Cation-tuned synthesis of the A2SO4·SbF3 (A = Na+, NH4+, K+, Rb+) family with nonlinear optical properties

Article abstract of DOI:10.1039/c8dt04400g

Four antimony fluoride sulfates named A₂SO₄·SbF₃ (A = Na⁺, NH₄⁺, K⁺, Rb⁺) have been successfully synthesized using a hydrothermal method by introducing Sb³⁺ cations with a stereochemically active lone pair in sulfates and subsequently tuning the structure through the second monovalent cations. All of the title compounds are stoichiometrically equivalent materials which share a common structural motif composed of a distorted SO₄ tetrahedron and an asymmetric SbF₃ polyhedron. However, the macroscopic centricities of these four compounds are significantly influenced by the size and coordination environment of cations; Na₂SO₄·SbF₃ crystallizes in centrosymmetric space groups Cmca and (NH₄)₂SO₄·SbF₃ in Pbca, while K₂SO₄·SbF₃ and Rb₂SO₄·SbF₃ crystallizes in noncentrosymmetric space group P2₁2₁2₁. Complete characterization including thermal analyses, infrared and UV-vis spectroscopy, and theoretical calculations is also reported. Powder second harmonic generation measurement for noncentrosymmetric K₂SO₄·SbF₃ and Rb₂SO₄·SbF₃ indicated that both of them are type I phase-matchable.

Full text of DOI:10.1039/c8dt04400g

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
Cation-tuned synthesis of the A2SO4·SbF3 (A = Na+,
+
NH4 , K+, Rb+) family with nonlinear optical
properties†
Cite this: Dalton Trans., 2018, 47,
17486
Fangfang He,a Lei Wang,a Cuifang Hu,b Jing Zhou,a Qian Li,a Ling Huang,*a
b
Daojiang Gao,a Jian Bi,a Xin Wangb and Guohong Zou
*
Four antimony fluoride sulfates named A2SO4·SbF3 (A = Na+, NH4+, K+, Rb+) have been successfully syn-
thesized using a hydrothermal method by introducing Sb3+ cations with a stereochemically active lone
pair in sulfates and subsequently tuning the structure through the second monovalent cations. All of the
title compounds are stoichiometrically equivalent materials which share a common structural motif
composed of a distorted SO4 tetrahedron and an asymmetric SbF3 polyhedron. However, the macro-
scopic centricities of these four compounds are significantly influenced by the size and coordination
environment of cations; Na2SO4·SbF3 crystallizes in centrosymmetric space groups Cmca and
(NH4)2SO4·SbF3 in Pbca, while K2SO4·SbF3 and Rb2SO4·SbF3 crystallizes in noncentrosymmetric space
group P212121. Complete characterization including thermal analyses, infrared and UV-vis spectroscopy,
and theoretical calculations is also reported. Powder second harmonic generation measurement for
noncentrosymmetric K2SO4·SbF3 and Rb2SO4·SbF3 indicated that both of them are type I phase-
matchable.
Received 5th November 2018,
Accepted 14th November 2018
DOI: 10.1039/c8dt04400g
rsc.li/dalton
However, what needs special attention is that it is the necess-
ary but not the sufficient condition to produce NCS com-
Introduction
Recently, noncentrosymmetric (NCS) compounds have pounds by employing acentric units. That is, lots of com-
attracted great attention attributed to their technologically pounds exhibit centrosymmetric structures due to the acentric
advanced properties1–10 such as pyroelectricity, ferroelectricity units in an antiparallel arrangement. Also, some other impor-
and piezoelectricity, especially, second-order nonlinear optical tant factors including the cation size, the coordination
(NLO) behavior promoting the development of laser environment, the hydrogen bond, etc. may influence the
technology.11–15 Continuous efforts have been made by syn- symmetry.26–28 Hence, it is crucial to find ways to make these
thetic chemists for discovering NCS functional materials influence factors cooperate together for the exploration of NCS
through molecule structure design, for example, regulating the materials with custom functions.
alignment and orientation of fundamental building
Nearly 80% of the NCS oxides possess either tetrahedrally
blocks.16–20 But it is still a tremendous challenge to synthesize coordinated cations or second-order Jahn–Teller (SOJT) dis-
new compounds that happen to be NCS. Generating macro- torted cations.1 The SOJT distorted cations include d0, d10 and
scopic noncentrosymmetry through combining local unsym- stereochemically active lone pair (SCALP) containing cations
metrical units has been proved to be effective by continuous which are frequently used to participate in the synthesis of
experimental and theoretical calculation investigations.21–25 NLO materials exhibiting large second-harmonic generation
(SHG) responses, especially, Pb2+ and Bi3+ cations with
SCALP.29–32 Though Sb3+ cations with a similar lone pair of
electrons are conducive to NLO effects, Sb-containing NLO
oxides have seldom been reported.33–35 SHG efficiency is
usually cancelled attributed to the inversion twinning for the
lone pairs. Therefore, it is critical to make the lone pairs
effective in designing and synthesizing new antimonite NLO
materials. In this work, tetrahedrally coordinated sulfate
anions were introduced to increase the structural diversity and
the probability of NCS compounds. Subsequently, second
aCollege of Chemistry and Materials Science, Sichuan Normal University, Chengdu,
610068, China. E-mail: huangl026@sina.com
bCollege of Chemistry, Sichuan University, Chengdu, 610064, China.
