Synthesis, crystal structures and spectroscopic characterization of [Ti8O8(OOCR)16] (where R = But, CH2But, C(CH3)2Et)

Article abstract of DOI:10.1016/j.poly.2005.01.014

Multinuclear titanium(IV) oxo carboxylates of the general formula [Ti ₈O₈(OOCR)₁₆] (where R = Bu^t (1), CH₂Bu^t (2), C(CH₃)₂Et (3)) have been synthesized in a reaction of titanium isopropoxide with the appropriate organic acids in a molar ratio of 1:2. The composition and structure of these compounds were identified by elemental analysis, IR, NMR and X-ray single-crystal diffraction. The crystal structure of 1 was solved in the orthorhombic space group Pbca. Titanium atoms form oligomeric [Ti₈(μ₂-O) ₈] rings, where each Ti cation is surrounded by six oxygen atoms (two μ₂-oxo and four μ-carboxylato bridges). Within the ring the Ti-Ti distances between neighboring titanium ions range from 3.333(1) to 3.366(1) A? and the mean value of the Ti-Ti-Ti angle is 134.2(1.3)°. Results of IR, NMR and MS studies proved that in the structures of 2 and 3, multinuclear [Ti₈(μ₂-O)₈] clusters stabilized by carboxylate bridges are also formed. TGA/DTG, MS and variable temperature IR + (VT-IR) studies have been carried out in order to determine the thermal stability and thermal decomposition mechanism of the Ti(IV) carboxylates mentioned above.

Full text of DOI:10.1016/j.poly.2005.01.014

Polyhedron 24 (2005) 663–670
www.elsevier.com/locate/poly
Synthesis, crystal structures and spectroscopic characterization
t
of [Ti O (OOCR) ] (where R = Bu , CH Bu , C(CH ) Et)
t
8
8
16
2
3 2
a,
a
a
P. Piszczek , M. Richert , A. Grodzicki , T. Głowiak , A. Wojtczak
,b
*
a
*
a
Faculty of Chemistry, Nicolaus Copernicus University, ul. Gagarina 7, 87-100 Toru n´ , Poland
b
Faculty of Chemistry, University of Wrocław, ul. F. Joliot-Curie 14, 50-383 Wrocław, Poland
Received 3 December 2004; accepted 18 January 2005
Abstract
Multinuclear titanium(IV) oxo carboxylates of the general formula [Ti O (OOCR) ] (where R = Bu (1), CH Bu (2), C(CH ) Et
t
t
8
8
16
2
3 2
(3)) have been synthesized in a reaction of titanium isopropoxide with the appropriate organic acids in a molar ratio of 1:2. The
composition and structure of these compounds were identified by elemental analysis, IR, NMR and X-ray single-crystal diffraction.
The crystal structure of 1 was solved in the orthorhombic space group Pbca. Titanium atoms form oligomeric [Ti (l -O) ] rings,
8
2
8
where each Ti cation is surrounded by six oxygen atoms (two l -oxo and four l-carboxylato bridges). Within the ring the Ti–Ti
2
˚
distances between neighboring titanium ions range from 3.333(1) to 3.366(1) A and the mean value of the Ti–Ti–Ti angle is
1
8 2 8
34.2(1.3)ꢀ. Results of IR, NMR and MS studies proved that in the structures of 2 and 3, multinuclear [Ti (l -O) ] clusters stabilized
by carboxylate bridges are also formed. TGA/DTG, MS and variable temperature IR + (VT-IR) studies have been carried out in
order to determine the thermal stability and thermal decomposition mechanism of the Ti(IV) carboxylates mentioned above.
ꢁ
2005 Elsevier Ltd. All rights reserved.
Keywords: Titanium(IV); Multinuclear carboxylates; X-ray structure; IR; NMR; TGA; MS
t
(OOCBu ) ] were the main products of the reaction
1
. Introduction
2
2
between TiCl and trimethylacetic acid in a 1:2.5 molar
4
t
ratio. The crystal structure of [{TiCl (OOCBu )(Bu -
t
The study of the synthesis of titanium(IV) oxo carb-
2
oxylates, structural characteristics and pyrolysis path-
way are motivated by their potential applications as
sol–gel or chemical vapor deposition (CVD) precursors.
According to the literature reports, two methods are
used in preparation of Ti(IV) oxo carboxylate deriva-
tives. Complexes of the general formula O[Ti(OOCR)3]2
were the main products of a multistage reaction of tita-
nium tetrachlorine with organic acids [1,2]. During the
process mentioned above, [TiCl4 (OOCR) ] (x = 1–4)
COOH)} O] is formed of dimers, composed of Ti atoms
2
octahedrally surrounded by oxygen atoms of one oxy-
gen bridge (l -O) and two bifurcated carboxylates
2
(l-O) of the syn–syn type. The Ti–O distances were
˚
˚
1.77 A for Ti-(l -O) and 1.99–2.09 A for Ti-(l-O) [7].
2
The stoichiometric reaction of titanium alkoxides
0
0
i
(Ti(OR ) ; R = Et, Pr ) with carboxylic acids is the next
4
method of synthesizing titanium oxo carboxylates [8,9].
Titanium oxo carboxylato alkoxides were crystallized
ꢀ x
x
0
derivatives have also been isolated [3–5]. Barrow
et al. [6,7] showed that titanium(IV) oxo chloro-carb-
from 1:1–4 molar ratio mixtures of Ti(OR ) /HOOCR.
4
X-ray diffraction studies exhibited that the follow-
ing four types of complexes may be formed:
t
t
oxylates O[TiCl (OOCBu )(Bu COOH)] and O[TiCl
2
2
0
a) [Ti O (OR) (O CR ) ], (b) [Ti O (OR) (O CR ) ],
6 4 12 2 4 6 4 8 2
0
(
8
0
0
*
(c) [Ti O (OR) (O CR ) ] and (d) [Ti O (OR) (O CR ) ]
6
Corresponding author. Tel.: +48 56 6114 316; fax: +48 56 652 477.
E-mail address: piszczek@chem.uni.torun.pl (P. Piszczek).
