The reaction of iron carboxylates with titanium alkoxides. Isolation and structural characterisation of [Ti6(μ3-O) 6(O2CPh)6(OCH2C(CH3) 3)6]

Article abstract of DOI:10.1016/S0020-1693(03)00242-1

The reaction of [Fe₄(μ₃-O)₂(O ₂CPh)₈(py)₂] (1) with Ti(OPrⁿ) ₄ in toluene yields separate Fe and Ti species each containing both carboxylate and alkoxide groups rather than a bimetallic Fe-Ti complex. The addition of neopentanol to the reaction mixture has enabled [Ti ₆(μ₃-O)₆(O₂CPh) ₆(OCH₂C(CH₃)₃)₆] (3) to be isolated and structurally identified. The compound [Ti₆(μ ₃-O)₄(O₂CPh)₈(OPrⁿ) ₈] (4) has also been characterised and shown not to convert to a {Ti₆(μ₃-O)₆}¹²⁺ core compound under the same temperature conditions used in the Fe-Ti reactions.

Full text of DOI:10.1016/S0020-1693(03)00242-1

Inorganica Chimica Acta 353 (2003) 75ꢁ81
/
www.elsevier.com/locate/ica
The reaction of iron carboxylates with titanium alkoxides. Isolation
and structural characterisation of
[Ti6(m3-O)6(O2CPh)6(OCH2C(CH3)3)6]
Paul S. Ammala, Stuart R. Batten, Christopher M. Kepert, Leone Spiccia *,
Adrian M. van den Bergen, Bruce O. West
School of Chemistry, P.O. Box 23, Monash University, Victoria 3800, Australia
Received 19 October 2002; accepted 21 March 2003
Abstract
The reaction of [Fe4(m3-O)2(O2CPh)8(py)2] (1) with Ti(OPrn)4 in toluene yields separate Fe and Ti species each containing both
carboxylate and alkoxide groups rather than a bimetallic FeÃ
/
Ti complex. The addition of neopentanol to the reaction mixture has
enabled [Ti6(m3-O)6(O2CPh)6(OCH2C(CH3)3)6] (3) to be isolated and structurally identified. The compound [Ti6(m3-O)4(O2C-
Ph)8(OPrn)8] (4) has also been characterised and shown not to convert to a {Ti6(m3-O)6}12ꢀ core compound under the same
temperature conditions used in the FeÃ
/
Ti reactions.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Fe carboxylates; Ti alkoxides; Hexanuclear Ti-oxo-carboxylato-alkoxide; X-ray structures
1. Introduction
Mixed oxides of FeÃ
counter-electrodes for use in electrochemical ‘smart
(O2CPh)6(H2O)3](O2CPh) and initially allotted the em-
pirical formula [Fe3(m3-O)(O2CPh)6(py)2(H2O)](O2CPh)
on the basis of analytical data only [5]. It was not
structurally characterised, but has subsequently been
/
Ti have shown potential as
windows’ [1] and as catalysts in the photochemical
shown to have magnetic and Mossbauer spectral
¨
decomposition of water [2], while mixed oxides of FeÃ
Zr are useful in the preparation of ‘stabilized’ zirconia
[3]. The synthesis of such mixed oxides by solꢁgel
processes would be aided by the use of suitable mixed
metal compounds involving alkoxide and carboxylate
groups.
/
properties more in agreement with the tetranuclear
formula [Fe4(m3-O)2(O2CPh)8(py)2] (1) [4], the C, H, N
analytical data being comparable for both formulations.
A similar reaction involving (1) and Ti(OPrn)4 did not
/
yield an isolable FeÃ
/
Ti complex but gave separate Fe
and Ti compounds presumably formed by group
exchange between the Fe and Ti reagents. A brief
mention of these observations identifying the Ti product
as a {Ti6(m-O)6}12ꢀ core compound was made in an
earlier communication [5]. It was also then reported that
reaction between [Fe3(m3-O)(O2CPh)6(H2O)3](O2CPh))
and Ti(OPrn)4 in n-propanol allowed isolation and
identification [5] of the known polynuclear Fe species
[Fe11(m-O)6(m-OH)6(O2CPh)15] [6] as a toluene adduct.
The present paper presents details of the characterisa-
tion of the {Ti6O6}12ꢀ core compound.
We have recently described the synthesis and structure
of such an FeÃZr-carboxylate-alkoxide [Fe2Zr2(m3-
/
O)2(m-O2CPh)6(OBut)4(py)2] [4], formed by reaction in
toluene between Zr(OBut)4 and an Fe(III) oxo-carbox-
ylate compound (1). Compound (1) was prepared by
reaction of excess pyridine with [Fe3(m3-O)-
* Corresponding author. Tel.: ꢀ
/
61-3-9905 4526; fax: ꢀ61-3-9905
/
4597.