E-mail: zough@scu.edu.cn
†Electronic supplementary information (ESI) available: Additional crystallo-
graphic data; TG curves; IR spectra. CCDC 1847859 for (NH4)2SO4·SbF3, 1847860
for Rb2SO4·SbF3, 1859397 for K2SO4·SbF3 and 1859398 for Na2SO4·SbF3. For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c8dt04400g
17486 | Dalton Trans., 2018, 47, 17486–17492
This journal is © The Royal Society of Chemistry 2018

View Article Online
Dalton Transactions
Paper
cations exhibiting the same valence but different cation sizes Instruments for physical property measurements
and coordination environments were employed to tune the
Data collection for single crystals of the four compounds was
performed on a Rigaku Oxford Diffraction Synergy-R and a
Bruker D8 Venture diffractometer with graphite monochro-
matic Mo-Kα radiation (λ = 0.71073 Å) at 293(2) and 150(2)
K. All the four structures were solved by direct methods and
refined by a full-matrix least-squares fitting on F2 using
SHELX-201439,40 and Olex2.41 All the structures were examined
using PLATON,42 and no higher symmetries were found.
Crystallographic data and structural refinements for the four
compounds are summarized in Table 1. Atomic coordinates
and isotropic displacement coefficients, and selected bond
lengths for the four compounds are listed in Tables S1–S8.†
X-ray powder diffraction patterns of the four compounds were
collected at room temperature with a Smart lab powder X-ray
diffractometer by using monochromatic Cu Kα radiation (λ =
1.540598 Å) in the angular range of 5–50° with a 0.08° (2θ) step
length and a fixed counting time of 0.2 s per step at room
temperature. IR data for the four compounds were obtained
with a Vertex 70 Fourier transform infrared (FT-IR) spectro-
meter. The powder samples were ground with dried KBr in a
ratio of about 1 : 100 and pressed into tablets. The spectra were
scanned in the range of 400–4000 cm−1. Thermogravimetric
analysis (TGA) was performed on a Discovery TGA thermal ana-
lyzer, and 10 mg of crystal samples were placed in platinum
crucibles and heated from room temperature to 800 °C at a
rate of 10 °C min−1 under a N2 gas atmosphere. UV/Vis diffuse
reflectance data for the four compounds were recorded with a
PerkinElmer Lamda-900 UV/vis/NIR spectrophotometer. The
spectra were collected in the wavelength range of 190–2500 nm
with a resolution of 1 nm for the UV/Vis range. The powder
second-harmonic generation (SHG) signal was measured with
a Q-switched Nd:YAG laser using 1064 nm radiation by the
Kurtz and Perry method.43 We know that SHG efficiencies
strongly depend on the particle size, and polycrystalline
A2SO4·SbF3 (A = K+, Rb+) samples were sieved into specific par-
ticle size ranges (25–45, 45–58, 58–75, 75–106, 106–150 and
framework as in mixed metal selenites and iodates.36,37
Guided by the abovementioned ideas, systematic investigations
+
on the A-Sb-SO4 (A = NH4 , alkali metal) system have been con-
ducted via a hydrothermal method.38 Four antimony fluoride
+
sulfates named A2SO4·SbF3 (A = Na+, NH4 , K+, Rb+) have been
successfully synthesized. Detailed characterization of these
stoichiometrically equivalent materials including thermal ana-
lyses, optical properties and NLO properties is presented. Also
theoretical calculation analysis was performed.
Experimental section
Synthesis of A2SO4·SbF3 (A = Na+, NH4 , K+, Rb+)
+
All of the starting reagents were of analytical grade and used
without further purification. (NH4)2SO4 (AR 99%, Shanghai
Macklin Biochemical Co., Ltd), Na2SO4 (99.9%, Aladdin
Industrial Corporation), K2SO4 (99.9%, Aladdin Industrial
Corporation), Rb2SO4 (99.9%, Aladdin Industrial Corporation),
and SbF3 (AR 99%, Shanghai Macklin Biochemical Co. Ltd)
were used.
