Diorganotin (IV) heptacoordinated complexes containing pentadentate [N 3O 2] ligands derived from 5-substituted-salicylaldehydes and diethylenetriamine: Synthesis, characterization, and molecular structure

Article abstract of DOI:10.1080/15533174.2012.680170

A series of heptacoordinated tin(IV) mononuclear complexes [(R) ₂Sn(5-X-saldien)] (X = H, OCH₃, NO₂) were synthesized by reaction of dimethyl-, di-n-butyl-, di-n-octyl-, and diphenyltin (IV) oxides with the pentadentate Schiff base ligands saldienH₂, 5-MeO-saldienH₂, and 5-NO₂-saldienH₂. All of the complexes were characterized by IR, mass spectrometry, and ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopies, and the spectra display chemical shifts corresponding to a seven-coordinated tin environment. The crystal structures of complexes 2a, 2d, and 4b were determined by X-ray diffraction. The complexes are isostructural and the tin atoms exhibit pentagonal-bipyramidal geometries with the methyl, n-butyl, and phenyl groups occupying the axial positions and the donor atoms from the ligand occupying the equatorial positions. A fluxional behavior was also observed that involves a dissociation-association mechanism of the N-Sn bonds.

Full text of DOI:10.1080/15533174.2012.680170

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Synthesis and Reactivity in Inorganic, Metal-Organic,
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Diorganotin (IV) Heptacoordinated Complexes
Containing Pentadentate [N3O2] Ligands Derived From
5-Substituted-Salicylaldehydes and Diethylenetriamine:
Synthesis, Characterization, and Molecular Structure
Armando Cortés-Lozada a , Elizabeth Gómez a & Simon Hernández a
a Instituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad
Universitaria, Mexico, D.F., Mexico
Accepted author version posted online: 21 Jun 2012.Published online: 28 Aug 2012.
To cite this article: Armando Cortés-Lozada , Elizabeth Gómez & Simon Hernández (2012): Diorganotin (IV) Heptacoordinated
Complexes Containing Pentadentate [N3O2] Ligands Derived From 5-Substituted-Salicylaldehydes and Diethylenetriamine:
Synthesis, Characterization, and Molecular Structure, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal
Chemistry, 42:8, 1143-1153
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 42:1143–1153, 2012
Copyright ꢀ Taylor & Francis Group, LLC
C
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2012.680170
Diorganotin (IV) Heptacoordinated Complexes Containing
Pentadentate [N3O2] Ligands Derived From
5-Substituted-Salicylaldehydes and Diethylenetriamine:
Synthesis, Characterization, and Molecular Structure
Armando Corte´s-Lozada, Elizabeth Go´mez, and Simon Herna´ndez
´
´
´
Instituto de Quımica, Universidad Nacional Autonoma de Mexico, Circuito Exterior, Ciudad
Universitaria, Mexico, D.F., Mexico
variety of coordination numbers and geometries. For example,
mononuclear species with pentacoordinated and hexacoordi-
nated geometries have been described with these types of lig-
ands.[3,4] The transition metal complexes of Schiff base ligands
have shown interesting redox properties[5,6] and applications in
catalytic processes.[7,8] It is notable that only a few structural
studies have been performed to elucidate the coordination mode
of the saldienH2 ligands. The few studies include structural elu-
cidations of Zn(II) and Cd(II) complexes. The former complex
was found to be a neutral mononuclear complex with a trigo-
nal bipyramidal geometry (TBP),[9] but the cadmium complex
shows a trinuclear structure with the metal centers in a distorted
octahedral environment.[10] Other examples of complexes lig-
ated by salen-type ligands are the rare-earth complexes that
possess luminescent properties, which show mononuclear 10-
coordinated structures in which the three nitrogen atoms do not
participate in the coordination sphere.[11] Additionally, homod-
inuclear complexes with hepta- and octacoordinated metallic
centers are also known.[12]
A series of heptacoordinated tin(IV) mononuclear complexes
[(Rꢁ)2Sn(5-X-saldien)] (X = H, OCH3, NO2) were synthesized by
reaction of dimethyl-, di-n-butyl-, di-n-octyl-, and diphenyltin (IV)
oxides with the pentadentate Schiff base ligands saldienH2, 5-MeO-
saldienH2, and 5-NO2-saldienH2. All of the complexes were char-
1
acterized by IR, mass spectrometry, and H, 13C, and 119Sn NMR
spectroscopies, and the spectra display chemical shifts correspond-
ing to a seven-coordinated tin environment. The crystal structures
of complexes 2a, 2d, and 4b were determined by X-ray diffrac-
tion. The complexes are isostructural and the tin atoms exhibit
pentagonal-bipyramidal geometries with the methyl, n-butyl, and
phenyl groups occupying the axial positions and the donor atoms
from the ligand occupying the equatorial positions. A fluxional be-
havior was also observed that involves a dissociation-association
mechanism of the N-Sn bonds.
