Article
Inorganic Chemistry, Vol. 48, No. 17, 2009 8481
single-source precursors (SSPs) to obtain crystalline oxide
materials upon their decomposition at significantly lower
temperatures compared with the solid state or multisource
precursor approaches.6 In addition, the use of SSPs makes it
possible to access new phases that are not available at higher
reaction temperatures and thus provides more flexibility in
the preparation of heterometallic oxide materials than con-
ventional methods.
and magnetic phase separation. The structurally character-
ized compounds in the Pb-Mn-O system include Pb2MnO4,14,15
PbMnO2.75,
16 a hollandite-type mineral of approximate com-
position Pb1þxMn8O16,17 and Pb3Mn7O15;15,18 while the
identity of several other phases, Pb0.43MnO2.18, Pb0.25MnO2,
and Pb0.25MnO1.99, have been established15 by their X-ray
powder diffraction patterns only. Although, a number of other
oxides have also been mentioned in the literature,16a,17b,19 the
careful examination of their X-ray powder diffraction spectra
suggests that these compositions are either mixtures of the
above-mentioned phases or cation-/oxygen-deficient varia-
tions of the latter. All known Pb-Mn oxides were synthesized
by conventional solid state reactions, and the application of
SSPs for their preparation remains unknown because of the
lack of suitable heterometallic Pb-Mn precursor complexes.
Metal β-diketonates have been widely explored as
MOCVD precursors for the synthesis of oxide materials.20
Diketonate complexes exhibit a number of advantages in
comparison with other ligands, such as higher volatility,
stronger resistancetohydrolysis, andeasier structuralcontrol
of precursors. However, because of their chelating character,
β-diketonates are not generally considered as proper ligands
for the formation of heterometallic species. Moreover, the
rational control of metal stoichiometry in heterometallic
complexes is one of the most significant challenges in the
synthesis of SSPs. Whitmire has proposed12 that the forma-
tion of Lewis acid-base heterometallic adducts is a viable
synthetic approach because of generally high yields, relatively
short reaction times, and the absence of complicating side
reactions. Recently, we have demonstrated the possibility of
utilizing Lewis acid-base interactions for the construction
of heterometallic β-diketonates. We suggested several low-
temperature solid state synthetic routes that utilize coordina-
tively unsaturated metal fragments for the formation of
bismuth-transition metal21a and manganese-containing21b
heterometallic diketonates. These compounds exhibit high
volatility, clean, low-temperature decomposition, and reten-
tion of heterometallic structures upon sublimation-deposi-
tion as well as in solutions of non-coordinating solvents.
Herein we expand this effective approach to the synthesis
of heterometallic lead-manganese diketonates. Compounds
with different Pb/Mn ratios (1:2 and 1:1) have been isolated
in pure form by several synthetic methods including solid
state and solution techniques. For the first time, it has been
shown that thermal decomposition of heterometallic diketo-
nates do produce mixed oxides, while both the structure of
precursors and thermolysis conditions have a significant
Despite the fact that many heterometallic lead-transition
metal compounds are known,6-12 only a few of those have
been explored as SSPs. The first account appeared in 1994,8
when a mixture of PbTiO3 and PbTi3O7 was obtained by
decomposition of Pb2Ti4O2(O2CCH3)2(OC2H5)14. Soon
after, Hubert-Pfalzgraf et al. reported9 a number of Pb-Tr
(Tr = Ti, Zr, Nb) alkoxides and studied their decomposition
at different temperatures leading to a variety of correspond-
ing tertiary oxides. It was found that the use of SSPs allows
one to obtain crystalline oxides at about 100 ꢀC lower than in
the process that involves a mixture of homometallic precur-
sors. On the other hand, the thermolysis of lead-rich Pb3ZrO-
(OPri)8 was shown10 to yield no heterometallic products. The
only reported example of an SSP that does not contain
alkoxide ligands11 is lead-zirconium oxalate, Pb2Zr(C2O4)4,
which affords a mixture of PbZrO3 and PbO as decomposi-
tion products.
Manganese-based oxides with mixed-valent Mn3þ/Mn4þ
ions have been intensively studied13 because of their unusual
properties, such as charge and orbital ordering, metal/
insulator transition, colossal magnetoresistive (CMR) effect,
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