Intramolecularly coordinated organoantimony(III) carboxylates

Article abstract of DOI:10.1016/j.jorganchem.2007.06.005

The reactions of organoantimony chlorides L^1,2SbCl₂ 1 and 2 ([2,6-(ROCH₂)₂C₆H₃]^-, R = Me; L¹ and R = t-Bu; L²) with silver salts of selected carboxylic acid

Full text of DOI:10.1016/j.jorganchem.2007.06.005

Journal of Organometallic Chemistry 692 (2007) 3969–3975
www.elsevier.com/locate/jorganchem
Intramolecularly coordinated organoantimony(III) carboxylates
a
a,
a
a
b
*
´
ˇ
´
´ˇ
´
Lubomır Machuca , Libor Dostal , Roman Jambor , Karel Handlır , Robert Jirasko ,
a
c
a
˚
´
´
Alesˇ Ruzˇicˇka , Ivana Cısarˇova , Jaroslav Holecˇek
a
Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, na´m.
ˇ
Cs. Legiı 565, CZ-532 10 Pardubice, Czech Republic
´
b
ˇ
Department of Analytical Chemistry, Faculty of Chemical Technology, University of Pardubice, na´m. Cs. Legiı 565, CZ-532 10 Pardubice, Czech Republic
´
c
Charles University in Prague, Faculty of Natural Science, Hlavova 2030, CZ-128 40, Prague 2, Czech Republic
Received 16 April 2007; received in revised form 31 May 2007; accepted 5 June 2007
Available online 15 June 2007
Abstract
The reactions of organoantimony chlorides L1,2SbCl2 1 and 2 ([2,6-(ROCH2)2C6H3]ꢀ, R = Me; L1 and R = t-Bu; L2) with silver salts
of selected carboxylic acids resulted to corresponding organoantimony carboxylates L1,2Sb(OOCR0)2, 1a–c (for L1) and 2a–c (for L2),
where R0 = CH3 for 1a, 2a; R0 = CH@CH2 for 1b, 2b and R0 = CF3 for 1c, 2c. All compounds were characterized by the help of
elemental analysis, ESI–MS, 1H and 13C NMR spectroscopy. The solid state structure investigation using single crystal X-ray diffraction
techniques (2a, c) and IR spectroscopy revealed significant differences in coordination mode of both O,C,O chelating ligand and carbox-
ylic groups in this set of compounds. The structure of all compounds in solution of non-coordinating solvent (CDCl3) was determined by
1
means of variable temperature H, 13C, 19F NMR spectroscopy and IR spectroscopy.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Antimony; Chelating ligand; Carboxylates; NMR spectroscopy; X-ray structure
1. Introduction
In contrast to organoantimony(V) carboxylates the
investigation of carboxylates containing Sb(III) atom is
rare. Organoantimony(III) carboxylates characterized in
the solid state by the XRD method include Sb(OOCCH3)3
[7], Sb(OOCCH2CH3)3 [8], Sb(OOCCF3)3 [9] and
SbPh2(OOCCH3), that forms polymeric chains in the solid
state through acetate bridges [10]. The phthalic acid was
used as a bridging ligand between two antimony centres
as well [11]. Compounds of the type Sb(OOCNR2)3 have
been recently investigated as precursors for deposition of
antimony oxides [12].
In order to further develop the chemistry of organoanti-
mony(III) carboxylates, we report here on synthesis, solu-
tion and solid state structure of six novel antimony
dicarboxylates, derivatives of O,C,O chelating ligands
([2,6-(ROCH2)2C6H3]ꢀ, R = Me; L1 and R = t-Bu; L2),
L1,2Sb(OOCR0)2, where R0 = CH3 for 1a, 2a;
R0 = CH@CH2 for 1b, 2b and R = CF3 for 1c, 2c. This
set of compounds enables us to follow the influence of both
The synthesis and structures of organoantimony(V)
carboxylates were extensively studied during the last two
decades [1]. Carboxylates as versatile ligands were shown
to act as unidentate [2], bidentate [3] or bridging ligands
[3a,4] in organoantimony(V) compounds by X-ray diffrac-
tion techniques (XRD). The carboxylates need not bridge
only two antimony centres, but also the heterobimetallic
compounds containing this unit as a spacer between Sb
and ferrocene moiety, or Sb and Ge atoms emerged [5].
