Abstract
More than 3900 crystalline borates, including borate minerals and synthetic inorganic borates, in addition to a wealth of industrially-important boron-containing glasses, have been discovered and characterized. Of these compounds, 99.9 % contain only the traditional triangular BO3 and tetrahedral BO4 units, which polymerize into superstructural motifs. Herein, a mixed metal K5Ba2(B10O17)2(BO2) with linear BO2 structural units was obtained, pushing the boundaries of structural diversity and providing a direct strategy toward the maximum thresholds of birefringence for optical materials design. 11B solid-state nuclear magnetic resonance (NMR) is a ubiquitous tool in the study of glasses and optical materials; here, density functional theory-based NMR crystallography guided the direct characterization of BO2 structural units. The full anisotropic shift and quadrupolar tensors of linear BO2 were extracted from K5Ba2(B10O17)2(BO2) containing BO2, BO3, and BO4 and serve as guides to the identification of this powerful moiety in future and, potentially, previously-characterized borate minerals, ceramics, and glasses.
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Introduction
Borates are in the spotlight owing to their extended structural diversity and broad applications in the design of photonic and optoelectronic devices1,2,3,4,5, nuclear waste separation and sequestration6,7, commercial glasses8,9, amorphous oxide catalysts10,11, as well as Li-ion12,13 and Mg-ion14,15 rechargeable batteries. Consequently, considerable effort has been put toward the search for borates with distinctive atomic structures and properties16,17,18,19,20,21,22. For borate-based nonlinear optical materials, (i) absorption edge energy, (ii) birefringence, and (iii) nonlinear optical coefficient are the three critical parameters. They are mainly affected by the electronic properties of the microscopic B–O basic units, especially for the alkali and/or alkaline earth metal borates (abbreviated as A-borates)23,24,25,26. Anionic group theory provides the basis for the structure–property relationships27. That is to say, the limits of the optical properties of borates lie in the capability of the microscopic units to produce a large bandgap, polarizability anisotropy, and hyperpolarizability18. Thus, the maximum thresholds of bandgap, birefringence, and nonlinear optical coefficient of A-borates comprising BO3 and BO4 units, are ~150 nm, ~0.07@1064 nm, and ~0.64 pm/V, respectively, assuming all the basic units are in optimally aligned configurations18,27. However, compounds with a higher absorption edge energy (lower wavelength), larger birefringence, and larger nonlinear optical coefficient are required to enable smaller optical devices leading to new uses and increased efficiency in industrial and scientific applications. For example, birefringent materials are essential for modulating polarized light and thus underpin critical optical devices such as beam-splitting polarizers for microscopes and isolators, circulators, and interleavers used in fiber optics for telecommunications18. The realization of strategies to push the current limitations of A-borates is still a grand challenge in the field of optical materials.
Vacant p orbitals in boron cause it to behave as an electron pair acceptor to interact with oxygen nucleophiles and form sp, sp2, and sp3 hybridized chemical bonds to construct linear BO2, triangular BO3, and tetrahedral BO4 basic units. Despite the nearly 300 natural borate minerals, 3000 borate crystals, and extensive glass research on non-crystalline alkali borates, the structure models are almost exclusively built up from the BO3 and BO4 polyhedra. Even, linear BO2 units are rare and have only been observed in apatite-type A10(PO4)6–x–y(SiO4)x(BO4)y(BO2) and Gd4(BO2)O5F28,29,30,31. It should be noted that the apatite compounds contain atomic disorder and the two isolated Gd4(BO2)O5F crystals are twinned31. Thus, among the thousands of borates, there is an absence of studies of borate-based optical materials with BO2 units. Structurally, the realization of borates with the BO2 functionality will dramatically enrich the structural diversity of this technologically important family of materials and offer a path toward improving the three critical optical parameters in A-borates. This basis stimulates the exploration of A-borates with BO2 configurations and routes toward a more fundamental understanding of the origin of this unique building unit.
Herein, a mixed metal borate K5Ba2(B10O17)2(BO2) with BO2 units was obtained. Boron solid-state nuclear magnetic resonance (NMR) spectroscopy has long been a core characterization tool in the study of borate crystals32,33 and glasses34,35. The resonances ascribed to BO4 units are observed from 2 to –4 ppm and are narrow due to their small quadrupolar coupling constants of typically <1 MHz while the resonances ascribed to BO3 units appear from 12 to 19 ppm and are broader with quadrupolar coupling constants of 2–3 MHz34,36,37. Differences in the number of non-bridging oxygen atoms within a given local coordination can often be determined through careful analysis of 11B shielding33,38. The 11B spectral characteristics of linear BO2 observed here in K5Ba2(B10O17)2(BO2) do not follow the chemical shift trend but rather are unique in the anisotropy of the shielding interaction. The ordered, diamagnetic structure enables clear identification of BO2 even in the presence of BO3 and BO4 units. The solid-state NMR signatures of the 11 distinct boron sites in K5Ba2(B10O17)2(BO2) are examined from multifield experimental spectra recorded under static and magic-angle spinning conditions through the support of DFT calculations and multiple-quantum magic-angle spinning (MQMAS) experiments.
