Article pubs.acs.org/IC
Iodide-Iodates M3[IO3]12·Ag4I, M = Bi, Tb, with a Framework Structure and High Second-Harmonic Generation Optical Response Elena L. Belokoneva,*,† Sergey Yu. Stefanovich,‡ Olga V. Dimitrova,† Alina S. Karamysheva,† and Anatoly S. Volkov† †
Geological Faculty, Department of Crystallography, Lomonosov Moscow State University, Leninskije Gory 1, Moscow, 119992 GSP2, Russia ‡ Chemical Faculty, Laboratory of Functional Materials, Lomonosov Moscow State University, Leninskije Gory 1, Moscow, 119992 GSP2, Russia S Supporting Information *
ABSTRACT: Single crystals of two new iodide-iodates, Bi3[IO3]12·Ag4I and Tb3[IO3]12·Ag4I, are synthesized in hydrothermal systems. The anionic parts in both iodide-iodates are characterized as a complex charged framework of isolated IO3 umbrella-like groups and large Bi(Tb)−O polyhedra similar to those previously found in La3[IO3]12[IO3](Pb3O). Broad channels along the c-axis contain compensators: (Ag3I)2+ umbrella-like groups and additional Ag+ ions which form Ag44+ tetrahedral clusters augmented with I− halogen. New iodates possess significantly higher second-order nonlinear optical characteristics compared to the previously known lead-containing compounds REE3[IO3]12[IO3](Pb3O), REE = La, Pr, Nd. The difference is related to the polar ordering of umbrella-like (Ag3I)2+ groups in the channels in the new iodide-iodate. Additionally, planar-coordinated Ag atoms add three Ag atoms in umbrellas forming [Ag4I]3+ polar clusters in the channels.
■
INTRODUCTION Iodates belong to the inorganic compounds which possess a trigonal [IO3] anionic group, where the iodine atom with a nonbonded pair of electrons makes a vertex of a pyramid, and three oxygen atoms lie in its base. This geometry provides a strongly polar distribution of the electron density within the group. When the local environment and the asymmetric coordination of the groups are aligned in a crystal structure, they yield a polar material.1 Multiple metal iodate compounds have been obtained and investigated in the past decade in a search for possible materials with nonlinear optical, ferroelectric, pyroelectric, magnetic, and piezoelectric properties. The results of this search are summarized in reviews on structures and properties of functional metal iodates2 and in recent reports on second-order nonlinear optical materials based on metal iodates.3 Special attention is paid to synthesis and investigation of iodates containing lone pair cations Pb2+ or Bi3+ or large polarizable ions as Ag1+. The best results for high second-harmonic generation (SHG) activity are achieved for BiO(IO3)1 and also for α- and β-AgI3O8.4 A series of isostructural iodates, containing Ag-metal, AgY(IO3)4, AgGd(IO3)4, AgBi(IO3)4, was reported in ref 5; all of them belong to the structure type of NaY(IO3)4 discovered earlier6 and demonstrate nonlinear optical and piezoelectric properties. A combination of the anionic part of iodate and halide (chloride) component was found in Pb3(IO3)2Cl47 and in K2Bi(IO3)4Cl.8 Combinations of Bi and Ag metal in the iodate class of compounds looks promising for high optical nonlinearity. We © XXXX American Chemical Society
undertook a search for new representatives of this class in hydrothermal systems. This work describes synthesis of crystals, crystal structure investigations, measurements of nonlinear optical properties, crystal chemical analyses of new and related iodates, as well as a discussion of structure−properties relationships.