The latter compounds were investigated in reference to
their potential antitumor activity. The utilization of dicar-
boxylic acids has been studied recently as well [6].
*
Corresponding author. Fax: + 420 466037068.
´
E-mail address: libor.dostal@upce.cz (L. Dostal).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.06.005

3970
L. Machucˇa et al. / Journal of Organometallic Chemistry 692 (2007) 3969–3975
Table 1
ligand (steric factors) and carboxylate (increasing electron
withdrawing ability of the polar groups OOCC-
F3 > OOCCH3 ꢁ OOCCH@CH2) on the coordination
polyhedron of the central atom and on their behaviour in
solution.
Crystal data and structure refinement of 2a and 2c
2a
2c
Empirical formula
C20H31O6Sb
0.5(C7H8)
C20H25F6O6Sb
0.5(C7H8)
Colour
Colourless
Colourless
2. Experimental
Crystal system
Space group
a (A)
Orthorhombic Triclinic
ꢀ
Pbca (No. 61) P1 (No. 2)
˚
16.0970(1)
13.6920(3)
22.9430(4)
9.6550(2)
12.4070(4)
12.4700(2)
89.0970(16)
70.5330(15)
67.7280(12)
2
2.1. General consideration
˚
b (A)
˚
C (A)
All manipulations were carried out under argon atmo-
sphere using standard Schlenk technique. All solvents were
dried by standard procedures and distilled prior to use. 1H,
13C and 19F NMR spectra were recorded on Bruker500
a (ꢁ)
b (ꢁ)
c (ꢁ)
Z
8
l (mmꢀ1
Dx (mg mꢀ3
)
1.124
1.406
1.147
1.652
1
Avance spectrometer. Appropriate chemical shifts in H
)
and 13C NMR spectra were calibrated on the residual sig-
nals of the solvent (CDCl3: d(1H) = 7.27 ppm and
d(13C) = 77.23 ppm). 19F NMR chemical shifts were
Crystal size (mm)
Crystal shape
h Range (ꢁ)
Tminimum, Tmaximum
No. of reflections measured
No. of unique reflections; Rint
0.4 · 0.25 · 0.1 0.22 · 0.2 · 0.15
Plate
Prism
1–27.5
1–27.5
0.785, 0.885a
68916
0.791, 0.847a
23763
related
according
to
the
external
standard
KFd(19F) = ꢀ130 ppm. Positive-ion and negative-ion elec-
trospray ionization (ESI) mass spectra were measured on
an ion trap analyzer Esquire 3000 (Bruker Daltonics, Bre-
men, Germany) in the range m/z 50–1000. The samples
were dissolved in acetonitrile and analyzed by direct infu-
sion at the flow rate 5 ll/min. The ion source temperature
was 300 ꢁC, the tuning parameter compound stability was
100% for measuring of positive ions and 20% for measuring
of negative, the flow rate and the pressure of nitrogen were
4 l/min and 10 psi, respectively.
5815, 0.056
5945, 0.036
5358
No. of observed reflections [I > 2r(I)] 4399
No. of parameters
Sb All data
Final Ra indices [I > 2r(I)]
wR2a indices (all data)
w1/wc2
256
309
1.058
1.054
0.041
0.029
0.109
0.072
0.0469/11.464
1.916, ꢀ1.058
0.0354/1.0657
0.923, ꢀ0.660
ꢀ3
˚
Dqmaximum, minimum (e A
)
a
Correction by SORTAV program.
2
b
Definitions: RðF Þ ¼ RkF o j ꢀk j F ck=R j F o j, wR2 ¼ ½RðwðF 2o ꢀ F c2Þ Þ=
2
1=2
2
1=2
RðwðF 2oÞ Þꢂ , S ¼ ½RðwðF o2 ꢀ F 2c Þ Þ=ðNreflns ꢀ NparamsÞꢂ
.
Weighting scheme w ¼ ½r2ðF 2Þ þ ðw1PÞ þ w2Pꢂꢀ1: P ¼ ½maxðF o2; 0Þþ
2F c2ꢂ=3:Rint ¼ R j F 2o ꢀ F o2ðmeanÞ j o=RF 2o (summation is carried out only
where more than one symmetry equivalent is averaged).
c
IR spectra were recorded in chloroform solution, nujol
or KBr suspension on Perkin Elmer 684 equipment (cmꢀ1).
