harmonic generation (SHG) effects, a number of methods have been discussed. Combining asymmetric building units, such as distorted octahedra with a d 0 transition metal cation [39][40][41], polyhedra with a d 10 metal cation revealing a polar displacement [42,43], and metal ions with ns 2 lone pair electrons [44] in the frameworks of new materials is a common approach to increase the incidence of many good NLO materials [45,46]. Incorporation of the above mentioned acentric building units into a nitrates system may also enlarge the SHG efficiency of materials.…”

Square‐Planar Noble Metal Iodate [M(IO3)4]n– (M = PdII, AuIII; n = 2, 1) Anions and Their Ability to Form Polar and Centrosymmetric Architectures

“…Iodate compounds have been the subject of intense interest because of their propensity for adopting noncentrosymmetric structures that are often polar, [1][2][3][4][5][6][7][8] a feature that is aptly illustrated by A[MoO 3 (IO 3 )] (A = Rb, Cs), [9] A[(VO) 2 -(IO 3 ) 3 O 2 ] (A = NH 4 , Rb, Cs), [10] and NaYI 4 O 12 . [11] This structural attribute can be exploited in the development of new nonlinear optical, pyroelectric, piezoelectric, and ferroelectric materials, with the first property being the most heavily investigated.…”