■
EXPERIMENTAL DETAILS
Hydrothermal Synthesis. Single crystals of new iodate-iodide Bi3[IO3]12·Ag4I were obtained under the hydrothermal conditions. All reagents were of analytical grade, AgNO3 (0.1 g, 0.6 mmol), NaNO3 (0.6 g, 7.1 mmol), Bi(NO3)3 (1 g, 2.5 mmol), LiIO3 (1 g, 5.5 mmol), and H3BO3 (0.6 g, 9.7 mmol), with their weight amounts corresponding to the ratio of 1:6:10:10:6. The same reagents were added to Tb(NO3)3 (0.6 g, 1.7 mmol) in the second experiment with their weight amounts corresponding to the ratio of 1:6:10:10:6:6. The weight ratio of solid and liquid phases was 1:5. The syntheses were performed at the temperature 270−280 °C under pressure of 70−100 atm. The experiments were carried out in standard autoclaves (volume 5−6 cm3) lined with Teflon. The lowest and the highest temperatures of the experiments were limited by kinetics of the hydrothermal reactions and the instrumental capabilities, respectively. Duration of the experiments (18−20 days) corresponded to the completion of the reaction. Final cooling after synthesis to the room temperature was done in 24 h. Grown crystals were isolated by filtration of the stock solution and washed with hot water. Received: September 14, 2016
A
DOI: 10.1021/acs.inorgchem.6b02191 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry Transparent small isometric lustrous crystals found in crystallization products in both experiments were faceted close to cubic symmetry and were colorless. The yield of the first experiment was ∼40%, and the yield was ∼15% for the second experiment. Aggregates of small individual crystals were present mainly in the first experiment. Compositions of the new phases were determined using a Jeol JSM6480LV scanning electronic microscope combined with WDX analysis. The test revealed the presence of Bi, Ag, I for one type of the crystals and Tb, Ag, I for the other. They were identified at this stage as Bi,Agand Tb,Ag-iodates, respectively. Crystals studied under an optical microscope reveal the habitus of Bi,Ag-iodate crystals (Figure 1),
the multiplier was measured with digital lock-in amplifier and then registered by PC to be compared with that of α-SiO2 powder standard sample. Powders of Bi,Ag- and Tb,Ag-iodates and SiO2 were in turn placed on a holder inside an optical chamber as was described elsewere.11 Large SHG response up to 480 SiO2 units was registered for the Bi,Agiodate (and up to 670 s.u. for coarser powder) while for its Tb,Agiodate counterpart the SHG signal was only a little smaller, about 400 SiO2 (up to 500 s.u. for coarser powder). Identity of grain size in the reference and a powder under investigation is the main condition for correct comparison of SHG optical activities. Under this condition, quantitative results for optical nonlinear coefficients may be obtained using easily attainable thin powders with grains smaller than the coherent length lc.11,12 In the case of isotropic oxides, lc is known to depend only on optical index dispersion, Δn. As far as lc = λω/4Δn,10 for Nd laser radiation with λω = 1064 nm, the dispersion for nonabsorbing in the visible oxide crystals typically is Δn ≈ 0.05−0.1, and that results in lc ≥ 0.003 mm. Birefringence in anisotropic crystals makes lc grow until it becomes infinity in phasematching substances. Therefore, in uncolored oxide powders with grain size L < lc, it is reasonable to neglect all effects of phase matching on SHG intensity I2ω. In this special case, a simple formula is applicable for space-averaged nonlinear coefficients ⟨d⟩ of substances A and B to be compared: I2ω(A)/I2ω(B) ≈ C{⟨d(A)⟩/ ⟨d(B)⟩}2. Coefficient C is a simple function of refractive indices11 and may be assumed as unity if refractivities of A and B are close. Averaging over the space of nonvanishing coefficients of a nonlinear third-rank tensor may be omitted if a pair of compared crystalline materials belong to one and the same crystal class and possess a similar matrix of coefficients. Otherwise, a correction up to 30% for determination of nonlinearity with the above formulas may be required.10 Crystal class 32 of α-quartz suggests matrices of third-rank coefficient where d11 = 0.364 pm/V is the only significant factor. Beside coefficient d11, the matrix in class 3m of Bi3[IO3]12·Ag4I and Tb3[IO3]12·Ag4I also includes independent coefficients d31 and d33, though these latter two are presumably smaller than d11 because of pseudocubic peculiarities. Supposing ⟨d⟩ ≈ d11, we estimate values of these nonlinear coefficients from ratios of SHG intensities for the 0.003−0.005 mm powders to be, correspondingly, 22 d11(SiO2) (7.7 pm/V) for Bi,Ag-iodate and 20 d11(SiO2) (7.0 pm/V) for Tb,Agiodate. These values are comparable with BiO(IO3) and KTP nonlinearity.13 However, a minor increase of the SHG activity for coarser powders of both Bi,Ag- and Tb,Ag-iodates indicates the absence of phasematching in these substances in full accordance with their pseudocubic morphology. Single-Crystal X-ray Diffraction and Structures. A transparent isometric lustrous crystal from the first experiment of size 0.075 × 0.0875 × 0.1 mm3 was glued on a glass fiber for single-crystal X-ray study. The unit cell of the new iodate was first determined as belonging to the cubic system and didn’t have any analogous compound in the ICSD Data Base. An Xcalibur S diffractometer equipped with a CCD area detector and graphite-monochromated Mo Kα radiation was used for the experimental data collection. The data was integrated using the CrysAlis program with the intensities corrected for the Lorentz and polarization factors. Cubic and trigonal symmetries were rejected by the program because of high Rint in averaging of intensities. Monoclinic