E-mail address: leone.spiccia@sci.monash.edu.au (L. Spiccia).
0020-1693/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0020-1693(03)00242-1

76
P.S. Ammala et al. / Inorganica Chimica Acta 353 (2003) 75ꢁ81
/
2. Experimental
2.4. Isolation of
[Ti6(m-O)6(O2CPh)6(OCH2C(CH3)3)6] (3)
2.1. Materials and reagents
Ti(OPrn)4 (0.6 g, 2.3 mmol) in toluene (20 ml) was
added to a suspension of (1) (1.0 g, 0.8 mmol) in toluene
(50 ml) and the solution refluxed for 4 h. On cooling,
neopentanol (2.0 g, 22.7 mmol) was added. Small
quantities of colourless and red crystals, insufficient
for microanalysis, were deposited together with a small
All operations involving moisture sensitive alkoxide
materials were performed either in a glove box or with
the aid of greaseless Schlenk apparatus and cannulation
techniques under dry nitrogen. Ti alkoxides (Aldrich)
and reaction products were stored in a nitrogen filled
dry box. Details of physical measurements and the
method of synthesis for (1) were as previously described
[4]. The empirical formula of (1) is assumed to be
[Fe4(m3-O)2(O2CPh)8(py)2] [4] for mole fraction calcula-
tions.
quantity of a redꢁbrown amorphous solid, upon the
/
solution standing for several weeks. Samples of each
crystalline material were ‘hand-picked’ on a microscope
stage. Microprobe examination showed that the red
crystals contained only Fe as the metallic component
but were twinned and unsuitable for X-ray study. The
colourless product contained only Ti and a suitable
crystal was selected allowing crystallographic
identification of the compound as [Ti6O6(O2CPh)6-
(OCH2C(CH3)3)6] (3).
Red crystals: IR (n cmꢂ1): 1596(s), 1548(s), 1532(s),
1492(m), 1414(vs), 1307(w), 1175(m), 1128(m), 1068(m),
1027(m), 980(m), 714(s).
Colourless crystals: IR (n cmꢂ1):1593(s), 1564(w),
1532(vs), 1493(m), 1414(vs), 1308(w), 1176(m), 1123(m),
1052(m), 1025(m), 971(s), 890(w), 852(w), 718(vs),
672(s).
2.2. Reaction of (1) with Ti(OPrn)4
A solution of Ti(OPrn)4 (1, 2, 3 or 6 molar equivalents
calc. as monomer) in toluene (10 ml) was added to a
warm suspension of (1) (approximately 0.5 g, 0.4 mmol).
The resulting mixtures were heated at reflux temperature
for 4 h, during which the solid (1) dissolved forming red
coloured solutions. Careful evaporation of the solutions
failed to give any crystalline product. A mustard
coloured solid could be precipitated by addition of
hexane. Yields 0.13ꢁ
/
0.26 g. Electron microprobe exam-
2.5. Preparation of
[Ti6(m3-O)2(m2-O)2(OPrn)8(O2CPh)8] (4)
ination of the products gave Fe:Ti ratios ranging from
approximately 1Fe:1Ti to approximately 5Fe:1Ti. Re-
peat experiments under supposedly the same conditions
generally gave differing Fe:Ti ratios. Attempts to
recrystallise the mustard coloured products from tolu-
ene/hexane were unsuccessful, powders or filmy deposits
being obtained. The solids had similar IR spectra, a
typical sequence being (n cmꢂ1): 1522(vs), 1493(m),
1412(vs), 1307(w), 1176(m), 1158(m), 1044(s), 1013(s),
974(m), 888(w), 846(m), 718(vs), 679(s).
Ti(OPrn)4 (1.58 g, 5.6 mmol) in toluene (10 ml) was
slowly added to a stirred solution of benzoic acid,
HO2CPh (1.36 g, 11.1 mmol) in toluene (30 ml). The
resulting solution was heated at reflux for 4 h. Cooling
overnight afforded colourless crystals which were fil-
tered, washed with toluene and dried under high
vacuum. Yield: 30% (0.5 g). A suitable crystal was
obtained for an X-ray structural study. Found: C, 53.6;
H, 5.3% Calc. for C80H96O28Ti6: C, 53.6; H, 5.4%.
IR (n cmꢂ1): 1595(s), 1555(s), 1537(s), 1493(m),
1449(s), 1421 (s), 1192(m), 1113 (m), 1069 (m), 1026
(m), 997 (m).
Reactions carried out with Ti(OBut)4 in toluene gave
similar red solutions but only yielded glassy material on
careful evaporation.