2.1.1. X-ray structure determination
Colourless single crystals of 2a and 2c were obtained by
crystallization from toluene/n-hexane (1:2) solution at
ꢀ30 ꢁC. The crystal of compounds of 2a, c were mounted
on glass fibre with epoxy cement and measured on four-cir-
cle diffractometer KappaCCD with CCD area detector by
silver salt by reaction with AgNO3 in minimum amount
of water) were obtained from commercial suppliers and
used as delivered. The compounds 1 and 2 were prepared
according to literature procedures [16]. All reaction flaks
were light protected by aluminum foil.
˚
monochromatized Mo Ka radiation (k = 0.71073 A) at
150(2) K. The crystallographic details are summarized in
Table 1, empirical absorption corrections [13] were applied
(multiscan from symmetry-related measurements). The
structures were solved by the direct method (SIR97 [14])
and refined by a full matrix least squares procedure based
on F2 (SHELXL97 [15]). Hydrogen atoms were fixed into ide-
alized positions (riding model) and assigned temperature
factors Hiso(H) = 1.2 Ueq (pivot atom), for the methyl moi-
ety multiple of 1.5 was chosen. The final difference maps
displayed no peaks of chemical significance. In the both
crystals the solvent molecules are disordered over two posi-
tions and were constrained into idealized geometry and
refined with rigid body approximation.
2.2.1. Preparation 2,6-(MeOCH2)2C6H3Sb(OOCCH3)2
(1a)
Silver acetate 126 mg (0.74 mmol) was added to a solu-
tion of 1 134 mg (0.37 mmol) in CH2Cl2 (15 ml) and result-
ing suspension was stirred overnight. Then insoluble
material was filtered off and solvent was evaporated in
vacuo. Compound 1a was obtained after washing with hex-
ane (5 ml) as colourless highly viscous oil (104 mg, 69%).
Anal. Calc. for C14H19O6Sb: C, 41.51; H, 4.73. Found:
1
C, 41.62; H, 4.62%. H NMR (CDCl3) d (ppm): 2.09 (s,
6H, COCH3); 3.52 (s, 6H, OCH3); 4.74 (s, 4H, OCH2);
7.17 (d, 2H, Ar–H3,5); 7.30 (t, 1H, Ar–H4). 13C NMR
(CDCl3) d (ppm): 21.7 (CH3CO); 59.1 (OCH3); 76.1
(OCH2); 125.2 (Ar–C3,5); 129.4 (Ar–C4); 146.3
(Ar–C2,6); 149.5 (Ar–C1); 175.4 (C@O). IR (neat, cmꢀ1):
1675 [mas(CO2)]; 1367 [ms(CO2)]. IR (CHCl3, cmꢀ1): 1675
2.2. Synthesis
The starting chemicals CH3COOAg (99.9%),
CF3COOAg (98%), CH2CHCOONa (98% – converted to

L. Machucˇa et al. / Journal of Organometallic Chemistry 692 (2007) 3969–3975
3971
[mas(CO2)];1372 [ms(CO2)]. ESI/MS – positive mode: m/z
345 [MꢀCH3COO]+, 100%.
815 [LSbOSbLOHꢀbuteneꢀH2O+CH3COOC(CH3)3]+ m/z
773 [LSbOSbLOH]+, 100%; m/z 699 [LSbOSbLOHꢀbutene
ꢀH2O]+; m/z 643 [LSbOSbLOHꢀ2*buteneꢀ H2O]+; m/z
429 [M+HꢀCH3COOH]+; m/z 387 [LSbOH]+; m/z 331
[LSbOHꢀbutane]+; m/z 313 [LSbOHꢀbutaneꢀ H2O]+;
m/z 257 [LSbOHꢀ2*butaneꢀH2O]+.
