T. Thao Tran

RbMgCO3F: A New Beryllium-Free Deep-Ultraviolet Nonlinear Optical Material

A new deep-ultraviolet nonlinear optical material, RbMgCO3F, has been synthesized and characterized. The achiral nonpolar acentric material is second harmonic generation (SHG) active at both 1064 and 532 nm, with efficiencies of 160 × α-SiO2 and 0.6 × β-BaB2O4, respectively, and exhibits a short UV cutoff, below 190 nm. RbMgCO3F possesses a three-dimensional structure of corner-shared Mg(CO3)2F2 polyhedra. Unlike other acentric carbonate fluorides, in this example, the inclusion of Mg(2+) creates pentagonal channels where the Rb(+) resides. Our electronic structure calculations reveal that the denticity of the carbonate linkage, monodentate or bidendate, to the divalent cation is a useful parameter for tuning the transparency window and achieving the sizable SHG response.

Role of acentric displacements on the crystal structure and second-harmonic generating properties of RbPbCO3F and CsPbCO3F.

Two lead fluorocarbonates, RbPbCO3F and CsPbCO3F, were synthesized and characterized. The materials were synthesized through solvothermal and conventional solid-state techniques. RbPbCO3F and CsPbCO3F were structurally characterized by single-crystal X-ray diffraction and exhibit three-dimensional (3D) crystal structures consisting of corner-shared PbO6F2 polyhedra. For RbPbCO3F, infrared and ultraviolet–visible spectroscopy and thermogravimetric and differential thermal analysis measurements were performed. RbPbCO3F is a new noncentrosymmetric material and crystallizes in the achiral and nonpolar space group P6̅m2 (crystal class 6̅m2). Powder second-harmonic generation (SHG) measurements on RbPbCO3F and CsPbCO3F using 1064 nm radiation revealed an SHG efficiency of approximately 250 and 300 × α-SiO2, respectively. Charge constants d33 of approximately 72 and 94 pm/V were obtained for RbPbCO3F and CsPbCO3F, respectively, through converse piezoelectric measurements. Electronic structure calculations indicate that the nonlinear optical response originates from the distorted PbO6F2 polyhedra, because of the even–odd parity mixing of the O 2p states with the nearly spherically symmetric 6s electrons of Pb2+. The degree of inversion symmetry breaking is quantified using a mode-polarization vector analysis and is correlated with cation size mismatch, from which it is possible to deduce the acentric properties of 3D alkali-metal fluorocarbonates.

Homochiral helical metal-organic frameworks of group 1 metals.

The reactions of (S)-2-(1,8-naphthalimido)propanoic acid (HL(ala)) and (S)-2-(1,8-naphthalimido)-3-hydroxypropanoic acid (HL(ser)), protonated forms of ligands that contain a carboxylate donor group, an enantiopure chiral center, and a 1,8-naphthalimide π···π stacking supramolecular tecton and in the case of HL(ser) an alcohol functional group, with the appropriate alkali metal hydroxide followed by a variety of crystallization methods leads to the formation of crystalline K(L(ala))(MeOH) (1), K(L(ala))(H2O) (2), Na(L(ala))(H2O) (3), KL(ser) (4), CsL(ser) (5), and CsL(ala) (6). Each of these new complexes has a solid state structure based on six-coordinate metals linked into homochiral helical rod secondary building unit (SBU) central cores. In addition to the bonding of the carboxylate and solvent (in the case of L(ser) the ligand alcohol) to the metals, both oxygens on the 1,8-naphthalimide act as donor groups. One naphthalimide oxygen bonds to the same helical rod SBU as the carboxylate group of that ligand forming a chelate ring. The other naphthalimide oxygen bonds to adjacent SBUs. In complexes 1-3, this inter-rod link has a square arrangement bonding four other rods forming a three-dimensional enantiopure metal-organic framework (MOF) structure, whereas in 4-6 this link has a linear arrangement bonding two other rods forming a two-dimensional, sheet structure. In the latter case, the third dimension is supported exclusively by interdigitated π···π stacking interactions of the naphthalimide supramolecular tecton, forming enantiopure supramolecular MOF solids. Compounds 1-3 lose the coordinated solvent when heating above 100 °C. For 1, the polycrystalline powder reverts to 1 only by recrystallization from methanol, whereas compounds 2 and 3 undergo gas/solid, single-crystal to single-crystal transformations to form dehydrated compounds 2* and 3*, and rehydration occurs when crystals of these new complexes are left out in air. The reversible single-crystal to single-crystal transformation of 2 involves the dissociation/coordination of a terminal water ligand, but the case of 3 is remarkable considering that the water that is lost is the only bridging ligand between the metals in the helical rod SBU and a carboxylate oxygen that is a terminal ligand in 3 moves into a bridging position in 3* to maintain the homochiral helical rods. Both 2* and 3* contain five-coordinate metals. There are no coordinated solvents in compounds 4-6, in two cases by designed ligand modification, which allows them to have high thermal stability. Compounds 1-3 did not exhibit observable Second Harmonic Generation (SHG) efficiency at an incident wavelength of 1064 nm, but compounds 4-6 did exhibit modest SHG efficiency for MOF-like compounds in the range of 30 × α-SiO2.

