inorganic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
ISSN 0108-2701
Lithium zincopyrophosphate,
Li2Zn3(P2O7)2
Lina Ji,a Hongwei Mab* and Jingkui Lianga,c
Figure 1
The atom-labelling scheme and coordination environments of the title
compound. Displacement ellipsoids are drawn at the 50% probability
level. Li cations disordered on the Zn sites have been omitted for clarity.
[Symmetry codes: (i) ꢀx, ꢀy + 1, ꢀz + 1; (ii) ꢀx + 1, ꢀy + 1, ꢀz + 1; (iii)
x ꢀ 1, y, ꢀz + 32; (iv) ꢀx + 1, y + 21, ꢀz + 23; (v) x + 1, y, ꢀz + 32; (vi) ꢀx + 1,
aInstitute of Physics, Chinese Academy of Sciences, Beijing 100080, People’s
Republic of China, bDepartment of Geological Sciences, Indiana University, 1001
E. 10th Street, Bloomington, IN 47405, USA, and cInternational Center for Materials
Physics, Academica Sinica, Shenyang 110016, People’s Republic of China
Correspondence e-mail: hongma@indiana.edu
ꢀy + 1, z + 12; (vii) x, y, ꢀz + 32; (viii) ꢀx + 1, y ꢀ , ꢀz + 32; (ix) ꢀx + 2, y ꢀ ,
1
2
1
2
3
ꢀz + .]
2
Received 9 January 2009
Accepted 27 March 2009
Online 25 April 2009
the starting materials. Therefore, the product was believed to
be Li2Zn3(P2O7)2 and single-crystal structure analysis was
performed to determine the structure and verify this new
phase. We hereby report the structure of this compound from
single-crystal diffraction analysis.
The title compound has two symmetry-independent sites for
Zn atoms. One is fully occupied with a trace amount (ꢁ0.9%)
of Li+ contamination, whereas the other is disordered by Zn2+
and Li+ cations in a Zn2+/Li+ ratio of 1:1. As shown in Fig. 1,
Zn atoms are coordinated by five O atoms, three of which are
in the equatorial plane, while the other two are in axial posi-
tions. For the fully occupied Zn sites, the average Zn—O bond
The title compound, dilithium(I) trizinc(II) bis[diphos-
phate(4ꢀ)], is the first quaternary lithium zincopyrophosphate
in the Li–Zn–P–O system. It features zigzag chains running
along c, which are built up from edge-sharing [ZnO5] trigonal
bipyramids. One of the two independent Zn sites is fully
occupied, whereas the other is statistically disordered by Zn2+
and Li+ cations, although the two Zn sites have similar
coordination environments. Li+ cations occupy a four-
coordinated independent site with an occupancy factor of
0.5, as well as being disordered on the partially occupied five-
coordinated Zn site with a Zn2+/Li+ ratio of 1:1.
˚
length in the equatorial plane is 1.97 (2) A, while the average
Zn—O distance between Zn and the axial O atoms is
˚
2.16 (1) A. The corresponding values for the partially occu-
˚
pied Zn site are 2.01 (6) and 2.09 (7) A, respectively. Two fully
Comment
occupied Zn1–O trigonal bipyramids are connected by sharing
one edge to form a [Zn2O8] dimer, and the partially occupied
Zn2–O polyhedra build up [Zn2O8] dimers in the same fashion
(Fig. 2). Fully and partially occupied [Zn2O8] dimers share
edges alternately to form chains of [ZnO5] trigonal bipyramids
running along the c axis. The Zn1ꢂ ꢂ ꢂZn1 interatomic distance
between the centres of two adjacent fully occupied [ZnO5]
High-quality II–VI semiconductor zinc oxide (ZnO) crystals
have various applications in functional devices (Look, 2001;
Tsukazaki et al., 2005). Due to the high melting point (2248 K)
and serious volatilization of ZnO at high temperature, a
suitable flux is needed for growing high-quality ZnO crystals
at a lower temperature. The subsolidus phase relations of the
ternary system A2O–ZnO–P2O5 (A = Li, Na or K) were
systematically investigated to find such a flux. The title
compound, Li2Zn3(P2O7)2, is a possible new phase in this
system and Zn2P2O7 and Li4P2O7 were used for the synthesis.
The X-ray powder diffraction pattern was measured on the
reaction products and all peaks were indexed using TREOR
(Werner et al., 1985), with an orthorhombic unit cell a =
˚
polyhedra is 3.1995 (4) A, whereas the corresponding
Zn2ꢂ ꢂ ꢂZn2 distance for the partially occupied [ZnO5] poly-
˚
hedra is 2.857 (1) A. The Zn1ꢂ ꢂ ꢂZn2 distance between the
centres of neighbouring fully and partially occupied [ZnO5]
˚
pyramids is 3.2500 (7) A. The difference between the
Zn1ꢂ ꢂ ꢂZn1 and Zn2ꢂ ꢂ ꢂZn2 distances leads to Zn2+/Li+ disor-
dering on the Zn2 site rather than on both Zn1 and Zn2 sites.
The shorter Zn2ꢂ ꢂ ꢂZn2 distance favours lower charges on the
Zn2 sites, produced by replacing half of the Zn2+ cations with
the same number of Li+ cations, whereas the Zn1 site needs a
fully occupied Zn2+ ion to stablize the structure. The infinite
chains are crosslinked by sharing tetrahedra vertices with
[P2O7]4ꢀ pyrophosphate groups to build up the three-dimen-
sional framework structure of Li2Zn3(P2O7)2 (Fig. 2). Half of
the Li+ cations are disordered with Zn2+ on the partially
occupied Zn2 positions and the other half are situated in the
interstitial positions of the framework, with an occupancy
˚
5.191 (1), b = 13.226 (4) and c = 16.166 (5) A [M(20) = 17 and
F(20) = 27], which indicates that the product is a single phase.
This unit cell, being in good agreement with that from single-
crystal diffraction, is similar but not identical to the cell
parameters of ꢀ-Zn2P2O7 (Bataille et al., 1998). Also, the
measured powder diffraction pattern did not match PDF entry
49–1240 (ICDD, 2004) for ꢀ-Zn2P2O7 very well. In addition,
the warming, heating and cooling scheme guaranteed that the
volatilization of Li, Zn and P was avoided, hence the
compositon of the product was not significantly different from
i30 # 2009 International Union of Crystallography
doi:10.1107/S0108270109011457
Acta Cryst. (2009). C65, i30–i32