2.2.2. Preparation of 2,6-(MeOCH2)2C6H3Sb-
(OOCCHCH2)2 (1b)
Similarly to procedure as for 1a:1 73 mg (0.2 mmol), sil-
ver acrylate 146 mg (0.4 mmol) yielded colourless highly
viscous oil (1b; 101 mg, 75%). Anal. Calc. for C16H19O6Sb:
2.2.5. Preparation 2,6-(tBuOCH2)2-
C6H3Sb(OOCCHCH2)2 (2b)
1
C, 44.79; H, 4.46. Found: C, 44.59; H, 4.65%. H NMR
(CDCl3) d (ppm): 3.50 (s, 6H, OCH3); 4.74 (s, 4H,
Similarly to procedure as for 1a:2 147 mg (0.33 mmol),
silver acrylate 119 mg (0.66 mmol) yielded white crystals
(2b; 144 mg, 84%), m.p. 132–134 ꢁC. Anal. Calc. for
C22H31O6Sb: C, 51.49; H, 6.09. Found: C, 51.24; H,
6.27%. 1H NMR (CDCl3) d (ppm): 1.32 (s, 18H,
C(CH3)3); 4.74 (s, 4H, OCH2); 5.68 (d, 2H, trans CH2@,
OCH2); 5.75 (d, 2H, trans CH2@, 3J(1Htrans
,
,
1Hgem) = 10.2 Hz); 6.15 (dd, 2H, –CH@, 3J(1Htrans
1Hgem) = 10.2 Hz, 3J(1Hcis, Hgem) = 17.1 Hz); 6.34 (d,
2H, cis CH2@, 3J(1Hcis,1Hgem) = 17.1 Hz); 7.19 (d, 2H,
Ar–H3,5); 7.32 (t, 1H, Ar–H4). 13C NMR (CDCl3) d
(ppm): 59.2 (OCH3); 76.1 (OCH2); 125.1 (Ar–C3,5); 127.2
(CH2@) 129.4 (Ar–C4); 130.2 (–CH@); 146.4 (Ar–C2,6);
149.8 (Ar–C1); 170.0 (C@O). IR (neat, cmꢀ1): 1670
[mas(CO2)]; 1608 [m(C@C)]; 1310 [ms(CO2)]. IR (CHCl3,
cmꢀ1): 1670 [mas(CO2)]; 1608 [m(C@C)]; 1318 [ms(CO2)].
ESI/MS – positive mode: m/z 357 [MꢀCH2CHCOO]+,
100%.
1
3J(1Htrans
3J(1Htrans
,
,
1Hgem) = 10.2 Hz); 6.13 (dd, 2H, –CH@,
1
1Hgem) = 10.2 Hz, 3J(1Hcis, Hgem) = 17.3 Hz);
3
1
6.27 (d, 2H, cis CH2@, J(1Hcis, Hgem) = 17.3 Hz); 7.18
(d, 2H, Ar–H3,5); 7.26 (t, 1H, Ar–H4). 13C NMR (CDCl3)
d (ppm): 28.0 (C(CH3)3); 65.6 (OCH2); 77.8 (OC(CH3)3);
124.8 (Ar–C3,5); 128.9 (Ar–C4); 129.7 (–CH@); 130.8
(CH2@); 148.0 (Ar–C2,6); 149.4 (Ar–C1); 169.7 (C@O).
IR (nujol, cmꢀ1): 1669 [mas(CO2)]; 1610 [m(C@C)]; 1319
[ms(CO2)]. IR (CHCl3, cmꢀ1): 1673 [mas(CO2)]; 1610
[m(C@C)]; 1318 [ms(CO2)]. ESI/MS – positive mode: m/z
2.2.3. Preparation of 2,6-(MeOCH2)2C6H3Sb(OOCCF3)2
(1c)
Similarly to procedure as for 1a:1 120 mg (0.34 mmol),
silver trifluoroacetate 148 mg (0.68 mmol) yielded white
crystals of (1c; 101 mg, 59%), m.p. 148–150 ꢁC (decomposi-
tion). Anal. Calc. for C14H13F6O6Sb: C, 37.78; H, 2.55.
