A new mixed framework compound with corrugated [Si6O15] ∞∞ layers: K2TiSi6O15

Article abstract of DOI:10.1006/jssc.2000.8972

The hydrothermal reaction in an aqueous mixture of TiCl₃, colloidal silica, KF, and KOH yielded colorless prismatic crystals of K₂TiSi₆O₁₅. The structure contains one unique TiO₆ octahedron and six unique SiO₄ tetrahedra. The SiO₄ tetrahedra are corner-shared with each other, forming a corrugated [Si₆O₁₅]_∞∞ layer containing four-, six-, and eight-membered rings. These layers are connected by isolated TiO₆ octahedra into a three-dimensional octahedral-tetrahedral mixed anion framework. Four-, five-, and seven-membered rings are formed by mixed SiO₄ tetrahedra and TiO₆ octahedra. The two potassium cations are located in the cage formed by the six- and seven-membered rings. The structure of the title compound is compared with those of related silicates. Crystal data: monoclinic, space group P2₁, a=6.916(3), b=12.812(3), c=7.661(2) A, β=106.25(4)°, V=651.7(4) A³, Z=2, and M=534.64. R_F=0.0329 for 2565 unique reflections with I>2σ(I) and 218 parameters. ￠ 2001 Academic Press.

Full text of DOI:10.1006/jssc.2000.8972

Journal of Solid State Chemistry 156, 135}142 (2001)
doi:10.1006/jssc.2000.8972, available online at http://www.idealibrary.com on
A New Mixed Framework Compound with Corrugated
1
[Si6O15] Layers: K2TiSi6O15
ꢀꢀ
Xiaodong Zouꢁ and Mike S. Dadachov
Structural Chemistry, Stockholm University, S-106 91 Stockholm, Sweden
Received May 22, 2000; in revised form August 21, 2000; accepted September 15, 2000; published online December 21, 2000
example TS-1 (1) has been widely used as a catalyst for
The hydrothermal reaction in an aqueous mixture of TiCl3, selective oxidation reactions with hydrogen peroxide in
colloidal silica, KF, and KOH yielded colorless prismatic crys-
tals of K2TiSi6O15. The structure contains one unique TiO6
octahedron and six unique SiO4 tetrahedra. The SiO4 tetrahedra
are corner-shared with each other, forming a corrugated
industry scale.
There exist more than 70 di!erent titanium silicates. The
structures of most of them are mixed anion frameworks (2).
During the past decades, great e!orts have been made in
synthesizing new titanium silicates and their analogs to the
minerals. Many synthetic analogues of titanium silicate min-
erals have been reported, such as natisite Na (TiO)[SiO ]
[Si6O15]
layer containing four-, six-, and eight-membered
ꢀꢀ
rings. These layers are connected by isolated TiO6 octahedra into
a three-dimensional octahedral+tetrahedral mixed anion frame-
work. Four-, 5ve-, and seven-membered rings are formed by
mixed SiO4 tetrahedra and TiO6 octahedra. The two potassium
cations are located in the cage formed by the six- and seven-
membered rings. The structure of the title compound is com-
ꢁ
ꢃ
ꢁ
(3, 4) and its polymorph modi"cation Na Ti O (OH)
ꢅꢆꢇ ꢁ
[SiO ] (5), zorite Na [Ti(Ti Nb )(Si O ) (O,OH) ] '
ꢃ ꢃ ꢉꢆꢊ ꢉꢆꢂ ꢈ ꢂꢋ ꢁ
11H O (6, 7), sitinakite Na (H O) (Ti Nb (OH)O
ꢅꢆꢄ ꢉꢆꢁ
(8, 9), and fresnoite Ba (TiO)[Si O ]
ꢁ ꢋ
(10, 11). Ti analogs of the minerals wadeite K TiSi O (12),
ꢅ ꢊ
nenadkevichite (Na,Ca)(Nb,Ti)Si O ' 2H O (13, 14), phar-
ꢁ ꢋ
macosiderite Me HTi O (SiO ) ' 4}8H O (Me"H or al-
ꢃ ꢃ ꢃ ꢅ
ꢄ
ꢈ
ꢇ
ꢁ
ꢁ
ꢁ
ꢁ
ꢇ
pared with those of related silicates. Crystal data: monoclinic, (SiO ) ' K(H O)
ꢃ ꢁ
ꢁ
ꢂꢆꢋ
ꢁ
space group P21, a ؍ 6.916(3), b ؍ 12.812(3), c ؍ 7.661(2) A,
b ؍ 106.25(4)3, V ؍ 651.7(4) A3, Z ؍ 2, and M ؍ 534.64. RF ؍
0.0329 for 2565 unique re6ections with I92r(I) and 218
parameters. ( 2001 Academic Press
Key Words: hydrothermal synthesis; silicates; titanium sili-
cates; framework; mixed framework; crystal structure; X-ray
structure determination.
