Informatics-Based Learning of Oxygen Vacancy Ordering Principles in Oxygen-Deficient Perovskites.

Ordered oxygen vacancies (OOVs) in perovskites can exhibit long-range order and may be used to direct materials properties through modifications in electronic structures and broken symmetries. Based on the various vacancy patterns observed in previously known compounds, we explore the ordering principles of oxygen-deficient perovskite oxides with ABO2.5 stoichiometry to identify other OOV variants. We performed first-principles calculations to assess the OOV stability on a data set of 50 OOV structures generated from our bespoke algorithm. The algorithm employs uniform planar vacancy patterns on (111) pseudocubic perovskite layers and the approach proves effective for generating stable OOV patterns with minimal computational loads. We find as expected that the major factors determining the stability of OOV structures include coordination preferences of transition metals and elastic penalties resulting from the assemblies of polyhedra. Cooperative rotational modes of polyhedra within the OOV structures reduce elastic instabilities by optimizing the bond valence of A- and B cations. This finding explains the observed formation of vacancy channels along low-index crystallographic directions in prototypical OOV phases. The identified ordering principles enable us to devise other stable vacancy patterns with longer periodicity for targeted property design in yet to be synthesized compounds.

Beyond π-π Stacking: Understanding Inversion Symmetry Breaking in Crystalline Racemates.

The design of noncentrosymmetric (NCS) solid state materials, specifically how to break inversion symmetry between enantiomers, has intrigued chemists, physicists, and materials scientists for many years. Because the chemical complexity of molecular racemic building units is so varied, targeting these materials is poorly understood. Previously, three isostructural racemic compounds with a formula of [Cu(H2O)(bpy)2]2[MF6]2·2H2O (bpy = 2,2'=bipyridine; M = Ti, Zr, Hf) were shown to crystallize in the NCS space group Pna21, of polar, achiral crystal class mm2. In this work, we synthesized five new racemic compounds with the formula [Cu(H2O)(dmbpy)2]2[MF6]2·xH2O (dmbpy = 4,4'/5,5'-dimethyl-2,2'-bipyridine; M = Ti, Zr, Hf). Single crystal X-ray diffraction reveals that the five newly synthesized compounds feature equimolar combinations of Δ- and Λ-Cu(dmbpy)2(H2O)2+ complexes that are assembled into packing motifs similar to those found in the reported NCS structure but all crystallize in centrosymmetric (CS) space groups. Seven structural descriptors were created to analyze the intermolecular interactions on the assembly of Cu racemates in the CS and NCS structures. The structural analysis reveals that in the CS structures, the inversion center results from parallel heterochiral π-π stacking interactions between adjacent Cu racemates regardless of cation geometries, hydrogen bonding networks, or interlayer architectures, whereas in the NCS structure, nonparallel heterochiral π-π interactions between the adjacent Cu racemates preclude an inversion center. The parallel heterochiral π-π interactions in the CS structures can be rationalized by the restrained geometries of the methyl-substituted ligands. This work demonstrates that the introduction of nonparallel stacking can suppress the formation of an inversion center for an NCS racemate. A conceptual framework and practical approach linking the absence of inversion symmetry in racemates is presented for all NCS crystal classes.

NaRb6(B4O5(OH)4)3(BO2) Featuring Noncentrosymmetry, Chirality, and the Linear Anionic Group BO2.