827
[LSbOSbLOHꢀbuteneꢀH2O+CH2@CHCOOC
(CH3)3]+ m/z 773 [LSbOSbLOH]+, 100%; m/z 699
[LSbOSbLOHꢀbuteneꢀH2O]+; m/z 643 [LSbOSb-
LOHꢀ2*buteneꢀH2O]+; m/z 441 [M+HꢀCH2@ CHCO-
OH]+; m/z 387 [LSbOH]+; m/z 331 [LSbOHꢀbutane]+;
m/z 313 [LSbOHꢀbutaneꢀH2O]+; m/z 257 [LSbOHꢀ
2*butaneꢀH2O]+.
1
Found: C, 37.62; H, 2.61%. H NMR (CDCl3) d (ppm):
3.61 (s, 6H, OCH3); 4.86 (s, 4H, OCH2); 7.22 (d, 2H, Ar–
H3,5); 7.34 (t, 1H, Ar–H4). 13C NMR (CDCl3) d (ppm):
59.3 (OCH3); 75.6 (OCH2); 115.1 (q, CF3, 1J(19F,
13C) = 286.2 Hz); 125.2 (Ar–C3,5); 130.0 (Ar–C4); 145.8
2.2.6. Preparation 2,6-(tBuOCH2)2C6H3Sb(OOCCF3)2
(2c)
2
(Ar–C2,6); 160.4 (q, C@O, J(19F, 13C) = 40.2 Hz); (Ar–
C1) not detected. 19F NMR (CDCl3) d (ppm): ꢀ74.4. IR
(KBr, cmꢀ1): 1738, 1690 [mas(CO2)]; 1458, 1402 [ms(CO2)].
IR (CHCl3, cmꢀ1): 1721 [mas(CO2)]; 1400 [ms(CO2)]. ESI/
MS positive mode: m/z 623 [LSbOSbLOH+H2O]+, 100%;
m/z 605 [LSbOSbLOH]+; m/z 399 [M+HꢀCF3COOH]+;
m/z 321 [LSbOH+H2O]+; m/z 303 [LSbOH]+. ESI/MS –
negative mode: m/z 625 [M+CF3COO]ꢀ, 100%.
Similarly to procedure as for 1a:2 200 mg (0.45 mmol),
silver trifluoroacetate 200 mg (0.9 mmol) yielded white
crystals (2c; 175 mg, 65%), m.p. 108–110 ꢁC. Anal. Calc.
for C20H25 F6O6Sb: C, 40.23; H, 4.22. Found: C, 40.14;
H, 4.36%. 1H NMR (CDCl3) d (ppm): 1.41 (s, 18H,
C(CH3)3); 4.79 (s, 4H, OCH2); 7.26 (d, 2H, Ar–H3,5);
7.38 (t, 1H, Ar–H4). 13C NMR (CDCl3) d (ppm): 28.2
(C(CH3)3); 66.0 (OCH2); 80.3 (OC(CH3)3); 115.0 (q, CF3,
1J(19F, 13C) = 287.5 Hz); 124.4 (Ar–C3,5); 130.1 (Ar–C4);
2.2.4. Preparation 2,6-(tBuOCH2)2C6H3Sb(OOCCH3)2
(2a)
147.0 (Ar–C2,6); 147.4 (Ar–C1); 160.2 (q, C@O, J(19F,
2
Similarly to procedure as for 1a:2 200 mg (0.45 mmol),
silver acetate 151 mg (0.9 mmol) yielded white crystals
(2a; 154 mg, 70%), m.p. 105–108 ꢁC. Anal. Calc. for
C20H31O6Sb: C, 49.10; H, 6.39. Found: C, 49.24; H,
6.27%. 1H NMR (CDCl3) d (ppm): 1.32 (s, 18H,
C(CH3)3); 2.02 (s, 6H, COCH3); 4.72 (s, 4H, OCH2); 7.14
(d, 2H, Ar–H3,5); 7.23 (t, 1H, Ar–H4). 13C NMR (CDCl3)
d (ppm): 22.0 (CH3CO); 27.7 (C(CH3)3); 65.3 (OCH2); 77.7
(OC(CH3)3); 124.5 (Ar–C3,5); 128.7 (Ar–C4); 147.7 (Ar–
C2,6); 148.6 (Ar–C1); 174.8 (C@O). IR (nujol, cmꢀ1):
1680 [mas(CO2)]; 1365 [ms(CO2)]. IR (CHCl3, cmꢀ1): 1676
[mas(CO2)]; 1370 [ms(CO2)]. ESI/MS – positive mode: m/z
13C) = 40 Hz). 19F NMR (CDCl3) d (ppm): ꢀ74.5. IR
(KBr, cmꢀ1): 1723, 1693 [mas(CO2)]; 1411, 1386 [ms(CO2)].