ꢁ
ꢁ
ꢅ
ꢁ
kali metal) (15}18) have also been synthesized. However,
only a few novel titanium silicates, such as ETS-10 (19}21)
and JDF-L1 (22) have been prepared. Both hydrothermal
crystallization and high temperature solid state ceramic
methods have been used for synthesis of titanium silicates.
Many titanium silicates have open mixed-framework struc-
tures and show great potential as ion-exchange compounds
(7}9, 14}21, 23).
INTRODUCTION
Natural (minerals) and synthetic mixed framework com-
pounds, with their diverse structures built from common
polyhedral units, octahedra and tetrahedra, are of great
interest due to their shape-selective catalytic activity and
ion-exchange and adsorption properties. Titanium silicates
are among those that have been widely studied. For
Recently we have synthesized several new mixed frame-
work titanium silicates, a rhombohedrally distorted Na
ꢃ
[Ti O (SiO ) ] ' 6H O (24), an orthorhombic K TiSi O '
ꢃ ꢃ
ꢃ ꢅ
ꢁ
ꢁ
ꢅ ꢊ
H O (25), and Na (Na,H)Ti O [Si O ] ' 2.2H O (26), and
ꢁ
ꢅ
ꢁ ꢁ ꢁ ꢈ
ꢁ
determined their crystal structures. As a part of our ongoing
search for new mixed framework titanium silicates, we re-
port here the synthesis and crystal structure of a novel
tetrahedral}octahedral mixed framework of anhydrous
ꢂ See NAPS Document No. 00000 for 00 pages of supplementary mater-
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potassium titanium silicate K TiSi O
.
ꢁ
ꢈ ꢂꢇ
EXPERIMENTAL
Synthesis
The title compound K TiSi O was synthesized under
hydrothermal conditions from aqueous alkaline potassium
titanium silicate mixture, containing titanium(III) chloride,
ꢁ
ꢈ ꢂꢇ
ꢁ To whom correspondence should be addressed. Fax: #46 8 16 31 18.
E-mail: zou@struc.su.se.
135
0022-4596/01 $35.00
Copyright ( 2001 by Academic Press
All rights of reproduction in any form reserved.

136
ZOU AND DADACHOV
colloidal silica Ludox HS-40, potassium #uoride and potas-
sium hydroxide. KOH (10.240 g) and 2.531 g Ludox (HS-40,
Aldrich) were added to 59.974 g distilled water. KF (0.968 g)
and then 5.760 g TiCl solution (15wt% TiCl , 10wt% HCl,
ꢅ
ꢅ
Aldrich) were added under continuous stirring. Finally
3.084 g KOH was added to increase the pH to 13.0. The
"nal molar ratio is 1.0 TiCl :3.0 SiO :3.0 KF:42 KOH:
ꢅ
ꢁ
&600 H O. About 10 ml of this mixture was sealed in a
ꢁ
23-ml Te#on-lined autoclave (Parr, USA) and heated at
488 K under autogeneous pressure for 212 h. The products
contained three crystalline phases with di!erent morpholo-
gies: large spherical particles (&120 lm) formed by pris-
matic crystal rods (Fig. 1a, phase A) dominated, small
spherical particles (&50 lm) of aggregated crystal plates
(Fig. 1b, phase B), and thin plates (&2 lm wide) (Fig. 1c,
ꢁ
phase C). The large spherical particles, which were about
ꢅ
of the total products, were separated from the other phases
by washing and decanting the mixture with distilled water.
They were then "ltered and dried at 328 K. The formation
of the large spherical particles of the title compound
K TiSi O , occurred only within a narrow range of pH
(13.0$0.5) and molar ratio of Ti:Si (1:3). When the time for
the synthesis was reduced to 100 h, only the thin plates
(phase C) and some amorphous material were obtained.
ꢁ
ꢈ ꢂꢇ
Analytical Methods
X-ray powder di!raction analysis was performed on
a Guinier}Hagg focusing camera, with CuKa radiation.
ꢂ
Fine silicon powder was used as an internal standard. The
X-ray powder di!raction patterns indicated that phases
A and C were new, while phase B was K TiSi O ' H O (25).