Heating a sample of (4) in refluxing toluene for 5 h
resulted in crystallisation of a white product on cooling.
Crystallographic examination of the product showed it
to be identical with the starting material.
2.3. Reaction of [Fe3O(O2CPh)6(py)3](NO3) (2) and
Ti(OBut)4
Reactions between [Fe3O(O2CPh)6(py)3](NO3) (2) [7]
(0.18 g, 0.15 mmol) and three molar equivalents of
Ti(OBut)4 (0.15 g, 0.45 mmol) were attempted in
benzene, toluene and CH2Cl2 (using 5 ml of solvent).
[Fe3O(O2CPh)6(py)3](NO3) did not show appreciable
solubility in either benzene or toluene even when
Ti(OBut)4 was added. Full solubility of the Fe(III)
complex was achieved in CH2Cl2 when Ti(OBut)4 was
added but a glassy product only was obtained upon
careful concentration of these solutions.
3. Structure determination
Crystal data and details of the structure determina-
tions of (3) and (4) are presented in Table 1. Data were
collected at 123(2) K on a Nonius Kappa CCD
diffractometer with graphite monochromated Mo Ka
˚
radiation (lꢃ
/
0.71073 A), using f and v rotations with
18 frames. No absorption corrections were applied to the

P.S. Ammala et al. / Inorganica Chimica Acta 353 (2003) 75ꢁ
/81
77
Table 1
Crystal data for [Ti6(m-O)6(O2CPh)6(OCH2C(CH3)3)6] (3) and
[Ti6(m-O)4(O2CPh)8(OPrn )8] (4)
atoms were refined anisotropically, and hydrogen atoms
were included at calculated positions but not refined.
The structure of (4) was solved by direct methods and
refined on F using the TEXSAN program [9]. All non-
hydrogen atoms were refined with anisotropic thermal
parameters, while all hydrogen atoms were assigned to
calculated positions but not refined.
3
4
Formula
M
C72H96O24Ti6
1632.89
rhombohedral
C80H96O28Ti6
1739.02
triclinic
Crystal system
Space group
¯
3 (#148)
¯
P1 (#2)
R/
/
˚
a (A)
30.202(2)
30.202(2)
29.102(2)
90
12.5877(5)
12.9803(5)
14.6046(3)
69.969(2)
87.545(2)
67.084(2)
2053.6(1)
1
˚
b (A)
4. Results and discussion
˚
c (A)
a (8)
b (8)
g (8)
90
120
4.1. Synthetic considerations
3
˚
U (A )
Z
22 989(2)
9
The variable FeÃ
/
Ti composition of the products
Dc (g cmꢂ3
)
1.062
5.02
1.45
6.36
formed when (1) and Ti(OPrn)4 were reacted in various
ratios strongly suggested that mixtures of separate Fe
and Ti species were being formed rather than a single
m (cmꢂ1
T (K)
)
123(2)
2, 60
123(2)
2umin, 2umax (8)
Data collected
Unique data
2, 60.4
18 327
11 154
FeÃ
/
Ti complex but attempts to recrystallise the solids
41 652
14 232
2425
deposited from toluene by hexane failed to give crystal-
line products suitable for single crystal X-ray examina-
tion. However, the addition of the bulky alcohol
neopentanol to a reaction mixture of (1) and Ti(OPrn)4
afforded a very small amount of a mixture of red and
colourless crystals. This procedure had previously [5]
allowed the isolation and structural characterisation of
the octanuclear compound [Fe8(m3-O)2(m4-O)2(m-OCH2-
But)2(m-O2CPh)12(O2CPh)2(HOCH2But)2]. Microprobe
examination showed that the colourless material con-
tained only Ti and the red, Fe, as their metallic
components.
The Fe-containing crystals were unsuitable for X-ray
study but a structural solution was obtained for the Ti
material (3), revealing it had the formula [Ti6O6(O2C-
Ph)6(OCH2C(CH3)3)6] with a {Ti6(m3-O)6}12ꢀ core,
benzoate groups occupying bridging modes between
pairs of Ti atoms and terminally placed alkoxide groups
(Fig. 1). The structural results are discussed in more
detail below. The core structure of (3) has been found
for other structurally characterised complexes of general
Observed data [I ꢀ
/
6509
3s(I)]
Parameters
Final R-values
425
514
R1ꢃ
0.4641 a,d
1.93 (ꢂ1.76)
/
0.0999 a,c wR2ꢃ
/
R1ꢃ
0.042 b,c
1.03 (ꢂ0.72)
/
0.045 b,c Rw
ꢃ/
Drmin, Drmax (e
/
/
ꢂ3
˚
A
)
a
b
c
Refined on F2.
Refined on F.