4
4
4
0
2
4
6
6
6
2
i
(R = Et, Pr , R = Me, Np (neopentyl), Bu , Ph) [10–16].
t
0
277-5387/$ - see front matter ꢁ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.01.014

664
P. Piszczek et al. / Polyhedron 24 (2005) 663–670
The main factor influencing the formation of these types
of multinuclear Ti(IV) clusters is the nature of the alkox-
ide and carboxylate ligands [13]. Ammala et al. [17] re-
of the reaction mixture under argon atmosphere (glove-
box). The colorless crystals were obtained after 2–3
days.
t
port
[
that
n
[Ti O (OCH Bu ) (O CPh) ]
and
Ti O (OPr ) (O CPh) ] were also synthesized in the
6
6
2
6
2
6
t
2.1.1. Ti O (OOCBu ) (1)
6
4
8
2
8
8
8
16
n
reaction of [Fe (l -O) (O CPh) (py) ] with Ti(OPr )
Yield: 0.56 g (55.0%). The % Ti was gravimetrically
determined as TiO , according to the Meth-Cohn et al.
4
3
2
2
8
2
4
in toluene. The application of the large excess of organic
acid leads to the formation of Ti(IV) oxo carboxylato
derivatives (e.g., polymeric chains of [TiO(OAc) ] were
2
method [13]. Anal. Calc. for C H O Ti · C H : C,
8
0
144 40
8
7
8
47.03; H, 6.85; Ti, 17.30. Found: C, 47.33; H, 7.03; Ti,
ꢀ
2
n
1
obtained for the ratio 1:10) [8,9].
17.46%. IR (KBr, cm ) 1545 (s, COO), 1512 (m,
COO), 1429 (s, COO), 1417 (m, COO), 1229 (m, C–
Me ), 750 (m, Ti–O), 611 (m, Ti–O), 504 (m, Ti–O).
In the reported work we have focused on structural
studies and spectral characteristics of multinuclear
Ti(IV) carboxylato derivatives, synthesized from tita-
3
1
3
C NMR (solid, d, ppm) 26.5 (CH ), 38.7 (C–(CH ) ),
3
3 3
t
t
nium isopropoxide and HOOCR, R = Bu , CH Bu ,
2
188.2, 186.7 (COO).
2.1.2. Ti O (OOCCH Bu ) (2)
Yield: 0.25 g (24.2%). Anal. Calc. for C H O -
C(CH ) Et. Analysis of the thermogravimetric (TGA),
2
3
t
MS-EI, and variable temperature IR spectroscopy have
been used in order to study the thermal stability of the
synthesized compounds and their thermal decomposi-
tion pathway.
8
8
2
16
8
1
146 40
Ti : C, 48.99; H, 7.47; Ti, 16.30. Found: C, 47.66;
8
ꢀ
1
H, 7.45; Ti, 16.80%. IR (KBr, cm ) 1540 (s, COO),
1
1
507 (m, COO), 1421 (s, COO), 1410 (s, COO),
209 (m, C–Me ), 754 (m, Ti–O), 601 (m, Ti–O),
3
3
1
2
. Experimental
507 (m, Ti–O). C NMR (solid, d, ppm) 49.5 (CH ),
3
2
9.8 (C–(CH ) ), 181.5 (COO).
3 3
The studied compounds were synthesized under ar-
gon atmosphere, using standard Schlenk line and glove-
i
box techniques. Ti(OPr ) (prepared from TiCl4
4
(
trimethylamine) was freshly vacuum distilled prior to
Aldrich) and 2-propanol (Aldrich) in the presence of
Table 1
t
8 8
Crystal data and structure refinement for [Ti O (OOCBu )16]
t
use, whereas Bu COOH, Bu CH COOH and Et(Me) -
t
2
2
Empirical formula (chemical unit)
C80H144O40Ti8
CCOOH, (Aldrich) were used as received.
Infrared (IR) spectra were recorded on a Perkin–
Elmer Spectrum 2000 spectrometer within the range
Formula weight
Temperature (K)
˚
Wavelength (A)
2129.18
293(2)
0.71073
orthorhombic
Pbca (no. 61)
ꢀ
1
60–4000 cm with a medium slit width and a peak res-
Crystal system
Space group
Unit cell dimensions
1
olution of 2.0 cm . The crystals were studied as a pow-
ꢀ
1
ꢀ1
der dispersed in a KBr pellet (400–4000 cm ) and as a
˚
a (A)
30.464(4)
27.361(4)
32.549(4)
27130.42(629)
8
ꢀ1
Nujol suspension between CsI plates (160–700 cm ).
The low temperature IR spectra (liquid nitrogen temper-
ature (LNT)) have been recorded using a SPECAC var-
b ( A˚ )
˚
c (A)
˚
3
Volume (A )
1
13
Z
iable temperature cell. Solution H and C NMR
spectra ([D ]toluene) were recorded using a 5-mm solu-
3
D
calc (Mg/m )
1.222
0.52
ꢀ1
8
Absorption coefficient (mm
F(0 0 0)
Crystal size (mm)
)
1
3
tion probe on a Varian Gemini 200. Solid state
C
10 552
0.30 · 0.25 · 0.20
NMR spectra were registered on a Bruker AMX 300.
Thermogravimetric analysis (TGA) was carried out
using the SDT 2960 TA Instrument, in nitrogen atmo-
Theta range for data collection (deg) 3.30–28.56
Index ranges
h
ꢀ40 to 29
ꢀ36 to 34
ꢀ42 to 43
181 753
ꢀ
1
sphere from 25 to 500 ꢀC at a ramp rate of 3ꢀ min
Mass spectra were recorded with a MS AMD-604 spec-
.
k
l
trometer, using the EI method, at 70 eV, in the range
1
Reflections collected
Independent reflections [Rint
Refinement method
Data/parameters/restraints
]
32 502 [0.0857]
50–350 ꢀC.
.1. Preparation of [Ti O (OOCR) ]
2
full-matrix least-squares on F
32 502/1627/90
1.086
2
2
8
8
16
Goodness-of-fit on F
Final R indices [I > 2sigma(I)]
R indices (all data)
R
R
1
1
= 0.0999; wR
= 0.1587; wR
2
= 0.2523
= 0.3132
i
Ti(OPr ) (1.00 g, 3.52 mmol) was added dropwise
to a solution of organic acid (7.04 mmol, 0.72 g of
4
2
Largest difference between
peak and hole
3.341; ꢀ0.754
t
Bu COOH, 6.90 mmol, 0.80 g of Bu CH COOH or
t
2
P
P
3
R = (iF j ꢀ jF i)/ jF j.