ꢁ
ꢅ ꢊ
ꢁ
In order to test the thermal stability of the phase C, X-ray
powder di!raction patterns of the phase C were also col-
lected at di!erent temperatures from the room temperature
up to 9003C in air on a Huber Imaging Plate Guinier
Camera 670 with a heating facility.
Quantitative energy dispersive spectroscopy (EDS) analy-
sis was performed on a JEOL JSM820 scanning electron
microscope equipped with a LINK AN1000 system which
gave the compositions K:Ti:Si"1.8:1.0:6.0 for phase A
and K:Ti:Si"1:2:2 for phase C.
FIG. 1. Scanning electron micrographs of the di!erent phases found in
the synthesis. (a) Phase A (the title compound K TiSi O ), (b) phase B
ꢁ
ꢈ ꢂꢇ
(K TiSi O ' H O), and (c) phase
C
(new, with
a composition of
Structure Solution and Rexnement
ꢁ
ꢅ
ꢊ
ꢁ
K Ti Si O ' nH O) and some remaining amorphous material.
ꢁ
ꢃ
ꢃ
ꢂꢋ
ꢁ
Among the three crystalline phases, only phase A was
suitable for single crystal X-ray di!raction. A transparent,
twin-like prismatic crystal of phase A with dimensions and 0.75 A (2h"3.8}56.33) could be collected. Two hun-
0.020;0.025;0.10 mm was selected for single crystal X-ray dred exposures (ꢀ between 0 and 2003) were recorded with
di!raction analysis. Intensity data were collected at 293 K a ꢀ increment of 1.03.
on a STOE IPDS di!ractometer using graphite-mono-
The unit cell of phase A, the title compound, was found to
chromatized MoKa radiation (0.71073 A) from a rotating be monoclinic with lattice parameters a"6.916(3), b"
anode generator. The distance between the crystal and the 12.812(3), c"7.661(2) A, b"106.25(4)3 and a cell volume of
ꢅ
detector was 60 mm so that di!raction data between 10.72 651.7(4) A , re"ned using 1003 re#ections. No indication of

SYNTHESIS AND CRYSTAL STRUCTURE OF K TiSi O
ꢂꢇ
137
ꢁ
ꢈ
TABLE 1
twinning was found from reciprocal space. A total of 5198
re#ections were integrated with a dynamic pro"le function
using e!ective mosaic spread of 0.010.
Crystal Data and Structure Re5nement for K2TiSi6O15
Crystal data
Two space groups, P2 and P2 /m, were consistent with
ꢂ
ꢂ
Empirical formula
K2 O15 Si6 Ti
the systematic extinctions. Analysis of the statistical distri-
Structural formula
Formula weight
Space group
a, b, c [A]
a, b, c [3]
Z, Volume [Aꢅ]
D(calc) [g/cmꢅ]
F(000)
K [(TiO )(SiO ) ]
ꢁ
ꢅ
ꢁ ꢈ
ꢁ
bution of the normalized structure factors, i.e., "1E !12",
534.64
P2 (No. 4)
indicated that the structure was acentric and the space
ꢂ
6.916(3) 12.812(3) 7.661(2)
group was P2 . This was also con"rmed later by the success-
ꢂ
90 106.25(4) 90
2, 651.7(4)
2.724
528
1.936
ful solution and re"nement of the structure.
The crystal structure of the title compound was solved by
direct methods, using the SHELXS-97 (27) software pack-
age. The composition was K TiSi O , which agreed with
l (MoKa) [mm\ꢂ ]
ꢁ
ꢈ ꢂꢇ
that obtained by EDS analysis. The nine unique nonoxygen
atoms were found directly by direct methods and all the 15
unique oxygen atoms could be located easily from the
di!erence Fourier map. Structure re"nement was carried
out by SHELXL-97 (28) using atomic scattering factors for
neutral atoms. The Flack parameter x (29), estimated by
SHELXL-97, was 0.46(7), indicating that the crystal was an
inversion twin. Due to the twinning, it was di$cult to
estimate the shape using X-SHAPE (30) and very little
improvement was obtained by numerical absorption correc-
tion using X-RED (31). An empirical absorption correction
was applied using DIFABS (32), prior to the re"nement of
anisotropic thermal displacement parameters. The structure
was "nally re"ned anisotropically against the intensities,
resulting in a "nal R1 index of 3.29% and a weighted Rw
index of 7.36% for 2565 re#ections with I'2p(I). The
crystallographic data and the results of the structure re"ne-
ment are given in Table 1.
