Inorganic Chemistry - ACS Publications - American Chemical Society

---

Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

pubs.acs.org/IC

MIMIIP3O9 (MI = Rb, MII = Cd, Mg, Ca; MI = Cs, MII = Pb, Sr; MI = K, MII = Mg): Cation Substitution Application in Cyclophosphate Family and Nonlinear Optical Properties Maierhaba Abudoureheman,†,‡ Xiaobo Pan,† Shujuan Han,*,† Yilimiranmu Rouzhahong,† Zhihua Yang,† Hongping Wu,† and Shilie Pan*,† †

CAS Key Laboratory of Functional Materials and Devices for Special Environments, Xinjiang Technical Institute of Physics & Chemistry, CAS; Xinjiang Key Laboratory of Electronic Information Materials and Devices, 40-1 South Beijing Road, Urumqi 830011, People’s Republic of China ‡ University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China S Supporting Information *

ABSTRACT: By the application of cation substitution, five new members of cyclophosphates, RbCdP3O9, CsPbP3O9, CsSrP3O9, RbMgP3O9, and RbCaP3O9, were obtained by a high-temperature melt method and structurally analyzed. The five compounds have identical stoichiometries, and all of them feature a three-dimensional network, which consists of MIIO6 (MII = Cd, Mg, Ca, Pb, Sr) octahedra and cyclic P3O9 units, while alkali-metal atoms are located within the network. However, RbCdP3O9 and CsPbP3O9 belong to the asymmetric space groups P6̅c2 and Pna21, respectively, and the other three compounds belong to orthorhombic space group Pnma. Detailed structure comparisons in the MI-MII-P-O and (MIMIIP3O9)n (n = 1, 2, 6) systems are discussed. Remarkably, KMgP3O9 as one of the cyclophosphate members exhibits a second harmonic generation (SHG) intensity about 0.2 times that of KH2PO4 (KDP), RbCdP3O9, and CsPbP3O9 also show SHG responses 0.1 times that of KDP. In addition, the related optical properties are discussed. Furthermore, theoretical calculations and dipole moments were calculated to explain the relation of structure and optical properties.

■

Rb2Ba3(P2O7)2,23 Ba5P6O10,24 AMgPO4·6H2O (A = Rb, Cs),25 CsLiCdP2O7,26 CsCdPO4,27 Cs6Mg6(PO3)18,28 RbNaMgP2O7,29 M4Mg4(P2O7)3 (M = K, Rb),30 etc., which show large/moderate SHG responses and UV/DUV cutoff edges. In addition, new structures such as magnetic compounds also have been reported.31 The outstanding performances of phosphates can be attributed to the different linkages of the PO4 groups, which can be linked to form isolated clusters, chains, layers, or three-dimensional (3D) networks. In addition, the P−O anionic groups are further connected by the cations to form different structures. As one effective way to design new compounds, cation substitution in the host crystal structure has been successfully used to obtain new compounds with various structures and properties. For example, the series of NLO phosphates AB2(PO3)5 (A = K, Rb, Cs; B = Ba, Pb)32−34 have been reported by replacing alkali or alkaline-earth metals. Such successful examples can also be observed in borate35−38 and carbonate39−42 systems.

INTRODUCTION Recently, inorganic phosphates have attracted considerable interest in the development of materials chemistry, since they have been widely used as cathode materials, ionic conductors, nonlinear optical (NLO) materials, ion-exchange materials, etc.1−14 In particular, phosphates are some of the vital sources of NLO materials. For example, KH2PO4 (KDP)15 and KTiOPO4 (KTP)16 have already become applied NLO materials for the UV and visible regions, respectively. In addition, after the first report of the deep-UV (DUV) NLO material Ba3P3O10X (X = Cl, Br),17 phosphates have attracted more attention as potential NLO candidates with wide transmittance. Without d−d and f−f orbital electronic transitions, alkali and alkaline-earth metals are beneficial for a violet shift of the absorption edge of a compound. In addition, by introducing d0 and d10 transition metals or cations with a lone pair into the phosphates, the material may exhibit a considerable second harmonic generation (SHG) response.1,18,19 For this reason, phosphates with the above cations have been widely studied, and some promising new phosphate compounds have been discovered, including Pb3Mg3TeP2O14,20 A3B3CP2O14,21 LiCs2PO4,22 RbBa2(PO3)5,23 © XXXX American Chemical Society