1
o
c
o
0
stirred for 12 h. Crystals were grown by slow evaporation
.80 g of Et(CH ) CCOOH) in toluene (3.00 cm ), and
3 2
P
P
2
2
2
2 2 1=2
wR2 ¼ ½ wðF ꢀ F Þ = ðwjF oj Þ ꢁ
.
o
c

P. Piszczek et al. / Polyhedron 24 (2005) 663–670
665
b
Table 2 (continued)
O31
a
O12
O32
x
y
z
U
eq
c
O41
Ti2
O42
O51
2767(1)
3586(1)
4158(1)
3561(1)
4174(1)
4725(1)
4920(1)
4005(1)
4284(1)
4721(1)
4313(1)
4464(1)
4123(1)
3750(1)
3095(1)
3441(1)
2796(1)
2216(1)
1595(1)
2609(1)
1917(1)
1153(1)
1088(1)
1549(1)
1313(1)
1143(2)
1951(2)
2531(2)
2354(2)
3914(2)
3930(2)
5005(2)
4129(2)
4658(2)
4386(2)
3491(2)
3084(2)
1819(2)
2258(2)
963(1)
7105(1)
6948(1)
7116(1)
5930(1)
6108(1)
6792(1)
6518(1)
7373(1)
7204(1)
6653(1)
6512(1)
5773(1)
5602(1)
5931(1)
5584(1)
6783(1)
6493(1)
5761(1)
5954(1)
5112(1)
5161(1)
5592(1)
5393(1)
6512(1)
6391(1)
5979(2)
5067(2)
6133(2)
7162(2)
7192(2)
5820(2)
6670(2)
7496(2)
6687(2)
5497(2)
5688(2)
6827(2)
5890(2)
4919(2)
5381(2)
6644(2)
4687(1)
4369(1)
4775(1)
4638(1)
4984(1)
5340(1)
5960(1)
5595(1)
6214(1)
6765(1)
7326(1)
6378(1)
6970(1)
7704(1)
7821(1)
7327(1)
7549(1)
7735(1)
7393(1)
7181(1)
6944(1)
6717(1)
6052(1)
6644(1)
5998(1)
4959(2)
5163(2)
4061(2)
4716(2)
4464(2)
4782(2)
5607(2)
5950(2)
7146(2)
6677(2)
7919(1)
7517(2)
7727(2)
7050(1)
6426(1)
6322(2)
31(1)
35(1)
41(1)
36(1)
38(1)
38(1)
38(1)
37(1)
38(1)
38(1)
40(1)
36(1)
35(1)
41(1)
36(1)
36(1)
36(1)
33(1)
35(1)
34(1)
34(1)
35(1)
40(1)
33(1)
36(1)
36(1)
34(1)
37(1)
32(1)
34(1)
37(1)
34(1)
36(1)
37(1)
33(1)
33(1)
35(1)
31(1)
31(1)
31(1)
35(1)
O11
O42
O51
O61
Ti3
O52
O61
O21
O2
O152
O162
O161
O1
O62
O71
O52
O62
Ti1
O8
O3
O72
O81
Ti4
O81
O82
O71
O82
O91
O151
O4
Ti8
O92
O7
O132 O142
O141
Ti5
O101
O102
O111
O112
O121
O122
O131
O132
O141
O142
O151
O152
O161
O162
C11
O5
O72
O6
O101
Ti7
Ti6
O102
O121
O91
Ti
O131
O122
O
C
O112
O92
O111
t
Fig. 1. Crystal structure of 1 with the atom numbering scheme, Bu
groups have been omitted for clarity.
2
.1.3. Ti O (OOCC(CH ) Et) (3)
8 8 3 2 16
Yield: 0.30 g (29.0%). Anal. Calc. for C H O Ti :
8
1
146 40
8
C21
C, 48.99; H, 7.47; Ti, 16.30. Found: C, 48.77; H, 7.70;
ꢀ
1
C31
C41
Ti, 16.06%. IR (KBr, cm ) 1552 (s, COO), 1411 (s,
COO), 1417 (m, COO), 1203 (m, C–Me ), 756 (m, Ti–
3
C51
C61
1
3
O), 641 (m, Ti–O), 552 (m, Ti–O). C NMR (solid, d,
ppm) 9.1, 33.9 (Et), 24.5 (CH ), 43.3, 43.1 (C–(CH ) Et),
1
C71
C81
3
3 2
88.0, 186.5 (COO).
C91
C101
C111
C121
C131
C141
C151
C161
Table 2
4
Atomic coordinates of the [Ti
8
(l
2
-O)
8
(O
2
C)16] cluster (·10 ) and
˚
2
3
equivalent isotropic displacement parameters (A · 10 ) for glow
x
y
z
U
eq
1344(2)
Ti1
Ti2
Ti3
Ti4
Ti5
Ti6
Ti7
Ti8
O1
1596(1)
2119(1)
3142(1)
4033(1)
4329(1)
3768(1)
2757(1)
1807(1)
1981(1)
2742(1)
3475(1)
4047(1)
3844(1)
3228(1)
2339(1)
1910(1)
1128(1)
1483(1)
1793(1)
2116(1)
2222(1)
2904(1)
2094(1)
5768(1)
6119(1)
6493(1)
6734(1)
6473(1)
6206(1)
5809(1)
5865(1)
6137(1)
6159(1)
6708(1)
6387(1)
6451(1)
5863(1)
6042(1)
5716(1)
5828(1)
6091(1)
5158(1)
5383(1)
6057(1)
6318(1)
6840(1)
5804(1)
4945(1)
4716(1)
5285(1)
6246(1)
7098(1)
7321(1)
6810(1)
5463(1)
4977(1)
5171(1)
5789(1)
6612(1)
7024(1)
6937(1)
6244(1)
5314(1)
4758(1)
5519(1)
4928(1)
4298(1)
4160(1)
4844(1)
31(1)
30(1)
28(1)
31(1)
29(1)
29(1)
28(1)
29(1)
30(1)
29(1)
29(1)
28(1)
30(1)
29(1)
28(1)
30(1)
38(1)
38(1)
35(1)
32(1)
40(1)
36(1)
38(1)
U
eq is defined as one third of the trace of the orthogonalized Uij tensor.