Data collection
Radiation [A]
Theta min-max [3]
Scan(type and range) [3]
MoKa, 0.71073
3.1, 27.9
Stoe IPDS di!ractometer, area
detector scans
Data set
!7(" h(" 7, !14(" k(
"14, !8(" l("8
5198, 2921, 0.049
No. measured, unique re#s., R(int)
No. unique re#s. with I'2p (I)
Absorption correction
2565
Empirical (DIFABS, Walker and
Stuart, 1983)
¹
, ¹
0.556, 0.867
ꢀ*ꢁ ꢀ!ꢂ
Re"nement
Re"nement method
Full-matrix least-squares on Fꢁ
2921, 218
0.0329, 0.0736, 0.980
0.0415, 0.0765
No. unique re#s., No. parameters
Final R indices (I'2p(I)) R1, wR2, S
Final R indices (all data) R1, wR2,
w"1/[pꢁ(Fꢁ)#(0.0432P)ꢁ] where
Max. and min. residual dens. [e/Aꢅ]
P"(Fꢁ)#2Fꢁ)/3
0.455, !0.471
ꢃ
ꢃ
#
(Fig. 3b). Three types of mixed rings are formed: 4-(¹}¹}
¹}O ), 5-(¹}¹}¹}¹}O ) and 7-(¹}¹}O }¹}¹}¹}¹}O )
RESULTS AND DISCUSSION
F
F
F
F
Structure Description
membered rings (¹"SiO tetrahedron and O "TiO oc-
ꢃ
F
ꢈ
tahedron). The two potassium cations are located in the
cage formed by the six- and seven-membered rings.
Atomic coordinates and isotropic displacement para-
meters of the title compound are given in Table 2 and
selected bond distances and angles in Table 3. The results of
¹iO octahedra. The only crystallographically unique
ꢈ
a bond-valence calculation, according to the method of TiO octahedron is slightly distorted (Table 3), with cation-
ꢈ
Pyatenko (33), are shown in Table 4.
anion distances (Ti}O) between 1.910 and 1.992 A (average
1.953 A) and O}Ti}O angles between 84.81 and 93.423. This
is characteristic for Ti octahedra observed in silicate struc-
Structure topology. There are 24 crystallographically
unique atoms, 2 potassium, 1 titanium, 6 silicon, and 15
oxygen. An ORTEP presentation of the asymmetric unit,
with all the atoms labeled, is shown in Fig. 2. The polyhed-
tures with isolated TiO units.
ꢈ
SiO4 tetrahedra. All the six SiO tetrahedra are corner-
ꢃ
ral presentations of the structure model are shown in Fig. 3a shared either with each other or with TiO octahedra. The
ꢈ
(along the c axis) and Fig. 3b (along the a axis). The princi- Si}O bond lengths are in the range of 1.576}1.647 A, similar
pal structure motif in K TiSi O can be described as to those found in other silicates including anhydrous tita-
ꢁ
ꢈ ꢂꢇ
corrugated [Si O
ꢈ ꢂꢇ ꢀꢀ
ab plane, zigzagged along the b axis. The building units of atoms involved in the Ti}O}Si bridging are systematically
]
layers. The layers are parallel to the nium/zirconium silicates. The Si}O distances of all oxygen
the [Si O ]
layers are four- and six-membered rings, shorter (1.576}1.594 A) than those in the Si}O}Si bridging
ꢈ ꢂꢇ ꢀꢀ
which are connected to each other forming chair-like eight- (1.615}1.647 A). The Si}O bonds are slightly oversaturated
membered rings (Fig. 3a). The [Si O ] layers are con- for those oxygen atoms involved in Ti}O}Si bridging (aver-
ꢈ ꢂꢇ ꢀꢀ
nected by isolated TiO octahedra and stacked along the age bond valence 1.15) compared with those involved only
ꢈ
c axis to form a three-dimensional mixed framework in Si}O}Si bridging (average bond valence 0.97).