Observed data.
All data.
d
data. The structure of (3) was solved by direct methods
and refined on F2 using the SHELX suite of programs [8].
The data collected were very weak, and thus the
refinement was less than ideal, leading to high R values.
¯
Solutions were tried in both the R3 and R3 space
/
groups. In the non-centrosymmetric R3 space group the
neopentyl groups were poorly resolved, and not all the
atoms could be found. These problems were worsened
upon going to even lower symmetry, such as P1. High
correlation matrix elements, an intermediate Flack
parameter value, and problems with atoms becoming
non-positive definite in the R3 solution also indicated
formula
C6H4OPh, Rꢃ
Pri, RꢃCH2But [12]). In (3) as in each other Ti6(O)6
[Ti6(m3-O)6(O2CR?)6(OR)6]
(R?ꢃ
/
Me,
/
Et, Pri [10] R?ꢃ
/
H, Rꢃ
/
Pri [11]; R?ꢃ
/
/
¯
the likely presence of an inversion centre. In the R3
/
molecule, all carboxylate groups bridge pairs of Ti
atoms and none are chelating. It may be observed that
the IR spectrum of (3) could not provide unambiguous
evidence for the bridging mode in the absence of a
structural study. Thus, in line with previous allocations
of IR spectra arising from bridging acetate coordination
to Ti [12], the bands at 1593, 1564 and 1532 cmꢂ1 may
be assigned to the splitting of the nas (CO2ꢂ) band with
the ns (CO2ꢂ) band at 1493 cmꢂ1. The spectrum is
similar to that reported for [Ti6(m3-O)6(O2CPri)6(OCH2-
space group the cluster lies across an inversion centre
and all neopentyl groups could be resolved. This space
group also gave significantly better R-values, and
generally gave a better solution. Nonetheless, there
was still significant movement of the neopentoxide
ligands on the periphery which also affected the quality
of the refinement. The connectivity of the atoms,
however, was unambiguous. The methyl carbons of
the neopentoxide ligands were refined isotropically, and
no hydrogen atoms were assigned to these atoms. In
addition, one of the methyl groups was disordered
equally over two positions. All other non-hydrogen
But)6] [12]. The values of Dn (nasꢂ
39ꢁ
179 cmꢂ1 within which are values that indicate
chelating or bridging carboxylate groups [13].
/ns) cover a range from
/

78
P.S. Ammala et al. / Inorganica Chimica Acta 353 (2003) 75ꢁ81
/
would contain benzoate and n-propoxide groups and
moreover be formed at the boiling point of toluene, the
nature of the complex formed by direct reaction between
Ti(OPrn)4 and benzoic acid in toluene was also deter-
mined. Little reaction was detected between the reagents
over several hours at room temperature but it proceeded
rapidly under reflux conditions. The product isolated (4)
was structurally characterised as a {Ti6(m-O)4}16ꢀ core
compound of molecular formula [Ti6(m-O)4(O2C-
Ph)8(OPrn)8] (Fig. 2). Its structure is discussed below.
It thus appears that the propoxide precursor of (3)
together with a presently unidentified Fe complex were
formed from an intermediate complex derived from the
Fe carboxylate and Ti-n-propoxide reagents which
underwent group exchange and rearrangement to give
stable Fe and Ti species rather than a single FeÃ
/
Ti
complex. Exchange of propoxide with neopentanol
would subsequently lead to the neopentoxide Ti com-
pound isolated. This contrasts with the reaction of (1)
and Zr(OBut)4 [4] where a stable FeÃ
/Zr complex could
be isolated containing both benzoate and alkoxide
residues. It is noteworthy that a mixed benzoate-
alkoxide-oxo-Zr compound was also structurally de-
fined as a second product in a reaction mixture having a
high Zr(OR)4/Fe mole ratio. There is a great deal of
Fig. 1. ORTEP diagrams: (a) [Ti6(m3-O)6(O2CPh)6(OCH2C(CH3)3)6]
(3); (b) the {Ti6(m3-O)6}12ꢀ skeletal core. Thermal ellipsoids at 50%
probability.
An alternative core with composition {Ti6(O)4}16ꢀ
has been recognised in two other structurally defined
classes of Ti-alkoxy-carboxylate derivatives each differ-
ing in the ratio of alkoxide to carboxylate residues, viz.
[Ti6(m-O)4(O2CR?)8(OR)8]
O)4(O2CR?)4(OR)12] [17ꢁ19].