Polar and Magnetic Mn2FeMO6 (M = Nb, Ta) with LiNbO3-type Structure - High Pressure Synthesis

Polar oxides are of much interest in materials science and engineering. Their symmetry-dependent properties such as ferroelectricity/multiferroics, piezoelectricity, pyroelectricity, and second-order harmonic generation (SHG) effect are important for technological applications. [1] However, polar crystal design and synthesis is challenging, because multiple effects, such as steric or dipole-dipole interactions, typically combine to form non-polar structures; so the number of known polar materials, especially polar magnetoelectric materials, is still severely restricted. [2] Therefore, it is necessary for the material science community to develop new strategies to create these materials.

Mixed-Metal Carbonate Fluorides as Deep-Ultraviolet Nonlinear Optical Materials

Noncentrosymmetric mixed-metal carbonate fluorides are promising materials for deep-ultraviolet (DUV) nonlinear optical (NLO) applications. We report on the synthesis, characterization, structure-property relationships, and electronic structure calculations on two new DUV NLO materials: KMgCO3F and Cs9Mg6(CO3)8F5. Both materials are noncentrosymmetric (NCS). KMgCO3F crystallizes in the achiral and nonpolar NCS space group P6̅2m, whereas Cs9Mg6(CO3)8F5 is found in the polar space group Pmn21. The compounds have three-dimensional structures built up from corner-shared magnesium oxyfluoride and magnesium oxide octahedra. KMgCO3F (Cs9Mg6(CO3)8F5) exhibits second-order harmonic generation (SHG) at both 1064 and 532 nm incident radiation with efficiencies of 120 (20) × α-SiO2 and 0.33 (0.10) × β-BaB2O4, respectively. In addition, short absorption edges of <200 and 208 nm for KMgCO3F and Cs9Mg6(CO3)8F5, respectively, are observed. We compute the electron localization function and density of states of these two compounds using first-principles density functional theory, and show that the different NLO responses arise from differences in the denticity and alignment of the anionic carbonate units. Finally, an examination of the known SHG active AMCO3F (A = alkali metal, M = alkaline earth metal, Zn, Cd, or Pb) materials indicates that, on average, smaller A cations and larger M cations result in increased SHG efficiencies.

Beryllium‐Free β‐Rb2Al2B2O7 as a Possible Deep‐Ultraviolet Nonlinear Optical Material Replacement for KBe2BO3F2

A new beryllium-free deep-ultraviolet (DUV) nonlinear optical (NLO) material, β-Rb2 Al2 B2 O7 (β-RABO), has been synthesized and characterized. The chiral nonpolar acentric material shows second-harmonic generation (SHG) activity at both 1064 and 532 nm with efficiencies of 2×KH2 PO4 and 0.4×β-BaB2 O4 , respectively, and exhibits a short absorption edge below 200 nm. β-Rb2 Al2 B2 O7 has a three-dimensional structure of corner-shared Al(BO3 )3 O polyhedra. The discovery of β-RABO shows that through careful synthesis and characterization, replacement of KBe2 BO3 F2 (KBBF) by a Be-free DUV NLO material is possible.