2.2. X-ray crystallography
The diffraction data were collected at 100(2) K for
a 0.30 · 0.25 · 0.20 mm single crystal using Kuma
CCD diffractometer, Mo Ka radiation k = 0.71073 A.
The 181753 reflections were measured with the
x ꢀ 2h method. A shape-based absorption correction
was applied for 1 (RED167 package of programs, Ox-
ford Diffraction, 2000) with the maximum and mini-
mum transmissions of 0.9037 and 0.8603. The
structure was solved by direct methods and refined
O2
O3
˚
O4
O5
O6
O7
O8
O11
O12
O21
O22
O31
O32
O41
2
with a full-matrix least-squares procedure on F using
the SHELX-97 program package [18]. Details of the
data collection and structure refinement are presented
in Table 1.

666
P. Piszczek et al. / Polyhedron 24 (2005) 663–670
Table 3
Table 3 (continued)
Angles [ꢀ]
˚
Selected bond distances [A] and angles [ꢀ] for 1
˚
Distances [A]
Ti3–O3–Ti4
Ti4–O4–Ti5
134.67(18)
133.32(17)
133.59(18)
133.14(18)
133.63(18)
133.60(18)
Ti-(l-O)
Ti1–O1
Ti1–O8
Ti2–O1
Ti2–O2
Ti3–O2
Ti3–O3
Ti4–O3
Ti4–O4
Ti5–O4
Ti5–O5
Ti6–O5
Ti6–O6
Ti7–O6
Ti7–O7
Ti8–O8
Ti8–O7
1.904(3)
1.727(3)
1.738(3)
1.904(3)
1.746(3)
1.892(3)
1.741(3)
1.896(3)
1.733(3)
1.900(3)
1.731(3)
1.910(3)
1.734(3)
1.894(3)
1.915(3)
1.739(3)
Ti5–O5–Ti6
Ti6–O6–Ti7
Ti7–O7–Ti8
Ti8–O8–Ti1
3
. Results and discussion
3
.1. Synthesis
i
Ti(OPr ) was added to a stirred solution of
t
HOOCR (R = Bu , CH Bu , C(CH ) Et) in toluene,
4
t
2
3 2
t
Ti-(OOCBu )
(molar ratio alkoxide/acid = 1:2, Ar atmosphere, room
temperature (RT)). At the beginning, the reaction mix-
ture became turbid but after 2 h, a clear solution was
formed. Colorless crystals were grown by slow evapo-
ration (glovebox) of the solvent over 2–3 days. Based
on the results of elemental analysis, the general for-
mula of the synthesized complexes was determined
Ti1–O11
Ti1–O21
Ti1–O152
Ti1–O162
Ti2–O22
Ti2–O12
Ti2–O41
Ti2–O31
Ti3–O51
Ti3–O42
Ti3–O32
Ti3–O61
Ti4–O62
Ti4–O52
Ti4–O71
Ti4–O81
Ti5–O72
Ti5–O82
Ti5–O101
Ti5–O91
Ti6–O111
Ti6–O121
Ti6–O102
Ti6–O92
Ti7–O122
Ti7–O112
Ti7–O141
Ti7–O131
Ti8–O142
Ti8–O132
Ti8–O151
Ti8–O161
2.146(3)
2.001(3)
2.025(3)
2.013(3)
2.015(3)
2.030(3)
2.002(3)
2.138(4)
2.156(3)
2.031(3)
2.006(3)
2.014(3)
2.020(3)
1.996(3)
2.120(3)
2.021(4)
2.031(3)
2.006(3)
2.007(3)
2.128(3)
2.112(3)
2.010(3)
2.019(3)
2.003(3)
2.016(3)
2.024(3)
2.013(3)
2.134(3)
2.003(3)
2.018(3)
2.152(3)
2.010(3)
t
t
as [Ti O (OOCR) ], where R = Bu (1), CH Bu (2),
8
8
16
2
C(CH ) Et (3). However microanalysis data suggest
3
2
the presence of solvent molecules (toluene) in the crys-
tal lattice of 1. Single crystals, suitable for crystallo-
graphic studies were obtained only for compound 1,
but their stability was very low, and they were de-
stroyed in air (RT), with the formation of a white
crystalline powder. During the crystallization of 2
and 3 only crystalline powder was formed. Com-
pounds 1–3 were insoluble in aliphatic and sparingly
soluble in aromatic solvents.
3.2. Crystal structure
Due to the low stability of 1 in the air at RT, the
X-ray measurements were carried out at low tempera-
ture (ꢂ100 K). The poor quality of crystals obtained
for 2 and 3 made their crystallographic studies impos-
sible. The chemical unit of 1, with the atom-number-
ing scheme, is shown in Fig. 1. Crystal data and
atomic coordinates are listed in Tables 1 and 2. The
selected bond distances and angles are presented in
Table 3.
The ring molecule of the reported complex is com-
posed of eight distorted [TiO ] octahedra linked by
two l -O (cis) and four l-O (carboxylate) bridges (Fig.
1, Table 3). The [Ti (l -O) ] ring is not planar. The
8 2 8
Ti ring conformation with alternating positive and neg-
Ti–Ti
Ti1–Ti2
3.358(12)
3.366(12)
3.352(12)
3.333(12)
3.338(12)
3.344(12)
3.341(12)
3.348(13)
Ti2–Ti3
Ti3–Ti4
Ti4–Ti5
Ti5–Ti6
6
2
Ti6–Ti7
Ti7–Ti8
Ti8–Ti1
8
ative values of Ti–Ti–Ti–Ti torsion angles resembles the
cyclohexane chair conformation, but their absolute val-
ues vary from 5.11(7)ꢀ for Ti1–Ti2–Ti3–Ti4 to 37.14(7)ꢀ
Ti-(l-O)-Ti
Ti1–O1–Ti2
Ti2–O2–Ti3
134.34(18)
134.45(17)

P. Piszczek et al. / Polyhedron 24 (2005) 663–670
667
˚
for Ti6–Ti7–Ti8–Ti1. The rms deviation of Ti ions from
˚
the Ti best plane is 0.2073 A.
bonds of l -oxo bridges (1.90–1.93 and 1.72–1.74 A)
2
were compensated by asymmetric Ti–O distances of
˚
trans carboxylate groups (1.97–2.11 and 2.09–2.16 A).
