New Fluoride Carbonates: Centrosymmetric KPb₂(CO₃)₂F and Noncentrosymmetric K_2.70Pb_5.15(CO₃)₅F₃

Two new potassium lead fluoride carbonates, KPb₂(CO₃)₂F and K_2.70Pb_5.15(CO₃)₅F₃, have been synthesized and characterized. The materials were synthesized through solvothermal and conventional solid-state techniques. KPb₂(CO₃)₂F and K_2.70Pb_5.15(CO₃)₅F₃ were structurally characterized by single crystal X-ray diffraction and exhibit two-dimensional crystal structures consisting of corner-shared PbO₆F and PbO₆F₂ polyhedra. K_2.70Pb_5.15(CO₃)₅F₃ is noncentrosymmetric, and crystallizes in the <i>achiral</i> and <i>nonpolar</i> space group <i>P</i>6̅<i>m</i>2 (crystal class −6m2). Powder second-harmonic generation (SHG) measurements using 1064 nm radiation revealed a SHG efficiency of approximately 40 × α-SiO₂, whereas a charge constant, <i>d</i>₃₃, of approximately 20 pm/V was obtained through converse piezoelectric measurements. For the reported materials, infrared, UV–vis, thermogravimetric, and differential thermal analysis measurements were performed

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 <i>achiral</i> and <i>nonpolar</i> space group <i>P</i>6̅<i>m</i>2 (crystal class 6̅<i>m</i>2). 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 <i>d</i>₃₃ 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 2<i>p</i> states with the nearly spherically symmetric 6<i>s</i> 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

Synthesis and Selective Topochemical Fluorination of the Cation and Anion-Vacancy Ordered phases Ba₂YCoO₅ and Ba₃YCo₂O_7.5

The synthesis and characterization of two cation-ordered, anion-vacancy ordered phases, Ba₂YCoO₅ and Ba₃YCo₂O_7.5, is described. Neutron powder diffraction data reveal both phases adopt structures in which octahedral Y³⁺ and tetrahedral Co³⁺ centers are ordered within a “cubic” perovskite lattice. The unusual ordered pattern adopted by the cations can be attributed to the large concentration of anion vacancies within each phase. Reaction of Ba₂YCoO₅ with CuF₂ under flowing oxygen topochemically inserts fluorine into the host material to form Ba₂YCoO₅F_0.42(1). In contrast Ba₂YCoO₅ does not intercalate oxygen, even under high oxygen pressure. The selective insertion of fluorine, but not oxygen, into Ba₂YCoO₅ is discussed and rationalized on the basis of the lattice strain of the resulting oxidized materials. Magnetization and neutron diffraction data reveal Ba₃YCo₂O_7.5 and Ba₂YCoO₅F_0.42 adopt antiferromagnetically ordered states at low-temperature, while in contrast Ba₂YCoO₅ shows no sign of long-range magnetic order

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 <i>P</i>6̅2<i>m</i>, whereas Cs₉Mg₆(CO₃)₈F₅ is found in the polar space group <i>Pmn</i>2₁. 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

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 Mg²⁺ 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

K₈(K₅F)U₆Si₈O₄₀: An Intergrowth Uranyl Silicate

Single crystals of K₈(K₅F)­U₆Si₈O₄₀ were grown from a mixed alkali halide flux. K₈(K₅F)­U₆Si₈O₄₀ is the first intergrowth uranyl silicate, being composed of alternating slabs related to two previously reported uranyl silicates: Cs₂USiO₆ and [Na₉F₂]­[(UO₂)­(UO₂)₂(Si₂O₇)₂]. It exhibits intense luminescence, which is influenced by the [(UO₂)₂O] dimers present in the structure

K₈(K₅F)U₆Si₈O₄₀: An Intergrowth Uranyl Silicate

Single crystals of K₈(K₅F)­U₆Si₈O₄₀ were grown from a mixed alkali halide flux. K₈(K₅F)­U₆Si₈O₄₀ is the first intergrowth uranyl silicate, being composed of alternating slabs related to two previously reported uranyl silicates: Cs₂USiO₆ and [Na₉F₂]­[(UO₂)­(UO₂)₂(Si₂O₇)₂]. It exhibits intense luminescence, which is influenced by the [(UO₂)₂O] dimers present in the structure