K5Ba2(B10O17)2(BO2) expands the frontiers of structural diversity and functionality. Structurally, this is the first compound that contains all three borate motifs simultaneously, namely linear BO2, trigonal BO3, and tetrahedral BO4. The BO2 units have the largest polarizability anisotropy, and thus push the maximum thresholds of birefringence in A-borates to 0.18@1064 nm, which is much higher than can be attained in compounds with only BO3 and BO4. Such a large theoretical birefringence from this motif sets a target for the design of optical materials.
Results and discussion
Crystal structure of K5Ba2(B10O17)2(BO2)
Single crystals of K5Ba2(B10O17)2(BO2) were obtained (Supplementary Fig. 1) by a high-temperature solution method in an open system, and a phase-pure polycrystalline sample was obtained by a stoichiometric solid-state reaction. The crystal structure was solved and refined from single-crystal X-ray diffraction (XRD) data. K5Ba2(B10O17)2(BO2) crystallizes in the triclinic crystal system in space group \(P\bar{1}\) (Supplementary Table 1). The crystal structure of K5Ba2(B10O17)2(BO2) features two dimensional (2D) 2[B10O17]∞ double layers with K- and Ba-based polyhedra residing in the tunnels and interlayers (Fig. 1). The asymmetric unit of K5Ba2(B10O17)2(BO2) contains three, one, eleven, and eighteen crystallographically independent K, Ba, B, and O atoms, respectively (Supplementary Table 2). With respect to the B–O polyanionic framework, the B(11) atom resides in linear BO2 coordination, while B(1, 2, 4, 6, 8, 9) atoms sit in trigonal BO3 sites and B(3, 5, 7, 10) have tetrahedral oxygen coordination (Fig. 1a and Supplementary Table 2). The B–O bond lengths in BO2 (1.255 Å) are shorter than the mean values of BO3 (1.385 Å) and BO4 (1.475 Å), respectively, and the O–B–O angle refined to 180°, which conforms to sp hybridization. The geometries of BO3 and BO4 here are consistent with those of reported borates28,29,30,31,39,40,41,42. In K5Ba2(B10O17)2(BO2), three BO3 and two BO4 units form a B5O11 ring, which is further linked to form a B10O21 double ring by sharing a common O(7) atom. The double rings spread out over the ac- plane by sharing terminal O atoms to construct a 2[B5O9]∞ infinite layer, then adjacent layers further link to form a 2[B10O17]∞ double layer (Fig. 1c). The double layers are stacked along the [010] direction in the –AAAA– sequence and held together via electrostatic K–O and Ba–O interactions (Fig. 1b). Topologically, the structural framework of K5Ba2(B10O17)2(BO2) can be simplified to a four-connected unimodal net with the Schläfli symbol {48·62}, in which the B5O11 single ring is considered as the four-connected node. According to the rules proposed by Xue et al.2, the linear BO2 unit can be denoted by the letter ‘L’, and the algebraic description of the title compound can be written as {11:2∞[2 < 3∆+2 T>]&L}.
Solid-state nuclear magnetic resonance spectroscopy of K5Ba2(B10O17)2(BO2)
Multifield 11B static and magic-angle spinning (MAS) NMR spectroscopy, aided by DFT calculations of the chemical shielding and quadrupolar coupling, was used to study the local structure of the boron moieties and to gain fundamental physical insights into the anisotropy of the BO2 site (Fig. 2, Supplementary Fig. 2). The signal centered about 1.5 ppm in the MAS spectra (Fig. 2a, Supplementary Fig. 2a) was ascribed to the four overlapped BO4 resonances predicted from DFT32,34. This low-frequency signal is better resolved at a high magnetic field (Supplementary Fig. 2a) and is resolved into three distinct sites (in 2:1:1 ratio) by multiple-quantum MAS (MQMAS) (Supplementary Figs. 3–4)43, confirming the expected number of distinct BO4 sites. The low-field (9.4 T) MAS spectrum also revealed a broad shoulder centered about 13 ppm that is characteristic of BO333. This feature is nearly baseline-resolved at high field (16.4 T, Supplementary Fig. 2a). The overall MAS lineshapes could almost be reproduced by performing numerical simulations of the shift and quadrupolar parameters of the four BO4 and six BO3 sites directly from DFT calculations of the K5Ba2(B10O17)2(BO2) XRD structure model. Owing to a large number of adjustable shift and quadrupolar parameters from the ten overlapping distinct BO4 and BO3 crystallographic sites, all parameters except the isotropic shift were fixed to their calculated values and not refined in the fit (see Supplementary Table 5). However, after calculating the overall lineshape from BO3 and BO4 contributions, a small feature resembling a powder ‘horn’ line-shape was unaccounted for, which is most distinct at –12 