Analysis of the literature reports exhibited that in an-
other type of [Ti (l -O) ] (n = 2, 3) cluster the Ti–O dis-
tances were shorter, e.g., in the structure of
8
Eight of the bridging carboxylates are positioned
approximately in the ring plane (Fig. 1), the dihedral an-
gles between the Ti COO planes and the best plane of the
2
x
n
y
Ti ring range from 8.88(5)ꢀ to 21.85(3)ꢀ, with the mean
8
i
t
value being 16.5(4)ꢀ. The remaining eight carboxylates
form the bridges between the Ti ions alternating between
the two sides of the ring plane and are approximately
perpendicular to that plane. The dihedral angles between
the Ti best plane and the Ti COO planes vary from
([Ti O (OPr ) (O CBu ) ], Ti-(l -O) = 1.878(4), 1.890(2)
6 6 6 2 6 3
n
˚
and 2.142(3) A [14], and in [Ti O (Opr ) (O CR) ]
6
4
8
2
8
(R = CH3, Ph), Ti-( -O) = 1.724(6)–1.768(2) and
2
˚
1.900(6)–1.942(2) A, and Ti-(l -O) = 1.911(2), 1.941(2)
3
˚
and 2.082(2) A [9,16].
8
2
7
2.81(7)ꢀ to 81.29(6)ꢀ, with a mean value of 77.8(3)ꢀ.
The bridging oxygen atoms in the [Ti (l -O) ] rings
form alternating longer and shorter Ti–O bonds, the
The low temperature experiment for the reported
complex 1 allowed building a satisfactory model for
8
2
8
t
the majority of the OOCBu moieties. Only for two
t
Bu groups the rotational disorder was accounted for
average Ti–O distances and esd in the series being
˚
.904(8) and 1.735(7) A for the longer and shorter
1
bonds, respectively. The angles in that ring vary from
in the final model. Both these groups do not participate
in intermolecular interactions between the adjacent
rings. The complex molecules of 1 form some hydropho-
1
33.15(1)ꢀ–134.67(1)ꢀ to 132.42(1)ꢀ–136.28(1)ꢀ for Ti–
t
O–Ti and Ti–Ti–Ti, respectively (Table 3). Also the
oxo bridges form alternating shorter 1.997(3)–
bic interactions with the adjacent molecules via their Bu
groups on the side surfaces and around the ring. How-
ever, the important component of the packing interac-
tions is due to the toluene molecules found in the
structure. Two of them are positioned near the ring cen-
˚ ˚
.031(3) A and longer 2.114(3)–2.156(3) A Ti–O bonds.
2
In the octahedral environment of each Ti ion, they occu-
py the trans positions relative to the shorter and longer
carboxylate Ti–O bonds mentioned above. The other
two trans trimethyl acetate bridges are positioned
outside the [Ti (l -O) ] rings, and the corresponding
t
ter, between the OOCBu moieties perpendicular to the
molecule ring plane. Another two toluene molecules
participate in the packing interactions involving the car-
boxylate ligands positioned in the ring plane.
8
2
8
Ti–O(carboxylate) distances vary in the range
2
˚
.002(3)–2.013(3) and 2.013(3)–2.031(3) A.
Kickelbick and Scubert [16] reported an oligomeric
ring structure of the general formula [Ti O -
3.3. Analysis of NMR data
9
8
i
13
The C NMR spectroscopy in the solid state have
been used to study the structural similarities between
(
Ia). That complex consisted of a ring of nine [TiO ] octa-
OPr ) (OOCC(Me)@CH ) ] (monoclinic, space group
4
2 16
6
1
13
1, 2 and 3. Also, H and C NMR spectra of [D ]tolu-
hedra linked by six l -O, two l -O and 16 l -O(OOC)
2
3
2
8
bridges. Also in that case, the non-equivalent Ti–O
ene solutions of these compounds were registered in
Table 4
t
(OOCR)16] (R = Bu (1), CH
t
Bu (2), C(CH
The solid-state and solution NMR studies of [Ti
Compound Method d [ppm]
CH (Et)
8
O
8
2
3
)
2
Et (3))
t
(Bu )
t
C (Bu )
3
CH
2
(Et)
CH
2
CH
3
2
(CMe )
CH
3
C (CMe
2
)
C (COO)
186.7
1
1
1
3
(
1)
C – s. st.
C – C
26.5
38.7
1
88.2
3
7
D
8
27.2
39.3
39.5
187.4
188.6
2
7.4
1.2 (s)
.1 (s)
7 8
H – C D
1
1
3
(
(
2)
3)
C – s. st.
49.5
48.9
29.8
30.1
181.5
183.6
182.7
13
C – C
7
D
8
30.9
31.1
5
0.1
1
1
H – C
7
D
8
2.3 (s)
1.2 (s)
3
C – s. st.
9.1
33.9
24.5
43.3
3.1
186.5
188.0
187.4
189.0
4
1
3
C – C
H – C
7
D
8
9.7
0.3
34.3
34.6
25.0
25.6
43.6
43.7
1
1
7
D
8
1.1 (t)
1.7 (q)
JH–H = 4.0 Hz
1.3 (s)
J
H–H = 4.0 Hz
1
3
1
The solid-state C NMR spectra were registered on a Bruker AMX 300, solution H, C NMR spectra ([D
13
8
] toluene) were recorded using a 5-mm
solution probe on a Varian Gemini 200 spectrometer.

668
P. Piszczek et al. / Polyhedron 24 (2005) 663–670
order to determine the structural changes of the investi-
gated compounds after their solubilization. The ob-
served chemical shifts are listed in Table 4.
Table 5
Wavenumbers [cm ] for the vibrations of acetate ions and oxo bridges
ꢀ1
t
(
8 8
M–O–M) in LNT spectra of [Ti O (OOCR)16] (where R = Bu (1),
t
CH
2 3 2
Bu (2), C(CH ) Et (3))
The signals due to the carbon atoms of coordinated
carboxylate groups are located between 180.3 and
1
ꢀ
1
ꢀ1
ꢀ1
3 [cm ]
Modes
1 [cm
]
2 [cm
]
1
88.2 ppm in the solid-state C NMR spectra of 1–3.