Noncentrosymmetric (NCS) structures are of particular interest owing to their symmetry-dependent physical properties, e.g., pyroelectricity, ferroelectricity, piezoelectricity, and nonlinear optical (NLO) behavior. Among them, chiral materials exhibit polarization rotation and host topological properties. Borates often contribute to NCS and chiral structures via their triangular [BO3] and tetrahedral [BO4] units and their numerous superstructure motifs. However, no chiral compound with the linear [BO2] unit has been reported to date. Herein, an NCS and chiral mixed-alkali-metal borate, NaRb6(B4O5(OH)4)3(BO2), with a linear BO2- unit in the structure was synthesized and characterized. The structure features a combination of three types of basic building units (BBUs), [BO2], [BO3], and [BO4] with sp-, sp2-, and sp3-hybridization of boron atoms, respectively. It crystallizes in the trigonal space group R32 (No. 155), one of the 65 Sohncke space groups. Two enantiomers of NaRb6(B4O5(OH)4)3(BO2) were found, and their crystallographic relationships are discussed. These results not only expand the small family of NCS structures with the rare linear BO2- unit but also prompt recognition to the fact that NLO materials have generally overlooked the existence of two enantiomers in achiral Sohncke space groups.

Wet to Dry Controls Lanthanide Scandate Synthesis.

The choice of temperature and gas conditions used in a water pressure-controlled reactor is guided by density functional theory (DFT) to synthesize nearly phase-pure lanthanide scandate nanoparticles (LnScO3, Ln = La, Nd, Sm, Gd). In this synthetic method, low water-vapor partial pressures, well below water's gas liquidus, inhibit particle growth, while an excess of water vapor results in undesired rare-earth hydroxide and oxyhydroxide secondary phases. The optimal humidity for high-purity LnScO3 particle synthesis is shown to vary with the lanthanide; DFT is used to calculate the thermodynamics of secondary phase formation for each lanthanide tested such that the role of water vapor may be quantified and used to maintain phase purity (greater than 96 mol %) across the series. The combination of thermodynamic calculation and experimental confirmation with this pressure-controlled reactor provides an opportunity to explore analogous syntheses of other inorganic perovskite nanoparticles.

Borates: A Rich Source for Optical Materials.

The primary goal of this review is to present a clear chemical perspective of borates in order to stimulate and facilitate the discovery of new borate-based optical materials. These materials, which exhibit structures as varied as they are complex, are needed to meet the urgent technological milestones. In the current period of rapid sociotechnological breakthroughs, the need for the rational design and discovery of novel borates with superior performance is greater than ever before. Through the sustained efforts of chemists and material scientists, more than 3900 boron-containing compounds, including borate minerals and synthetic borates, have been documented in the scientific literature. This review provides a survey of all the reported anhydrous borates and an analysis of their complex structural chemistry. State-of-the-art progress related to technological advances in borate-based nonlinear optical, birefringent, and self-frequency-doubling materials is surveyed, with special emphasis on the relationships between structural architectures and optical properties. More importantly, this review serves both as a scientific introduction for graduates and post-doctoral researchers to the chemical richness of solid-state borates and as a comprehensive reference for researchers interested in borate-based optical materials.

Triple-Wavelength Lasing with a Stabilized ß-LaBSiO5:Nd3+ Crystal.

Multi-wavelength lasers, especially the triple-wavelength laser around 1060 nm, could be produced by the 4F3/2 → 4I11/2 transition of Nd3+ and present numerous challenges and opportunities in the field of optoelectronics. The Nd3+-doped high-temperature phase of LaBSiO5 (ß-LBSO) is an ideal crystal to produce triple-wavelength lasers; however, the crystal growth is challenging because of the phase transition from ß-LBSO to low-temperature phase (α-LBSO) at 162 °C. This phase transition is successfully suppressed when the doping content of Nd3+ is larger than 6.3 at. %, and the Nd3+-doped ß-LBSO is stable at room temperature. The local disorder of BO4 tetrahedra due to Nd3+ doping is essential to the stabilization of ß-LBSO. For the first time, the ß-LBSO:8%Nd3+ crystal with a dimension of 1.8 × 1.8 × 1.8 cm3 is obtained through the top-seeded solution method. The crystal shows strong optical absorption in the range of 785-815 nm, matching well with the commercial laser diode pumping source. The optical emission of 4F3/2 → 4I11/2 splits into four peaks with the highest optical emission cross section of 2.14 × 10-20 cm2 at 1068 nm. The continuous-wave triple-wavelength generation of coherent light at 1047, 1071, and 1092 nm is achieved with the highest output power of 235 mW and efficiency of 12.1%.