138
ZOU AND DADACHOV
TABLE 2
TABLE 3=Continued
Fractional Atomic Coordinates and Equivalent Isotropic
Displacement Parameters (A2) for K2TiSi6O15
Si1O4 tetrahedron
Si4O4 tetrahedron
Si1}O7
1.615(4)
1.630(3)
1.639(3)
1.591(4)
1.619
Si4}O1
Si4}O6
Si4}O9
1.637(4)
1.589(4)
1.630(3)
1.626(3)
1.620
Si1}O11
Si1}O13
Si1}O15
1Si1}O2
Atom
x
y
z
;(eq)
Si4}O11 c
}
Ti1
Si1
Si2
Si3
Si4
Si5
Si6
K1
K2
O1
O2
O3
O4
O5
O6
O7
O8
O9
O10
O11
O12
O13
O14
O15
0.7564(1)
0.0069(2)
0.4502(2)
0.6714(2)
0.0127(2)
0.5439(2)
0.3061(2)
0.1943(2)
0.2022(2)
0.2352(5)
0.5375(5)
0.7333(5)
0.2064(5)
0.5585(5)
0.0235(5)
!0.1330(5)
0.5889(5)
!0.1358(5)
0.4997(5)
!0.0757(5)
0.3861(5)
0.2265(5)
0.4519(5)
0.0245(5)
0.2495(1)
0.6780(1)
0.6661(1)
0.5090(1)
0.8423(1)
0.3340(1)
0.5069(1)
0.4064(1)
0.1081(1)
0.8825(3)
0.7588(3)
0.3911(3)
0.6088(3)
0.2779(3)
0.7927(3)
0.5755(3)
0.5620(3)
0.9435(2)
0.5284(3)
0.7604(3)
0.4318(3)
0.6356(3)
0.7006(3)
0.7260(3)
0.2487(1)
0.3311(2)
0.4433(2)
0.2924(2)
0.0441(2)
!0.1641(2)
!0.0688(2)
0.4206(2)
0.1500(2)
0.1629(5)
0.3409(5)
0.3346(5)
!0.1702(5)
0.0241(5)
!0.1431(5)
0.2778(5)
0.4533(5)
0.0014(5)
0.1028(5)
0.1649(5)
!0.2082(5)
0.3191(5)
0.6437(5)
0.5265(5)
0.0082(2)
0.0089(2)
0.0085(2)
0.0085(2)
0.0089(2)
0.0090(2)
0.0082(2)
0.0296(3)
0.0267(3)
0.0141(7)
0.0131(6)
0.0150(7)
0.0133(6)
0.0127(7)
0.0125(7)
0.0160(7)
0.0129(7)
0.0126(6)
0.0165(7)
0.0142(6)
0.0122(6)
0.0149(7)
0.0123(6)
0.0132(7)
1Si4}O2
O7}Si1}O11
O7}Si1}O13
O7}Si1}O15
O11}Si1}O13
O11}Si1}O15
O13}Si1}O15
1O}Si1}O2
106.0(2)
102.4(2)
115.8(2)
107.4(2)
113.7(2)
110.6(2)
109.4
O1}Si4}O6
O1}Si4}O9
O1}Si4}O11 c
O6}Si4}O9
O6}Si4}O11 c
110.7(2)
107.6(2)
109.4(2)
108.8(2)
112.1(2)
108.1(2)
109.4
}
}
}
O9}Si4}O11 c
1O}Si4}O2
Si2O tetrahedron
Si5O tetrahedron
ꢃ
ꢃ
Si2}O2
Si2}O8
Si2}O14
1.631(3)
1.632(3)
1.594(3)
1.621(4)
1.620
Si5}O1
Si5}O2
Si5}O5
Si5}O12
1Si5}O2
1.647(3)
1.628(4)
1.588(3)
1.634(3)
1.624
Si2}O13 c
}
1Si2}O2
O2}Si2}O8
O2}Si2}O14
O2}Si2}O13 c
O8}Si2}O14
O8}Si2}O13 c
O14}Si2}O13 c
1O}Si2}O2
109.0(2)
110.9(2)
108.3(2)
109.6(2)
106.5(2)
112.3(2)
109.4
O1}Si5}O2
O1}Si5}O5
O1}Si5}O12
O2}Si5}O5
O2}Si5}O12
O5}Si5}O12
1O}Si5}O2
109.4(2)
110.0(2)
106.0(2)
114.0(2)
103.0(2)
113.8(2)
109.4
}
}
}
Note. ;(eq) is de"ned as one third of the trace of the orthogonalized
Si3O tetrahedron
Si6O tetrahedron
;
tensor.