Keywords diorganotin(IV), heptacoordination, pentadentate ligands,
saldienH2, 119Sn NMR
INTRODUCTION
Despite the importance of this type of ligand, few examples
that involve main group elements are known, and to our knowl-
edge, only B(III),[13] and more recently Sn(IV), have been re-
ported.[14] In the synthesis of hypercoordinated tin(IV) species,
ligands containing N3O2 as donor atoms have been used, and
among N3O2 ligands, the diacetylpyridine derivatives gives
heptacoordinated complexes in which the organic substituents
bonded to the tin atoms occupy the axial positions and the donor
atoms from the ligand occupy the equatorial positions in the pen-
tagonal bipyramid. The rigidity of the ligands forces the metal
center to adopt that particular geometry (Scheme 1).[15–22]
Mixed ligands containing five-donor atoms have also been
used to obtain heptacoordinated tin(IV) compounds, where the
donor atoms adopt the axial position in the pentagonal bipyramid
similar to the previously mentioned systems.[23–25]
The complexes of pentadentate Schiff-base ligands contain-
ing nitrogen and oxygen donor atoms derived from salicylalde-
hydes and diethylentriamine such as saldienH2 derivatives
have been studied over the last several years due to their struc-
tural diversity and also to the ability of such ligands to sta-
bilize a number of interesting metal oxidation states such as
Mn(II) and [Re O]3+ in the solid state.[1,2] These ligands can
react with transition metals to form complexes with a great
Received 5 January 2012; accepted 24 March 2012.
The authors thank DGAPA (IN2009113) for financial support and
thank Elizabeth Huerta, Ere´ndira Garc´ıa, Javier Pe´rez, and Luis Ve-
lasco for technical support with the IR, elemental analysis, and mass
spectrometry.
Address correspondence to Elizabeth Go´mez, Instituto de
Qu´ımica, Universidad Nacional Auto´noma de Me´xico, Circuito Ex-
terior, Ciudad Universitaria, Me´xico 04510, D.F., Me´xico. E-mail:
eligom@.unam.mx
The aim of this work was to evaluate the effect of the
substituents on pentadentate saldienH2 ligands with N3O2 as
donor atom sets in the formation of hypercoordinated Sn(IV)
complexes.
1143