Received: April 14, 2018

A

DOI: 10.1021/acs.inorgchem.8b01017 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Table 1. Crystal Data and Structural Refinement Details for RbCdP3O9, KMgP3O9, CsPbP3O9, CsSrP3O9, RbMgP3O9, and RbCaP3O9 RbCdP3O9 formula wt cryst syst space group, Z unit cell dimens a (Å) b (Å) c (Å) V (Å3) calcd density (g/cm3) no. of collected/unique rflns goodness of fit on F2 final R indices (Fo2 > 2σ(Fo2))a R indices (all data)a abs structure param largest diff peak and hole (e Å−3) formula wt cryst syst space group, Z unit cell dimens a (Å) b (Å) c (Å) V (Å3) calcd density (g/cm3) no. of collected/unique rflns goodness of fit on F2 final R indices (Fo2 > 2σ(Fo2))a R indices (all data)a largest diff peak and hole (e Å−3) a

KMgP3O9

CsPbP3O9

434.78 hexagonal P6̅c2, 2

300.32 hexagonal P6̅c2, 2

577.01 orthorhombic Pna21, 4

6.8401(10) 6.8401(10) 10.176(3) 412.32(15) 3.502 2192/345 (R(int) = 0.0259) 1.066 R1 = 0.0153, wR2 = 0.0418 R1 = 0.0163, wR2 = 0.0425 0.004(12) 0.391 and −0.431 CsSrP3O9

6.6026(13) 6.6026(13) 9.775(4) 369.05(18) 2.703 1991/312 (R(int) = 0.0364) 1.095 R1 = 0.0187, wR2 = 0.0462 R1 = 0.0193, wR2 = 0.0464 −0.11(12) 0.249 and −0.218 RbMgP3O9

8.686(5) 13.136(7) 7.882(4) 899.4(9) 4.261 5065/1983 (R(int) = 0.0448) 0.948 R1 = 0.0280, wR2 = 0.0519 R1 = 0.0320, wR2 = 0.0533 0.054(9) 0.932 and −1.586 RbCaP3O9

457.44 orthorhombic Pnma, 4

346.69 orthorhombic Pnma, 4

362.46 orthorhombic Pnma, 4

10.100(4) 7.743(3) 13.000(5) 1016.6(7) 2.989 5705/1200 (R(int) = 0.0525) 1.046 R1 = 0.0284, wR2 = 0.0492 R1 = 0.0457, wR2 = 0.0529 0.777 and -0.635

9.330(4) 7.173(3) 11.993(6) 802.5(6) 2.869 4643/990 (R(int) = 0.0538) 1.117 R1 = 0.0308, wR2 = 0.0701 R1 = 0.0419, wR2 = 0.0750 0.468 and −0.650

9.729(4) 7.525(3) 12.480(5) 913.6(6) 2.635 5255/1126 (R(int) = 0.0446) 1.223 R1 = 0.0448, wR2 = 0.0868 R1 = 0.0568, wR2 = 0.0900 0.616 and −0.773