3
1574 (m)
1552 (s)
m
as(COO)
1546 (s)
1552 (s)
540 (s)
1507 (m)
In spectra of 1 and 3, the carbon atoms show two lines
of equal intensity at 186.6 and 188.1 ppm, whereas a
wide single signal at 180.5 ppm is found in the spectrum
of 2 (Table 4). However, a detailed analysis of the
C(COO) peak in the spectrum of this compound re-
vealed that it also consists of two components, with
d = 180.3 and 180.7 ppm. Considering crystallographic
data, the above phenomenon can be explained by the
presence of two different types of carboxylate groups
in the structures of 1–3. Crystallographic data showed
that the COO groups formed the bridges in the plane
of the [Ti (l -O) ] ring, exhibiting asymmetry of the
1
1
512 (m)
1486 (m)
458 (w)
1429 (s)
419 (m)
1519 (m)
d
as(CH
3
), das(CH
2
)
1478 (m)
1463 (m)
1477 (m)
1455 (m)
1
m
s
(COO), das(CH
3
)
1421 (s)
1405 (m)
1436 (m)
1413 (m)
1
d(CH
d(CH
d(CH
3
3
3
)
1378 (m)
1376 (m)
1388 (m)
1371 (m)
1367 (m)
)
)
1361 (m)
750 (s)
1357 (m)
754 (m)
m
as(Ti–O–Ti)(l
3
-O)
758 (m)
722 (m)
7
14 (m)
8
2
8
d(OCO)
d(OCO)
q(OCO); out of plane
q(OCO); out of plane
m(CCC)
611 (s)
641 (m)
552 (w)
502 (m)
478 (m)
450 (w)
435 (vw)
420 (w)
C–O bond lengths, 1.237(6)–1.250(5) (shorter) and
1
583 (m)
504 (m)
481 (m)
601 (s)
507 (w)
480 (w)
460 (w)
435 (w)
429 (w)
˚
.263(6)–1.299(6) A (longer). Differences in the length
of bonds formed by the carboxylate group bridges out-
side of the ring plane were smaller (1.258(6)–1.276(5)
1
3
˚
q(OCO); in plane
q(OCO); in plane
443 (m)
431 (w)
and 1.261(5)–1.275(6) A). The C NMR studies suggest
that 1 and 3 form a similar type of carboxylate group
interaction in [Ti O (OOCR) ] molecules. Undetected
8
8
16
1
3
ꢀ1
band components were 116 and 94 cm , 116 and
splitting of the C(COO) signal, observed in the
C
ꢀ
1
ꢀ1
NMR spectrum of 2, can be interpreted as a result of
the smaller differences between the length of the C–O
bonds formed by COO groups outside compared to
within the [Ti (l -O) ] ring plane.
107 cm for 1 and 3, as well as 131 and 103 cm for
2. Comparison of the above results with the literature
data [19–22] indicate that the detected m (COO) fre-
quencies and D parameter values correspond to biden-
date carboxylate groups, participating in syn–syn
bridges. The different interactions of COO ligands in
the structure of the studied compounds are the main fac-
tor that causes splitting of the stretching band. That
conclusion is consistent with the structural and NMR
data presented in this paper.
as
8
2
8
1
3
Analysis of C NMR spectra of 1–3 [D ]toluene
8
solutions shows clear similarities in the chemical shift
and splitting of the resonance signals with their analogs
in the solid state spectra (Table 4). The NMR data re-
veal the presence of two types of carboxylate groups in
the structure of the studied compounds, which is consis-
1
tent with the X-ray structure of 1. In H NMR spectra
of 1–3 [D ]toluene solutions, only the signals attributed
to appropriate hydrocarbon groups were detected.
ꢀ
3.4.2. Absorption bands between 400 and 900 cm
The bands due to vibrations of carboxylate ligands
1
8
and M–O–M titanium-oxide bridges of [Ti (l -O) ]
8
ꢀ
2
8
1
3
.4. Infrared spectra studies
rings have been found in the range 400–900 cm (Table
). According to the literature data [19,22], their
frequencies can be assigned to COO bending (d (O-
5
IR spectra of the studied carboxylates were registered
s
ꢀ1
at liquid nitrogen temperature (LNT), in conditions
analogous to the single crystal X-ray measurements.
In order to study similarities between the structures of
CO) = 551–641 cm ) and rocking (q(COO) = 419–
507 cm ) modes.
ꢀ
1
The band for Ti–O–Ti stretching modes (m (Ti–O–
a
ꢀ
1
Ti)) was found in the range 714–758 cm (Table 5).
1
–3, a detailed analysis of IR spectra in the following
ꢀ
1
ꢀ1
ranges (a) 1350–1600 cm and (b) 400–900 cm have
been carried out. The wavenumbers of absorption bands
registered in the above regions are listed in Table 5.
According to NakamotoÕs report on vibrational spectra
of complexes containing M-(l -O) bridges in their struc-
2
ture [19], the bands assigned to M–O–M asymmetric
vibrations appear in the IR spectrum, while symmetric
ones appear in the Raman spectrum. The frequency
for the bands mentioned above depends on the type of
oxygen bridge and the number of concomitant carboxyl-
3
.4.1. Stretching frequencies of carboxylate ligands
The split bands attributed to m (COO) and m (COO)
as
s
vibrations were found in the ranges 1500–1575 and
1
1
ꢀ
400–1440 cm
(Table 5). Values of the D[mas-
ate bridges. For the linear M-(l -O) monobridges
2
ꢀ
1
(
COO) ꢀ m (COO)] parameter, calculated for the suitable
ma(M–O–M) @ 843–885 cm , and for non-linear one,
s

P. Piszczek et al. / Polyhedron 24 (2005) 663–670
669
ꢀ1
ma(M–O–M) @ 827 cm . Presence of the oxygen bridge
in the vicinity of carboxylate bridges causes the fre-
7
7
65
60
quency shift of the m (M–O–M) vibrations towards
a
ꢀ
1
49–772 cm [19]. In IR spectra of 2 and 3, the appear-
7
ꢀ
1
ance of m (TiOTi) bands at 714, 754 cm (2), and at
a
ꢀ
1
22, 758 cm (3) was observed. That confirms the for-
7
mation of non-linear Ti–O–Ti bridges near the Ti-car-
boxylate ones in the structure of these compounds,
similar to those found in the structure of 1.