The majority of
[14ꢁ
/
16]
and
[Ti6(m-
/
previously
reported
[Ti6(O)6(O2CR?)6(OR)6] compounds have been prepared
by reaction of Ti(OR)4 with HO2CR? in refluxing
toluene although several instances have been reported
where Ti6O6 compounds have been formed by long
heating of Ti6O4 compounds in toluene [10]. Represen-
tatives of Ti6O4 core compounds have also been
synthesised by reaction of Ti(OR)4 with free acid but,
at present, there is no clear rationale as the conditions
(substituents, mole ratios, temperature, etc.) required to
form a member of a particular class.
Fig. 2. ORTEP diagrams: (a) [Ti6(m3-O)4(O2CPh)8(OPrn )8; (b) the
{Ti6(m3-O)4}16ꢀ skeletal core. Thermal ellipsoids at 50% probability.
Since any Ti carboxylato-alkoxo complex formed as a
result of the interaction between (1) and Ti(OPrn)4

P.S. Ammala et al. / Inorganica Chimica Acta 353 (2003) 75ꢁ
/81
79
structural evidence [20] that bridging by both carbox-
ylate and alkoxide groups supports the metal-oxo group
core structures of mixed metal compounds containing
each type of group and this must derive from initial
transition states involving both metal reagents used.
Table 2
˚
Selected bond distances (A) and angles (8) for
O)6(O2CPh)6(OCH2C(CH3)3)6] (3)
3
and 4[Ti6(m-
TiÃ
/
(m3-O)
TiÃO(ORterminal)
/
Bond distances
Ti(1)Ã
Ti(1)Ã
Ti(1)Ã
Ti(2)Ã
/
O(1)
O(2)
O(3)
O(1)
2.137(7)
1.916(6)
1.884(7)
1.889(6)
Ti(1)Ã
Ti(2)Ã
Ti(3)Ã
TiÃ
/
O(41)
O(51)
O(61)
1.786(7)
1.782(8)
1.773(8)
4.2. Crystal structures
/
/
/
/
Selected bond distances and angles for each com-
pound reported are listed in Table 2.
/
/
O(O2CRbridging
)
Ti(2)Ã
Ti(2)Ã
Ti(3)Ã
Ti(3)Ã
Ti(3)Ã
/
O(2)
2.149(7)
1.922(7)
1.915(7)
2.150(7)
1.879(7)
/
O(3*)
Ti(1)Ã
Ti(1)Ã
Ti(2)Ã
Ti(3)Ã
/
O(11)
O(21)
O(13)
O(23)
2.101(8)
2.044(7)
2.048(8)
2.061(7)
4.2.1. [Ti6(O)6(O2CPh)6(OCH2C(CH3)3)6] (3)
Fig. 1(a) is a structural diagram of complex (3)
showing positions of associated groups and Fig. 1(b)
shows only the Ti6(m3-O)6 core, the bridging CO2 and
the O atoms of the terminal OR groups. The difficulties
experienced in obtaining a structural solution of the
highest quality because of the relatively poor data set
were commented on in Section 3 and show in the rather
large thermal ellipsoids of peripheral atoms. However
the definition of the Ti6O6 core of this molecule (Fig.
1(b)) is quite clear and shows it to be formed by two
approximately planar hexagonal Ti3(m3-O)3 units linked
by the six oxo groups in the form of a hexagonal
/
O(1)
/
/
O(3)
/
/
O(2*)
/
Bond angles
Ti(1)ÃO(1)Ã
Ti(1)ÃO(2)Ã
Ti(1)ÃO(3)Ã
Ti(2)ÃO(1)Ã
Ti(3)ÃO(3)Ã
O(1)ÃTi(1)Ã
O(1)ÃTi(1)Ã
O(2)ÃTi(1)Ã
O(2)ÃTi(1)Ã
O(11)ÃTi(1)Ã
O(2)ÃTi(2)Ã
O(1)ÃTi(3)Ã
/
/
Ti(2)
Ti(2)
Ti(3)
Ti(3)
Ti(2*)
O(3)
100.2(3)
98.9(3)
100.1(3)
133.6(4)
99.2(3)
78.7(3)
175.4(3)
86.4(3)
97.2(3)
93.1(3)
92.4(3)
87.2(3)
Ti(1)Ã
Ti(1)Ã
Ti(1)Ã
Ti(2)Ã
O(1)ÃTi(1)Ã
O(1)ÃTi(1)Ã
O(2)ÃTi(1)Ã
O(2)ÃTi(1)Ã
O(3)ÃTi(1)Ã
O(21)Ã
O(2)ÃTi(2)Ã
O(3)ÃTi(3)Ã
/
O(1)Ã
O(2)Ã
O(3)Ã
O(2)Ã
/
Ti(3)
99.5(3)
135.1(4)
133.9(4)
100.6(2)
78.2(3)
87.5(3)
102.5(3)
159.2(3)
102.3(3)
96.9(3)
86.6(3)
87.2(3)
/
/
/
/
Ti(3*)
Ti(2*)
Ti(3*)
O(2)
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
O(21)
O(3)
/
/
O(41)
O(11)
O(41)
/
/
/
/
/
/
O(21)
O(41)
/
/
/
/
/
/O(41)
/
Ti(1)ÃO(41)