Single crystals of the four title compounds were obtained by
a hydrothermal method from the reactions of 0.5 mL de-
ionized water with A2SO4 (A = Na, NH4, K, Rb) and SbF3. The
loaded compositions are as follows: (NH4)2SO4 (0.198 g,
1.5 mmol) and SbF3 (0.356 g, 2 mmol) for (NH4)2SO4·SbF3,
Na2SO4 (0.213 g, 1.5 mmol) and SbF3 (0.358 g, 2 mmol) for
Na2SO4·SbF3, K2SO4 (0.209 g, 1.2 mmol) and SbF3 (0.286 g,
1.6 mmol) for K2SO4·SbF3, and Rb2SO4 (0.267 g, 1 mmol), and
SbF3 (0.179 g, 1 mmol) for Rb2SO4·SbF3. The reactants were
sealed into a 23 mL Teflon autoclave, and heated at 220 °C for
4 days, and then slowly cooled to ambient temperature at a
rate of 3 °C h−1. The products were obtained after cooling and
washing with alcohol, followed by drying in air. Transparent
colorless crystals were obtained in 35–45% yield (based on Sb).
a
Table 1 Crystal data and structure refinement for Na2SO4·SbF3, (NH4)2SO4·SbF3, K2SO4·SbF3 and Rb2SO4·SbF3
Formula
Na2SO4·SbF3
(NH4)2SO4·SbF3
K2SO4·SbF3
Rb2SO4·SbF3
Formula weight
Crystal system
Space group
a (Å)
320.79
Orthorhombic
Cmca
15.1698(6)
7.1773(3)
11.0738(4)
1205.70(8)
2
310.89
Orthorhombic
Pbca
10.8684(4)
10.9090(5)
13.3631(6)
1584.37(12)
8
353.01
445.75
Orthorhombic
P212121
5.60751(13)
9.0874(2)
14.1966(4)
723.43(3)
2
Orthorhombic
P212121
9.2727(7)
5.7702(4)
14.4934(9)
775.47(9)
2
b (Å)
c (Å)
V (Å3)
Z
Dcalcd (g cm−3
)
3.534
2.607
3.241
3.818
Temperature (K)
λ (Å)
293(2)
0.71073
1184
5.088
1.005
0.0195/0.0530
0.0200/0.0532
150(2)
0.71073
1184
3.777
1.038
0.0222/0.0551
0.0310/0.0595
293(2)
1.54184
656
21.83
1.062
0.0533/0.1310
0.0542/0.1324
150(2)
0.71073
800
16.319
1.074
0.0237/0.0530
0.0278/0.0545
F (000)
μ (mm−1
)
GOF on F2
R1, wR2 (I > 2σ(I))a
R1, wR2 (all data)
a R1(F) = ∑||Fo| − |Fc||/∑|Fo|wR2 (Fo2) = [∑w(Fo2 − Fc2)2/∑w(Fo2)2]1/2
.
This journal is © The Royal Society of Chemistry 2018
Dalton Trans., 2018, 47, 17486–17492 | 17487

View Article Online
Paper
Dalton Transactions
150–212 μm) and packed into different tubes. The micro- μ4-O to the one-dimensional chain and further linked with
crystalline crystals of known NLO material KDP served as the Na1–F and Na1–O to the 3-D framework constructed from Na
reference with the same particle size ranges.
atoms (Fig. 1b and d).
Another centrosymmetric material, (NH4)2SO4·SbF3, crystal-
lizes in the space group of Pbca with an orthorhombic crystal
system and features a different framework from that of
Na2SO4·SbF3. One unique Sb, one S, two N, three F, four O and
eight H atoms are contained in the asymmetric unit of
(NH4)2SO4·SbF3. As shown in Fig. 2a, SbF3 units are connected
Theoretical calculations
Band structures and density of states (DOS) of Rb2SO4·SbF3
were calculated using the density functional theory (DFT) in
the CASTEP program implemented in the Materials Studio
package.44 All calculations were performed using the Perdew–
Burke–Ernzerhof (PBE) functional under generalized gradient
approximation (GGA).45 The kinetic cutoff energy is set to 300
eV and the k-point sampling in the Brillouin zone was set to 1
× 2 × 1 for Rb2SO4·SbF3. All the atoms were described using
the Ultrasoft pseudopotentials.46
2−
by SO4 to the 1-D zigzag [SbF3SO4]2− chain, and in the
chain, each Sb3+ cation is bonded with three fluorine atoms
2−
and two O atoms from two SO4 to the tetragonal pyramid
[SbF3O2]4− complex, with the bond length of Sb–F ranging
from 1.942 to 1.954 Å and that of Sb–O between 2.611 and
2.661 Å, respectively. The distances of the S–O bond in the
[SO4]2− tetrahedron are slightly different and fall in the range
of 1.468–1.483 Å. [SbF3SO4]2− chains are bridged via N1–H⋯O
hydrogen bonds to form a two-dimensional (2-D) layer; mean-
Results and discussion
Crystal structure
+
while, N1H4 locates in the different directions and forms two
kinds of 4-MR with two SO42−. The adjacent 2-D layers present
an almost symmetric arrangement, and are further connected
by N2–H⋯O hydrogen bonds to form the 3-D framework, and
Crystallographic data reveal that the structure of Na2SO4·SbF3
belongs to the centrosymmetric space group Cmca with an
orthorhombic crystal system. The asymmetric unit of
Na2SO4·SbF3 consists of one graphically independent Sb, one
S, two Na, two F and two O atoms. As shown in Fig. 1a, two
+
the adjacent N2H4 units also show an almost symmetric
+
arrangement similar to N1H4 , and result in the centro-
2−
symmetric structure of (NH4)2SO4·SbF3.