ppm in the low-field MAS data where it does not overlap with other boron sites. Turning to the static 11B spectra, the BO4 and BO3 regions are poorly resolved due to the presence of broadening from chemical shift anisotropy (CSA), dipolar, and second-order quadrupolar interactions. Meanwhile, small but distinct features were observed at ca. 100 and –110 ppm at low field (Fig. 2b) and ca. 80 ppm at high field (Supplementary Fig. 2b), outside the expected range for known borates. DFT calculations predicted a relatively large CQ for BO2 but within the same range as BO3; the CSA of BO2, on the other hand, was calculated to be an order of magnitude larger than those of BO3 and BO4 units32. Finally, the calculated shift of 9 to 10 ppm is intermediate between BO4 at lower frequency and BO3 at higher frequency. A simulated lineshape based on the DFT-calculated CSA and quadrupolar parameters for the B(11) (BO2) site agrees well with the unexplained features in the MAS and static spectra. Allowing the lineshape to be refined against the experimental data yielded an isotropic shift of 13.5(3) ppm, a reduced CSA (Haeberlen convention, see “Methods”) of –123(3) ppm, a quadrupolar coupling constant of 3.31(5) MHz, asymmetries near zero, and coincident shielding and quadrupolar tensors aligned along O–B–O (Fig. 2, Supplementary Figs. 2, 5, and 6, and Supplementary Table 5). The BO2 site could not be detected in the MQMAS spectrum due to its low intensity and large CQ44,45; however, the BO3 and BO4 resonances gave good agreement with the DFT-calculated NMR parameters for the K5Ba2(B10O17)2(BO2) structure model. That the observed CQ and CSA were smaller than the calculated values for the BO2 B(11) site—and B(11) only—is an indication of partial averaging from dynamics within this isolated (i.e., not covalently bound) moiety46. This observation is in agreement with the diffraction-derived atomic displacement parameters of B(11) and O(17) from BO2 being approximately a factor of three larger than all the other boron and oxygen atoms for which motion is restricted within the polymeric borate framework.
The intermediate 11B shift of BO2 is unexpected and does not follow the trend of, e.g., 27Al in aluminates wherein the shift increases as the coordination number decreases (δ 27Al: AlO4 > AlO5 > AlO6)47. However, the origin of the intermediate shift can be explained by a change in bonding from B–O single bonds in BO4 and BO3 to B = O double bonds in BO2. Note that O=B=O has a formal negative charge on the boron center. The borate NMR picture is consistent with the isoelectronic carbon analogues: The 13C shift of CO2 (126–129 ppm) is shielded relative to CO3 (163–171 ppm)48,49. Moreover, the large CSA of BO2 (–123(3) ppm) is analogous to the large CSA of CO2 (–210 ppm)50, further highlighting the similarities between these two species. Finally, the shift and quadrupolar asymmetry parameters ηCSA and ηQ, respectively, for the central atom of a linear species with D∞h symmetry should be zero (δXX = δYY; VXX = VYY). An ηCSA of zero was found for solid 13CO2 within experimental uncertainty47. Similarly, ηCSA and ηQ for 11BO2 in K5Ba2(B10O17)2(BO2) were calculated to be slightly above zero due to interactions with neighboring atoms and were observed to be zero or near zero within the experimental uncertainty.
The chemical shift anisotropy is by far the most distinctive NMR feature of the elusive BO2 moiety and thus careful experiments are required to take advantage of this characteristic. Acquiring high signal-to-noise and performing measurements at multiple magnetic field strengths is useful to differentiate line broadening arising from CSA versus the quadrupolar interaction. Furthermore, magic-angle spinning effectively averages CSA but only partially averages second-order quadrupolar interactions, so it is useful to compare static and MAS spectra. The 11B parameters of the BO2 site are consistent between considerations of symmetry and bonding, DFT calculations, and experimental lineshapes across multiple magnetic field strengths and MAS/static conditions. It was possible to identify the linear BO2 unit in K5Ba2(B10O17)2(BO2) although it only comprises 1/21 of the boron atoms in the structure and thus 5 % of the integrated intensity, which is distributed over a broad frequency range. Extending these principles beyond this compound, solid-state 11B NMR, as well as 17O NMR (see Supplementary NMR Discussion in the Supporting Information), may serve as powerful tools for the identification of BO2 groups in borates even in the absence of atomically ordered single crystals.