IR (CHCl3, cmꢀ1): 1738 [mas(CO2)]; 1400 [ms(CO2)]. ESI/
MS – positive mode: m/z 869 [LSbOSbLOHꢀbuteneꢀ
H2O+CF3COOC(CH3)3]+ m/z 773 [LSbOSbLOH]+,
100%; m/z 699 [LSbOSbLOHꢀbuteneꢀH2O]+; m/z 643
[LSbOSbLOHꢀ2*buteneꢀH2O]+; m/z 483 [M+HꢀCF3-
COOH]+; m/z 387 [LSbOH]+; m/z 331 [LSbOHꢀbutane]+;
m/z 313 [LSbOHꢀbutaneꢀH2O]+; m/z 257 [LSbOHꢀ
2*butaneꢀH2O]+. ESI/MS – negative mode: m/z 709
[M+CF3COO]ꢀ, 100%.

3972
L. Machucˇa et al. / Journal of Organometallic Chemistry 692 (2007) 3969–3975
˚
3. Results and discussion
1.206(5); C(19)–O(5) 1.322(4) and C(19)–O(6) 1.245(6) A).
The coordination polyhedron of Sb(1) can be best
described as a trigonal pyramid formed by Sb(1), C(1),
O(3) and O(5), sum of angles around the SbCO2 girdle
being 259.6ꢁ. The resulting trigonal pyramid is further
attacked by medium-strength Sb–O intramolecular interac-
tions of both donor atoms of the ligand L2 (Sb(1)–O(1)
3.1. Synthesis of studied compounds 1a–c and 2a–c
All compounds 1a–c and 2a–c were prepared via reac-
tion of starting organoantimony dichlorides 1 and 2 [16]
with two equivalents of silver salt of appropriate carboxylic
acid in CH2Cl2 (Scheme 1) as colourless highly viscous oils
(1a, 1b) or white crystalline solids. All derivatives are spar-
ingly soluble in aliphatic hydrocarbons and readily soluble
in chlorinated solvents as well as in THF. The purity of all
compounds was established with the help of satisfactory
˚
˚
2.692(3) and Sb(1)–O(2) 2.596(2) A; Rcov(Sb, O) 2.14 A
and RvdW(Sb, O) 3.78 A [17]). If these interaction are taken
˚
into account the overall geometry can be described as a
strongly distorted square pyramid, with donor oxygen
atoms located mutually in cis fashion (angle O(1)–Sb(1)–
O(2) 119.92(7)ꢁ) similarly to the starting compound 2 [16].
An entirely different coordination mode of both ligand
L2 and carboxylic groups was detected for compound 2c
(Fig. 2). While one of the trifluoracetate groups acts as
unidentate ligand in 2c as demonstrated by bond lengths
Sb(1)–O(3) 2.215(5) and Sb(1)–O(4) 3.063(3) A the second
one represents bidentate carboxylate with bond distances
Sb(1)–O(5) 2.575(2) and Sb(1)–O(6) 2.580(2) A and nearly
identical C(19)–O(5) 1.239(4) and C(19)–O(6) 1.243(3) A
elemental analyses, ESI-MS spectrometry and H and 13C
NMR spectroscopy (see Section 2).
1
3.2. Solid state structures
˚
The molecular structures of 2a and 2c were determined
by single crystal X-ray diffraction and are depicted in Figs.
1 and 2, selected bond lengths and bonding angles are given
in Table 2.
˚
˚
Both acetate groups are coordinated to the central anti-
mony atom Sb(1) in unidenate fashion in 2a as demon-
strated by fairly different Sb–O bond lengths within each
carboxylic group (Sb(1)–O(3) 2.080(3) and Sb(1)–O(4)
2.890(3); Sb(1)–O(5) 2.059(3) and Sb(1)–O(6) 3.078(2) A),
the distances of C–O bonds in carboxylic moieties also sup-
port this statement (C(17)–O(3) 1.311(4) and C(17)–O(4)
distances within carboxylic moiety. Such a symmetric
bidentate carboxylic group in organoantimony compounds
was found only in PhSb(OOCCH3)4 [3b]. Both donor
atoms of ligand L2 in 2c are coordinated to the central atom
through strong intramolecular interaction (Sb(1)–O(1)
2.312(2) and Sb(1)–O(2) 2.334(2) A) mutually in pseudo
trans position with angle O(1)–Sb(1)–O(2) 146.11(6)ꢁ,
˚
˚
Scheme 1. Synthesis of studied compounds.