SbF3 units are connected by two SO4 to form the four-mem-
bered ring (4-MR) containing [(SbF3)2(SO4)2]4− dimer. Each
Sb3+ cation also interacts with three fluorine atoms and two O
K2SO4·SbF3 and Rb2SO4·SbF3 are isostructural with each
other and share the same noncentrosymmetric space group
P212121 (crystal system: orthorhombic), and only Rb2SO4·SbF3
will be described in detail as a representative. Being similar to
(NH4)2SO4·SbF3, in Rb2SO4·SbF3, SbF3 units are connected by
2−
atoms from two SO4 with the bond length of Sb–F in the
range of 1.961–1.963 Å and Sb–O 2.486 Å, respectively. The Sb–
O bond is longer than the Sb–F bond, and the lengthening of
the Sb–O bonds is mainly caused by the additional coordi-
nation of fluorine with antimony, which results in greater dis-
tortion in the antimony polyhedron. The four S–O bonds in
[SO4]2− exhibit two kinds of distances, 1.470 or 1.486 Å. The
[(SbF3)2(SO4)2]4− dimers are sequentially packed in the ac
plane in the same direction in one layer and in the axisym-
metric direction in the adjacent layer, and these isolated
dimers are further bridged with Na+ cations to form a three-
dimensional (3-D) framework (Fig. 1c). Na2+ is bridged with
2−
SO4 to the 1-D zigzag [SbF3SO4]2− chain, while an obvious
discrepancy of the O–Sb–O angle was observed, 94.62° in
Rb2SO4·SbF3 and 96.15° in (NH4)2SO4·SbF3, respectively
(Fig. 3a). In the chain, each Sb3+ cation is bonded with
2−
three fluorine atoms and two oxygen atoms from two SO4 to
the tetragonal pyramid [SbF3O2]4− complex, with the bond
length of Sb–F ranging from 1.939–2.001 Å, Sb–O
2.355–2.447 Å, and S–O 1.455–1.501 Å, respectively (Fig. 3b).
Fig. 1 (a) Ball-and-stick representation of the [(SbF3)2(SO4)2]4− dimer
and the coordination mode of Sb3+ and SO42−; (b) the 2-D layer con-
structed with Na+; (c) the 3-D framework of Na2SO4·SbF3 viewed down
the b axis; and (d) the 3-D framework constructed with Na+.
Fig. 2 (a) Ball-and-stick representation of the 1-D chain of [SbF3SO4]2−
;
(b) the coordination mode of Sb3+ and SO42−; (c) the 2-D layer of
(NH4)2SO4·SbF3 viewed down the c axis; and (d) the 3-D framework of
(NH4)2SO4·SbF3 viewed down the a axis.
17488 | Dalton Trans., 2018, 47, 17486–17492
This journal is © The Royal Society of Chemistry 2018

View Article Online
Dalton Transactions
Paper
bonds are the shortest in the Rb-containing compound, which
are 2.355 and 2.447 Å, respectively, and the Sb–O bond is
2.468 Å in Na2SO4·SbF3 and 2.661 Å in (NH4)2SO4·SbF3 (Fig. 1a,
2b and 3b). When the [(SbF3)2(SO4)2]4− dimers or the
[SbF3SO4]2− chains are taken into consideration, we find that
the dimers or chains in Na2SO4·SbF3 and (NH4)2SO4·SbF3 both
show a neat and anti-parallel arrangement, while being alter-
nately arranged in Rb2SO4·SbF3 (K2SO4·SbF3), as the larger Rb+
and K+ cations demand larger space for effective packing
(Fig. 1c, 2d and 3c). A slight discordance is observed in
(NH4)2SO4·SbF3 owing to the existence of hydrogen bonds.
Powder x-ray diffraction
The powder XRD patterns of A2SO4·SbF3 (A = Na+, NH4 , K+,
+
Fig. 3 (a) Ball-and-stick representation of the 1-D chain of [SbF3SO4]2−
;
Rb+) are shown in Fig. 4, indicating that the experimental XRD
(b) the coordination mode of Sb3+ and SO42−; (c) the 3-D framework of
Rb2SO4·SbF3 viewed down the b axis; (d) the coordination and linkage patterns are in good agreement with the calculated XRD pat-
mode of Rb1 and Rb2 atoms.
terns from the single crystal models.