symmetry was suggested with the cell parameters a = 15.5216(4) Å, b = 21.9490(3) Å, c = 13.4422(4) Å, β = 125.267(4)° and possible space group Cc which accorded to the positive SHG test. The model was found by the direct method determination using SHELXS.14a It included positions of 3 Bi, 12 I, and 36 O atoms as well as 4 Ag atoms and 1 additional I atom on the basis of the peak heights, interatomic distances, and temperature vibration parameters using SHELXL.14b The chemical formula of the new compound was Bi3[IO3]12·Ag4I. Despite a good final R = 0.048 and satisfied model with the normal atomic and temperature displacement parameters, the analysis of the structure drawn in the graphical program ATOMS15 revealed a distinct trigonal symmetry instead of a monoclinic one, with the c-axis of the monoclinic unit cell being the main direction. Analysis of the vectors in the direct space
Figure 1. Image of Bi3[IO3]12·Ag4I crystals. which corresponds to cubic morphology including facing of the tetragon-trioctahedra and rhombo-dodecahedra forms. Thin crystalline white powder prevailed in the crystallization products in both experiments was observed with powder X-ray diffraction data and by composition (Bi, I) as a recently discovered new phase BiO(IO3) with a very high optical nonlinearity.1 Indeed, in our SHG experiment this powder produced an intense doubled-frequency signal as high as 450 powder standard SiO2 units. One more satellite phase was found in the second hydrothermal synthesis as sufficiently large flattened colorless crystals typically with hatching. They were identified as the centrosymmetrical Tb(IO3)3 by means of powder X-ray diffraction data and confirmed by composition (Tb, I) analysis and absence of signal in a SHG experiment. The XRD patterns of two morphologically isometric crystals from two hydrothermal experiments were almost identical but had no analogues in the ICDD database (Figure S1a). After crystal structure determination (see below), indexing of reflections of experimental pattern was performed (Table S1), and a theoretical powder pattern (Figure S1b) was calculated on the basis of the.cif file using the STOE XPow program.9 The simulated pattern matches well with the experimentally registered one. Second-Harmonic Generation. For examination of the nonlinear optical properties, the isometric crystal aggregates were picked out by hand from the crystallization products. For production of thin powders, the crystalline aggregates were crushed with a pestle in a mortar filled with alcohol. The typical grain size of the powders was 0.003−0.005 mm and is exactly the same as that of the SiO2 powder used as a standard. Preparation of other grain-size powders was restricted due to small amounts of the crystals. Only one more fraction of a coarser powder was prepared without sieving, and there is detailed grain-size characterization for both Bi,Ag- and Tb,Ag-iodates. Careful control of powders by means of X-ray diffraction measurements excluded the presence of BiO(IO3) and other satellite phases. A test on second-harmonic generation was conducted using the Kurtz−Perry powder technique.10 A Minilite-I Nd:YAG laser, operated in Q-switched mode with repetition rate 10 Hz, was a source of radiation at λω = 1064 nm. The radiation was doubled to second harmonics, λ2ω = 532 nm, in materials under investigation. Green light of the second harmonics was collected in reflection and detected by a photomultiplier tube. In order to detect only light at 532 nm, a narrow band-pass interference filter was attached to the tube. The signal from B
DOI: 10.1021/acs.inorgchem.6b02191 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
In the new compound Bi3[IO3]12·Ag4I, only two atoms occupy special positions on the 3-fold axis (Table 2). Graphical visualization showed that the heaviest Bi atom positions in the pseudocubic unit cell correspond to the m3 point group and determine a strongly pronounced pseudosymmetry. Absorption of the crystal was not corrected because of the arbitrary form of the crystal which requests facing approximation with the distances to every face; insufficient accuracy of this procedure introduces mistakes comparable to necessary correction and does not give a positive result. Nevertheless, absorption was not high (μrav = 1.1) and did not influence the result. Flack parameter x = −0.014(5) stated the absolute configuration as correctly determined for a single crystal under investigation. Crystallographic data, atomic coordinates, and selected bonds for Bi3[IO3]12·Ag4I are presented in Tables 1−3. Single crystals from the second experiment with Tb were structurally tested as well. For the Tb,Ag,I- composition, the trigonal space group R3c was found by the CrysAlis program. Lower scattering power of Tb compared to Bi led to a less pronounced cubic pseudosymmetry and also confirmed the conclusion that the Bi(Tb) atoms are responsible for this effect. Experimental data was collected as before, and the calculations in SHELXL confirmed that Tb3[IO3]12· Ag4I is isostructural to Bi3[IO3]12·Ag4I with the Bi atom in its position replaced by Tb. Smaller ionic radius led not only to the significant smaller unit cell parameters of the Tb representative, a = 21.7997(3), c = 13.3019(2) Å, but also to a strong tendency to twinning. Introduction of a mirror plane m as a twin element in several orientations (100/010/001̅; 1̅00/01̅0/001; 110/1̅00/001) in the calculations using SHELXL14b with or without combinations with racemic twin did improve the result to R = 0.088 because (as we suppose) of several twin laws presenting simultaneously. There is no doubt that Bi,Ag- and Tb,Ag-iodide-iodates are new isostructural compounds.