ꢃ
ꢃ
GH
Si3}O3
Si3}O7
Si3}O8
Si3}O10
1Si3}O2
1.579(3)
1.629(3)
1.643(3)
1.618(4)
1.617
Si6}O4
Si6}O9
1.576(3)
1.629(3)
1.644(3)
1.616(4)
1.616
Si6}O12 c
}
Si6}O10 l
}
Cation environment around K ions. The framework has
1Si6}O2
>
large voids in which the K ions are trapped as charge-
compensating countercations. Both potassium cations are
nine-coordinated and exhibit similar framework}oxygen
environments (Figs. 4a and 4b), with four short, three
intermediate and two long K}O distances. The K1}O
O3}Si3}O7
O3}Si3}O8
109.4(2)
111.9(2)
114.8(2)
107.8(2)
105.9(2)
106.8(2)
109.4
O4}Si6}O9
O4}Si6}O12 c
O4}Si6}O10 l
}
O9}Si6}O12 c
O9}Si6}O10 l
O10 l}Si6}O12 c
1O}Si6}O2
108.3(2)
110.2(2)
114.1(2)
108.6(2)
109.6(2)
106.0(2)
109.4
}
O3}Si3}O10
O7}Si3}O8
O7}Si3}O10
O8}Si3}O10
1O}Si3}O2
}
}
}
}
TABLE 3
K1 polyhedron
K2 polyhedron
2.741(4)
Selected Bond Distances (A) and Bond Angles (3) for K2TiSi6O15
K1}O6 m
2.668(4)
2.800(4)
2.853(3)
2.908(4)
3.062(4)
3.076(4)
3.102(4)
3.180(4)
3.332(4)
K2}O14
K2}O6 m
}
K1}O12
K1}O15
K1}O2
2.826(4)
2.873(3)
2.898(4)
3.035(4)
3.036(4)
3.117(4)
3.204(4)
3.359(4)
}
TiO6 octahedron
K2}O4 g
}
Ti1}O3
Ti1}O4 a
1.952(3)
1.940(3)
1.972(4)
1.952(3)
1.910(4)
1.992(3)
1.953
O3}Ti1}O15 e
O3}Ti1}O14 g
O3}Ti1}O5 h
87.87(15)
90.90(14)
91.17(16)
91.28(14)
89.61(15)
90.61(14)
91.25(15)
87.12(14)
93.42(14)
84.81(14)
90.80(14)
91.00(14)
90.0
}
}
}
K2 }O1 g
K2}O11 n
}
}
K1}O13 f
}
}
Ti1}O15 e
}
K1}O3 f
K1}O7 f
K2}O8
}
}
}
}
Ti1}O14 g
O3}Ti1}O6 h
}
}
K2}O9 g
}
Ti1}O5 h
O4 a}Ti1}O15 e
}
} }
K1}O9 m
K1}O8 i
K2}O7 n
}
Ti1}O6 h
O4 a}Ti1}O14 g
} }
}
K2}O10 n
}
1Ti}O2
O4 a}Ti1}O5 h
} }
O4 a}Ti1}O6 h
}
}
Note. Translation of symmetry code to equivalent positions: a"
!1#x, !1#y, z; b"!1#x, y, z; c"1#x, y, z; d"1#x, 1#y, z;
e"!x, !ꢂ#y, 1!z; f"!x, ꢂ#y, 1!z; g"1!x, !ꢂ#y, 1!z;
O14 g}Ti1}O15 e
}
}
}
}
O6 h}Ti1}O15 e
}
O5 h}Ti1}O14 g
ꢁ
ꢁ
ꢁ
}
h"1!x, !ꢂ#y, 2!z; i"1!x, ꢂ#y, 1!z; j"1!x, ꢂ#y, 2!z;
O5 h}Ti1}O6 h
ꢁ
ꢁ
ꢁ
}
}
k"2!x, !ꢂ#y, 2!z; l"2!x, ꢂ#y, 2!z; m"!x, !ꢂ#y,
1O}Ti}O2
ꢁ
ꢁ
ꢁ
1!z; n"!x, !ꢂ#y, 1!z; o"1!x, !ꢂ#y, 1!z;
ꢁ
ꢁ

SYNTHESIS AND CRYSTAL STRUCTURE OF K TiSi O
ꢂꢇ
139
ꢁ
ꢈ
TABLE 4
Bond-Valence Sum in the Structure of K2TiSi6O15
Ti
Si1
Si2
Si3
Si4
Si5
Si6
K1
K2
+<
"* "
GH
G
O1
O2
O3
O4
O5
O6
O7
O8
0.937
0.911
0.984
0.120
1.968
2.064
1.919
1.972
1.889
2.001
2.152
2.051
2.105
2.067
2.043
1.989
2.006
1.909
1.865
0.032
0.064
0.081
0.028
0.111
0.001
0.152
0.051
0.105
0.067
0.043
0.011
0.006
0.091
0.135
6.5%
0.962
0.118
0.102
0.667
0.690
0.742
0.603
1.150
1.159
0.123
1.147
1.124
0.146
0.100
0.084
0.094
0.128
0.094
0.107
0.100
0.083
0.107
1.008
0.950
0.909
0.951
O9
0.964
0.975
0.947
0.994
O10
O11
O12
O13
O14
O15
SUM
0.990
0.961
0.919
0.959
4.00
0.900
0.130
0.104
0.983
1.104
0.667
0.631
4.00
0.138
1.00
1.111
4.00
0.123
1.00
4.00
4.00
4.00
4.00
30.0
distances are between 2.668}2.908 A, 3.062}3.102 A, and
3.180}3.332 A and the K2}O distances between 2.741}
2.898 A, 3.035}3.117 A, and 3.204}3.359 A, respectively. The
thermal displacement parameters of both potassium atoms
are larger than those of the framework atoms (Table 2),
similar to what has been found in other titanium silicate
framework structures.