Thermal analysis
Being similar to Na2SO4·SbF3, [SbF3SO4]2− chains also pack
sequentially in the ac plane in two-directions compared with
the adjacent four chains, and are further bridged with Rb+ to
the 3-D framework (Fig. 3c). There are two unique Rb atoms in
the asymmetric unit of Rb2SO4·SbF3. Rb1 is ten coordinated
with six fluorine atoms and four oxygen atoms, and Rb2 is
seven coordinated with three fluorine atoms and four oxygen
atoms with the Rb–O bands in the range of 2.845–3.022 Å and
the Rb–F band in the range of 2.803–3.119 Å. Four Rb1 and
two Rb2 atoms are connected to the Rb6 cluster, and con-
nected with the adjacent almost centrosymmetric Rb6 clusters
to form the 3-D framework and between the two Rb atoms,
Rb1 plays a role in layer construction and Rb2 acts as the
bridges (Fig. 3d).
Thermogravimetric analysis spectra of A2SO4·SbF3 (A = Na+,
+
NH4 , K+, Rb+) under a N2 gas atmosphere are displayed in
Fig. S1.† The TG curve shows that Na2SO4·SbF3 is stable up to
257 °C, and a total weight loss of about 30.31% occurred in
the temperature regions of about 257–696 °C. The powder XRD
proved that the residue of Na2SO4·SbF3 after melting at 800 °C
is Na2SO4 (Fig. 4a). As shown in Fig. S1b,† (NH4)2SO4·SbF3 is
stable up to 170 °C, and it can be seen that in the range of
170–603 °C, a total weight loss of about 63.30% occurred. The
residue of (NH4)2SO4·SbF3 after melting at 800 °C is SbO2
(Fig. 4b). We can see from Fig. S1c† that K2SO4·SbF3 is stable
up to 249 °C, and in the range from 249–800 °C, the com-
pound undergoes a total weight loss of about 44.44%, which
corresponds to the removal of a SbF3 molecule (calculated
value: 50.60%). The decomposition reaction may be
K2SO4·SbF3 → K2SO4 + SbF3 based on the powder XRD of the
The bond valence calculations47,48 indicate that the oxi-
dation states of O, F, Na, S, K, Rb and Sb atoms in A2SO4·SbF3
+
(A = Na+, NH4 , K+, Rb+) are −2, −1, +1, +6, +1, +1 and +3,
respectively (Tables S1–S4†).
Cation size influencing macroscopic centricities and the
framework structures
As discussed previously, the four compounds A2SO4·SbF3 (A =
+
Na+, NH4 , K+, Rb+) are stoichiometrically equivalent, but
exhibit three different structural backbones. There is no differ-
ence except for the A+ cations; so we can conclude that A+
cations play an important role in structure-directing and bring
about the discrepancy among the four compounds. In
Na2SO4·SbF3, considering that the radius of Na+ is the smallest
with the minimal steric hindrance among the four A+ ions, it
2−
is reasonable that SbF3 and SO4 tend to self-aggregate and
form the [(SbF3)2(SO4)2]4− dimers. However, in (NH4)2SO4·SbF3
2−
and K2SO4·SbF3/Rb2SO4·SbF3, SbF3 and SO4 are inclined to
+
form the 1-D zigzag [SbF3SO4]2− chain, because NH4 , K+ and
Rb+ are bigger than Na+, and the decentralized arrangement is
conducive to the maximum use of space. Because the Rb+ is
larger than NH4+, the angle of O–Sb–O in Rb2SO4·SbF3 is
Fig. 4 Experimental and calculated XRD patterns for compounds
Na2SO4·SbF3 (a), (NH4)2SO4·SbF3 (b), K2SO4·SbF3 (c), Rb2SO4·SbF3 (d)
smaller than that in (NH4)2SO4·SbF3. Meanwhile, the Sb–O before and after melting, respectively.
This journal is © The Royal Society of Chemistry 2018
Dalton Trans., 2018, 47, 17486–17492 | 17489

View Article Online
Paper
Dalton Transactions
decomposition product of the sample shown in Fig. 4c. As 5.13, 4.54, 4.44 and 4.15 eV, with the corresponding UV
shown in Fig. S1d,† Rb2SO4·SbF3 is stable up to 277 °C, and a absorption edge being 242, 273, 279 and 298 nm, respectively,
total weight loss of about 34.56% in the range from which indicates that all of the four title compounds are poten-
277–800 °C corresponds to the release of a SbF3 molecule with tial UV optical materials.
a calculated value of 40.10%. The decomposition reaction of
Rb2SO4·SbF3 may be similar to that of its isostructural com-
pound K2SO4·SbF3 on the basis of the powder XRD of the
melting sample as shown in Fig. 4d.