between the pseudocubic and the monoclinic unit cells revealed only one true trigonal axis between four possible equivalents (Figure 2).
Figure 2. Correlation between cubic (bold), monoclinic, and trigonal axes in the hexagonal setting of Bi3[IO3]12·Ag4I crystal; stars represent a lattice node which is a center cubic cell (I), or a monoclinic cell (C). That hindered the correct choice of symmetry and unit cell by the CrysAlis program. The transformation matrix from monoclinic to trigonal axes, 0 1 0/−1.5 −0.5 −1.0/0 0 1, was used for recalculation and merging of reflection data in SHELXL as well as for calculation of the new a,c-axes. In the new R3c space group, the number of independent atoms was 3 times smaller. Final refinement using the least-squares procedure was carried out with the anisotropic approximation of thermal displacement for all the atoms using SHELXL14b (Table 1).
■
RESULTS AND DISCUSSION Structures. The new iodide-iodate Bi3[IO3]12·Ag4I is built of isolated umbrella-like IO3 groups. Interatomic distances I−O are very consistent (Table 3), average I−O = 1.820 Å. Bi atoms are coordinated by 8 O atoms at distances which vary from 2.310 to 2.570 Å with an absence of ordering of the short−long distances with respect to the polar c-axis. They are multiplied around the 3-fold axis, and together with the IO3 groups produce a framework with an open channel along the c-axis with a cross section of ∼5 Å. The channels are centered on the 3-fold axes (Figure 3 a). Ag1 atoms are located near the channel walls, thus giving two triplets (3-fold axis) at two heights (c-glide) along the c-axis. Every triplet has a central I5− atom which is shared among all three Ag1+ species. Together they form a large [(Ag1)3I5]2+ umbrella oriented along the c-axis in a polar way as is shown by the ball−stick presentation in Figure 3b. Along the identity period, two umbrellas alternating with two Ag2+, and 3 Ag1+ and 1 Ag2+, built a large tetrahedral cluster (Ag4)4+ with distances Ag1−Ag1 ∼ 4.4 and Ag1−Ag2 ∼ 3.8 Å. Ag1 atom coordination includes one I5 and four O atoms from the wall side; Ag2 has an unusual coordination of six O atoms located approximately in the same plane as Ag2 added by I5 along the c-axis in the form of a pseudohexagonal pyramid (Table 3). Deviation of zO1 of the zAg2 level is 0.0192 or 0.26 Å up to the caxis; deviation of zO12 of the zAg2 level is 0.043 or 0.54 Å down the c-axis, and that is in common with a flat hexagon. Thus, the Ag2 atom is loosely bonded in the channel especially along the polar c-axis. The filling of the channel, which compensates for the framework’s charge, may be described in general as alternation of polar umbrellas [(Ag1)3I5]2+ and a single Ag2+. Being in the channel, both Ag atoms demonstrate increased temperature vibration parameters especially along the polar c-
Table 1. Crystal Data and Structure Refinement for Bi3[IO3]12·Ag4I formula
Bi3[IO3]12·Ag4I
formula weight (g/mol) T (K) cryst syst space group, Z a (Å) c (Å) V (Å 3) cryst size (mm3) ρcalcd (g/cm 3) μ (mm−1) F(000) wavelength (Å) θ range/deg limiting indices reflns collected/unique completeness to θ, % data/restraints/params GOF R1, wR2a [I > 2σ(I)] R1, wR2 (all data)a Δρmax and Δρmin (e Å −3)
3284.12 293 trigonal R3c, 6 21.9500(3) 13.4420(3) 5608.7(2) 0.1000 × 0.0875 × 0.0750 5.834 26.869 8484 0.71073 3.369−32.61 −32 ≤ h ≤ 31, −32 ≤ k ≤ 31, −19 ≤ l ≤ 20 36936/4374 [Rint = 0.0866] 97.2 4374/1/168 1.119 0.0362, 0.0736 0.0423, 0.0770 1.803 and −2.898
R(F) = ∑||Fo| − |Fc||/∑|Fo | and wR2 = [∑w(Fo2− Fc2)2/ ∑w(Fo2)2]1/2 for Fo2 > 2σ(Fo2).