Fig. 1. ORTEP drawing (50% probability atomic displacement ellipsoids) of 2,6-(tBuOCH2)2C6H3Sb(OOCCH3)2 (2a). Hydrogen atoms and solvent
(toluene) molecule have been omitted for clarity.

L. Machucˇa et al. / Journal of Organometallic Chemistry 692 (2007) 3969–3975
3973
fact, that both donor atoms of the ligand L2 are bound
to the central atom more tightly than the chelating
trifluoroacetate.
All these results are in good agreement with data
obtained by IR spectroscopy in the solid state (Table 3).
Compounds 1a, 1b, 2a and 2b revealed only one band for
antisymmetric and symmetric CO2 stretching proving
equivalently bonded carboxylic groups. The Dm between
the antisymmetric and symmetric CO2 stretching ranging
from 308 to 360 cmꢀ1 proves unidentate coordination of
both carboxylates in 1a, 1b, 2a and 2b as well [2g]. On
the other hand IR spectra of 1c and 2c contained in both
cases two signals for antisymmetric and symmetric CO2
stretching indicating non-equivalence of both triflouroace-
tates. The Dm between the antisymmetric and symmetric
CO2 stretching for 1c (336 and 232 cmꢀ1) and for 2c (337
and 282 cmꢀ1) points to [2g] one trifluoroacetate is coordi-
nated as chelating ligand while the second one remains
unidenate (as was shown for 2c by X-ray diffraction).
3.3. Solution structure
Compounds 1a, b and 2a–c displayed analogous struc-
1
ture in solution. H and 13C NMR spectra of these deriva-
Fig. 2. ORTEP drawing (50% probability atomic displacement ellipsoids)
of 2,6-(tBuOCH2)2C6H3Sb(OOCCF3)2 (2c). Hydrogen atoms and solvent
(toluene) molecule have been omitted for clarity.
tives contained one set of signals corresponding to the
proposed structures at ambient temperature (see Section
2). Upon cooling the samples the signals appropriate to
1
benzylic OCH2 groups in H NMR spectra were split to
Table 2
an AX pattern indicating cis coordination of both ligands
donor groups at low temperatures [16]. IR spectra (CHCl3)
of these compounds revealed one antisymmetric and sym-
metric CO2 stretching with Dm (range from 303 to
355 cmꢀ1) indicating unidentate coordination mode of
both carboxylates [2g]. This means 1a, b and 2a–c have a
similar structure in solution as detected for 2a in the solid
state (vide supra).
˚
Selected bond distances (A) and bonding angles (ꢁ) of 2a and 2c
Compound 2a
Compound 2c
Sb1–O1
Sb1–O2
Sb1–O3
Sb1–O4
Sb1–O5
Sb1–O6
Sb1–C1
C17–O3
C17–O4
C19–O5
C19–O6
O1–Sb1–O2
O3–Sb1–O5
C1–Sb1–O3
C1–Sb1–O5
2.692(3)
2.596(2)
2.080(3)
2.890(3)
2.059(3)
3.078(2)
2.147(3)
1.311(4)
1.206(5)
1.322(4)
1.245(6)
119.92(7)
80.63(10)
90.77(11)
88.22(11)
Sb1–O1
Sb1–O2
Sb1–O3
Sb1–O4
Sb1–O5
Sb1–O6
Sb1–C1
C17–O3
2.312(2)
2.334(2)
2.215(2)
3.063(3)
2.575(2)
2.580(2)
2.091(2)
1.278(3)
1.212(3)
1.239(3)
1.243(3)
146.11(6)
81.65(7)
80.15(7)
50.99(6)
75.08(8)
74.47(8)
82.84(9)
86.39(9)
84.94(8)
The solution structure of 1c seems to be more complex.