Nonlinear optical properties
Among the four stoichiometrically equivalent compounds,
K2SO4·SbF3 and Rb2SO4·SbF3 are NCS and their powder SHG
signals were measured using a Q-switch laser of 1064 nm by
the Kurtz–Perry method (Fig. 6). The known NLO material KDP
(KH2PO4) is used as the reference, and the results indicate that
the SHG efficiencies of K2SO4·SbF3 and Rb2SO4·SbF3 are about
0.1 and 0.3 times that of KDP. With the increase of the particle
size, the second harmonic generation intensity signal
enhances gradually. Hence, both the compounds K2SO4·SbF3
and Rb2SO4·SbF3 are type I phase-matchable. The SHG inten-
sity increase from K2SO4·SbF3 to Rb2SO4·SbF3 should be attrib-
uted to the increasing polarizability of alkali metal cations as
in our previous work, A3VO(O2)2CO3 (A = K, Rb, and Cs),20
which has been investigated in detail.
Optical properties
The infrared spectra of the title compounds are showed in
Fig. S2.† The strong absorption peaks of (NH4)2SO4·SbF3
observed at 3137 and 1401 cm−1 correspond to the stretching
vibrations of N–H.49 Overlapping peaks of the four compounds
Na2SO4·SbF3, (NH4)2SO4·SbF3, K2SO4·SbF3 and Rb2SO4·SbF3
can be viewed at 1161/1120/1074 cm−1, 1191/1130/1055 cm−1
1193/1124/1048 cm−1, and 1176/1128/1050 cm−1 due to ν3
,
2−
2−
SO4 asymmetric stretching, respectively. The ν1 SO4 sym-
metric stretching vibrations of the four compounds can be
viewed at 983, 967, 967 and 962 cm−1. The bands at 624/530/
506 cm−1 (Na2SO4·SbF3), 616/560/490 cm−1 ((NH4)2SO4·SbF3),
617/555/478 cm−1 (K2SO4·SbF3), and 612/556/479 cm−1
(Rb2SO4·SbF3) are assigned to Sb–O asymmetric stretching and
Sb–O bending and stretching, respectively. The assignments
are in accordance with other previously reported
compounds.50,51
Theoretical calculations
To further investigate the NLO properties, the theoretical cal-
culation based on the DFT method for Rb2SO4·SbF3 was done.
The calculated band structure of Rb2SO4·SbF3 is shown in
Fig. 7a. The calculated band gap of Rb2SO4·SbF3 is 4.16 eV,
and the experimental value is 4.15 eV; the high similarity of
the two values indicates that the computational strategy
adopted is suitable for the present systems, while the band
gap calculated by the DFT-GGA method is generally
underestimated.54,55
The total and partial density of states (DOS) are widely used
to study the band structure and the orbital components. As
shown in Fig. 7b, the valence bands (VB) of Rb2SO4·SbF3
ranging from −25.0 eV to −10.0 eV are contributed by Rb-5s,
S-3s, S-3p, O-2s, and F-2s states. The near Fermi level (−10 eV
to 0 eV) arises from mostly Rb-4p, S-3p, O-2p, Sb-5s, Sb-5p and
F-2p states. The peaks located between 0 eV and 10 eV (con-
duction bands) are mainly composed of the Sb-5p state. The
strong covalent interactions of S–O bonds and Sb–F bonds are
The optical diffuse reflectance spectra and the UV-vis
absorption spectra for the four title compounds were
measured. The Kubelka–Munk formula, F(R) = K/S = (1 − R)2/
2R, was used to calculate the absorption (K/S) data from the
reflectance spectra. In the formula, R, K and S represent the
reflectance, absorption, and scattering coefficient, respect-
ively.52,53 As shown in Fig. 5, the optical band gaps of
Na2SO4·SbF3, (NH4)2SO4·SbF3, K2SO4·SbF3 and Rb2SO4·SbF3 are
Fig. 6 (a) Phase-matching curves for K2SO4·SbF3 and Rb2SO4·SbF3: the
red rhombus for K2SO4·SbF3, the blue square for Rb2SO4·SbF3, and the
black circle for KDP; and (b) the SHG intensities for K2SO4·SbF3 and
Rb2SO4·SbF3 with KDP as a reference.
Fig. 5 UV absorption spectra and optical diffuse reflectance spectra for
Na2SO4·SbF3 (a), (NH4)2SO4·SbF3 (b), K2SO4·SbF3 (c), Rb2SO4·SbF3 (d).
17490 | Dalton Trans., 2018, 47, 17486–17492
This journal is © The Royal Society of Chemistry 2018

View Article Online
Dalton Transactions
Paper
2 S. G. Zhao, X. Y. Yang, Y. Yang, X. J. Kuang, F. Q. Lu,
P. Shan, Z. H. Sun, Z. S. Lin, M. C. Hong and J. H. Luo,
J. Am. Chem. Soc., 2018, 140, 1592–1595.
3 Q. Wei, S. J. Sun, J. Zhang and G. Y. Yang, Chem. – Eur. J.,
2017, 23, 7614–7620.
4 L. Cheng and G. Y. Yang, Chem. Commun., 2014, 50, 344–
346.
5 Y. Wang and S. L. Pan, Coord. Chem. Rev., 2016, 323, 15–
35.
6 F. R. Guo, C. Chen, K. C. Wang, Q. H. Zhang and Z. E. Lin,
Inorg. Chem., 2016, 55, 7817–7819.