a
C
DOI: 10.1021/acs.inorgchem.6b02191 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
Table 2. Atomic Coordinates (×104) and Equivalent Isotropic Displacement Parameters (Å2 × 10 3) for Bi3[IO3]12·Ag4Ia
a
atom
Wyckoff position and point symmetry
x
y
z
Ueq
Bi I1 I2 I3 I4 I5 Ag1 Ag2 O(1) O(2) O(3) O(4) O(5) O(6) O(7) O(8) O(9) O(10) O(11) O(12)
18b, 1 18b, 1 18b, 1 18b, 1 18b, 1 6a, 3 18b, 1 6a, 3 18b, 1 18b, 1 18b, 1 18b, 1 18b, 1 18b, 1 18b, 1 18b, 1 18b, 1 18b, 1 18b, 1 18b, 1
37570(2) 7063(3) −2960(3) 16682(3) 19502(3) 33333 22406(6) 33333 2898(4) 1181(4) 477(4) 1856(5) −33(4) 1615(4) 1684(5) 1275(4) 2555(4) −512(4) 158(4) 1931(5)
49968(2) 51903(3) 33319(3) 38492(3) 48755(4) 66667 67813(6) 66667 5329(4) 6028(4) 4209(4) 4416(5) 5280(5) 3088(4) 4844(5) 5568(4) 4217(4) 3376(5) 2849(4) 5645(5)
658 30598(5) 43497(6) 37482(5) 12648(6) 40006(12) 33538(10) 62625(19) 1454(6) 2395(5) 4352(6) 4805(7) 3472(7) 4392(6) 2545(6) 4134(6) 3292(7) 3055(6) 4210(7) 860(7)
9.55(8) 8.6(1) 10.2(1) 9.0(1) 10.3(1) 23.0(3) 32.4(3) 44.1(6) 15(2) 12(1) 15(2) 23(2) 21(2) 15(2) 22(2) 19(2) 21(2) 22(2) 24(2) 27(2)
U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.
Table 3. Selected Interatomic Distances for Bi3[IO3]12·Ag4I atoms
axis, mostly pronounced for the Ag2 atom that is directly determined by its position and flat coordination. The structural formula is thus to be written as Bi3[IO3]12·Ag4I. It is possible to select a cluster group [Ag4I] 3+ charged as a dipole, a negative charge on I− and a positive charge on Ag44+. All Ag−O bonds are typical for Ag-iodates being in the interval 2.33−3.07 Å. The new compound should be classified as a iodide-iodate because it possesses I atoms in two fundamentally different valences: one atom in I5 position is I− as a typical halogen, and four others in I1−I4 positions are I5+, which have only lone pair electrons on the valence orbital. Such an unusual combination was also found in Pb3(IO3)2Cl27 and K2Bi(IO3)4Cl8 with 2-fold valence state of the halogens, namely, I5+ and Cl−. The compounds were characterized as a chloride-iodate in which the typical halogen Cl− plays the role of ion compensator for a heavy atom environment. In the former compound, except for four O atoms, two Cl ions add Pb1, and four Cl ions add Pb2 coordination in the layers on large distances. In the latter compound, Bi is coordinated by 7 O atoms; however, K2 atom coordination is aided by two Cl ions oriented between the layers for the charge balance. The new compound under investigation has a framework character, and the I− halogencompensators center channels of the structure together with the Ag ions. Structure−Properties Correlations. M3[IO3]12·Ag4I, M = Bi, Tb, demonstrate very high optical nonlinearities similar to that of BiO(IO3)1 and higher than that of KTP.13 The structural sources for possible contribution to nonlinear polarization in most substances are known to be connected with the outer shell electrons engaged in interatomic bonds and located asymmetrically with respect to the other similar electrons. The resulting strong electric polarization of the whole structure is only a necessary but not sufficient condition for high nonlinearity. Another condition is high optical electric field ionic polarizability that is more difficult to represent pictorially but which may be revealed in a comparison between a compound with high optical nonlinearity and relative structure compounds with lower nonlinearities. Investigation