Low Thermal Conductivity in Heteroanionic Materials with Layers of Homoleptic Polyhedra.

Although BiAgOSe, an analogue of a well-studied thermoelectric material BiCuOSe, is thermodynamically stable, its synthesis is complicated by the low driving force of formation from the stable binary and ternary intermediates. Here we have developed a "subtraction strategy" to suppress byproducts and produce pure phase BiAgOSe using hydrothermal methods. Electronic structure calculations and optical characterization show that BiAgOSe is an indirect bandgap semiconductor with a bandgap of 0.95 eV. The prepared sample exhibits lower lattice thermal conductivities (0.61 W·m-1·K-1 at room temperature and 0.35 W·m-1·K-1 at 650 K) than BiCuOSe. Lattice dynamical simulations and variable temperature diffraction measurements demonstrate that the low lattice thermal conductivity arises from both the low sound velocity and high phonon-phonon scattering rates in BiAgOSe. These in turn result primarily from the soft Ag-Se bonds in the edge-sharing AgSe4 tetrahedra and large sublattice mismatch between the quasi-two-dimensional [Bi2O2]2+ and [Ag2Se2]2- layers. These results highlight the advantages of manipulating the chemistry of homoleptic polyhedra in heteroanionic compounds for electronic structure and phonon transport control.

Two Distinct Cu(II)-V(IV) Superexchange Interactions with Similar Bond Angles in a Triangular "CuV2" Fragment.

The strength and sign of superexchange interactions are often predicted on the basis of the bond angles between magnetic ions, but complications may arise in situations with a nontrivial arrangement of the magnetic orbitals. We report on a novel molecular tetramer compound [Cu(H2O)dmbpy]2[V2O2F8] (dmbpy = 4,4'-dimethyl-2,2'-bipyridyl) that is composed of triangular "CuV2" fragments and displays a spin gap behavior. By combining first-principles calculations and electronic models, we reveal that superexchange Cu-V interactions carry drastically different coupling strengths along two Cu-F-V pathways with comparable bond angles in the triangular "CuV2" fragment. Counterintuitively, their strong disparity is found to originate from the restricted symmetry of the half-filled Cu dx2-y2 orbital stabilized by the crystal field, leading to one dominating antiferromagnetic Cu-V coupling in each fragment. We revisit the magnetic properties of the reported spin-gapped chain compound [enH2]Cu(H2O)2[V2O2F8] (enH2 = ethylene diammonium) containing similar triangular "CuV2" fragments, and the magnetic behavior of the molecular tetramer and the chain compounds is rationalized as that of weakly coupled spin dimers and spin trimers, respectively. This work demonstrates that fundamentally different magnetic couplings can be observed between magnetic ions with similar bond angles in a single spin motif, thus providing a strategy to introduce various exchange interactions combined with low dimensionality in heterometallic Cu(II)-V(IV) compounds.

Strong Nonlinearity Induced by Coaxial Alignment of Polar Chain and Dense [BO3 ] Units in CaZn2 (BO3 )2.

Discovery of new efficient nonlinear optical (NLO) materials with large second-order nonlinearity for the short-wave ultraviolet spectral region (λPM ≤266 nm, PM=phase-matching) is still very challenging. Herein, a new beryllium-free borate CaZn2 (BO3 )2 with Sr2 Be2 B2 O7 (SBBO) double-layered like configuration was rationally designed, which not only preserves the structural merits but also eliminates the limitations of the SBBO crystal. CaZn2 (BO3 )2 shows a large PM second harmonic generation (SHG) reponse of 3.8×KDP, which is 38 times higher than that of its barium analogue. This enhancement mainly originates from the 1 [Zn2 O6 ]∞ polar chains with a large net dipole moment and [BO3 ] units with a high NLO active density. Our findings show the great significance of the [ZnO4 ] tetrahedra introduced strategy to design beryllium-free SBBO-type NLO crystals and also verify the feasibility of using simple non-isomorphic substitution to induce giant second-order nonlinearity enhancement.

