Toward the Rational Design of Novel Noncentrosymmetric Materials: Factors Influencing the Framework Structures

Abstract

Solid-state materials with extended structures have revealed many interesting structure-related characteristics. Among many, materials crystallizing in noncentrosymmetric (NCS) space groups have attracted massive attention attributable to a variety of superb functional properties such as ferroelectricity, pyroelectricity, piezoelectricity, and nonlinear optical (NLO) properties. In fact, the characteristics are pivotal to many industrial applications such as laser systems, optical communications, photolithography, energy harvesting, detectors, and memories. Thus, for the past several decades, a great deal of synthetic effort has been vigorously made to realize these technologically important properties by improving the occurrence of macroscopic NCS space groups. A bright approach to increase the incidence of NCS structures was combining local asymmetric units during the initial synthesis process. Although a significant improvement has been achieved in obtaining new NCS materials using this strategy, the majority of solid-state materials still crystallize in centrosymmetric (CS) structures as the locally unsymmetrical units are easily lined up in an antiparallel manner. Therefore, discovering an effective method to control the framework structure and the macroscopic symmetry is an imminent ongoing challenge. In order to more effectively control the overall symmetry of solid-state compounds, it is critical to understand how the backbone and the subsequent centricity are affected during the crystallization. In this Account, several factors influencing the framework structure and centricity of solid-state materials are described in order to more systematically discover novel NCS materials. Recent studies on crystalline solid-state materials suggest three factors affecting the local coordination environment as well as the overall symmetry of the framework structure: (1) size variations of the various template cations, (2) a variable backbone arrangement occurring from the hydrogen-bonding interactions, and (3) the presence of framework flexibility. With regard to the first factor, the impact of size of the various metal cations and coordination numbers on the alignment of other adjacent polyhedra, linkers, and lone pairs determining the framework geometries of mixed metal oxides is analyzed. The second factor considers the regulation of crystallographic centricity determined by the availability of hydrogen-bonding interactions between anionic frameworks containing local asymmetric polyhedra and organic cations. Finally, the third factor explores the framework architecture and the space group symmetry influenced by the flexibility of polyhedra revealing variable coordination numbers. The centricity and framework of new solid-state materials might be controlled by using a variety of synthetically controllable asymmetric units such as organic structure-directing cations and linkers with different sizes and functional groups.

K3B6O9F3: A New Fluorooxoborate with Four Different Anionic Units

“…It is well known that borates possess diverse structures . In typical polyborate structures, there are two kinds of units, [BO 3 ] 3− triangles and [BO 4 ] 5− tetrahedra, which are hybridized by planar sp 2 and three dimensional sp 3 , respectively.…”

Synthesis, Crystal Structures, Optical Properties and Theoretical Calculations of Two Metal Chalcogenides Ba2AlSbS5 and Ba2GaBiSe5

“…Metal chalcogenides have been used as critical materials in the development of modern science and technology because of their structural complexities and fascinating properties [1][2][3][4][5][6][7][8][9][10][11][12]. Among them, many trivalent cations (such as M III ': As, Sb, or Bi) containing chalcogenides have been discovered and shown to have various application prospects.…”

(NH4)Bi2(IO3)2F5: An Unusual Ammonium‐Containing Metal Iodate Fluoride Showing Strong Second Harmonic Generation Response and Thermochromic Behavior

“…To date, various strategies have been implemented for the design and synthesis of new iodate NLO crystals. As a result, a series of excellent iodate SHG crystals have been reported, including AMoO 3 (IO 3 ) (A=Rb, Cs), BaNbO(IO 3 ) 5 , NaI 3 O 8 , A 2 Ti(IO 3 ) 6 (A=Li, Na), (NH 4 )[MoO 3 (IO 3 )], ReI 5 O 14 (Re=Y and Gd), BiO(IO 3 ), and Bi 2 (IO 4 )(IO 3 ) 3 . Recently, fluorine‐containing iodates, such as Bi(IO 3 )F 2 , Bi 3 OF 3 (IO 3 ) 4 , ABi 2 (IO 3 ) 2 F 5 (A=K, Rb, Cs), α‐ and β‐Ba[VFO 2 (IO 3 ) 2 ], α‐ and β‐Ba 2 [VO 2 F 2 (IO 3 ) 2 ]IO 3 , α‐ and β‐Ba 2 [GaF 4 (IO 3 ) 2 ](IO 3 ), RbIO 2 F 2 , CsIO 2 F 2 , and Ce(IO 3 ) 2 F 2 ⋅H 2 O, have been demonstrated to be new types of promising NLO iodate crystals.…”