´
1144
A. CORTES-LOZADA ET AL.
H
N
N
N
OH
HO
R
R
SaldienH2
N
N
R
R
Sn
R'
N
N
N
N
N
Y
NH
N
N
X
Sn
R'
X
O
O
X
X
O
O
n
[(R)2Sn(dapX)]
R = R' = n-Pr,
[(R)2Sn(dapX)]nY
I15
X = o-C6H5-OH
X = 2-thiophenyl
X = 2-thiophenyl
X = 2-thiophenyl
X = 2-furanyl
X18 R = R' = Me, X = 2-furanyl,
XI18 R = R' = Me, X = 2-furanyl,
XII18
Y = [Me2SnCl4], n = 2
Y = Br, n = 1
II16 R = R' = n-Et,
III16
R = n-Bu, R' = Cl,
R = R' = Me, X = 2-thiophenyl, Y = [Me2SnCl4], n = 2
IV16 R = R' = n-Bu,
XIII18 R = R' = Me, X = 2-thiophenyl, Y = Br,
n = 1
V18
R = Me, R' = Cl,
R = R' = Ph,
XIV19 R = R' = Me, X = NH2,
Y = [Me2SnCl4], n = 2
VI18
X = 2-furanyl
XV21
R = R' = Ph, X = NH2,
Y = Cl,
n = 1
VII18 R = Me, R' = Cl,
VIII18 R = R' = Ph,
X = 2-thiophenyl
X = 2-thiophenyl
X = o-C6H5-OH
IX20
R = R' = Me,
R
N
R
R
N
X
R'
N
N
N
N
N
N
Sn
X
Sn
R'
X
O
O
X
O
O
R
[(R)2Sn(dapf)]22
[(R)2Sn(dapb)]17
XXVIII
XXIX
XXX
XIX R = H, X = H,
XX R = H, X = Me, R' = Me
XXI R = H, X = Cl, R' = Me
XXII R = H, X = NO2, R' = Me
XXIII R = H, X = H, R' = n-Bu
XXIV R = H, X = Me, R' = n-Bu
XXV R = H, X = Cl, R' = n-Bu
XXVI R = H, X = NO2, R' = n-Bu
XXVII R = H, X = H, R' = Ph
R' = Me
R = Me, X = H,
R = Me, X = Me, R' = Me
R = Me, X = Cl, R' = Me
R = Me, X = NO2, R' = Me
R' = n-Bu
XXXIII R = Me, X = Me, R' = n-Bu
XXXIV
R' = Me
XVI R = Me,
XVII R = n-Bu, X = C6H5
XVIII
X = C6H5
R = Cl
X = C6H5
XXXI
XXXII R = Me, X = H,
R = Me, X = Cl,
R' = n-Bu
XXXV R = Me, X = NO2, R' = n-Bu
SCH. 1. Heptacoordinated complex of diorganotin (IV) with pentadentate ligands.
EXPERIMENTAL
Aldrich Chemical Co. (St. Louis, MO, USA) dioctyl oxide was
obtained from the Merck Chemical Co. (Whitehouse Station,
NJ, USA). The 1H, 13C, and 119Sn NMR spectra were recorded
on a JEOL Eclipse +300 NMR spectrometer (Peabody, MA,
USA) or a Bruker Advance 300 spectrometer (Madison, WI,
USA). Chemical shifts (ppm) are reported relative to (CH3)4Si,
Materials and Physical Measurements
Diethylenetriamine,
salicylaldehyde,
2-hydroxy-5-
nitrobenzaldehyde, 2-hydroxy-5-methoxybenzaldehyde, and
dimethyl, diphenyl, and dibutyltin oxide were obtained from the

DIORGANOTIN (IV) HEPTACOORDINATED COMPLEXES
1145
and coupling constants are reported in Hz. Melting points were 5-NO2-saldienH2 (1c)
measured on a Fisher Johns apparatus (Thermo Fisher Scien-
tific, Waltham, MA, USA) and are uncorrected. Mass spectra
were obtained with a JEOL JMS-AX505 HA mass spectrometer
(Peabody, MA, USA). The elemental analyses were obtained on
an Exeter Analytical CE-440 (North Chelmsford, MA, USA).
The IR spectra were recorded on a Bruker Tensor 27 (Madison,
WI, USA). The X-ray crystallographic studies were performed
on a Bruker Smart Apex CCD diffractometer (Madison, WI,
USA) with a λ(Mo-Kα) = 0.71073 Å, graphite monochromator
at T = 293 K. All structures were solved by direct methods;
all non-hydrogen atoms were refined anisotropically, using a
full-matrix, least-squares technique. All hydrogen atoms were
placed in idealized positions based on the hybridization with
thermal parameters fixed at 1.2 times (for –CH) and 1.5 times
(for –CH3) the value of the attached atom. Structure solutions
and refinements were performed using SHELXTL v 6.10
(Sheldrick, University of Go¨ttingen, Germany).