/
/
/O(13)
/
/
O(31)
cylinder. The sets of three TiÃ(m3-O) distances asso-
/
/
/O(23)
/
/
O(23)
ciated with each metal centre show two bonds of
approximately similar lengths for the pairs of atoms
lying in the same Ti3(m3-O)3 planes while the third, the
distances between Ti atoms in one plane and m3-O
[Ti6(m-O)4(O2CPh)8(OPrn )8] (4)
TiÃ(m3-O)
Bond distances
/
TiÃ(m2-O)
/
˚
groups in the other are approximately 0.2 A longer. The
Ti(1)Ã
Ti(2)Ã
/
O(1)
2.082(2)
1.911(2)
Ti(2)Ã
Ti(3)Ã
/
O(2)
1.768(2)
1.942(2)
sum of the TiÃOÃTi angles about each Ti atom averages
/
/
/O(1)
/O(1)
333.78 (cf. trigonal pyramidal theoretical 328.48). Simi-
lar structural features are found for the cores of other
hexanuclear Ti-oxo-carboxylato-alkoxo derivatives with
TiÃ/O(ORbridging
)
TiÃ/O(O2CRbridging
)
Ti(1)Ã
/
O(5)
1.963(2)
2.089(2)
Ti(1)Ã
/
O(7)
O(9)
O(8)
2.191(2)
2.045(2)
1.979(2)
general formula [Ti6(m3-O)6(O2CR)6(OR?)6] [10ꢁ
/
12] re-
Ti(2)Ã
/
O(5)
Ti(1)Ã
/
ferred to above. The values of TiÃO distances and bond
/
Ti(2)Ã
/
angles in (3) are comparable with those measured for
these compounds. The benzoate anions bridge between
pairs of Ti atoms, one in each Ti3(m3-O)3 unit forming a
zigzag equatorial belt around the Ti6(m3-O)6 core. Each
Ti is bound to two carboxylate residues and three m3-O
groups and becomes six coordinate in a distorted
octahedral fashion by the addition of a terminal
neopentoxide ligand.
TiÃ
/
O(ORterminal
)
Ti(2)Ã
/
O(11)
1.982(2)
Ti(1)Ã
Ti(1)Ã
Ti(3)Ã
/
O(3)
O(4)
O(6)
1.818(2)
1.770(2)
1.746(2)
Ti(2)Ã
/
O(13)
2.086(2)
2.046(2)
/
Ti(3)Ã
/
O(10)
/
Bond angles
Ti(1)ÃO(1)Ã
Ti(2)ÃO(1)Ã
O(1)ÃTi(1)Ã
O(1)ÃTi(1)Ã
O(1)ÃTi(1)Ã
O(1)ÃTi(2)Ã
O(1)ÃTi(2)Ã
O(1)ÃTi(3)Ã
O(2)ÃTi(2)Ã
O(1)ÃTi(3)Ã
/
/
Ti(2)
Ti(3)
O(3)
O(5)
O(9)
O(5)
O(11)
O(6)
O(8)
O(10)
101.66(7) Ti(1)Ã
130.07(9) O(1)ÃTi(1)Ã
164.49(8) O(1)ÃTi(1)Ã
77.98(7) O(1)ÃTi(2)Ã
88.24(7) O(1)ÃTi(2)Ã
78.94(7) O(1)ÃTi(2)Ã
92.52(8) O(2)ÃTi(2)Ã
98.96(8) O(2)ÃTi(2)Ã
/
O(1)Ã
/
Ti(3)
O(4)
O(7)
O(2)
O(8)
O(13)
O(5)
O(11)
127.91(9)
97.78(8)
79.99(7)
106.32(8)
91.11(8)
161.34(7)
173.90(8)
92.12(8)
/
/
/
/
/
/
/
/
/
/
/
/
4.2.2. [Ti6(O)4(O2CPh)8(OPrn)8] (4)
/
/
/
/
Discrete hexanuclear Ti molecules of formula
[Ti6(O)4(O2CPh)8(OPrn)8] (Fig. 2(a)) exist in the crystal
lattice of this compound based upon Ti6(m-O)2(m3-O)2
cores (Fig. 2(b)). Each molecule is centrosymmetric
having two identical {Ti3(m3-O)}10ꢀ core units linked
by a pair of m-O atoms thus giving the cyclic group of Ti
atoms so formed, an overall chair configuration as
found for other molecules having such Ti6O4 cores. The
/
/
/
/
/
/
/
/
/
/
/
/
/
/
95.86(8)
/
/
92.39(7)
associated with the core include eight benzoate anions
bridging pairs of neighbouring Ti atoms together with
six terminally bound n-propoxide groups and two m-
dihedral angle between the planes Ti(1)Ã
/
Ti(2)Ã
/
Ti(3) and
Ti(2)ÃTi(2*)ÃTi(3*)ÃTi(3) is 169.88. Peripheral groups
/
/
/

80
P.S. Ammala et al. / Inorganica Chimica Acta 353 (2003) 75ꢁ81
/
bridging n-propoxides {Ti(1)Ã
O(5*)ÃTi(2*)}. The TiÃ(m3-O) distances lie in the range
1.911(2)ꢁ2.082(2) A with the two Ti atoms also bound
to m2-O atoms (Ti(2) and Ti(3)) being at shorter
distances from m3-O. The TiÃ(m2-O) distances are each
