New stibines containing acetal and formyl group: Platinum complex and unexpected oxastibol derivative

Article abstract of DOI:10.1016/j.jorganchem.2005.09.037

A new tertiary stibine ligand (1) containing acetal group at the ortho-position has been synthesized. This new stibine was then complexed with PtCl42- to obtain trans-PtCl₂L₂ (2) where stibine acts as a monodentate ligand. The acetal was hydrolyzed in a slightly acidic medium and forms a very new stibine (3) containing formyl group at the ortho-position. When (3) was reduced with NaBH₄ an unusual oxastibol (4) derivative was obtained under the experimental conditions used. All the compounds were characterized by IR, mass, ¹H, ¹³C, COSY and HETCOR NMR spectroscopy. The molecular structures of (2), (3) and (4) were determined. Compound (3) crystallizes in two different polymorphs (3a) and (3b) and both the polymorphs show hypervalent antimony with three Sb?O interactions and the molecule exists in O-cis-exo configuration. Compound (4) shows intramolecular Sb?O interactions. To the best of our knowledge this is the first report on organoantimony compounds containing carbonyl groups though their phosphorus and bismuth analogues are well known. Compound (2) shows helicoidal chirality, which is a very new concept in antimony chemistry

Full text of DOI:10.1016/j.jorganchem.2005.09.037

Journal of Organometallic Chemistry 691 (2006) 579–584
www.elsevier.com/locate/jorganchem
New stibines containing acetal and formyl group: Platinum
complex and unexpected oxastibol derivative
*
´
´
Pankaj Sharma , Diego Perez, Noe Rosas, A. Cabrera, A. Toscano
Departmento de Quimica Inorganica, Instituto de Quı´mica, Universidad Nacional Autonoma De, UNAM,
Circuito Exterior Coyoacan, 04510 Me´xico D.F., Mexico
Received 10 August 2005; received in revised form 19 September 2005; accepted 19 September 2005
Available online 27 October 2005
Abstract
A new tertiary stibine ligand (1) containing acetal group at the ortho-position has been synthesized. This new stibine was then com-
plexed with PtCl24À to obtain trans-PtCl2L2 (2) where stibine acts as a monodentate ligand. The acetal was hydrolyzed in a slightly acidic
medium and forms a very new stibine (3) containing formyl group at the ortho-position. When (3) was reduced with NaBH4 an unusual
oxastibol (4) derivative was obtained under the experimental conditions used.
All the compounds were characterized by IR, mass, 1H, 13C, COSY and HETCOR NMR spectroscopy. The molecular structures of
(2), (3) and (4) were determined. Compound (3) crystallizes in two different polymorphs (3a) and (3b) and both the polymorphs show
hypervalent antimony with three SbÁ Á ÁO interactions and the molecule exists in O-cis-exo configuration. Compound (4) shows intramo-
lecular SbÁ Á ÁO interactions. To the best of our knowledge this is the first report on organoantimony compounds containing carbonyl
groups though their phosphorus and bismuth analogues are well known. Compound (2) shows helicoidal chirality, which is a very
new concept in antimony chemistry.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Hypervalent; Stibines; Intramolecular Sb–O interactions; Chiral molecule; Pt–Sb complexes
1. Introduction
Because of our interest in functionalized triarylstibines
ligands for their applications in catalysis with rhodium, co-
balt and ruthenium, especially those comprising triple sub-
stitution in ortho-positions [13–15], here we wish to report
the preparation, structural characterization of some Sb
(III) compounds containing SbÁ Á ÁO interactions this work
was undertaken.
Slight shortening of the inter atomic distances in com-
parison to the sum of the van der Waals radii of group
14–16 elements and other hetero atoms such as oxygen or
nitrogen have found in certain compounds. This hyperva-
lent interaction is of interest because of the effect it may
have on the structures, chemical properties and biological
activities [1–8]. Most of the interactions involving group
15 elements were observed in compounds with a cyclic
structure, suggesting the influence of steric factors [9–11].
Recently our group has reported some new stibines con-
taining CH2NMe2 pendant arm in the ortho-position,
which also show these interactions [12].