For 2-hydroxy-5-nitrobenzaldehyde, 3.3424 g (20.0 mmol)
and diethylentriamine 1.032 g, 1.08 mL, (10.0 mmol), a yellow
precipitate was obtained, which was filtered and washed with
cold ethanol (90.3% yield). 1H NMR (300 MHz, DMSO-d6) δ:
2.90 (4H, t, J = 6.00, H-2), 3.65 (4H, t, J = 5.70, H-3), 6.54 (2H,
d, J = 9.9, H-8), 7.97 (2H, dd, J = 9.75, 3.00, H-9), 8.34 (2H,
s, H-11), 8.35 (2H, s, H-5); 13C NMR (75 MHz, DMSO-d6) δ:
48.1 (C-2), 50.5 (C-3), 114.2 (C-8), 122.3 (C-6, C-11), 128.7
(C-9), 132.1 (C-10), 133.5 (C-7), 177.2 (C-5).
Synthesis of the Complexes
To a solution of the corresponding ligand in methanol/toluene
(2:3), methanol or toluene, the corresponding organotin oxide
was added. The reaction mixture was refluxed for 30 h. Then,
the solvent was removed under reduced pressure, giving the
corresponding complex.
[(Me)2Sn(saldien)] (2a)
0.9449 g (3.03 mmol) of ligand 1a and 0.5006 g (3.03 mmol)
of dimethyltin oxide were allowed to react in methanol, and
a yellow solid was obtained (68.79% yield), m.p. 238–243◦C.
13C NMR CP-MAS (75 MHz) δ: 5.3 (Sn-CH3), 16.9 (Sn-CH3),
52.2 (C-2), 58.7 (C-3), 114.7 (C-8), 122.5 (C-6), 124.4 (C-10),
134.1 (C-11), 135.8 (C-9), 167.2 (C-7), 168.7 (C-5); 119Sn NMR
(300 MHz, DMSO-d6) δ: −504; MS (EI) [m/z] (%): [M+, 459]
(5), [(M-CH3)+, 444] (24), [(M-H, -2CH3)+, 428] (6), [(M-
CH3, -C7H5NO)+, 325], (73), [(M-OSn(CH3)2]+(25). IR (KBr,
cm−1): 3262 (m, νN-H), 1638 (s, νC N).
Ligand Syntheses
To a solution of the corresponding salicylaldehyde in ethanol,
diethylenetriamine was added dropwise. The reaction mixture
turned yellow and was refluxed for 4 h. Then, the solvent was
removed under reduced pressure, giving the corresponding lig-
and.
saldienH2 (1a)
Salicylaldehyde (11.66 g, 10 mL 95.47 mmol) and (diethy-
lentriamine 4.925 g, 5.16 mL, 47.73 mmol) were allowed to
react as described previously, and the yellow oil obtained was
dissolved in CH2Cl2 and filtered through celite. The evaporation
of the solvent gives a red oil (87.5% yield). 1H NMR (300 MHz,
CDCl3) δ: 2.82 (4H, s, H-2), 3.53 (4H, s, H-3), 6.75 (2H, t, J =
7.41, H-10), 6.86 (2H, d, J = 8.25, H-8), 7.09 (2H, J = 7.71,
H-11), 7.19 (2H, t, J = 7.41, H-9), 8.17 (2H, s, H-5); 13C NMR
(75 MHz, CDCl3) δ: 49.71 (C-2), 59.5 (C-3), 117.0 (C-8), 118.6
(C-10), 118.8 (C-6), 131.5 (C-11), 132.3 (C-9), 161.5 (C-7),
166.1 (C-5).
