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RADIOCHEMISTRY, STABLE ISOTOPES,
NUCLEAR ANALYTICAL METHODS, GENERAL CHEMISTRY
THE STRUCTURES OF LEAD(II) COMPLEXES WITH TROPOLONE
Krzysztof Łyczko, Wojciech Starosta
61
Tropolone (2-hydroxy-2,4,6-cycloheptatriene-1-one),
abbreviated as Htrop, is a non-benzenoid aromatic
compound containing a seven-membered ring.
Tropolonato ligand is a bidentate anionic species,
which forms five-membered rings with metal ions
[1]. The functional groups in tropolone (carbonyl
and hydroxyl) make it possible its coordination
to a number of various metal ions. There are
many structural data on homoleptic complexes of
metals with tropolonato ligands, e.g. Cu(trop) 2 [2],
In(trop) 3 [3], Zr(trop) 4 [4]. Some dimeric species,
such as [Tl III (trop)Ph 2 ] 2 [5], [Bi III (trop) 2 (NO 3 )] 2 [6],
[Ni(trop) 2 H 2 O] 2 [7] and polymeric species of Zn 2+
[8] and Hg 2+ [9] with tropolone have also been obtained.
In the dimeric and polymeric compounds
the tropolone plays a bridging role.
Many structural data on coordination compounds
of tropolone with p-block metal cations,
such as gallium, indium [3], thallium(III) [5], tin(II)
[8], tin(IV) [10], bismuth(III) [6] and bismuth(V)
[11] have been reported. The methods of synthesis
of bis(tropolonato)lead(II) and tetrakis(tropolonato)lead(IV)
were described previously [12,13].
Apart from this information, there are no structural
data on any tropolonato-lead compound.
The aim of this work was to determine the structure
of complexes formed by the lead(II) ion and
tropolone molecules. We presumed that the composition
and the structure of the complexes may
depend on the anion. For this purpose, we have
used triflate, perchlorate, nitrate and acetate as
counter ions. The reason was a good solubility of
their lead(II) salts in a water/methanol mixture.
The reaction of tropolone with Pb(CF 3 SO 3 ) 2 ,
Pb(ClO 4 ) 2 , Pb(NO 3 ) 2 and Pb(CH 3 COO) 2 in solution
led to the formation of four different lead(II)
complexes: one dimeric and three polymeric. The
structure of the [Pb(trop)(CF 3 SO 3 )(H 2 O)] n (1),
[Pb 3 (trop) 4 (ClO 4 ) 2 ] n (2), [Pb 2 (trop) 2 (NO 3 ) 2 (CH 3 OH)] n
Fig.2. The structure of [Pb 3 (trop) 4 (ClO 4 ) 2 ] n (2). Selected
bond lengths [Å] and angles [ o ]: Pb1-O1 2.455(12),
Pb1-O2 2.344(13), Pb1-O11 2.838, Pb2-O11
2.297(14), Pb2-O12 2.362(14), Pb2-O1 2.436(12),
Pb2-O2 2.606(12), Pb2-O12’ 2.711(14), Pb1-O6
3.140, Pb2-O5 3.377, Pb2-O3 3.152, Pb2-O4 3.130,
O1-C1 1.276(22), O2-C2 1.287(21), O11-C11
1.303(22), O12-C12 1.292(24), O1-Pb1-O2 65.01(42),
O11-Pb2-O12 67.90(49).
form was obtained only from the acetate salt. For
the rest of salts, polymeric species were formed
with the anions coordinated to lead atoms and acting
as bridges. Each lead(II) ion in the polymeric
compounds is chelated by one tropolonato ligand,
apart from one type of lead atom in compound 2,
which is bound with two tropolone molecules. In
the dimeric complex 4, the metal ions are coordinated
by two ligand molecules.
Fig.1. The structure of [Pb(trop)(CF 3 SO 3 )(H 2 O)] n (1). Selected
bond lengths [Å] and angles [ o ]: Pb1-O1
2.339(5), Pb1-O2 2.293(5), Pb1-O3 2.776, Pb1-O4
2.784, Pb1-O6 2.446(6), Pb1-O2’ 2.853, Pb1-O1”
2.763, O1-C1 1.286(7), O2-C2 1.280(8), O1-Pb1-O2
68.38(16).
(3) and [Pb(trop) 2 ] 2 (4) compounds was determined
by single crystal X-ray diffraction (Figs.1-4). A simple
bis(tropolonato)lead(II) complex in the dimeric
Fig.3. The structure of [Pb 2 (trop) 2 (NO 3 ) 2 (CH 3 OH)] n (3).
Selected bond lengths [Å] and angles [ o ]: Pb1-O1
2.345(11), Pb1-O2 2.314(11), Pb1-O9 2.567(13),
Pb1-O11 2.599(10), Pb1-O1’ 2.770, Pb1-O3 2.677(12),
Pb1-O5 2.806, Pb2-O11 2.369(12), Pb2-O12
2.327(11), Pb2-O3 3.007, Pb2-O4 2.871, Pb2-O6
2.789, Pb2-O7(14), Pb2-O2 2.760, O1-C1 1.306(18),
O2-C2 1.287(19), O11-C11 1.277(18), O12-C12
1.319(19), O1-Pb1-O2 67.3(4), O11-Pb2-O12 67.2(4).
It is obvious that the counter anions play a decisive
role in the formation of the studied com-