shorter than any of the TiÃ(m3-O) distances. Despite the
variation in TiÃ(m3-O) bond lengths the m3-O atom
deviates from the Ti(1), Ti(2), Ti(3) plane by only 0.068
/
O(5)Ã
/
Ti(2), Ti(1*)Ã
/
(1) in that solvent, the Fe complex dissolved more
rapidly at room temperature indicating some form of
reaction was taking place. However after further heating
the system to complete any reaction, all attempts to
isolate crystalline material from the mixture failed,
/
/
˚
/
/
/
glassy orange products being the normal result. FeÃ
/
Ti
/
complex formation may possibly have been achieved but
further syntheses using monomeric Ti alkoxides defined
by larger subsituents may be necessary to prepare
˚
A. Each Ti atom is six coordinate but there is consider-
able variation from octahedral symmetry at each site
with cis-angles varying between 77.98(7) and 106.32(8)8,
while trans angles as low as 161.11(8)8 are observed.
crystalline FeÃ/Ti derivatives.
5. Supplementary material
4.3. A possible rationale for the differing reactivity of the
Fe carboxylate with Ti(OR)4 and Zr(OR)4
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 187335 (3) and 187336 (4).
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Structurally, the Fe2Zr2 complex [Fe2Zr2(m3-O)2(O2C-
Ph)6(OBut)4(py)2], may be viewed as retaining the
Fe2(m3-O)2(py)2 ‘body’ segment from the proposed Fe4
structure of (1) with Zr(OBut)2 units replacing the ‘wing-
tip’ Fe sites [4]. It further appears likely that the m3-O
atoms in the final complex are transferred from the
Cambridge, CB21EZ, UK (fax: ꢀ44-1233-336-033; e-
/
mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
initial Fe4Ã
having both initial Fe and Zr complexes linked through
one or more Feà Á Á ÁZr bonds. The remaining lone pair
of electrons on an FeÃ(m3-O) group would appear to
/
(m3-O)2 complex through a transition state
/
O
/
/
/
Acknowledgements
constitute a plausible point of attachment. Given the
general chemical similarity between Ti and Zr one can
presuppose a similar initial mode of reaction of their
alkoxides with Fe-oxo-carboxylato substrates. However,
whereas Zr(OBut)4 is monomeric in non-coordinating
solvents [21], Ti(OPrn)4 is associated in non-coordinat-
ing solvents, as are other straight chain alkyl derivatives
[22]. Therefore, if a polynuclear Ti alkoxide reacted with
the (m3-O) group of any Fe complex, for steric reasons,
only one Ti site would be initially involved. Any
subsequent metal-to-metal bridging by benzoate and
alkoxide ligands within what would be a labile transition
state complex could thus lead to a potential polynuclear
Ti entity. Oxo group formation within such a ‘proto’ Ti
complex, possibly by ester elimination at the high
temperature of reaction [23] could then provide the
This was supported by research grants from the
Australian Research Council and financial and scientific
support from Sustainable Technology Australia Lim-
ited. C.M.K. received an Australian Postgraduate
Award and P.S.A an Australian Postgraduate Award
(Industry) and a Monash University Research Scholar-
ship.
References
[1] M. Macek, B. Orel, T. Meden, J. Solꢁ/Gel. Sci. Technol. 8 (1997)
771.
[2] B. Morosin, R.J. Baughman, D.S. Ginley, M.A. Butler, Acta
Crystallogr. 11 (1978) 121.