Spectral analysis and optical properties combining theory and experiment
The infrared spectrum measurement and vibrational modes calculation of K5Ba2(B10O17)2(BO2) were respectively performed to further confirm the coordination environment of the B atoms. Clearly, the experimental infrared spectrum matches well with the first-principles calculations (Supplementary Fig. 7). In the upper range of both spectra (4000–2500 cm–1), no vibrational bands caused by OH− or H2O were detectable, which is consistent with the results concluded from the single-crystal data. With respect to the linear BO2 units, the weak peak at 2009 cm–1 and the strong peak at 1938 cm–1 are assigned to the 10B–O and 11B–O stretch in the linear B(11)O2 units29. K5Ba2(B10O17)2(BO2) is stable up to 732 °C (see TG–DSC curves and powder XRD patterns, Supplementary Fig. 8), thus sizable single crystals should be grown below this decomposition temperature. The UV−vis−NIR spectrum measured from a polycrystalline sample shows that the reflectance at 190 nm is still about 16.5% and thus its UV cutoff edge is shorter than 190 nm (corresponding to a bandgap larger than 6.52 eV) (Supplementary Fig. 9). Theoretical analysis indicates that K5Ba2(B10O17)2(BO2) has an indirect bandgap of 6.21 eV when calculated with a hybrid (HSE06) functional. With pure DFT, the predicted band gap is only 4.61 eV (Supplementary Fig. 10). This well-known underestimation mainly results from the approximation of exchange-correlation energy under DFT methods; nevertheless, it is useful for qualitative analysis51. The electronic transitions among the states near the Fermi level were analyzed. The top of the valence band is mainly composed of O 2p orbitals (Supplementary Fig. 11). The O 2p orbitals from the linear BO2 units are located deeper in the valence band than those in the 2[B10O17]∞ framework (Fig. 3a–c). In order to further probe the effect of the BO2 units on the electronic structure, the polarizability anisotropy and HOMO–LUMO bandgap were calculated for BO2, BO3, and BO4 units (Fig. 3d). The HOMO–LUMO bandgap of BO2 is larger than that of BO3 but smaller than that of BO4. More importantly, the polarizability anisotropy of BO2 is even larger than those of BO3 and BO4. Thus, larger birefringence, as determined by polarizability anisotropy, can be expected in BO2-containing borates. Structurally, the linear BO2 units can replace the position of halide ions in the related apatite structure28,29,30,31. In order to probe the structure–function relationship of BO2 units on the optical properties, BO2 was computationally substituted for halide ions (Cl–, Br–) to generate the isostructural halides of K5Ba2(B10O17)2(BO2), namely, K5Ba2(B10O17)2Cl, and K5Ba2(B10O17)2Br. Results show that the halides exhibit similar bandgaps (Supplementary Figs. 10 and 12) but smaller birefringence (0.057@1064 nm) than K5Ba2(B10O17)2(BO2) (0.062@1064 nm) (Supplementary Fig. 13). The birefringence enhancement from BO2 units is small due to the low density (1/21) of the boron sites in K5Ba2(B10O17)2(BO2). Facing this, we postulate that a borate with a high density of BO2 units would be a suitable candidate for a material with a wide bandgap and large birefringence. To test this hypothesis, a structure comprising solely BO2 units was investigated: K(BO2) (Figs. 3e, 3f). In the phonon spectrum of K(BO2), there are no soft modes at any wave vectors and no imaginary phonon modes are observed (Fig. 3g), demonstrating that K(BO2) is dynamically stable. The bandgap is 6.11 eV (HSE06 hybrid functional) and the birefringence is 0.18@1064 nm. This birefringence is larger than that of any previously reported A-borate, including Ca(BO2)2 (0.124@1064 nm) comprising infinite chains of co-planar BO3 trigonal rings52. The predicted birefringence in K(BO2) would lead to higher-efficiency beam splitting in light polarization processes across telecommunications and scientific instrumentation applications and provide enhanced ability to create and control polarized light. The BO2 functionality could enable optical capabilities, specifically in the rarely accessible deep UV range, and thus sets a target for synthetic crystal growth.
In summary, a mixed metal borate K5Ba2(B10O17)2(BO2) with linear BO2 units was obtained successfully. It also presents as the first compound that contains all three available B–O bonding motifs: BO2, BO3, and BO4 units. Solid-state 11B NMR spectroscopy unequivocally identified the nature of the BO2 units in K5Ba2(B10O17)2(BO2) and the experimental and calculated NMR parameters provide a quantitative basis for the future identification of BO2 units in polycrystalline and non-crystalline samples. The beneficial role of BO2 units on the bandgap and birefringence in K5Ba2(B10O17)2(BO2) were discussed and a model, K(BO2), with only BO2 units was designed and analyzed theoretically to motivate future directions for deep UV optical materials. Aligned BO2 units with the highest polarizability anisotropy push the maximum thresholds of birefringence in A-borates to 0.18@1064 nm—far beyond the birefringence limit with only BO3 and BO4. K5Ba2(B10O17)2(BO2) expands the frontiers of complex borate chemistry while the unique properties and spectroscopic characterization of the elusive BO2 unit motivate and provide a methodology for its broader study.
Methods
Synthesis and crystal growth
KNO3 (aladdin, 99.5%), Ba(NO3)2 (aladdin, 99.5%), K2CO3 (aladdin, 99.0%), B2O3 (aladdin, 99.9%) and H3BO3 (aladdin, 99.5%) were used as received. Single crystals of K5Ba2(B10O17)2(BO2) were grown by the high-temperature solution method. A mixture of KNO3 (0.379 g, 3.75 mmol), Ba(NO3)2 (0.392 g, 1.50 mmol), and B2O3 (0.548 g, 7.87 mmol) were loaded into a platinum crucible. The crucible was heated to 830 °C in 10 h, and held at this temperature for 17 h, and then cooled to 30 °C with a rate of 1.5 °C/h. Colorless and block-shaped crystals of K5Ba2(B10O17)2(BO2) were obtained and manually picked out from the crucible for structural characterization (Supplementary Fig. 1). Polycrystalline samples of K5Ba2(B10O17)2(BO2) can also be obtained by the lower temperature through solid-state reaction based on the following reaction: 2.5K2CO3 + 2Ba(NO3)2 + 21H3BO3 → K5Ba2(B10O17)2(BO2) + 2.5CO2↑ + 4NO2↑ + 31.5H2O↑. A mixture of K2CO3, Ba(NO3)2, and H3BO3 was preheated at 200 °C for 10 h. After that, the temperature was gradually raised to 700 °C with several intermediate grindings and mixings, and then held at a selected temperature for 24 h. The powder XRD pattern of the polycrystalline samples matches well with the one calculated from single-crystal XRD analysis except for some preferred orientation peaks.