Homochiral Helical Metal–Organic Frameworks of Group 1 Metals

The reactions of (<i>S</i>)-2-(1,8-naphthalimido)­propanoic acid (H<b>L</b>_<b>ala</b>) and (<i>S</i>)-2-(1,8-naphthalimido)-3-hydroxypropanoic acid (H<b>L</b>_<b>ser</b>), 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 H<b>L</b>_<b>ser</b> an alcohol functional group, with the appropriate alkali metal hydroxide followed by a variety of crystallization methods leads to the formation of crystalline K­(<b>L</b>_<b>ala</b>)­(MeOH) (<b>1</b>), K­(<b>L</b>_<b>ala</b>)­(H₂O) (<b>2</b>), Na­(<b>L</b>_<b>ala</b>)­(H₂O) (<b>3</b>), K<b>L</b>_<b>ser</b> (<b>4</b>), Cs<b>L</b>_<b>ser</b> (<b>5</b>), and Cs<b>L</b>_<b>ala</b> (<b>6</b>). 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 <b>L</b>_<b>ser</b> 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 <b>1</b>–<b>3</b>, this inter-rod link has a square arrangement bonding four other rods forming a three-dimensional enantiopure metal–organic framework (MOF) structure, whereas in <b>4</b>–<b>6</b> 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 <b>1</b>–<b>3</b> lose the coordinated solvent when heating above 100 °C. For <b>1</b>, the polycrystalline powder reverts to <b>1</b> only by recrystallization from methanol, whereas compounds <b>2</b> and <b>3</b> undergo gas/solid, single-crystal to single-crystal transformations to form dehydrated compounds <b>2*</b> and <b>3*</b>, and rehydration occurs when crystals of these new complexes are left out in air. The reversible single-crystal to single-crystal transformation of <b>2</b> involves the dissociation/coordination of a terminal water ligand, but the case of <b>3</b> 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 <b>3</b> moves into a bridging position in <b>3*</b> to maintain the homochiral helical rods. Both <b>2*</b> and <b>3*</b> contain five-coordinate metals. There are no coordinated solvents in compounds <b>4</b>–<b>6</b>, in two cases by designed ligand modification, which allows them to have high thermal stability. Compounds <b>1</b>–<b>3</b> did not exhibit observable Second Harmonic Generation (SHG) efficiency at an incident wavelength of 1064 nm, but compounds <b>4</b>–<b>6</b> did exhibit modest SHG efficiency for MOF-like compounds in the range of 30 × α-SiO₂

Homochiral Helical Metal–Organic Frameworks of Group 1 Metals

The reactions of (<i>S</i>)-2-(1,8-naphthalimido)­propanoic acid (H<b>L</b>_<b>ala</b>) and (<i>S</i>)-2-(1,8-naphthalimido)-3-hydroxypropanoic acid (H<b>L</b>_<b>ser</b>), 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 H<b>L</b>_<b>ser</b> an alcohol functional group, with the appropriate alkali metal hydroxide followed by a variety of crystallization methods leads to the formation of crystalline K­(<b>L</b>_<b>ala</b>)­(MeOH) (<b>1</b>), K­(<b>L</b>_<b>ala</b>)­(H₂O) (<b>2</b>), Na­(<b>L</b>_<b>ala</b>)­(H₂O) (<b>3</b>), K<b>L</b>_<b>ser</b> (<b>4</b>), Cs<b>L</b>_<b>ser</b> (<b>5</b>), and Cs<b>L</b>_<b>ala</b> (<b>6</b>). 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 <b>L</b>_<b>ser</b> 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 <b>1</b>–<b>3</b>, this inter-rod link has a square arrangement bonding four other rods forming a three-dimensional enantiopure metal–organic framework (MOF) structure, whereas in <b>4</b>–<b>6</b> 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 <b>1</b>–<b>3</b> lose the coordinated solvent when heating above 100 °C. For <b>1</b>, the polycrystalline powder reverts to <b>1</b> only by recrystallization from methanol, whereas compounds <b>2</b> and <b>3</b> undergo gas/solid, single-crystal to single-crystal transformations to form dehydrated compounds <b>2*</b> and <b>3*</b>, and rehydration occurs when crystals of these new complexes are left out in air. The reversible single-crystal to single-crystal transformation of <b>2</b> involves the dissociation/coordination of a terminal water ligand, but the case of <b>3</b> 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 <b>3</b> moves into a bridging position in <b>3*</b> to maintain the homochiral helical rods. Both <b>2*</b> and <b>3*</b> contain five-coordinate metals. There are no coordinated solvents in compounds <b>4</b>–<b>6</b>, in two cases by designed ligand modification, which allows them to have high thermal stability. Compounds <b>1</b>–<b>3</b> did not exhibit observable Second Harmonic Generation (SHG) efficiency at an incident wavelength of 1064 nm, but compounds <b>4</b>–<b>6</b> did exhibit modest SHG efficiency for MOF-like compounds in the range of 30 × α-SiO₂

A Cubic Non-Centrosymmetric Mixed-Valence Iron Borophosphate–Phosphite

A first member of a new family of metal borophosphate–phosphite Fe_1.834^IIFe_0.166^IIIB_0.5­[PO₃(OH)]_0.8­(HPO₃)_2.033 has been successfully synthesized by using the boric acid–phosphorous acid flux. The compound crystallizes in the cubic crystal system in a non-centrosymmetric space group <i>I</i>4̅3<i>d</i> (No. 220) with unit cell parameters of <i>a</i> = 21.261(3) Å, and <i>Z</i> = 48, featuring a very condensed network of FeO₆ octahedra and disordered phosphate-phosphite moieties with mixed valency of iron. The compound contains a novel fundamental building unit (FBU), a cyclic borophosphate-phosphite ring which is further connected to form a propeller like partial anionic structure. Metal polyhedra also form a propeller-like structure through edge-sharing and are further connected to the partial anionic structure to form the three-dimensional structure. Thermal analyses, infrared and Mössbauer spectroscopy, magnetic and second harmonic generating (SHG) measurements using 1064 nm radiation have been performed on this compound. SHG measurements indicate that the compound has an efficiency approximately equal to α-SiO₂