Crystal Chemical Relations
The new compound K TiSi O has several structural
ꢁ
ꢈ ꢂꢇ
similarities with other silicates, although it is not isostruc-
tural with any of them. It has the same/similar formula as
many silicate minerals and synthetic silicates, for example
the isostructural pair davanite K TiSi O (34) and dalyite
ꢁ
ꢈ ꢂꢇ
K ZrSi O (35), the synthetic epididymite K Be Si O
ꢈ ꢂꢇ ꢁ ꢈ ꢂꢇ
(36), hydrated armstrongite CaZrSi O ' 2.5H O (37),
ꢈ ꢂꢇ
Cs TiSi O (38), Cs ZrSi O (39), elpidite Na ZrSi O
ꢈ ꢂꢇ ꢈ ꢂꢇ ꢈ ꢂꢇ
3H O (40), K CeSi O (41), K GeSi O (42), and
ꢈ ꢂꢇ ꢈ ꢂꢇ
ꢁ
ꢁ
ꢁ
'
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
FIG. 3. The structure of the title compound K TiSi O , (a) viewed
ꢂꢇ
layer with four-, six-, and
ꢁ
ꢈ
along the c axis showing the [Si O
]
ꢈ
ꢂꢇ ꢀꢀ
eight-membered rings constructed from tetrahedral units. The isolated
TiO octahedra are located in the middle of the four-rings in this projec-
ꢈ
tion, (b) viewed along the a axis showing a side view of the [Si O
]
ꢈ
ꢂꢇ ꢀꢀ
layer and the connection of the layers by isolated TiO octahedra. The
ꢈ
FIG. 2. An ORTEP plot of the asymmetric unit of K TiSi O
showing the atomic labeling scheme.
TiO octahedra are in dark gray, SiO tetrahedra light gray, and potassium
ꢁ
ꢈ
ꢂꢇ
ꢈ
ꢃ
ions in "lled black circles.

140
ZOU AND DADACHOV
con}oxygen ribbons, similar to the eight-membered rings in
the mineral xonotlite Ca (Si O ) (OH) (44). In the other
ꢈ
ꢈ ꢂꢋ
ꢁ
direction (horizontally in Fig. 5), the chair-like units are
connected by two corner-sharing SiO tetrahedra. As a re-
ꢃ
sult, four- and six-membered rings are formed in all the
cases. The relative orientation of the chair-like units in each
structure is di!erent. In davanite (Fig. 5b) and armstrongite,
all the chair-like units are oriented in the same way (Fig. 5c),
while in the title compound (Fig. 5a) and epididymite
(Fig. 5d) they are oriented di!erently, such that a twofold
screw axis is generated (horizontally in Fig. 5).
FIG. 4. ORTEP drawings of the environments for potassium ions in
K TiSi O . (a) Around K1 and (b) around K2.
ꢁ
ꢈ ꢂꢇ
The [Si O
ꢈ ꢂꢇ ꢀꢀ
rugated, as seen from the side view of the [Si O ] layers
ꢈ ꢂꢇ ꢀꢀ
sazhinite Na CeSi O (OH) ' 1.5(H O) (43). All these struc- in Fig. 6. Among these four silicates, the wave amplitudes
ꢈ ꢂꢃ
tures have in"nite corrugated [Si O ]
ꢈ ꢂꢇ ꢀꢀ
them, namely davanite, epididymite and armstrongite are didymite are much larger than those for the [Si O ]
]
layers are complex and very much cor-
ꢁ
ꢁ
layers. Three of for the [Si O ]
ꢈ ꢂꢇ ꢀꢀ
layers of the title compound and epi-
ꢈ ꢂꢇ ꢀꢀ
more closely related to the title compound.
layers of davanite and armstrongite.