Characterization
Single-crystal XRD data were collected on a Bruker SMART APEX II 4 K CCD diffractometer using Mo Kα radiation (λ = 0.71073 Å) at room temperature. Data integration, cell refinement, and absorption corrections were carried out with the program SAINT53. The structure was solved by direct methods and refined on F2 by full-matrix least-squares techniques using the program suite SHELXTL54. Solutions were checked for missed symmetry using PLATON. The crystal data give Rint = 0.0249 and the structure solution parameters are R1 = 0.0340, wR2 = 0.0812, GOF = 1.077. Powder XRD data were collected with a Bruker D2 PHASER diffractometer (Cu Kα radiation with λ = 1.5418 Å, 2θ = 5–70°, scan step width = 0.02 °, and counting time = 1 s/step). During the structure analysis, we found that K(3) and Ba(1) can also be set to share the same sites with the corresponding Ba and K (occupancies of about 97 and 92%, respectively.). But, it has no effect on the B-O framework, thus, in order to build an ideal model to study the BO2 units, a disorder-free model was considered. Thermal gravimetric (TG) and differential scanning calorimetry (DSC) measurements were carried out on a simultaneous NETZSCH STA 449 F3 thermal analyzer instrument in a flowing N2 atmosphere. The sample was placed in Pt crucible, heated from 40 to 900 °C at a rate of 5 °C/min. Infrared spectroscopy was carried out on a Shimadzu IR Affinity-1 Fourier transform infrared spectrometer in the 400–4000 cm–1 range. UV–vis–NIR diffuse-reflectance spectroscopy data in the wavelength range of 190–2600 nm were recorded at room temperature using a powder sample of K5Ba2(B10O17)2(BO2) on a Shimadzu SolidSpec-3700DUV spectrophotometer. 11B MAS NMR experiments were performed in static magnetic fields of 9.4 and 16.4 T on Bruker Avance spectrometers at 11B Larmor frequencies of 128.25 MHz or 224.60 MHz, respectively. MAS 11B NMR spectra were recorded with a single non-selective excitation pulse in a 1.6 mm Phoenix probe (9.4 T) or Bruker 4.0 mm probe (16.4 T) using a short pulse length in an effort to obtain quantitative results under quadrupolar nutation. Static spectra were recorded under similar conditions with the exception of a spin-echo pulse sequence at 16.4 T to mitigate probe background. For the MAS spectra, 2400 scans were acquired with a recycle delay of 40 s (9.4 T) and 16 scans with a recycle delay of 0.25 s (16.4 T); for the static spectra, 768 scans were acquired with a recycle delay of 5 s (9.4 T) and 65,536 scans with a recycle delay of 1 s (16.4 T). The measured T1, integrated over the overlapped resonances from 19 to –2 ppm, was 6.0 s (via saturation recovery) but no difference was seen in the lineshape for recycle delays from 0.02 to 90 s. Experimental details for MQMAS experiments are given in Supplementary Figs. 3 and 4. Lineshape simulations were performed in the Solid Lineshape Analysis program in Bruker TopSpin 3.6.1. 11B isotropic shifts were externally referenced to 0.1 M aqueous H3BO3 at 19.6 ppm37. In this work, the Haeberlen convention is used to describe the chemical shift tensor in terms of the isotropic shift (δiso), chemical shift anisotropy (δCSA, sometimes called the reduced CSA), and shift asymmetry parameter (ηCSA)55,56,57. In terms of the principal components of the shift tensor (δXX, δYY, and δZZ):
and the principal components are ordered such that \(\left|{\delta }_{{{ZZ}}}-{\delta }_{{{iso}}}\right|\ge \left|{\delta }_{{{XX}}}-{\delta }_{{{iso}}}\right| > \left|{\delta }_{{{YY}}}-{\delta }_{{{iso}}}\right|\). The quadrupolar tensor is described by the nuclear quadrupolar coupling constant (CQ) and quadrupolar asymmetry parameter (ηQ). In terms of the principal components of the electric field gradient (VXX, VYY, VZZ):
where e is the electric charge, Q is the nuclear quadrupole moment, and h is Planck’s constant.