Perovskite-like K3TiOF5 Exhibits (3 + 1)-Dimensional Commensurate Structure Induced by Octahedrally Coordinated Potassium Ions.

Elpasolite- and cryolite-type oxyfluorides can be regarded as superstructures of perovskite and exhibit structural diversity. While maintaining a similar structural topology with the prototype structures, changes in the size, electronegativity, and charge of cation and/or anion inevitably lead to structural evolution. Therefore, the nominal one-to-one relation suggested by a doubled formula of perovskite does not guarantee a simple 2-fold superstructure for many cases. Herein, the commensurately modulated perovskite-like K3TiOF5 was refined at 100 K from single-crystal X-ray diffraction data by using a pseudotetragonal subcell with lattice parameters of a = b = 6.066(2) Å and c = 8.628(2) Å. The length of the modulation vector was refined to 0.3a* + 0.1b* + 0.25c*. In the commensurate supercell of K3TiOF5, the B-site Ti4+ and K+ cations in [TiOF5]3- and [KOF5]6- octahedral units were found to be significantly displaced from the average atomic positions refined in the subcell. The displacements of the K+ cations are ±0.76 Å, and those for the Ti4+ cations are approximately ±0.13 Å. One- and two-dimensional solid-state 19F NMR measurements revealed two tightly clustered groups of resonances in a ratio of ca. 4:1, assigned to equatorial and axial fluorine, respectively, consistent with local [TiOF5]3- units. S/TEM results confirmed the average structure. Electronic structure calculations of the idealized I4mm subcell indicate the instability to a modulated structure arises from soft optical modes that is controlled by the octahedrally coordinated B-site potassium ions in the cryolite-type structure.

Fluoridation of HfO2.

Fluoridation of HfO2 was carried out with three commonly used solid-state fluoridation agents: PVDF, PTFE, and NH4HF2. Clear and reproducible differences are observed in the reaction products of the fluoropolymer reagents and NH4HF2 with the latter more readily reacting in air. Strong evidence of distinct, previously unreported hafnium oxyfluoride phases is produced by both reactions, and efforts to isolate them were successful for the air-NH4HF2 reaction. Synchrotron XRD, 19F NMR, and elemental analysis were employed to characterize the phase-pure material which appears to be analogous to known Zr-O-F phases with anion-deficient α-UO3 structures such as Zr7O9F10. Comparison with the hydrolysis of ß-HfF4 under identical conditions depicts that the NH4HF2 route produces the oxyfluoride with greater selectivity and at lower temperatures. Thermodynamic calculations were employed to explain this result. Potential reaction pathways for the NH4HF2 fluoridation of HfO2 are discussed.

Periodic Tendril Perversion and Helices in the AMoO2F3 (A = K, Rb, NH4, Tl) Family.

Although compounds of the formula AMoO2F3 (A = K, Rb, Cs, NH4, Tl) have been known for decades, crystal structures have only been reported for CsMoO2F3 and NH4MoO2F3. The three compounds (Rb/NH4/Tl)MoO2F3 are isostructural and crystallize in the centrosymmetric space group C2/c (No. 15). The compounds contain the MoO2F3- anionic chain, composed of corner-sharing MoO2F4 octahedra, with Mo6+ coordinated by two cis bridging fluoride anions that are trans to terminal oxide anions. The MoO2F3- chain has a very unusual and complex chain structure; a single chain contains alternating zigzag and helical sections. These helical regions alternate in chirality along the chain, and thus the chains exhibit periodic tendril perversion. To the best of the authors' knowledge, no other materials with a similar chain structure have been reported. On the other hand, KMoO2F3 is noncentrosymmetric and chiral, crystallizing in the enantiomorphic space group P212121 (No. 19). KMoO2F3 also contains the MoO2F3- anionic chain. However, the chain is helical, with only one enantiomer present, resulting in a chiral, noncentrosymmetric structure.