The [Si O ] layers of the silicates discussed above are
The Si}Si connections in the [Si O ]
layers, for the
ꢈ ꢂꢇ ꢀꢀ
ꢈ ꢂꢇ ꢀꢀ
title compound (Fig. 5a), davanite (Fig. 5b), armstrongite connected into three-dimensional mixed frameworks by oc-
(Fig. 5c), and epididymite (Fig. 5d) constitute an interesting tahedrally coordinated atoms (Ti and Zr) (Fig. 7), except for
sequence of structures. The building units of the [Si O ]
layers are the same in all the structures, i.e., four-, six-, and beryllium}oxygen tetrahedra. The octahedra in the title
epididymite where the layers are connected by pairs of
ꢈ ꢂꢇ ꢀꢀ
eight-membered SiO tetrahedral rings. The eight-mem- compound are zigzagged while those in davanite (Fig. 7b)
ꢃ
bered rings form a chair-like unit (highlighted in Fig. 5). In and armstrongite (Fig. 7c) are lying on a straight line. There
one direction (perpendicularly in Fig. 5), the chair-like units are only two types of titanium involved polyhedral ring
are connected by two shared SiO tetrahedra-forming sili- systems in the structures of davanite and armstrongite:
ꢃ
FIG. 5. Comparison of the [Si O
]
layers in di!erent compounds. All the layers have four, six-, and chair-like eight-membered rings. The latter is
ꢈ
ꢂꢇ ꢀꢀ
highlighted in each structure. (a) The title compound K TiSi O
,
(b) davanite K TiSi O
,
(c) armstrongite CaZrSi O ' 2.5H O, and
ꢁ
ꢈ
ꢂꢇ
(d) epididymite K Be Si O . Only the Si}(O)}Si connections are drawn for clarity.
ꢂꢇ
ꢁ
ꢈ
ꢂꢇ
ꢈ
ꢂꢇ
ꢁ
ꢁ
ꢁ ꢈ

SYNTHESIS AND CRYSTAL STRUCTURE OF K TiSi O
ꢂꢇ
141
ꢁ
ꢈ
FIG. 6. The [Si O
]
layers viewed perpendicular to the layers.
ꢈ
ꢂꢇ ꢀꢀ
(a) The title compound K TiSi O , (b) davanite K TiSi O , (c) arms-
ꢂꢇ ꢂꢇ
trongite CaZrSi O ' 2.5H O, and (d) epididymite K Be Si O . Only the
ꢂꢇ ꢂꢇ
Si}(O)}Si connections are drawn.
ꢁ
ꢈ
ꢁ
ꢈ
ꢈ
ꢁ
ꢁ
ꢁ ꢈ
FIG. 7. Comparison of the connection of the [Si O
]
layers by
ꢈ
ꢂꢇ ꢀꢀ
isolated octahedra. (a) The tile compound K TiSi O , (b) davanite
ꢂꢇ
K TiSi O , and (c) armstrongite CaZrSi O ' 2.5H O. Only the Si}(O)}
ꢂꢇ ꢂꢇ
ꢁ
ꢈ
5- (¹}¹}¹}¹}O ) and 6-(¹}¹}O }¹}¹}O ) rings, which are
F
F
F
ꢁ
ꢈ
ꢈ
ꢁ
di!erent from those in the title compound (4-(¹}¹}¹}O ), Si connections are drawn.
F
5-(¹}¹}¹}¹}O ), and 7-(¹}¹}O }¹}¹}¹}¹}O ) rings).
F
F
F
In addition to the layered con"guration [Si O ]
,
ꢈ ꢂꢇ ꢀꢀ
structures of Si O -based silicates can also adapt double- example temperature and initial composition, are the main
ꢈ ꢂꢇ
chain, double ring, and framework con"gurations, as factors that determine the structure of a polymorph.
reviewed by Haile and Wuensch (45).
The discovery of the new K TiSi O makes an impor-
ꢁ
ꢈ ꢂꢇ
tant contribution to hydrothermal methods and crystal
chemistry of titanium silicates as well as mixed anion
framework compounds in general.
Thermal Behavior
X-ray powder di!raction showed that the title compound,
K TiSi O , was stable up to 7503C in air and then decom-
ACKNOWLEDGMENT
ꢁ
ꢈ ꢂꢇ
posed into cristobalite SiO , Si, and anatase TiO .
ꢁ
ꢁ
Ken Okamoto was involved in the early experiments of titanium silicate
syntheses. This work is supported by the Swedish Natural Science Research
Council (NFR).
CONCLUSIONS
The geometry and orientation of the building units and
the way they are connected can result in a great variation of
the "nal crystal structures. Even for compounds with the
same stoichiometry, as for example here davanite and the
title compound, the structure can be di!erent. This is a good
illustration of the fact that crystallization conditions, for
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