2. Results and discussion
The colorless crystalline stibine 1 was prepared via a salt
elimination reaction of o-lithiated benzaldehyde diethylac-
etal with SbCl3 in THF at À78 ꢁC. Stibine 1 forms complex
PtCl2 Æ L2 (2) on reaction with [PtCl4]2À. Acidic hydrolysis
of (1) produces yellow colored tris(2-formylphenyl)stibine
(3). When stibine (3) was reduced with NaBH4 in ethanol
water mixture, an unexpected oxastibol (4) was obtained
(Scheme 1). In order to isolate tris[(2-hydroxymethyl)-
*
Corresponding author. Fax: +52 555 6162217.
E-mail address: pankajsh@servidor.unam.mx (P. Sharma).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.09.037

580
P. Sharma et al. / Journal of Organometallic Chemistry 691 (2006) 579–584
C10
H
C9
O
O
O
8
H
C7
O
O
C9
C7
Sb
O
O
1) n-Bu/LiTHF,
N2, -70oC
C7
Sb
EtOH
Sb
NaBH4
Br
3
3
2) SbCl3
HCl 0.3M
EtOH/H2O
C3
(4)
3
C3
(3)
C3
(1)
Na2[PtCl4]
Acetone/H2O
Cl
O
O
Sb
3
Pt
O
O
Sb
Cl
3
(2)
Scheme 1.
phenyl]stibine, the reduction was carried out for 30 min,
2 h and 4 h. Under the experimental conditions used, only
the yield of the oxastibol product (4) changes marginally
with the time of the reaction and attempts to obtain the
tris[(2-hydroxymethyl)phenyl]stibine failed. It is to be
noted that under the similar reaction conditions tris[(2-
hydroxymethyl)phenyl]phosphine [16] was obtained from
the corresponding formylphosphine.
H3 protons show a more downfield shift in antimony com-
pound (7.91 ppm) than in phosphorus (7.62 ppm). A cou-
pling between H9 protons with the hydroxyl proton (H8)
was also observed, which may be due to SbÁ Á ÁO intramolec-
ular interaction (see Fig. 1).
The molecular structures of 2–4 have been confirmed by
X-ray crystallography. Tables 1 and 2 summarize the crystal
data and bond lengths and bond angles for these com-
pounds, respectively. All these compounds are monomeric
in nature and no significant intermolecular interactions were
observed, except compound (4). Compound (3) crystallizes
All the compounds are stable and melts without decom-
position and are soluble in polar organic solvents, e.g.,
chloroform , dichloromethane, ether and are insoluble in
water and non polar solvents, e.g., hexane, pentane It is
important to mention that Sb–C bonds in these stibines
do not break in slightly acidic aqueous medium, but in gen-
eral, Sb–C bond is sensitive to such conditions and breaks.
Molecular ion peaks were observed for all compounds in
the FAB+ MS, along with significant fragments arising from
Sb–C cleavage. In all the cases the assignment of individual
protonic signals in the 1H NMR spectra was based on JHH
coupling constant values and was confirmed by COSY and
HETCOR. Though SbÁ Á ÁO interactions were observed in
the structural characterizations, evidence for such interac-
tions could not be detected in 1H NMR spectra of compound
ꢀ
in two different crystalline forms: trigonal form with P3
space group (3a) with chloroform as a solvent of crystalliza-
tion and rhombohedral form with R3 space group (3b) with
toluene as a solvent of crystallization. In both the polymor-
phs, molecule is chiral and compound crystallizes with two
independent molecules per asymmetric unit (Figs. 2 and 3).
The metrical parameters and stereochemical features of the
two independent molecules are very similar. It is to be
mentioned here that very few examples are known in organ-
oantimony compounds showing polymorphism. In both the
polymorphs, three SbÁ Á ÁO intramolecular interactions were
observed and the three formyl groups adopt O-cis-exo con-
formation. It is to be noted that in the phosphorus analog,
two of the three formyl groups possess the O-cis-exo while
the third formyl group was best described as O-trans-exo.
This may be due to the SbÁ Á ÁO intramolecular interactions
observed in (2) in lieu hypervalency of antimony.