bonds (Å) Bi Polyhedron
Bi−O(6) O(2) O(8) O(10) O(3) O(12) O(4) O(1) I(5)−Ag(1) Umbrella I(5)−Ag(1) × 3 Ag(1)−O(9) Ag(1)−O(2) Ag(1)−O(1) Ag(1)−O(8) Ag(2) Polyhedra Ag(2)−O(1) × 3 Ag(2)−O(12) × 3 Ag(2)−I(5) I(1)−O Umbrella I(1)−O(8) O(2) O(5) I(2)−O Umbrella I(2)−O(11) O(10) O(3) I(3)−O Umbrella I(4)−O(12) O(7) O(1) I(4)−O Umbrella I(4)−O(12) O(7) O(1)
2.310(7) 2.373(7) 2.383(7) 2.411(8) 2.446(8) 2.467(9) 2.548(8) 2.570(7) 2.679(1) 2.365(8) 2.440(8) 2.625(8) 2.652(8) 2.607(8) 2.811(8) 3.040(3) 1.815(8) 1.830(7) 1.817(8) 1.791(8) 1.819(8) 1.821(8) 1.795(8) 1.807(8) 1.821(8) 1.795(8) 1.807(8) 1.821(8) D
DOI: 10.1021/acs.inorgchem.6b02191 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
Figure 3. (a, b) Crystal structure of Bi3[IO3]12·Ag4I. Ag atoms are shown as large gray spheres, and I ions in the channel are given by large dark spheres; Bi atoms are shown as smaller dark spheres with I atoms and O atoms as larger and smaller open spheres. Ball−stick presentation is used for the Bi−O polyhedra (dark gray) and the IO3 groups (open). (a) ab-projection. (b) Side projection of one channel; Ag atoms are shown as large gray spheres, and I ions are given by large dark spheres. O atoms are given by open spheres; ball−stick presentation is for the (Ag1)3I5 umbrellas and Ag2−O (gray). c-axis is shown by vertical line.
Figure 4. (a, b) Crystal structure of La3[IO3]12[IO3](Pb3O). Pb atoms are shown as dark gray spheres; La atoms are given by larger open spheres, with I atoms and O atoms given by smaller open spheres. Ball−stick presentation is used for La−O polyhedra (dark gray) and IO3 groups (open). (a) ab-projection. (b) Side projection of one channel, Pb atoms are shown as dark-gray spheres; I atoms and O atoms are shown as gray and open spheres. Ball−stick presentation is for the Pb3O umbrellas (dark gray) and opposite oriented I−O umbrellas (open). The c-axis goes thorough in the channel through two types of umbrellas.
in the field of iodates gives good examples for that. In particular, La3Pb3[IO3]13O16 has the same space group R3c and a similar unit cell as that of the silver−metal iodates under investigation. Despite the similarity of their frameworks built of the Bi(La) polyhedra and IO3 groups, the structures are
different (Figure 4a). Besides La,Pb-iodate, its analogues with REE Pr and Nd were also obtained and investigated; all three form a group of noncentrosymmetrical iodates with relatively weak SHG signals 2.0, 1.0, and 0.8 times that of KDP, E
DOI: 10.1021/acs.inorgchem.6b02191 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
may help to elucidate the source of the high SHG signal in detail, and we do not exclude induced contribution from the other atoms in the structure especially of Bi atoms.
