The high-temperature (
![](/images/gifchars/beta2.gif)
-) modification of Hg
2MoO
4 was prepared by solid-state reaction of HgO with MoO
2 at400
![](/images/entities/deg.gif)
C. Well-crystallized samples of the low-temperature (
![](/images/gifchars/alpha.gif)
-) modification of Hg
2MoO
4 and isotypic Hg
2WO
4were obtained by hydrothermal recrystallization of the microcrystalline powders at 180
![](/images/entities/deg.gif)
C. The crystal structuresof these transparent yellow compounds were determined by single-crystal X-ray diffractometry.
![](/images/gifchars/beta2.gif)
-Hg
2MoO
4:
P2
1/
c,
Z = 4,
a = 511.31(6) pm,
b = 901.83(7) pm,
c = 1086.0(1) pm,
![](/images/gifchars/beta2.gif)
= 101.01(3)
![](/images/entities/deg.gif)
.
![](/images/gifchars/alpha.gif)
-Hg
2MoO
4 andHg
2WO
4:
C2/
c,
Z = 4,
a = 873.52(6) and 873.0(1) pm,
b = 1155.19(7) and 1147.6(3) pm,
c = 493.05(3) and493.24(6) pm,
![](/images/gifchars/beta2.gif)
= 115.196(5)
![](/images/entities/deg.gif)
and 114.86(1)
![](/images/entities/deg.gif)
, respectively. In
![](/images/gifchars/beta2.gif)
-Hg
2MoO
4 the molybdenum atoms aretetrahedrally coordinated by oxygen atoms and the MoO
4 tetrahedra are linked via Hg
2 dumb-bells, thus forminginfinite zigzag chains. The low-temperature (
![](/images/gifchars/alpha.gif)
-)modification of Hg
2MoO
4 contains MoO
6 octahedra, which arelinked via common edges to form zigzag chains, which are further linked via Hg
2 dumb-bells, resulting in puckeredtwo-dimensionally infinite sheets. Bonding between adjacent sheets is achieved only via weak (secondary) Hg-Obonds of 254.8 pm, while the strong Hg-O bonds of the nearly linear O-Hg-Hg-O groups within the sheetshave a length of 214.8 pm. The Hg-Hg bond lengths are practically the same in the three compounds with252.3(1), 253.49(7), and 253.3(1) pm in
![](/images/gifchars/beta2.gif)
-Hg
2MoO
4,
![](/images/gifchars/alpha.gif)
-Hg
2MoO
4, and Hg
2WO
4, respectively. The average Mo-Odistances within the MoO
4 tetrahedra and the MoO
6 octahedra are 176.2, and 196.5 pm, respectively. The structuralchemistry of these compounds is discussed together with that of previously reported mercury I and II molybdatesand tungstates.