1
(3). For the compound (2), H NMR signals appeared at
slightly downfield in comparison to the free ligand. Com-
pounds (1) and (3) show higher chemical shift of aromatic
protons [(7.79 ppm for compound (1) and 7.53 ppm for com-
pound (3)] in comparison to the corresponding phosphorus
compounds [7.6 ppm for tris(2-formylphenyl)phosphine
and 6.87 ppm for tris(1,3-dioxaolan-2-yl phenyl)phosphine)
[17,18]. Similar to 1H NMR , in 13C NMR a higher chemical
shift were observed in stibines in comparison to reported
phosphines. For compound (4), a chemical shift at
4.61 ppm corresponds to methylene protons (H7) which is
at slightly downfield in comparison to the chemical shift
(4.58 ppm) observed in a similar compound of phosphorus
namely tris [2-(hydroxymethyl)phenyl]phosphine. Similarly
The primary coordination sphere consists of a trigonal
pyramidal SbC3 skeleton, and including the three SbÁ Á ÁO
interactions the antimony can be described as heptacoordi-
nate with one position occupied by a lone pair of electrons.
It is to be noted that heptacoordination in antimony is not
very common.
In the compound (4) , the distance between oxygen atom
˚
of O–H group and the central antimony atom is 2.458(3) A,
which is much shorter than the sum of their van der Waals

P. Sharma et al. / Journal of Organometallic Chemistry 691 (2006) 579–584
581
Fig. 1. Molecular structure of compound (2).
Table 1
Crystal data for compounds (2), (3a), (3b) and (4)
Compounds
(2)
(3a)
(3b)
(4)
Empirical formula
Formula weight
Crystal system
Space group
C
66H90Cl2O12PtSb2
C21H15O3Sb,CHCl3
556.45
Trigonal
C21H15O3Sb,0.3,C7H8
467.12
Rhombohedral
R3
C14H13O2Sb
334.99
Orthorhombic
Pbca
1584.87
Triclinic
ꢀ
ꢀ
P1
P3
Crystal size
a (A)
0.212 · 0.196 · 0.164
10.6275(6)
12.3149(7)
142174(8)
101.503
91.730
108.186
1723.7(2)
1
0.162 · 0.158x0.136
12.1779(3)
12.1779(3)
17.258(1)
90
90
120
2216.5(2)
4
1.668
0.318 · 0.278 · 0.182
0.134 · 0.066 · 0.064
˚
12.3310(4)
12.3310(4)
26.517(2)
90
90
120
3491.8(3)
6
1.333
8.6368(6)
12.3974(8)
23.253(2)
90
90
90
2489.8(3)
8
1.787
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Dcalc (Mg/cm3)
1.527
2.936
l (mmÀ1
)
1.627
1.202
2.202
Reflections collected
Independent reflections
R[I > 2(I)]
33943
12248
0.0527
0.992
18469
2650
0.0378
0.981
9581
2744
0.0588
1.002
2.026/À0.453
18822
2195
0.0354
0.990
GOF
D/re (A
À3
˚
)
2.109/À0.831
0.770/À0.571
0.943/À0.502
radii. Thus, the coordination of O–H group forms a hyper-
valent 10-Sb-4 compound (Fig. 4). The geometry about
antimony atom is distorted pseudotrigonal bipyramid
where the two carbon atoms bound to antimony atom
occupy the equatorial plane. The apical positions are
occupied by two oxygen atoms, while the lone pair of elec-
trons can be considered to occupy the equatorial position.
There exists intermolecular hydrogen bonding O–HÁ Á ÁO
num stibine complexes have been reported in the literature.
The average Pt–Cl bond length in (2) is 2.293(11) A, which
˚
is slightly shorter than the average PtÁ Á ÁCl distance in cis-
˚
[PtCl2(SbPh3)2] 2.338(12) A. The Pt–Sb bond length is
˚
slightly [2.582(3)A] longer than found in trans-[PtBrPh-
˚
˚
(SbPh3)2] [2.548(1) A] and trans-[PtI2(SbPh3)2] [2.552(1) A]
[19,20].
˚
[1.72(4) A] in the crystal structure.
3. Experimental
In complex (2), the stibine ligand (1) acts as a monoden-
tate ligand. Platinum is in square planar geometry, and the
two stibine ligands lie in a trans configuration (Fig. 1). To
best of our knowledge very few X-ray structures of plati-
All the solventsweredistilled immediately prior touse and
the reactions were performed under an atmosphere of oxy-
gen-free, dry nitrogen. Elemental analyses were determined

582
P. Sharma et al. / Journal of Organometallic Chemistry 691 (2006) 579–584
Table 2
analytical face indexed absorption correction was applied.