respectively, that is significantly weaker in comparison with SHG in Bi3[IO3]12·Ag4I and Tb3[IO3]12·Ag4I. On the basis of the structural data, it was expected in ref 16 that the contributions to polarization of the Pb ions, to I1, I2, and I4 groups, are small since their dipole moments are mainly aligned in the ab-plane, which cancel out each other. The main polarization contribution is coming from the I5O3 and I3O3 groups since their dipole moments are aligned in the same direction along the c-axis. Pb atoms in La3Pb3[IO3]12[IO3]O are located in the walls of the channels. Together with one shared O atom, the Pb atoms form umbrella-like polar groups Pb3O as Ag3I groups similar to the Bi,Ag-iodate (Figure 4b). This similarity suggests that the structural formulas for both compounds should be written as La3[IO3]12[IO3](Pb3O) and Bi3[IO3]12Ag(Ag3I) = Bi3[IO3]12· Ag4I, respectively, with one very important structural difference that in the first compound provides the resulting smaller polarization. Contribution to the optical nonlinearity from electronic polarizability could not be accounted for on the basis of tabulated data for individual ions because they do not reflect how the atoms’ environment influences the neighboring atoms’ geometry. Usually attributed to Bi3+ ions, the lone pair electron electrical activity, in structures under consideration, seems not to play a self-dependent crucial role because of the symmetric surroundings of this ion with oxygen atoms. Indeed, in both compounds, REE or Bi atoms are coordinated by O atoms without a large difference in bond lengths up and down the polar c-axis. Apparently, a noticeable contribution to the optical nonlinearity comes from the polar oriented IO3 groups as it takes place in many iodates without a center of symmetry, and especially from the Ag cations in an unusual almost planar configuration and in umbrellas. Both (Ag2)O6 and (Ag1)3I5 groups lie on the polar c-axis and have no visible structural restrictions for their outer electronic shells’ polarization along c. In M3[IO3]12·Ag4I, M = Bi, Tb, polar oriented umbrella-like groups (Ag1)3I5 are augmented by additional Ag2 atoms in the channels which are weakly bonded and are prone to polarization especially taking into account the large tetrahedral cluster Ag44+ topped with a negatively charged I− halogen. This case demonstrates a good opportunity to increase the nonlinear optical properties in the solid by chemical substitution of the Ag for Pb atoms and Ag for IO3 group in similar positions in the structure. Synthesis of compounds with other REEs (Nd, Sm, Gd) and Ag will be of interest to obtain untwinned crystals as with Tb and with high nonlinear optical properties.
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b02191. Figure S1a,b containing experimental and simulated theoretical powder XRD pattern and Table S1 containing powder diffraction data and indexing (PDF) Crystallographic information (CIF)
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Phone: +7(495) 9394926. ORCID
Elena L. Belokoneva: 0000-0003-1550-4941 Notes
The authors declare no competing financial interest. Crystallographic data for the structure reported in this paper have been deposited with the Karlsruhe Inorganic Crystallographic Structural Data Centre as supplementary publications CSD numbers 431436 for Bi3[IO3]12·Ag4I. Copies of the data can be obtained free of charge on application to ICSD FIZ− Karlsruhe−Leibnitz−Institut fuer Informationsinfrastructur, Termann-von-Helmholtz Platz 1, 76344 Eggenstein, Leopoldshafen, CrysDATA@fiz-karlsruhe.de, http://www.fiz-karlsruhe. de.
■
ACKNOWLEDGMENTS We thank the Russian Foundation for Basic Research (RFBR), funded by the Ministry of Science & Education, Russia (Grant 14-03-00480a), for support. The authors are grateful to Natalie Zubkova, Department of Crystallography, Geological Faculty, MSU, for her aid in collection of experimental diffraction, to Elena Guseva, the Laboratory of Local Methods of Materials Investigation, Geological Faculty, MSU, for determination of compositions and image of crystals, and to Pavel Plachinda for his help with consultations regarding theoretical calculations and the production of this paper.