Computational methods
The electronic structure as well as optical property calculations were performed by employing CASTEP58, a plane-wave pseudopotential DFT package, with the norm-conserving pseudopotentials (NCP)59. The Perdew–Burke–Ernzerhof (PBE) functional within the generalized gradient approximation (GGA) was used.60 The plane-wave energy cutoff was set at 850 eV. NMR calculations utilized ultrasoft pseudopotentials generated “on-the-fly” in CASTEP61,62. The all-electron magnetic response was calculated with the gauge-including projector-augmented wave (GIPAW) method63. Self-consistent field (SCF) calculations were performed with a convergence criterion of 1 × 10−6 eV/atom on the total energy. The k-point separation was set as 2π × 0.04 Å–1 in the Brillouin zone corresponding to primitive cell, resulting in Monkhorst–Pack k-point meshes of 4 × 3 × 4. In addition, we also calculated bandgaps adopting the nonlocal exchange functional HSE06 a widely used hybrid functional with relatively high efficiency in calculating bandgaps64. The HSE XC functional energy is calculated as follows,
In HSE06, the parameters are suggested as a = 0.25 and ω = 0.11 bohr–1.
Data availability
All the characterization data and experimental protocols are provided in this article and its Supplementary Information. The X-ray crystallographic coordinates for structures reported in this study have been deposited at the Cambridge Crystallographic Data Centre (CCDC), under deposition numbers 1845847. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.”
References
Becker, P. Borate materials in nonlinear optics. Adv. Mater. 10, 979–992 (1998).
Yuan, G. & Xue, D. Crystal chemistry of borates: the classification and algebraic description by topological type of fundamental building blocks. Acta Crystallogr. B 63, 353–362 (2007).
Chen, C. et al. Nonlinear Optical Borate Crystals: Principles and Applications (Wiley-VCH, Weinheim, 2012).
Sasaki, T., Mori, Y., Yoshimura, M., Yap, Y. & Kamimura, T. Recent development of nonlinear optical borate crystals: key materials for generation of visible and UV light. Mater. Sci. Eng. R. 30, 1–54 (2000).
Shi, G. et al. Finding the next deep-ultraviolet nonlinear optical material: NH4B4O6F. J. Am. Chem. Soc. 139, 10645–10648 (2017).
Polinski, M. et al. Unusual structure, bonding and properties in a californium borate. Nat. Chem. 6, 387–392 (2014).
Yin, X. et al. Rare earth separations by selective borate crystallization. Nat. Commun. 8, 14438 (2017).
Volkova, E. A., Naprasnikov, D. A. & Leonyuk, N. I. Thin films and glass-ceramic composites of huntite borates family: a brief review. Crystals 10, 487–496 (2020).
Micoulaut, M. Relaxation and physical aging in network glasses: a review. Rep. Prog. Phys. 79, 066504 (2016).
Dincă, M., Surendranath, Y. & Nocera, D. G. Nickel-borate oxygen-evolving catalyst that functions under benign conditions. Proc. Natl Acad. Sci. USA 107, 10337–10341 (2010).
Tan, T., Han, P., Cong, H., Cheng, G. & Luo, W. An amorphous cobalt borate nanosheet-coated cobalt boride hybrid for highly efficient alkaline water oxidation reaction. ACS Sustain. Chem. Eng. 7, 5620–5625 (2019).
Yamada, A. et al. Lithium iron borates as high-capacity battery electrodes. Adv. Mater. 22, 3583–3587 (2010).
Janssen, Y., Middlemiss, D. S., Bo, S. H., Grey, C. P. & Khalifah, P. G. Structural modulation in the high capacity battery cathode material LiFeBO3. J. Am. Chem. Soc. 134, 12516–12527 (2012).
Bo, S. H., Grey, C. P. & Khalifah, P. G. Defect-tolerant diffusion channels for Mg2+ ions in ribbon-type borates: structural insights into potential battery cathodes MgVBO4 and MgxFe2–xB2O5. Chem. Mater. 27, 4630–4639 (2015).
Glass, H. F. J. et al. MgxMn2–xB2O5 pyroborates (2/3 ≤ x ≤ 4/3): high capacity and high rate cathodes for Li-ion batteries. Chem. Mater. 29, 3118–3125 (2017).
Chen, C. et al. Design and synthesis of an ultraviolet-transparent nonlinear optical crystal Sr2Be2B2O7. Nature 373, 322–324 (1995).
Li, L., Li, G., Wang, Y., Liao, F. & Lin, J. Bismuth borates: one-dimensional borate chains and nonlinear optical properties. Chem. Mater. 17, 4174–4180 (2005).
Mutailipu, M., Poeppelmeier, K. R. & Pan, S. L. Borates: a rich source for optical materials. Chem. Rev. 121, 1130–1202 (2021).
Merlino, S. & Sartori, F. Ammonioborite: new borate polyion and its structure. Science 171, 377–379 (1971).
Mutailipu, M., Zhang, M., Yang, Z. & Pan, S. Targeting the next generation of deep-ultraviolet nonlinear optical materials: expanding from borates, borate fluorides to fluorooxoborates. Acc. Chem. Res. 52, 791–801 (2019).