Crystal structures were refined by full-matrix least-squares.
SMART software (data collection and data reduction) and
SHELXTL program were used for solution and refinement
of the structures.
˚
Selected bond lengths (A) and bond angles (ꢁ)
Compound (2)
Sb(1)–Pt(1)
Sb(1)–C(12)
Pt(1)–Cl(1A)
Sb(1)–C(23)
2.5821(3)
2.151(4)
2.2925(11) Pt(1)–Cl(1)
1.143(4) Cl(1A)–Pt(1)–Sb(1)
Cl(1A)–Pt(1)–Sb(1A)
Sb(1A)–Pt(1)
Sb(1)–C(1)
2.5821(3)
1.153(4)
2.2925(11)
84.40(3)
3.2. Syntheses
Cl(1)–Pt(1)–Cl(1A) 180.0(7)
95.60(3)
Cl(1)–Pt(1)–Sb(1)
Cl(1)–Pt(1)–Sb(1A)
C(23)–Sb(1)–Pt(1)
95.60(3)
84.40(3)
127.66(10)
Sb(1A)– Pt(1)– Sb(1) 180.0(11)
C(12)–Sb(1)–Pt(1)
C(1)– Sb(1)–Pt(1)
107.49(11)
110.00
3.2.1. Tris(2-diethylacetal formyl phenyl)stibine (1)
In a Schlenk tube a solution of antimony trichloride
(0.485 g, 2.13 mmol) in anhydrous THF (10 ml) was added
dropwise under a nitrogen atmosphere to 2-lithiobenzalde-
hyde diethylacetal which was synthesized ‘‘in situ’’ accord-
ing to reported method (to 4 ml of nBuLi (2.5 M in hexane)
under inert atmosphere, a solution of 1.89 ml (9 mmol) of
2-bromobenzaldehyde diethyl acetal in 10 ml of THF at
À78 ꢁC was added dropwise for 1 h in THF À20 ꢁC with
continuous stirring). The mixture was further stirred for
2 h at room temperature and then reaction was quenched
with ice. After extraction with dichloromethane
(3 · 10 ml) and drying over sodium sulfate, solvent was re-
moved under vacuum. Slow concentration from chloro-
form solution obtains colorless microcrystalline
compound. Yield: 0.92 g (80%); m.p.: 96–97 ꢁC; Anal.
Found (Calc.): C, 59.69 (60.18); H, 6.26 (6.83)%. For
C33H30O6Sb; IR (m cmÀ1): 476 (Sb–C), 2979 (C–H aro-
matic), 1058, 1096 (C–O–C); FAB+ m/z 658 (3%) [M]+,
479(12%) [M À L]+, 358 (34%) [L À L]+, 302 (5%)
Compound (3a)
Sb(1)–C(1)
Sb(1)–C(1B)
Sb(1)–O(1)
Sb(2)–C(8A)
C(1)–Sb(1)–C(1A)
C(1)–Sb(1)–C(1B)
C(1A)–Sb(1)–C(1B)
C(8A)–Sb(2)–O(2)
C(8)–Sb(2)–O(2)
C(8B)–Sb(2)–O(2)
O(1)–C(7)–C(2)
2.207(16)
2.207(16)
2.899(13)
2.128(16)
96.1(6)
96.1(6)
96.1(6)
157.9(5)
67.4(5)
78.2(6)
Sb(1)–C(1A)
Sb(1)–O(2)
Sb(2)–C(8)
Sb(2)–C(8A)
C(1)–Sb(1)–O(1)
C(1A)–Sb(1)–O(1)
C(1B)–Sb(1)–O(1)
C(8A)–Sb(2)–C(8)
C(8A)–Sb(2)–C(8B)
C(8)–Sb(2)–C(8B)
2.207(16)
2.899(15)
2.128(15)
2.128(16)
68.4(5)
163.4(5)
80.4(5)
93.1(6)
93.1(6)
93.1(6)
131.4(15)
Compound (3b)
Sb(1)–C(1)
Sb(1)–C(1B)
Sb(2)–O(1)
Sb(2)–C(8A)
C(1A)–Sb(1)–C(1B)
C(1A)–Sb(1)–C(1)
C(1B)–Sb(1)–C(1)
C(8A)–Sb(2)–O(2)
C(8)–Sb(2)–O(2)
C(8B)–Sb(2)–O(2)
2.190(4)
2.190(4)
2.850(3)
Sb(1)–C(1A)
Sb(1)–O(2)
Sb(2)–C(8)
2.190(4)
2.883(3)
2.186(4)
2.186(4)
94.72(13)
94.72(13)
94.72(13)
161.79(12)
68.09(12)
78.82(12)
C(1)–Sb(1)–O(1)
68.48(12)
77.80(12)
160.62(12)
95.56(13)
95.56(14)
95.56(14)
C(1A)–Sb(1)–O(1)
C(1B)–Sb(1)–O(1)
C(8A)–Sb(2)–C(8)
C(8A)–Sb(2)– C(8B)
C(8B)–Sb(2)– C(8)
1