Crystal Growth, Structure, Polarization, and Magnetic Properties of Cesium Vanadate, Cs2V3O8: A Structure–Property Study

Cesium vanadate, Cs2V3O8, a member of the fresnoite-type structure, was synthesized via a hydrothermal route and structurally characterized by single-crystal X-ray diffraction. Cs2V3O8 crystallizes in a noncentrosymmetric polar space group, P4bm, with crystal data of a = 8.9448(4) Å, c = 6.0032(3) Å, V = 480.31(4) Å(3), and Z = 2. The material exhibits a two-dimensional layered crystal structure consisting of corner-shared V(5+)O4 and V(4+)O5 polyhedra. The layers are separated by the cesium cations. The alignment of the individual polyhedra results in a macroscopic polarity for Cs2V3O8. Frequency-dependent polarization measurements indicate that the material is not ferroelectric. A pyroelectric coefficient of -2.0 μC m(-2) K(-1) was obtained from pyroelectric measurements taken as a function of the temperature. The magnetic susceptibility data were measured as a function of the temperature and yielded an effective magnetic moment of 1.78 μB for the V(4+) cation. Short-range magnetic ordering was observed around 7 K. The susceptibility data were fit to the Heisenberg square-lattice model supporting that the short-range magnetic interactions are antiferromagnetic and two-dimensional. IR and thermal properties were also characterized.

Syntheses of two vanadium oxide-fluoride materials that differ in phase matchability.

The syntheses of two noncentrosymmetric (NCS) vanadium oxide–fluoride compounds that originate from the same synthetic reagent concentrations are presented. Hydrothermal and low-temperature syntheses allow the isolation of metastable products that may form new phases (or decompose) upon heating and allow creation of chemically similar but structurally different materials. NCS materials synthesis has been a long-standing goal in inorganic chemistry: in this article, we compare two chemically similar NCS inorganic materials, NaVOF4(H2O) (I) and NaVO2–xF2+x (II; x = 1/3). These materials originate from the same, identical reagent mixtures but are synthesized at different temperatures: 100 °C and 150 °C, respectively. Compound I crystallizes in Pna21: a = 9.9595(4) Å, b = 9.4423(3) Å, and c = 4.8186(2) Å. Compound II crystallizes in P21: a = 6.3742(3) Å, b = 3.5963(2) Å, c = 14.3641(7) Å, and β = 110.787(3)°. Both materials display second-harmonic-generation activity; however, compound I is type 1 non-phase-matchable, whereas compound II is type 1 phase-matchable.

U3F12(H2O), a noncentrosymmetric uranium(IV) fluoride prepared via a convenient in situ route that creates U4+ under mild hydrothermal conditions.

A new noncentrosymmetric U(4+)-containing fluoride, U3F12(H2O), has been synthesized via a mild hydrothermal route and its crystal structure determined by single-crystal X-ray diffraction. The material exhibits a complex three-dimensional structure that is based on [U6F33(H2O)2)](9-) hexanuclear building units consisting of corner- and edge-shared UF8, UF9, and UOF7 polyhedra. Powder second-harmonic generation (SHG) measurements revealed that the SHG efficiency for U3F12(H2O) is comparable to that of α-SiO2. Magnetic susceptibility measurements indicated that the U(4+)(f(2))-containing material exhibits a singlet ground state at low temperature. IR and UV-vis reflectance spectra were obtained, and the thermal behavior was investigated by thermogravimetric analysis.

Macroscopic polarity control with alkali metal cation size and coordination environment in a series of tin iodates

A series of stoichiometrically similar tin(IV) iodates, A2Sn(IO3)6 (A = Li, Na, K, Rb, Cs) and Sn2+Sn4+(IO3)6 have been hydrothermally synthesized. X-ray diffraction was used to determine the crystal structures of the reported materials. All six materials reveal zero-dimensional molecular structures that consist of SnO6 octahedra and IO3 polyhedra. However, the size and coordination environment of cations significantly influence the macroscopic centricities of the materials. While Li2Sn(IO3)6 and Na2Sn(IO3)6 crystallize in the noncentrosymmetric (NCS) polar space group, P63, the K, Rb, Cs, and Sn phases crystallize in the centrosymmetric (CS) nonpolar space group, R. Infrared and UV-vis spectroscopy, thermal analyses, and local dipole moment calculations are reported. With NCS polar materials, powder second-harmonic generation (SHG) properties, polarization, and piezoelectric measurements are also presented. The NCS properties are mainly attributable to the parallel alignment of the lone pairs in I5+ cations.