One set of broad signals detected for both OCH2 and CH3
groups in 1H NMR spectrum at 300 K (indicating fast
C17–O4
C19–O5
C19–O6
O1–Sb1–O2
O1–Sb1–O3
O2–Sb1–O3
O5–Sb1–O6
C1–Sb1–O1
C1–Sb1–O2
C1–Sb1–O3
C1–Sb1–O5
C1–Sb1–O6
Table 3
IR data of studied compounds (cmꢀ1
)
Compound
Conditions
mas(CO2)
ms(CO2)
Dm
1a
Neat
CH3Cl
1675
1675
1367
1372
308
303
1b
1c
2a
2b
Neat
CH3Cl
1670
1670
1310
1318
360
352
KBr
CH3Cl
1738/1690a
1721
1458/1402a
1400
336/232a
321
Nujol
CH3Cl
1680
1676
1365
1370
315
306
which is in contrast to the cis position of both oxygen
donor atoms in 2a. The overall geometry around the anti-
mony atom can be best described as a pentagonal pyramid
with C(1) in apical position and with Sb(1) and all oxygen
atoms (O(1), O(2), O(3), O(5) and O(6)) forming the basal
plane (the sum of angles around this girdle 355.75ꢁ). An
interesting aspect of the structure of 2c can be seen in the
Nujol
CH3Cl
1669
1673
1319
1318
350
355
2c
KBr
CH3Cl
1723/1693a
1738
1411/1386a
1400
337/282a
338
a
Two signals.

3974
L. Machucˇa et al. / Journal of Organometallic Chemistry 692 (2007) 3969–3975
fluxional behaviour of 1c at this temperature) has changed
to one AX and two AB patterns for OCH2 groups and
three signals for CH3 group (two of them in 1:1 integral
ratio) at 220 K (Fig. 3). The possible explanation for these
findings is the presence of two isomers of 1c in solution at
low temperature. The first one (AX for OCH2 and one sig-
4. Conclusions
In summary we have prepared six novel organoanti-
mony carboxylates containing O,C,O chelating ligand. It
turns out, that structures of the studied compounds depend
both on the ligand used as well as on the polar group: (i)
using of a more electron-withdrawing trifluoroacetate
group in 2c leads to increase of intramolecular Sb–O inter-
actions in comparison to 2a, (ii) trifluoroacetate groups
were shown to act as bidentate ligand both in the solid state
(1c and 2c) and in solution (1c), and (iii) on the other hand
carboxylates (acetates and acrylates) in other compounds
remain unidentate.
nal for CH , marked with in Fig. 3) represents an analo-
*
3
gous structure detected for other compounds (i.e. cis
coordination of both ligands arms and trifluoroacetates
remain unidentate). The second isomer is most probably
a structure with cis coordinated oxygen donor atoms of
L1, where one of the trifluoroacetates is unidentate and
the second one bidentate, in turn it leads to non-equiva-
lence of both OCH2 and CH3 (two AB patterns for
OCH2 groups and two signals for CH3 groups in 1:1 inte-
gral ratio marked with s in Fig. 3).
5. Supplementary material
This hypothesis is further supported by 19F NMR spec-
tra, where one sharp signal at ꢀ74.4 ppm observed at
300 K is split into three signals at 220 K (ꢀ73.4, ꢀ73.7
and ꢀ75.1 ppm, see Fig. 4). One of these signals can be
CCDC 639795 and 639796 contain the supplementary
crystallographic data for 2a and c. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@
ccdc.cam.ac.uk.
assigned to the isomer ( ) with both unidentate carboxylic
*
groups and the remaining two signals prove non-equiva-
lence of trifluoroacetates in the second isomer (ꢃ) of 1c.
For instance only one signal was detected for compound
2c in 19F NMR spectra (300–220 K), where both trifluoro-
acetates are believed to be identically bound.
Acknowledgements
The authors thank the Grant agency of the Czech
Republic project 203/07/P094 and the Ministry of Educa-
tion of the Czech Republic (MSM0021627501) for financial
support. R.J. acknowledges the support of Grant project
No. MSM0021627502 sponsored by The Ministry of Edu-
cation, Youth and Sports of the Czech Republic.
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