Fig. 7 (a) Calculated band structure of Rb2SO4·SbF3; and (b) total and
partial DOS for Rb2SO4·SbF3; the fermi level is normalized to 0 eV.
7 S. P. Guo, Y. Chi and G. C. Guo, Coord. Chem. Rev., 2017,
335, 44–57.
8 L. D. Luan, J. Li, C. Chen, Z. E. Lin and H. Huang, Inorg.
Chem., 2015, 54, 9387–9389.
9 S. P. Guo, Y. Chi, B. W. Liu and G. C. Guo, Dalton Trans.,
2016, 45, 10459–10465.
10 J. Shi, K. Wang, J. Li, H. Zeng, Q. Zhang and Z. Lin, Dalton
Trans., 2018, 47, 654–658.
verified by the overlaps of S-3s and S-3p with O-2s and O-2p
states and the overlaps of Sb-5s with Sb-5p states from −25.0
eV to 0.00 eV. It is clear that the highest valence band and the
smallest conduction band are mainly contributed by O-2p,
F-2p and Sb-5p, respectively, and the nonlinear properties of
the Rb2SO4·SbF3 compound mainly come from the contri-
bution of the [SbF3O2]4− and SO42− units.
11 P. Yu, L. M. Wu, L. J. Zhou and L. Chen, J. Am. Chem. Soc.,
2014, 136, 480–487.
12 Y. Wang, B. B. Zhang, Z. H. Yang and S. L. Pan, Angew.
Chem., Int. Ed., 2018, 57, 2150–2154.
Conclusions
13 L. Kang, S. Y. Luo, H. W. Huang, N. Ye, Z. S. Lin, J. G. Qin
and C. T. Chen, J. Phys. Chem. C, 2013, 117, 25684–25692.
14 M. Luo, F. Liang, Y. X. Song, D. Zhao, F. Xu, N. Ye and
Z. S. Lin, J. Am. Chem. Soc., 2018, 140, 3884–3887.
15 X. H. Dong, L. Huang, Q. Y. Liu, H. M. Zeng, Z. E. Lin,
D. G. Xu and G. H. Zou, Chem. Commun., 2018, 54, 5792–
5795.
16 G. H. Zou, H. Jo, S. Lim, T. You and K. M. Ok, Angew.
Chem., Int. Ed., 2018, 57, 8619–8622.
17 F. F. He, Q. Wang, M. J. Liu, L. Huang, D. J. Gao, J. Bi and
G. H. Zou, Cryst. Growth Des., 2018, 18, 4756–4765.
18 Q. Wang, F. F. He, L. Huang, D. J. Gao, J. Bi and G. H. Zou,
Cryst. Growth Des., 2018, 18, 3644–3653.
19 L. Huang, G. H. Zou, H. Q. Cai, S. C. Wang, C. S. Lin and
N. Ye, J. Mater. Chem. C, 2015, 3, 5268–5274.
20 G. H. Zou, Z. Lin, H. M. Zeng, H. Jo, S. Lim, T. You and
K. M. Ok, Chem. Sci., 2018, DOI: 10.1039/C8SC03672A.
21 M. L. Liang, Y. X. Ma, C. L. Hu, F. Kong and J. G. Mao,
Dalton Trans., 2018, 47, 1513–1519.
+
By systematically exploring the A-Sb-SO4 (A = NH4 , alkali
metal) system, four antimony fluoride sulfates named
A2SO4·SbF3 (A = Na+, NH4 , K+, Rb+) were successfully syn-
+
thesized through a hydrothermal method. A+ cation plays an
important role in effecting the coordination mode and the
arrangement of the four compounds resulting in three
different space groups with different centricities. Detailed
characterization such as IR, TGA, XRD, UV and theoretical cal-
culations were carried out. The powder second harmonic gene-
ration for K2SO4·SbF3 and Rb2SO4·SbF3 indicates that both the
compounds are type I phase-matchable and exhibit SHG
efficiencies about 0.1 and 0.3 times that of KDP. Tuning the
crystal structures through metal cations will be helpful for the
subsequent exploring of new NLO materials.
Conflicts of interest
22 M. Luo, F. Liang, Y. X. Song, D. Zhao, N. Ye and Z. S. Lin,
J. Am. Chem. Soc., 2018, 140, 6814–6817.
There are no conflicts to declare.
23 X. Y. Dong, Q. Jing, Y. J. Shi, Z. H. Yang and S. L. Pan,
J. Am. Chem. Soc., 2015, 137, 9417–9422.
Acknowledgements
24 H. Zhang, M. Zhang, S. L. Pan, X. Y. Dong, Z. H. Yang,
X. L. Hou, Z. Wang, K. B. Chang and K. R. Poeppelmeier,
J. Am. Chem. Soc., 2015, 137, 8360–8363.
25 G. H. Zou, C. S. Lin, H. Jo, G. Nam, T. S. You and K. M. Ok,
Angew. Chem., Int. Ed., 2016, 55, 12078–12082.