Machine-Learning-Assisted Synthesis of Polar Racemates.

Racemates have recently received attention as nonlinear optical and piezoelectric materials. Here, a machine-learning-assisted composition space approach was applied to synthesize the missing M = Ti, Zr members of the Δ,Λ-[Cu(bpy)2(H2O)]2[MF6]2·3H2O (M = Ti, Zr, Hf; bpy = 2,2'-bipyridine) family (space group: Pna21). In each (CuO, MO2)/bpy/HF(aq) (M = Ti, Zr, Hf) system, the polar noncentrosymmetric racemate (M-NCS) forms in competition with a centrosymmetric one-dimensional chain compound (M-CS) based on alternating Cu(bpy)(H2O)22+ and MF62- basic building units (space groups: Ti-CS (Pnma), Zr-CS (P1̅), Hf-CS (P2/n)). Machine learning models were trained on reaction parameters to gain unbiased insight into the underlying statistical trends in each composition space. A human-interpretable decision tree shows that phase selection is driven primarily by the bpy:CuO molar ratio for reactions containing Zr or Hf, and predicts that formation of the Ti-NCS compound requires that the amount of HF present be decreased to raise the pH, which we verified experimentally. Predictive leave-one-metal-out (LOO) models further confirm that behavior in the Ti system is distinct from that of the Zr and Hf systems. The chemical origin of this distinction was probed via fluorine K-edge X-ray absorption spectroscopy. Pre-edge features in the F1s X-ray absorption spectra reveal the strong ligand-to-metal π bonding between Ti(3d - t2g) and F(2p) states that distinguishes the TiF62- anion from the ZrF62- and HfF62- anions.

Multimodal Structure Solution with 19F NMR Crystallography of Spin Singlet Molybdenum Oxyfluorides.

Complex crystal structures with subtle atomic-scale details are now routinely solved using complementary tools such as X-ray and/or neutron scattering combined with electron diffraction and imaging. Identifying unambiguous atomic models for oxyfluorides, needed for materials design and structure-property control, is often still a considerable challenge despite their advantageous optical responses and applications in energy storage systems. In this work, NMR crystallography and single-crystal X-ray diffraction are combined for the complete structure solution of three new compounds featuring a rare triangular early transition metal oxyfluoride cluster, [Mo3O4F9]5-. After framework identification by single-crystal X-ray diffraction, 1D and 2D solid-state 19F NMR spectroscopy supported by ab initio calculations are used to solve the structures of K5[Mo3O4F9]·3H2O (1), K5[Mo3O4F9]·2H2O (2), and K16[Mo3O4F9]2[TiF6]3·2H2O (3) and to assign the nine distinct fluorine sites in the oxyfluoride clusters. Furthermore, 19F NMR identifies selective fluorine dynamics in K16[Mo3O4F9]2[TiF6]3·2H2O. These dual scattering and spectroscopy methods are used to demonstrate the generality and sensitivity of 19F shielding to small changes in bond length, on the order of 0.01 Å or less, even in the presence of hydrogen bonding, metal-metal bonding, and electrostatic interactions. Starting from the structure models, the nature of chemical bonding in the molybdates is explained by molecular orbital theory and electronic structure calculations. The average Mo-Mo distance of 2.505 Å and diamagnetism in 1, 2, and 3 are attributed to a metal-metal bond order of unity along with a 1a21e4 electronic ground state configuration for the [Mo3O4F9]5- cluster, leading to a rare trimeric spin singlet involving d2 Mo4+ ions. The approach to structure solution and bonding analysis is a powerful strategy for understanding the structures and chemical properties of complex fluorides and oxyfluorides.