[M À 2L]+, 179 (23%) [L]+; NMR H (CDCl3, d in ppm)
7.7853 (3H, d, H3JHH 7.5 Hz), 7.2943 (6H, m, H4, H6),
7.0590 (3H, t, H5JHH 5.5 Hz), 5.7724 (3H, s, H7), 3.4108
(6H, q, H9 JHH 6.3 Hz), 1.1142 (9H, d, H10 JHH 7.1 Hz);
NMR 13C (CDCl3, d in ppm) 138.0390 (C2), 132.8175
(C3),129.9472 (C phen),128.3747 (C phen), 127.3059 (C
phen), 123.0616 (C phen), 101.3817 (C7), 62.4648 (C9),
15.3035 (10).
Compound (4)
Sb(1)–C(1)
Sb(1)–O(1)
O(1)–C(7)
C(3)–C(4)
2.128(4)
2.056(3)
1.403(5)
1.367(7)
96.56(15)
80.45(15)
Sb(1)–C(8)
Sb(1)–O(2)
2.145(4)
2.458(3)
O(2)–C(14)
1.422(5)
C(1)–Sb(1)–O(2)
O(1)–Sb(1)–C(8)
O(1)–Sb(1)–O(2)
81.46(14)
90.97(14)
154.60(12)
C(1)–Sb(1)–C(8)
O(1)–Sb(1)– C(1)
3.2.2. Trans-dichloro-bis[tris(2-diethylacetal formyl
phenyl)stibine] platinum (II) (2)
on a Perkin–Elmer 240 instrument. Melting points were ob-
tained using a MEL-TEMP II Fisher and are uncorrected. EI
and FAB+ mass spectra were recorded on a JEOL SX102
double-focusing mass spectrometer with reverse geometry
using a 6-kV Xenon beam (10 am); nitrobenzyl alcohol was
used as matrix for recording the mass spectra. IR spectra
were recorded on a Nicolet-Magna 750 FT-IR spectrometer
as nujol mulls. 1H (300.5311 MHz) and 13C (75.5757 MHz)
NMR spectra were recorded in CDCl3 on a JEOL ECLIPSE
300 spectrometer.
To a solution of stibine (1) (0.436 g, 1 mmol) made in
10 ml of acetone was added Na2[PtCl4] (0.207 g, 0.5 mmol)
dissolved in 10 ml of water. The resulting mixture was stir-
red for 12 h at room temperature and poured into 50 ml of
water. The complex was extracted with chloroform (50 ml).
The extract was dried over anhydrous sodium sulphate,
concentrated to ꢀ10 ml and mixed with hexane (20 ml).
The resulting orange solid was filtered, washed with hexane
and dried in vacuo. The single crystals of the complex 2
were grown from chloroform:hexane mixture (1:1). Yield:
1.04 g (66%); m.p.: 92–94 ꢁC; IR (m cmÀ1): 476 (Sb–C),
2973 (C–H aromatic), 1056, 1091 (C–O–C) ; FAB+ m/z
1577 (0.3%) [M À 4H]+, 1777 (1.5%) [M + PtCl2L]+, 179
3.1. X-ray crystallography
The X-ray intensity data were measured at 293 ꢁK on a
Bruker SMART APEX CCD-based X-ray diffractometer
using a monochromatized Mo Ka radiation (Ka =
1
(23%) [L]+; NMR H (CDCl3, d in ppm) 7.6954(6H, d,
H3), 7.0819–7.6011 (18H, m, H4, H5, H6), 5.7037 (6H, s,
H7), 3.4300 (12H, q, H9), 0.9540 (18H, t, H10); NMR
13C (CDCl3, d in ppm) 144.3750 (C2), 140.0085 (C3),
137.8405 (C phen), 128.4357 (C phen), 127.0914 (C phen),
˚
0.71073 A). The detector was placed at a distance of
4.837 cm from the crystal in all the cases. Analyses of data
show negligible decay during the data collections. An

P. Sharma et al. / Journal of Organometallic Chemistry 691 (2006) 579–584
583
Fig. 2. Molecular structure of compound (3) in trigonal form.
