Unusual complexes of cyclic pentameric perfluoroisopropylidenemercury
[(CF3)2CHg]5 (I) with nitrate anions have been synthesized by the interaction

of AgNO3 at 20°C with (PPh4)2{[(CF3)2CHg]5Br2} and (PyH)2{[(CF3)2CHg]5Cl2},
respectively. The both complexes, (PPh4)2{[(CF3)2CHg]5(NO3)2} (II) and (PyH)2{[
(CF3)2CHg]5(NO3)2} (III), contain two anionic species per molecule of I but differ
strongly from each other in their structures. In the case of II, one of the nitrate
anions behaves as a bidentate ligand while the other one is a tridentate ligand.
The bidentate nitrate ligand in II coordinates with all five Hg centres of I by one
of the oxygen atoms and with two Hg centres by the second oxygen atom. In the
tridentate nitrate ligand (whose plane is practically parallel to the metallacycle
plane), two oxygen atoms are coordinated each with one Hg centre of I whereas
the third oxygen atom interacts with two Hg centres. A characteristic feature of
complex III is the presence of hydrogen bonds between the pyridinium counter
cations and the oxygen atom of one of the nitrate ligand. Two other oxygen atoms
of this nitrate ligand are bonded each to two Hg centres of I. The second nitrate

anion in complex III interacts with all five Hg centres of I by one oxygen atom
and with a single Hg centre by the second oxygen atom. In both complexes, the
nitrate anions are located above and below the metallacycle plane.
This work was supported by the Russian Foundation for Basic Research
(Project code 05-03-32891) and the Russian Science Support Foundation
(K.I.T.).