NaRb3B6O9(OH)3(HCO3): A Borate-Bicarbonate Nonlinear Optical Material.

A noncentrosymmetric mixed alkali metal borate-bicarbonate, NaRb3B6O9(OH)3(HCO3), was synthesized and characterized. The compound crystallizes in the monoclinic space group P21 (No. 4) with a = 8.988(3) Å, b = 8.889(2) Å, c = 10.068(4) Å, and ß = 114.6(4)°. The structure features a combination of chains of boron-oxygen [B6O9 (OH)3]3- groups and isolated HCO3- groups, with charge compensation provided by Rb+ and Na+ cations. It exhibits a second harmonic generation response of about 0.5 × KDP. The UV-vis-NIR absorption spectrum indicated a transparency of about 40% at 200 nm. The IR spectrum confirms the coordination environments of anionic groups, and thermogravimetric measurements indicate the material is thermally stable up to approximately 320 °C. Additionally, first-principles calculations were performed in order to gain insight into the role of boron-oxygen and HCO3- groups with respect to the band structure and NLO properties.

Predicting the Structure Stability of Layered Heteroanionic Materials Exhibiting Anion Order.

We report a workflow for heteroanionic materials discovery using Pauling's second rule to filter for and predict new candidate materials for synthesis with reduced computational overhead. Using oxyfluoride and oxynitride n = 1 Ruddlesden-Popper compounds as a use-case, we show that a minimization scheme based on the global instability index (GII) efficiently filters up to 50% of highly unstable candidate compositions based on crystal-chemistry grounds. We then validate the minimization scheme using density functional theory (DFT) calculations and find that unexpectedly the GII of stable heteroanionic materials is higher than that of homoanionic oxides owing to significant charge redistribution in compounds containing more than one anionic species. Using this workflow, we predict Sr2AlO3F to be stable and describe our attempts to synthesize a phase-pure material.

(CuxZn1-x)0.456In1.084Ge0.46O3 (0 ≤ x ≤ 1): A Complex, Ordered, Anion-Deficient Fluorite with Unusual Site-Specific Cation Mixing.

The anion-deficient fluorite-related family of materials exhibits a number of commercially useful properties arising from the specific arrangement of anion vacancies in each structure. One recently reported member, Zn0.456In1.084Ge0.46O3, is the only known example with its particular complex structure in which cation coordinations span one 4-coordinate (4b), two 6-coordinate (8e and 16f), and one 8-coordinate (4a) site. A new, complete, solid solution (CuxZn1-x)0.456In1.084Ge0.46O3, (0 ≤ x ≤ 1) has been discovered via the isovalent substitution of Cu2+ for Zn2+, significantly expanding the known phase space of this structure. Synchrotron X-ray data confirm the ZIGO structure over the entire composition range. Inclusion of Cu in the structure is found to occur exclusively at the 16f site, increasing the number of cations mixed on that site from three to four, while all others remain singly occupied, including the other 6-coordinate (8e) position. Furthermore, transmission electron microscopy investigations show no evidence of long-range cation ordering. Thus, disorder on the 16f site appears remarkably favorable in this otherwise highly ordered structure. Nonideal trends in the lattice parameters and diffuse reflectance spectra as a function of Cu content are examined. Further implications of the mixed order and disorder in the solid solution for materials discovery and possible properties of interest are briefly discussed.

Research and Development of Zincoborates: Crystal Growth, Structural Chemistry and Physicochemical Properties.