755
The possible low temperature phase transition and
thermal stability of Ti–O bonds in [Ti (l -O) ] clusters
7
50
8
2
8
have been investigated by means of variable temperature
IR spectroscopy (VT-IR). Analysis of the dependence
1
00
200
300
400
500
between the frequency of Ti–O–Ti motions (m (TiOTi))
o
a
T [ C]
and the temperature exhibited only insignificant shifts
(
ꢀ1
Fig. 2. Temperature evolution of the m
a
(TiOTi) band in the VT-IR
6–7 cm ) of this band towards higher wavenumbers
t
spectra of [Ti
2
8 8 2
O (O
CBu )16] (SPECTRUM 2000, KBr, ꢀ175 to
in the spectra of 2 and 3. These results suggest that
the stability of [Ti (l -O) ] rings is very high and a tem-
perature phase transition does not occur. The tempera-
50 ꢀC).
8
2
8
the temperature range 25–550 ꢀC with a heating rate
1
ꢀ
ture evolution of the m (TiOTi) frequency, observed in
of 3 ꢀC min
under a nitrogen atmosphere. The
a
VT-IR spectra of 1, was significantly higher (15–
ꢀ
TGA/DTA data of 1 show that the decomposition pro-
ceeded in four endothermic stages, with maxima at 63,
260, 370 and 421 ꢀC, with a weight loss of 73.4%. A mul-
tistep thermal decomposition was also observed for 2
and 3; the maxima of endothermic stages were found
at 108, 311, 381, 417 ꢀC (weight loss: 70.1%) for 2, and
00, 340, 393, 410 ꢀC (weight loss: 71.2%) for 3. Ther-
mogravimetric analysis exhibited that the pyrolysis of
–3 proceed with their complete conversion to TiO2.
1
6 cm ). Moreover only for this compound, clear
1
changes in the diagram slopes between 0 and 60 ꢀC were
observed (Fig. 2). Considering crystallographic and
TGA data, the latter effect can be explained by the loss
of solvent molecules from the crystal lattice of 1.
3
3
.5. Thermal characterization
1
The thermal decomposition mechanism of Ti(IV) ring
carboxylates was studied using thermogravimetric and
differential thermal analysis (TG/DTA) methods over
Moreover, one endothermic peak near 63 ꢀC is observed
for 1, which can be explained by the loss of solvent mol-
ecules from the crystal lattice of this compound.
Table 6
t
(OOCR)16], where R = Bu (1), CH
t
Bu (2), C(Me)
The mass spectra of [Ti
O
8 8
2
2
Et (3), registered between 150 and 350 ꢀC (MS-EI 70 eV)
Fragmentation Ion
m/z
T [ꢀC]
1
50
200
85.7
100
30.4
240
260
280
300
320
350
t
CBu )(O
+
(
(
(
1)
2)
3)
[Ti
4
3
8
8
8
8
8
O
4
(O
2
2
CH)
2
]
448
53.3
100
15.3
t
CBu )
+
[Ti
[Ti
[Ti
[Ti
[Ti
[Ti
O(O
2
2
(O
2
CCH
3
)
2
]
480
1286
1554
1655
1926
2027
t
CBu )
+
O
O
O
O
O
8
(O
2
7
t
(O CC
2
2
H
2
)]
+
10(O
10(O
2
CBu )10
]
5.7
43.9
38.1
49.7
32.2
100
28.9
100
t
+
2
CBu )11
]
t
+
8
(O
(O
2
CBu )14
]
11.0
100
10.6
63.2
t
+
8
2
CBu )15
]
5.5
29.4
62.8
100
14.6
t
+
[Ti
2
8
8
8
8
8
8
O
2
O
8
O
8
O
8
O
8
O
8
O
8
(O
2
(O
2
(O
2
(O
2
(O
2
(O
2
(O
2
CCH
CCH
CCH
CCH
CCH
CCH
CCH
2
2
2
2
2
2
2
Bu )
2
]
356
849
68.8
6.6
35.2
14.2
5.8
t
+
[Ti
[Ti
[Ti
[Ti
[Ti
[Ti
Bu )(O
2
CCH
3
)
3
(O
2
+
CH)]
41.1
41.8
43.5
14.5
20.3
35.0
6.2
22.1
1.7
t
Bu )
3
4
9
(O
(O
(O
2
2
2
CC
4
H
8
)]
(O
)(O CCH)
(O
956
3.9
36.5
19.5
21.0
8.2
6.7
t
+
Bu )
CCH
CCH
3
3
2
)
4
2
CC
3
H
6
)]
1064
1696
1811
2241
4.3
17.6
t
+
Bu )
2
2
]
5.6
29.6
6.6
16.7
70.7
20.3
18.8
90.4
11.4
1.1
4.6
t
+
Bu )10(O
2
CH)
2
CCH
3
)]
100
100
100
t
+
Bu )14(O
2
CCH
3
)
2
]
75.6
58.4
28.2
+
[Ti
2
8
8
8
8
8
8
2 2
O(O CCMe Et)(O
2
CCH)(O
)
2
CC
(O CH)]
(O CC
2
H
4
)]
356
849
100
100
+
[Ti
[Ti
[Ti
[Ti
[Ti
[Ti
O
8
O
8
O
8
O
8
O
8
O
8
(O
2
(O
2
(O
2
(O
2
(O
2
(O
2
CCMe
2
2
2
2
2
2
Et)(O CCH
2
3
3
2
37.9
56.3
22.4
15.8
41.7
15.4
54.4
13.3
10.6
20.4
10.2
45.0
10.5
6.8
3.1
13.2
6.4
6.2
13.7
7.7
7.1
1.5
+
CCMe
CCMe
CCMe
CCMe
CCMe
Et)
Et)
Et)
Et)
2
8
9
9
(O
(O
(O
(O
2
2
2
2
CCH
t
CBu )]
3
)
4
+
2
3
H
6
)]
1064
1534
1696
1814
2240
8.2
+
CCH
CCH
3
)(O
2
CH)
2
]
3.6
7.4
9.8
33.0
13.6
41.1
+
3
)
3
(O CH)
2
2
]
2.8
4.7
11.4
+
Et)14(O
2
CCH
3
)
2
]
100
100
100
100
100
100

670
P. Piszczek et al. / Polyhedron 24 (2005) 663–670
Analysis of MS-EI spectra, registered in the tem-
perature range 150–350 ꢀC confirms the formation of
the [Ti-(l -O)] rings stabilized by carboxylate bridges
5. Supplementary data
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 256553. Copies of this infor-
mation may be obtained free of charge from The Direc-
tor, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(fax: +44-1233-336-033; e-mail: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk).