Fig. 4. Molecular structure of compound (4).
Fig. 3. Molecular structure of compound (3) in rhombohedral form.
stirred for 4 h at room temperature. The compound was ex-
tracted with chloroform and the extract was washed with
very dilute sodium carbonate solution and dried over so-
dium sulphate, concentrated to ꢀ10 ml and mixed with
hexane (20 ml). The resulting yellow solid was filtered
and dried in vacuo. The single crystals of the compound
were grown in toluene and chlorform.Yield: 0.390 g
(84%); m.p.: 210–212 ꢁC; Anal. Found (Calc.): C, 56.97
(57.79); H, 3.27 (3.44)% for C21H15O3Sb; IR (m cmÀ1):
480 (Sb–C), 1694 (C@O), 2937 (C–H aromatic); NMR
126.2525 (C phen), 102.7253 (C7), 61.3198 (C9), 14.8607
(10).
3.2.3. Tris (2-formylphenyl)stibine (3)
In a round bottom flask 1.974 g (3 mmol) of tris(2-di-
ethylacetal formyl phenyl)stibine was dissolved in acetone,
to this a 10 ml solution of 0.3 M HCl was added dropwise.
After the addition was completed the reaction mixture was

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P. Sharma et al. / Journal of Organometallic Chemistry 691 (2006) 579–584
1H (CDCl3, d in ppm) 7.5289 (3H, d, H3), 7.2245 (6H, m,
H4, H6), 7.0461 (3H, t, H5), 10.1413 (3H, s, H7); NMR 13
We are also thankful to Ing. Velasco Luis Ibarra and Javier
Perez Flores for their assistance in mass spectral studies.
C
(CDCl3, d in ppm) 137.3520 (C2), 135.0466 (C3), 133.7488
(C phen), 128.5884 (C phen), 127.9472 (C phen), 126.2677
(C phen), 194.6357 (C7).
References
[1] D.A. Atwood, A.H. Cowley, J. Ruiz, Inorg. Chim. Acta 198–200
(1992) 271.
[2] H. Suzuki, T. Murafuji, Y. Matano, N. Azuma, J. Chem. Soc.,
Perkin Trans. 1 (1993) 2969.
3.2.4. (2-Hydroxy methyl)phenyl[2-(3H-benzo[1,2]
oxastibol) (4)
In a 50 ml round bottom flask, a mixture of 1.308 g
(3 mmol) of tris(2-benzaldehyde)stibine and sodium boro-
hydride 0.5 g (12 mmol) in ethanol (30 ml) was stirred for
3 h at room temperature. The solution was concentrated,
and water was added. The product was filtered and dried.
After recrystallization from CH2Cl2:hexane (70:30) a color-
less crystalline product was obtained Yield: 0.292 g (87%);
m.p.: 184–185 ꢁC; Anal. Found (Calc.): C, 49.74 (50.29); H,
3.37 (3.89)% for C1413H15O2Sb; IR (m cmÀ1): 478 (Sb–C),
2930 (C–H), 3597 (OH); NMR 1H (CDCl3, d in ppm)
7.9146 (1H, m, H3), 7.28–7.8 (3H, m, H4, H5, H6),
4.6135 (1H, s, H7), 4.9664 (2H, s, H8) 4.7441 (2H, s,
H9); NMR 13C (CDCl3, d in ppm) 136.8023 (C2),
133.4893 (C3), 130.8480 (C phen), 128.2525 (C phen),
128.1151 (C phen), 127.6571 (C phen), 63.8084 (C7),
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of charge from The Director, CCDC, 12 Union Road, Cam-
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Acknowledgments
The authors are thankful to DGAPA (IN210905) and
CONACyT-TAMU joint project for financing the work.
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