Borates have been regarded as a rich source of functional materials due to their diverse structures and wide applications. Therein, zincobrates have aroused intensive interest owing to the effective structural and functional regulation effects of the strong-bonded zinc cations. In recent decades, numerous zincoborates with special crystal structures were obtained, such as Cs3Zn6B9O21 and AZn2BO3X2 (A = Na, K, Rb, NH4; X = Cl, Br) series with KBe2BO3F2-type layered structures were designed via substituting Be with Zn atoms, providing a feasible strategy to design promising non-linear optical materials; KZnB3O6 and Ba4Na2Zn4(B3O6)2(B12O24) with novel edge-sharing [BO4]5- tetrahedra were obtained under atmospheric pressure conditions, indicating that extreme conditions such as high pressure are not essential to obtain edge-sharing [BO4]5--containing borates; Ba4K2Zn5(B3O6)3(B9O19) and Ba2KZn3(B3O6)(B6O13) comprise two kinds of isolated polyborate anionic groups in one borate structure, which is rarely found in borates. Besides, many zincoborates emerged with particular physicochemical properties; for instance, Bi2ZnOB2O6 and BaZnBO3F are promising non-linear optical (NLO) materials; Zn4B6O13 and KZnB3O6 possess anomalous thermal expansion properties, etc. In this review, the synthesis, crystal structure features and properties of representative zincoborates are summarized, which could provide significant guidance for the exploration and design of new zincoborates with special structures and excellent performance.

Site-Selective Occupancy of Eu2+ Toward Blue-Light-Excited Red Emission in a Rb3 YSi2 O7 :Eu Phosphor.

Establishing an effective design principle in solid-state materials for a blue-light-excited Eu2+ -doped red-emitting oxide-based phosphors remains one of the significant challenges for white light-emitting diodes (WLEDs). Selective occupation of Eu2+ in inorganic polyhedra with small coordination numbers results in broad-band red emission as a result of enhanced crystal-field splitting of 5d levels. Rb3 YSi2 O7 :Eu exhibits a broad emission band at λmax =622 nm under 450 nm excitation, and structural analysis and DFT calculations support the concept that Eu2+ ions preferably occupy RbO6 and YO6 polyhedra and show the characteristic red emission band of Eu2+ . The excellent thermal quenching resistance, high color-rendering index Ra (93), and low CCT (4013 K) of the WLEDs clearly demonstrate that site engineering of rare-earth phosphors is an effective strategy to target tailored optical performance.

Assisting the Effective Design of Polar Iodates with Early Transition-Metal Oxide Fluoride Anions.

Polar materials are of great technical interest but challenging to effectively synthesize. That is especially true for iodates, an important class of visible and mid-IR transparent nonlinear optical (NLO) materials. Aiming at developing a new design strategy for polar iodates, we successfully synthesized two sets of polymorphic early transition-metal (ETM) oxide-fluoride iodates, α- and ß-Ba[VFO2(IO3)2] and α- and ß-Ba2[VO2F2(IO3)2]IO3, based on the distinct structure-directing properties of oxide-fluoride anions. α- and ß-Ba[VFO2(IO3)2] contain the trans-[VFO2(IO3)2]2- polyanion and crystallize in the nonpolar space groups Pbcn and P212121. In contrast, α- and ß-Ba2[VO2F2(IO3)2]IO3 contain the cis-[VO2F2(IO3)2]3- Λ-shaped polyanion and crystallize in the polar space groups Pna21 and P21, respectively. Detailed structural analyses show that the variable polar orientation of trans-[VFO2(IO3)2]2- polyanions is the main cause of the nonpolar structures in α- and ß-Ba[VFO2(IO3)2]. However, the Λ-shaped configuration of cis-[VO2F2(IO3)2]3- polyanions can effectively guarantee the polar structures. Further property measurements show that polar α- and ß-Ba2[VO2F2(IO3)2]IO3 possess excellent NLO properties, including the large SHG responses (∼9 × KDP), wide visible and mid-IR transparent region (∼0.5-10.5 µm), and high thermal stability (up to 470 °C). Therefore, combining cis-directing oxide-fluoride anions and iodates is a viable strategy for the effective design of polar iodates.