Chi, Y. et al. Triple-Kagomé-layer slabs of mixed-valence rare-earth ions exhibiting quantum spin liquid behaviors: synthesis and characterization of Eu9MgS2B20O41. J. Am. Chem. Soc. 141, 9533–9536 (2019).
Shi, Z.-H., Chi, Y., Yang, M., Liu, W. & Guo, S.-P. A series of chalcogenide borates RE6Ta2MgQB8O26 (RE = Sm, Eu, Gd; Q = S, Se) featuring a B4O10 cluster. Inorg. Chem. 59, 3532–3536 (2020).
Belokoneva, E. L. Borate crystal chemistry in terms of the extended OD theory: topology and symmetry analysis. Crystallogr. Rev. 11, 151–198 (2005).
Tran, T., Koocher, Z., Rondinelli, M. & Halasyamani, P. Beryllium‐free β‐Rb2Al2B2O7 as a possible deep‐ultraviolet nonlinear optical material replacement for KBe2BO3F2. Angew. Chem. Int. Ed. 56, 2969–2973 (2017).
Halasyamani, P. S. & Rondinelli, J. M. The must-have and nice-to-have experimental and computational requirements for functional frequency doubling deep-UV crystals. Nat. Commun. 9, 2972 (2018).
Kong, F., Huang, S., Sun, Z., Mao, J. & Cheng, W. Se2(B2O7): a new type of second-order NLO material. J. Am. Chem. Soc. 128, 7750–7751 (2006).
Chen, C., Wu, Y. & Li, R. The anionic group theory of the non-linear optical effect and its applications in the development of new high-quality NLO crystals in the borate series. Int. Rev. Phys. Chem. 8, 65–91 (1989).
Calvo, C. & Faggiani, R. Linear metaborate anions, BO2–, in apatitic phosphates. J. Chem. Soc., Chem. Commun. 17, 714–715 (1974).
Chen, S. et al. Sr10[(PO4)5.5(BO4)0.5](BO2): growth and crystal structure of a strontium phosphate orthoborate metaborate closely related to the apatite-type crystal structure. J. Solid State Chem. 183, 658–661 (2010).
Ci, Z. et al. The structure, photoluminescence and thermal properties of Ce3+, Mn2+ co-doped phosphosilicate Sr7La3[(PO4)2.5(SiO4)3(BO4)0.5](BO2) emission-tunable phosphor. J. Mater. Chem. C 2, 5850–5856 (2014).
Höppe, H. A. Gd4(BO2)O5F–a gadolinium borate fluoride oxide comprising a linear BO2 moiety. Z. Naturforsch. 70, 769–774 (2015).
Angel, Y. T. & Bryce, W. D. L. Chapter four-recent advances in 11B solid-state nuclear magnetic resonance spectroscopy of crystalline solids. Annu. Rep. NMR Spectrosc. 93, 213–279 (2018).
Kroeker, Scott & Stebbins, J. F. Three-coordinated boron-11 chemical shifts in borates. Inorg. Chem. 40, 6239–6246 (2001).
Edén, M. NMR studies of oxide-based glasses. Annu. Rep. Prog. Chem., Sect. C: Phys. Chem. 108, 177–221 (2012).
Eckert, H. Structural characterization of noncrystalline solids and glasses using solid state NMR. Prog. Nucl. Magn. Reson. Spectrosc. 24, 159–293 (1992).
Alderman, O. L. G. et al. Spectral assignments and NMR parameter-structure relationships in borates using high-resolution 11B NMR and density functional theory. Phys. Chem. Chem. Phys. 15, 8208–8221 (2013).
Hansen, M. R., Madsen, G. K. H., Jakobsen, H. J. & Skibsted, J. Refinement of borate structures from 11B MAS NMR spectroscopy and density functional theory calculations of 11B electric field gradients. J. Phys. Chem. A 109, 1989–1997 (2005).
Soleilhavoup, A., Delaye, J. M., Angeli, F., Caurant, D. & Charpentier, T. Contribution of first-principles calculations to multinuclear NMR analysis of borosilicate glasses. Magn. Reson. Chem. 48, 159–170 (2010).
McMillen, C. D., Stritzinger, J. T. & Kolis, J. W. Two novel acentric borate fluorides: M3B6O11F2 (M = Sr, Ba). Inorg. Chem. 51, 3953–3855 (2012).
Wang, J. et al. Na2B10O17·H2en: a three-dimensional open-framework layered borate co-templated by inorganic cations and organic amines. Chem. Commun. 51, 5066–5068 (2015).
Peng, G. et al. NH4Be2BO3F2 and γ-Be2BO3F: overcoming the layering habit in KBe2BO3F2 for the next generation deep-ultraviolet nonlinear optical materials. Angew. Chem. Int. Ed. 57, 8968–8972 (2018).
Zhao, S. et al. Beryllium-free Li4Sr(BO3)2 for deep-ultraviolet nonlinear optical applications. Nat. Commun. 5, 4019 (2014).
Medek, A., Harwood, J. S. & Frydman, L. Multiple-quantum magic-angle spinning NMR: a new method for the study of quadrupolar nuclei in solids. J. Am. Chem. Soc. 117, 12779–12787 (1995).