2
8
in the structures of all the studied compounds. Results
of MS-EI experiments are presented in Table 6. Mul-
tinuclear titanium species were detected below 200 ꢀC,
which indicates partial decomposition of these com-
pounds at lower temperatures. The characteristic
t
+
peaks at m/z = 2027 ([Ti O (OOCBu ) ] ), m/z = 1811
15
8
8
t
[Ti O (OOCCH Bu ) (OOCCH )(OOCH) ] )
+
(
m/z = 2240
and
+
8
8
2
10
3
2
([Ti O (OOCC(Me) Et) (OOCCH ) ] )
8 8 2 14 3 2
Acknowledgements
with 100% intensity appear above 240 ꢀC. Also TG/
DTA data show the beginning of the mass detachment
of samples 1–3 at this temperature. Simultaneously,
the presence of multinuclear fragmentation ions above
The authors acknowledge the Polish Committee for
Science Research for financial support Grant No.
4
T09A 152 23.
2
40 ꢀC indicates their thermal stability, which may be
useful for their transport in the gas phase. That factor
may be important for application of these compounds
as precursors in the chemical vapor deposition meth-
ods. Comparison of 1–3 MS data showed that the
thermal stability of multinuclear Ti(IV) fragmentation
References
[
1] R.N. Kapoor, K.C. Pande, R.C. Mehrotra, J. Indian Chem. Soc.
5 (1958) 157.
3
t
t
ions increases in the row Bu < CH Bu < C(Me) Et.
2
[2] R.Ch. Paul, R.Ch. Kumar, O.B. Baidya, R. Kapoor, Aust.
J. Chem. 31 (1978) 425.
2
[
[
[
[
[
3] K.L. Jaura, H.S. Banga, R.L. Kaushik, J. Indian Chem. Soc. 39
1962) 531.
(
4] D. Schwartz, C. Johnson, J. Ludwig, M.L. Morris, J. Inorg. Nucl.
Chem. 26 (1964) 2025.
4
. Conclusions
5] N.W. Alcock, D.A. Brown, T.F. Illson, S.M. Roe, M.G.H.
Wallbridge, J. Chem. Soc., Dalton Trans. (1991) 873.
6] N.W. Alcock, P.N. Bartlett, D. Gordon, T.F. Illson, M.G.H.
Wallbridge, J. Chem. Soc., Chem. Commun. (1986) 614.
7] M. Barrow, D.A. Brown, N.W. Alcock, H.J. Clase, M.G.H.
Wallbridge, J. Chem. Soc., Dalton Trans. (1994) 195.
New titanium multinuclear Ti(IV) oxo carboxylates,
with the general formula [Ti O (OOCR) ], where
t
R = Bu (1), CH Bu (2), C(CH ) Et (3), have been
8
8
16
t
2
3 2
synthesized in a reaction of titanium isopropoxide
i
(
ratio 1:2. X-ray studies of 1 revealed that the structure
Ti(OPr ) ) with suitable organic acids, in the molar
4
[8] I.D. Varma, R.C. Mehrotra, J. Prakt. Chemie 4 (1959) 235.
[9] S. Doeuff, M. Henry, C. Sanchez, Mater. Res. Bull. 25 (1990)
1
519.
10] S. Doeuff, Y. Dromzee, F. Taulelle, C. Sanchez, Inorg. Chem. 28
1989) 4439.
of this compound is formed by rings, composed of
eight distorted [TiO ] octahedra connected by two
[
[
6
(
l -O and four l -O (carboxylate) bridges. Structural
2
2
11] I. Laaziz, A. Larboot, C. Guizard, J. Durand, L. Cot, Acta
Crystallogr. C46 (1990) 2332.
[12] T.J. Boyle, T.M. Alam, C.J. Tafoya, Inorg. Chem. 37 (1998) 5588.
data exhibited the presence of solvent molecules (tolu-
ene) in the crystal lattice of 1. The thermogravimetric
and IR studies proved that solvent molecules are re-
moved from the structure of this compound between
[
[
13] X. Lei, M. Shang, T.P. Fehlner, Organometallics 15 (1996) 3779.
14] R. Papiernik, L.G. Hubert-Pfalzgraf, J. Vaissermann, M.C.
Henriques Baptista Goncalves, J. Chem. Soc., Dalton Trans.
0
and 60 ꢀC. The obtained results prove that the low
(1998) 2285.
15] P. Piszczek, A. Grodzicki, M. Richert, A. Wojtczak, Inorg. Chim.
Acta 357 (2004) 2769.
stability of the crystals of 1 is caused by the presence
of solvent molecules in the crystal lattice and their loss
at room temperature. Spectral analysis of 1–3 powders
showed that these compounds form a ring structure of
the general formula [Ti O (OOCR) ]. Variable tem-
[
[
[
16] G. Kickelbick, U. Schubert, Eur. J. Inorg. Chem. (1998) 159.
17] P.S. Ammala, S.R. Batten, C.M. Kepert, L. Spiccia, A.M. van
der Bergen, B.O. West, Inorg. Chim. Acta 353 (2003) 75.
18] G.M. Sheldrick, SHELXS97 and SHELXL97, University of G o¨ ttingen,
Germany, 1997.
8
8
16
[
perature IR studies indicate the high thermal stability
of the studied multinuclear Ti(IV) oxo carboxylates.
Analysis of MS-EI data suggests that during the ther-
mal decomposition of 1–3, volatile multinuclear Ti-
oxide species are formed above 240 ꢀC. The stability
[19] K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds, part B/V ed., Wiley, New York, 1997,
p. 58, 172.
[
[
20] G.B. Deacon, R.J. Phillips, Coord. Chem. Rev. 33 (1980) 227.
21] N.W. Alcock, V.M. Tracy, J. Chem. Soc., Dalton Trans. (1976)
2243.
t
t
of these species changes in the row Bu < CH Bu <
2
C(Me) Et.
2
[22] V. Koleva, D. Stoilova, J. Mol. Struct. 61 (2002) 1.