[3] R. Schmid, A. Mosset, J. Galy, C. R. Acad. Sci. Paris Ser. II 311
(1990) 1167.
driving force for dissociation of the initial FeÃ
/
Ti
transition state. A branched chain alkyl derivative
such as Zr(OBut)4, being non-associated, even when
coordinated could not become involved in oligomerisa-
tion reactions of this type and hence an initial bimetallic
product should remain stable. Oligomerisation of the
Fe-containing fragments from such processes would also
be anticipated, there being ample evidence that low
molecularity Fe(III) carboxylate-alkoxide species can
readily form higher nuclearity Fe derivatives such
as [Fe11(m-O)6(m-OH)6(O2CPh)15] [6], [Fe(OMe)-
(O2CCH2Cl)2]10 [24] and [Fe8(m-O)4(O2CPh)14(OCH2-
But)2(HOCH2But)2] [5]. When Ti(OBut)4, which also is
monomeric in toluene [22], is added to a suspension of
[4] P.S. Ammala, J.D. Cashion, C.M. Kepert, K.S. Murray, B.
Moubaraki, L. Spicciaand, B.O. West, J. Chem. Soc., Dalton
Trans. (2001) 2032.
[5] P. Ammala, J.D. Cashion, C.M. Kepert, B. Moubaraki, K.S.
Murray, L. Spiccia, B.O. West, Angew. Chem. Int. Ed. 39 (2000)
1688.
[6] S.M. Gorun, G.C. Papaefthymiou, R.B. Frankel, S.J. Lippard, J.
Am. Chem. Soc. 109 (1998) 3337.
[7] A.M. Bond, R.J.H. Clark, D.G. Humphrey, P. Panayiotopoulos,
B.W. Skelton, A.H. White, J. Chem. Soc., Dalton Trans. (1998)
1845.
[8] G.M. Sheldrick, SHELX-97, Program for crystal structure refine-
ment, University of Gottingen, Gottingen, Germany, 1997.
¨
¨
[9] TEXSAN: Single Crystal Structure Analysis Software, Version 1.6,
Molecular Structure Corporation, The Woodlands, TX.

P.S. Ammala et al. / Inorganica Chimica Acta 353 (2003) 75ꢁ
/81
81
[10] R. Papiernik, L.G. Hubert-Pfalzgraf, J. Wassermann, M.C.
Henriques Baptista Goncalves, J. Chem. Soc., Dalton Trans.
(1998) 2285.
[19] X. Lei, M. Shang, T.P. Fehlner, Organometallics 15 (1996)
3779.
[20] (a) K.G. Caulton, L.G. Hubert-Pfalzgraf, Chem. Rev. 90 (1990)
969;
[11] T.J. Boyle, T.M. Alam, C.J. Tafoya, B.L. Scott, Inorg. Chem. 37
(1998) 5588.
(b) C.D. Chandler, C. Roger, M.J. Hampden-Smith, Chem. Rev.
93 (1993) 1205;
[12] T.J. Boyle, R.P. Tyner, T.M. Alam, B.L. Scott, J.W. Ziller, B.G.
Potter, J. Am. Chem. Soc. 121 (1999) 12104.
[13] G.B. Deacon, R.J. Phillips, Coord. Chem. Rev. 33 (1980) 227.
[14] S. Doeuff, Y. Dromzee, F. Taulelle, C. Sanchez, Inorg. Chem. 28
(1989) 4439.
(c) L.G. Hubert-Pfalzgraf, Polyhedron 13 (1994) 1181;
(d) R.C. Mehrotra, A. Singh, Chem. Soc. Rev. 25 (1996) 1.
[21] D.C. Bradley, R.C. Mehrotra, W. Wardlaw, J. Chem. Soc. (1952)
4204.
[15] I. Gautier-Luneau, A. Mosset, J. Galy, Z. Krystallogr. 180 (1987)
83.
[22] D.C. Bradley, R.C. Mehrotra, D.P. Gaur, Metal Alkoxides,
Academic Press, London, 1978 (chapter 3).
[23] L.G. Hubert-Pfalzgraf, S. Daniele, R. Papiernik, M.-C. Massiani,
B. Septe, J. Vaissermann, J.-C. Daran, J. Mater. Chem. 7 (1997)
753.
[16] I. Laaziz, A. Larbot, C. Guizard, J. Durand, L. Cot, J. Joffre,
Acta Crystallogr. C 46 (1990) 2332.
[17] S. Doeuff, Y. Dromzee, C. Sanchez, C.R. Acad. Sci. Ser. II 308
(1989) 1409.
[24] K.L. Taft, C.D. Delfs, G.C. Papaefthymiou, S. Foner, D.
Gatteschi, S.J. Lippard, J. Am. Chem. Soc. 116 (1994)
823.
[18] N. Steunou, F. Robert, K. Boubekeur, F. Ribot, C. Sanchez,
Inorg. Chim. Acta 279 (1998) 144.