Zhang, X., Hu, L. & Ren, J. Structural studies of rare earth-doped fluoroborosilicate glasses by advanced solid-state NMR. J. Phys. Chem. C. 124, 8919–8929 (2020).
Hung, I. & Gan, Z. Low-power STMAS – breaking through the limit of large quadrupolar interactions in high-resolution solid-state NMR spectroscopy. Phys. Chem. Chem. Phys. 22, 21119–21123 (2020).
Nour, S. et al. Oxygen-17 NMR spectroscopy of water molecules in solid hydrates. Can. J. Chem. 94, 189–197 (2016).
MacKenzie, K. & Smith, M. E. Multinuclear Solid-State NMR of Inorganic Materials, Vol. 6 (Pergamon Press, 2002).
Forse, A. C. et al. Unexpected diffusion anisotropy of carbon dioxide in the metal–organic framework Zn2(dobpdc). J. Am. Chem. Soc. 140, 1663–1673 (2018).
Sevelsted, T. F., Herfort, D. & Skibsted, J. 13C chemical shift anisotropies for carbonate ions in cement minerals and the use of 13C, 27Al and 29Si MAS NMR in studies of Portland cement including limestone additions. Cem. Concr. Res. 52, 100–111 (2013).
Zheng, K., Fung, V., Yuan, X., Jiang, D. & Xie, J. Real time monitoring of the dynamic intracluster diffusion of single gold atoms into silver nanoclusters. J. Am. Chem. Soc. 141, 18977–18983 (2019).
Chan, M. & Ceder, G. Efficient band gap prediction for solids. Phys. Rev. Lett. 105, 196403–196406 (2010).
Chen, X. et al. Designing an excellent deep-ultraviolet birefringent material for light polarization. J. Am. Chem. Soc. 140, 16311–16319 (2018).
SAINT, Version 7.60A (Bruker Analytical X-ray Instruments, Inc., 2008).
Sheldrick, G. M. SHELXTL, Version 6.12 (Bruker Analytical X-ray Instruments, Inc., 2001).
Haeberlen, U. In Advances in Magnetic Resonance. Suppl. 1 (ed Waugh, J. S.) (Academic Press, 1976).
Mehring, M. Principles of High Resolution NMR in Solids. 2nd. edn. (Springer Verlag, 1983).
Spiess, H. W. In NMR Basic Principles and Progress Vol. 15 (eds Diehl, P., Fluck, E. & Kosfeld, R.) (Springer Verlag, 1978).
Segall, M. D. et al. First-principles simulation: ideas, illustrations and the CASTEP code. J. Phys. Condens. Matter 14, 2717–2744 (2002).
Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996).
Lin, J. S., Qteish, A., Payne, M. C. & Heine, V. Optimized and transferable nonlocal separable ab initio pseudopotentials. Phys. Rev. B 47, 4174–4180 (1993).
Yates, J. R., Pickard, C. J. & Mauri, F. Calculation of NMR chemical shifts for extended systems using ultrasoft pseudopotentials. Phys. Rev. B 76, 024401 (2007).
Profeta, M., Mauri, F. & Pickard, C. J. Accurate first principles prediction of 17O NMR parameters in SiO2: assignment of the zeolite ferrierite spectrum. J. Am. Chem. Soc. 125, 541–548 (2003).
Pickard, C. J. & Mauri, F. All-electron magnetic response with pseudopotentials: NMR chemical shifts. Phys. Rev. B 63, 245101 (2001).
Krukau, A. V., Vydrov, O. A., Izmaylov, A. F. & Scuseria, G. E. Influence of the exchange screening parameter on the performance of screened hybrid functionals. J. Chem. Phys. 125, 224106 (2006).
Acknowledgements
This work was financially supported by the National Natural Science Foundation of China (61922084, 52002397), the Science and Technology Service Network Initiative of CAS (KFJ-STS-QYZD-130), Xinjiang Tianshan Youth Program-Outstanding Young Science and Technology Talents (2019Q026), Tianshan Cedar Program of Scientific and Technological Talents (2018XS10), and Key Research Program of Frontier Sciences, CAS (ZDBS-LY-SLH035). This work made use of the IMSERC NMR facility at Northwestern University, which has received support from the National Science Foundation (NSF DMR-0521267), the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205), the State of Illinois, and the International Institute for Nanotechnology (IIN). K.J.G. and K.R.P. were supported as part of the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES).
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C. Huang grew the single crystals and solved the structure. M.M. performed the experiments, supporting characterization, and paper writing. F.Z. supervised the optical experiments. K.J.G. and J.M.G. performed the NMR experiments, calculations, and simulations. C. Hu and Z.Y. performed electronic structure and optical property calculations. K.R.P. and S.P. designed and supervised the study. All the authors discussed the results and commented on the manuscript.
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Huang, C., Mutailipu, M., Zhang, F. et al. Expanding the chemistry of borates with functional [BO2]− anions. Nat Commun 12, 2597 (2021). https://doi.org/10.1038/s41467-021-22835-4
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DOI: https://doi.org/10.1038/s41467-021-22835-4
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