■
■
REFERENCES
(1) Nguyen, S. D.; Yeon, J.; Kim, S.-H.; Halasyamani, P. Sh. A new polar iodate that exhibits an Aurivillius-type (B2O2)2+ layer and a large SHG response. J. Am. Chem. Soc. 2011, 133, 12422−12425. (2) Sun, C.-F.; Yang, B.-P.; Mao, J.-G. Structures and properties of functional metal iodates. Sci. China: Chem. 2011, 54, 911−922. (3) Hu, C.-L.; Mao, J.-G. Recent advances on second-order NLO materials based on metal iodates. Coord. Chem. Rev. 2015, 288, 1−17. (4) Xu, X.; Hu, C.-L.; Li, B.-X.; Yang, B.-P.; Mao, J.-G. α-AgI3O8 with large SHG responses: polymerization of IO3 groups into the I3O8 polyiodate anion. Chem. Mater. 2014, 26, 3219−3230. (5) Phanon, D.; Suffren, Y.; Taouti, M. B.; Benbertal, D.; Brenier, A.; Gautier-Luneau, I. Optical properties of Nd3+ and Yb3+-doped AgM(IO3)4 metal iodates: transparent host matrices for mid-IR lasers and nonlinear materials. J. Mater. Chem. C 2014, 2, 2715−2713. (6) Ok, K. M.; Halasyamani, P. S. New metal iodates: syntheses, structures, and characterizations of noncentrosymmetric La(IO3)3 and NaYI4O12 and centrisymmetric β-Cs2I4O11 and Rb2I6O15(OH)2.2H2O. Inorg. Chem. 2005, 44, 9353−9359.
CONCLUSION Single crystals of two new iodide-iodates, M3[IO3]12·Ag4I, M = Bi, Tb, are synthesized in multicomponent hydrothermal systems. The anionic part in both iodide-iodates is characterized as a complex framework of isolated IO3 umbrella-like groups and a large Bi(Tb)−O polyhedra close to that previously found in La3[IO3]12[IO3](Pb3O). Large channels are open along the c-axis and contain (Ag3I)2+ umbrella-like groups and additional Ag atoms forming Ag34+ tetrahedral clusters topped with I− halogen. New iodates possess significantly higher second-order nonlinear optical characteristics compared to compounds with lead, REE3[IO3]12[IO3](Pb3O), REE = La, Pr, Nd. The reason for that is filling of the channels in a polar way by umbrella-like (Ag3I)2+ polar groups and highly polarizable [Ag4I]3+ clusters. Theoretical calculations F
DOI: 10.1021/acs.inorgchem.6b02191 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry (7) Belokoneva, E. L.; Dimitrova, O. V. Synthesis and crystal structure of Pb3[IO3]2Cl4 - a representative of new class of compounds iodate chloride. Crystallogr. Rep. 2010, 55, 24−27. (8) Zhao, W.; Pan, S.; Dong, L.; Yang, Z.; Dong, X.; Chen, Z.; Zhang, M.; Zhang, F. Hydrothermal synthesis, growth, and properties of new chloride iodate. J. Mol. Struct. 2013, 1049, 288−292. (9) WinXPow Software; STOE & CIE GmbH, 2002. (10) Kurtz, S. K.; Perry, T. T. A powder technique for evaluation of nonlinear optical materials. J. Appl. Phys. 1968, 39, 3798−3813. (11) Belokoneva, E. L.; Stefanovich, S. Yu.; Dimitrova, O. V. New nonlinear optical potassium iodate K[IO3] and borates K3[B6O10]Br, KTa[B4O6(OH)4](OH)2 0.1,33H2O− synthesis, structures and relation to the properties. J. Solid State Chem. 2012, 195, 79−85. (12) Beskorovaynaya, D. A.; Deyneko, D. V.; Baryshnikova, O. V.; Stefanovich, S.Yu.; Lazoryak, B. I. Optical non-linearity tuning in Ca8‑xPbxMBi(VO4)7 whitlockite-like systems. J. Alloys Compd. 2016, 674, 323−330. (13) Yao, J.; Wang, Y. Nonlinear Optics and Solid-State Lasers; Springer Series in Optical Science; Springer, 2012; p 684. (14) (a) Sheldrik, G. M. SHELXS-97, A Program for Automatic Solution of Crystal Structures; University of Goettingen: Goettingen, Germany, 1997. (b) Sheldrick, G. M. SHELXL-97, A Program for Crystal Structure Refinement; University of Goettingen: Goettingen, Germany, 1997. (15) Dowty, E. Atoms 3.2−A Computer Program for Displaying Atomic Structures; Shape Software: Kingpost, TN, 1995. (16) Hu, T.; Qin, L.; Kong, F.; Zhou, Y.; Mao, J.-G. LnPb(IO)(μ#O) (Ln = La#nd): new types of second-order nonlinear optical materials containing two types of lone pair cations. Inorg. Chem. 2009, 48, 2193−2199.
G
DOI: 10.1021/acs.inorgchem.6b02191 Inorg. Chem. XXXX, XXX, XXX−XXX