26 K. M. Ok, Acc. Chem. Res., 2016, 49, 2774–2785.
27 D. W. Lee, S. J. Oh, P. S. Halasyamani and K. M. Ok, Inorg.
Chem., 2011, 50, 4473–4480.
This work was supported by the National Natural Science
Foundation of China (no. 21501161 and 21875146).
References
1 P. S. Halasyamani and K. R. Poeppelmeier, Chem. Mater., 28 Q. Wang, C. S. Lin, G. H. Zou, M. J. Liu, D. J. Gao, J. Bi and
1998, 10, 2753–2769.
L. Huang, J. Alloys Compd., 2018, 735, 677–683.
This journal is © The Royal Society of Chemistry 2018
Dalton Trans., 2018, 47, 17486–17492 | 17491

View Article Online
Paper
Dalton Transactions
29 M. Luo, Y. X. Song, F. Liang, N. Ye and Z. S. Lin, Inorg. 43 S. K. Kurtz and T. T. Perry, J. Appl. Phys., 1968, 39, 3798–
Chem. Front., 2018, 5, 916–921. 3813.
30 H. Yu, N. Koocher, J. Rondinelli and P. S. Halasyamani, 44 S. J. Clark, M. D. Segall, C. J. Pickard, P. J. Hasnip,
Angew. Chem., Int. Ed., 2018, 57, 6100–6103.
31 J. L. Song, C. L. Hu, X. Xu, F. Kong and J. G. Mao, Angew.
Chem., Int. Ed., 2015, 54, 3679–3682.
32 W. L. Zhang, W. D. Cheng, H. Zhang, L. Geng, C. S. Lin and
Z. Z. He, J. Am. Chem. Soc., 2010, 132, 1508–1509.
33 C. Huang, J. H. Zhang, C. L. Hu, X. Xu, F. Kong and
J. G. Mao, Inorg. Chem., 2014, 53, 3847–3853.
M. J. Probert, K. Refson and M. C. Payne, Z. Kristallogr.,
2005, 220, 567–570.
45 J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett.,
1996, 77, 3865–3868.
46 D. Vanderbilt, Phys. Rev. B: Condens. Matter Mater. Phys.,
1990, 41, 7892–7895.
47 I. D. Brown and D. Altermatt, Acta Crystallogr., Sect. B:
Struct. Sci., 1985, 41, 244–247.
34 H. Jo and K. M. Ok, Inorg. Chem., 2016, 55, 6286–6293.
35 F. F. He, Q. Wang, C. F. Hu, W. He, X. Y. Luo, L. Huang, 48 N. E. Brese and M. O’Keeffe, Acta Crystallogr., Sect. B:
D. J. Gao, J. Bi, X. Wang and G. H. Zou, Cryst. Growth Des.,
2018, 18, 6239–6247.
36 D. W. Lee and K. M. Ok, Inorg. Chem., 2013, 52, 5176–5184.
Struct. Sci., 1991, 47, 192–197.
49 M. Maczka, A. Pietraszko, B. Macalik and K. Hermanowicz,
Inorg. Chem., 2014, 53, 787–794.
37 Y. H. Kim, T. T. Tran, P. S. Halasyamani and K. M. Ok, 50 X. Zhao, D. J. Mei, J. L. Xu and Y. D. Wu, Z. Anorg. Allg.
Inorg. Chem. Front., 2015, 2, 361–368. Chem., 2016, 642, 343–349.
38 T. Birchall, B. Ducourant, R. Fourcade and G. Mascherpa, 51 X. Zhao, D. J. Mei, J. L. Xu and Y. D. Wu, Solid State Sci.,
J. Chem. Soc., Dalton Trans., 1982, 2313–2316. 2015, 50, 52–57.
39 G. M. Sheldrick, SHELXL-97, Progr. Slout. Cryst. Struct. 52 P. Kubelka, Ein beitrag zur optik der farbanstriche, Z. Tech.
Univ. Göttingen, Göttingen, Germany, 1997. Phys., 1931, 12, 593–601.
40 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. 53 J. Tauc, Mater. Res. Bull., 1970, 5, 721–729.
Crystallogr., 2008, 64, 112–122.
54 Q. Y. Liu, X. H. Dong, G. H. Zou, D. G. Xu and Z. E. Lin,
41 O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard
and H. Puschmann, J. Appl. Crystallogr., 2009, 42, 339–341.
42 A. L. Spek, J. Appl. Crystallogr., 2003, 36, 7–13.
Inorg. Chem. Commun., 2018, 96, 97–100.
55 Y. S. Zhong, W. Zhang, D. C. Ma, D. G. Xu and Z. E. Lin,
Inorg. Chem. Commun., 2017, 86, 108–111.
17492 | Dalton Trans., 2018, 47, 17486–17492
This journal is © The Royal Society of Chemistry 2018