R1 = ∑||Fo| − |Fc||/∑|Fo|, and wR2 = [∑w(Fo2 − Fc2)2/∑wFo4]1/2 for Fo2 > 2σ(Fo2). into a platinum crucible, heated to 650 °C (for CsPbP3O9), 800 °C (for KMgP3O9, RbCdP3O9, and CsSrP3O9) and 1100 °C (for RbCaP3O9 and RbMgP3O9), and held at this temperature for 2 h. The above temperatures were reduced at a rate of 2 °C/h to 600 °C for KMgP3O9, RbCdP3O9, and CsSrP3O9 (450 °C for CsPbP3O9, 900 °C for RbCaP3O9 and RbMgP3O9); finally, the melts were cooled to room temperature at a rate of 10 °C/h. Single crystals could be obtained for structural determinations. The polycrystalline samples of the title compounds were synthesized by conventional solid-state methods except for CsPbP3O9, which was obtained by a spontaneous crystallization method. Stoichiometric mixtures of reagents were ground thoroughly and heated at 250 °C for 24 h. After that, the temperature was raised to 700 °C (for KMgP3O9, RbCaP3O9, CsSrP3O9, and RbMgP3O9) and 490 °C (for RbCdP3O9) for 4 days. Characterization. The powder X-ray diffraction (XRD) data were collected to confirm the purity of the compounds. A Bruker D2 PHASER diffractometer with Cu Kα radiation (λ = 1.5418 Å, 2θ range of 10−70°) was used to collect the data. The results are shown in Figure S1 in the Supporting Information, which indicate that the experimental data are in good agreement with the calculated data. For structural determination, an APEX II CCD diffractometer with monochromatic Mo Kα radiation was used. To integrate the data, solve the structures, and check the symmetry of structures, the SAINT program,44 SHELXTL software,45 and the PLATON program46 were used, respectively. Structure refinement results, isotropic thermal parameters, atomic coordinates, and selected bond lengths and angles of the title compounds are given in Table 1 and Tables S1 and S2 in the Supporting Information.

On the basis of the above idea, much attention has been focused on the anhydrous MI-MII-P3O9 (MI, alkali metals; MII, alkaline-earth metals, d10 transition metals, stereochemical lonepair cation) system, with the expectation of obtaining new phosphates with different structures and properties caused by atom replacement. Our efforts have produced the five new compounds RbCdP3O9, CsPbP3O9, CsSrP3O9, RbMgP3O9, and RbCaP3O9. Among them, RbCdP3O9 and CsPbP3O9 crystallize in an asymmetric space group and can be investigated as NLO materials. Meanwhile, we also obtained another noncentrosymmetric compound, KMgP3O9, whose structure has been reported.43 To our knowledge, no further investigations about NLO properties as well as the electronic structure of KMgP3O9 have been reported. Herein, in this work, the synthesis and crystal structures including a summary of anhydrous compounds of MI-MII-P-O and structural comparisons are reported. More importantly, the NLO properties of noncentrosymmetric compounds and linear optical properties have been determined. Furthermore, first-principles calculations have been performed and dipole moments determined to illustrate the relationship between NLO properties and structure.

■

EXPERIMENTAL SECTION

Synthesis. The title compounds were grown by a high-temperature melt method. The mixtures of K2CO3/Rb2CO3/Cs2CO3, CdO/MgO/ CaCO3/SrCO3, and NH4H2PO4 in a molar ratio of 0.5:1:3 were weighed for the corresponding compounds. The mixtures were put B

DOI: 10.1021/acs.inorgchem.8b01017 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 1. 3D structures of (a) RbCdP3O9, (b) CsPbP3O9, and (c) CsSrP3O9.

Figure 2. “Connection” mode of MII cations and P3O9 cyclic rings in the structures of (a) RbCdP3O9, (b) CsPbP3O9, and (c) CsSrP3O9. A Shimadzu SolidSpec-3700 UV−vis−NIR spectrophotometer was performed to collect the optical diffuse reflectance data in the range of 190−2600 nm. Infrared (IR) spectra were performed on a Shimadzu IRAffinity-1 spectrometer in the range of 400−4000 cm−1. The powder SHG responses of RbCdP3O9, KMgP3O9, and CsPbP3O9 were measured using the Kurtz−Perry method.47 The samples of RbCdP3O9, KMgP3O9, CsPbP3O9, and KDP were ground and sieved into distinct particle size ranges (