[(Bu)2Sn(saldien)] (2b)
0.625 g (2.01 mmol) of ligand 1a and 0.5004 g (2.01 mmol)
of dibutyltin oxide were allowed to react in methanol, and a
yellow solid was obtained (83.85% yield), m.p. 198–201◦C; 1H
NMR (300 MHz, CDCl3) δ: 0.60 (6H, s, H-δ), 0.89–1.56 (12H,
br, H-α, H-β, H-γ ), 2.99 (4H, t, J = 5.7, H-2), 3.71 (4H, t, J =
5.7, H-3), 6.52 (2H, t, J = 7.2, H-8), 6.85 (2H, t, J = 7.5, H-11),
6.91–7.02 (2H, m, H-10), 7.20–7.31 (2H, m, H-9), 8.05 (2H, s,
H-5); 13C NMR (75 MHz, CDCl3) δ: 13.6 (C-δ), 26.5 (C-γ ),
28.1 (C-α, C-β), 49.6 (C-2), 49.7 (C-2ꢀ), 59.6 (C-3), 60.1 (C-3ꢀ),
114 (C-8), 116 (C-8ꢀ), 118.6 (C-10), 118.7 (C-6), 120.2 (C-6ꢀ),
123.9 (C-10ꢀ), 131.3 (C-11), 132.3 (C-11ꢀ), 133.6 (C-9), 134.2
(C-9ꢀ), 161–1 (C-7), 166.1 (C-5), 167.6 (C-5ꢀ), 168.2 (C-7ꢀ);
119Sn NMR (300 MHz, DMSO-d6) δ: −509; MS (EI) [m/z] (%):
[(M-H)+, 542] (3), [(M-nBu)+, 486] (100), [(M-H, -2nBu)+,
428] (17), [(M-C8H8NO)+, 409] (47), [(M-nBu, -C7H5NO)+,
367] (15), [(M-C13H18NO)+ 339] (18), [(M-C13H19N2)+, 324]
(27), [(M-OSn(nBu)2)+, 293] (53), [(M-C16H23N3)+, 286] (85),
[(M-C18H30N2O)+, 251] (48). IR (KBr, cm−1): 3259 (m, νN-H),
1633 (s, νC N).
5-MeO-saldienH2 (1b)
2-hydroxy-5-methoxybenzaldehyde (3.0525 g, 2.5 mL,
20.0 mmol) and diethylentriamine (1.035 g, 1.0 mL, 10.0 mmol)
were allowed to react as described previously and a brown oil
was obtained, which solidified after several days (80.5% yield).
1H NMR (300 MHz, CDCl3) δ: 2.90 (4H, t, J = 5.91, H-2),
3.52 (4H, t, J = 5.64, H-3), 3.58 (6H, s, -OCH3), 6.65 (2H,
d, J = 2.76, H-11), 6.72–6.88 (4H, m, H-8, H-9), 8.21 (2H, s,
H-5); 13C NMR (75 MHz, CDCl3) δ: 49.71 (C-2), 55.8 (-O-
CH3), 59.5 (C-3), 114.8 (C-8), 117.6 (C-11), 118.3 (C-9), 119.4
(C-6), 151.9 (C-10), 155.1 (C-7), 166.0 (C-5); MS (EI) [m/z]
(%): [M.+, 371] (10), [(M-CH2-NCH-C7H7O2)+, 207] (100),
[(M-(CH2)2-NCH-C7H7O2)+, 193] (10).
[(Octyl)2Sn(saldien)] (2c)
0.778 g (2.5 mmol) of ligand 1a and 0.905 g (2.50 mmol) of
dioctyltin oxide were allowed to react in methanol/toluene (2:3),

´
A. CORTES-LOZADA ET AL.
1146
and a white solid was obtained (61.03% yield), m.p. 98–100◦C;
1H NMR (300 MHz, CDCl3) δ: 0.82 (6H, t, J = 7.2, H-θ),
0.90–1.55 (28H,br, H-α, H-β, H-γ , H-δ, H-ε, H-ζ, H-η), 2.98
(4H, t, J = 6.0, H-2), 3.71 (4H, t, J = 5.7, H-3), 6.52 (2H, t,
J = 7.2, H-8), 6.85 (2H, t, J = 7.5, H-11), 6.91–7.02 (2H, m,
H-10), 7.20–7.31 (2H, m, H-9), 8.05 (2H, s, H-5); 13C NMR
(75 MHz, CDCl3) δ: 14.5 (C-θ), 22.6 (C-α, C-β,C-η), 26.1 (C-
δ), 29.2(C-ε), 31.8 (C-γ , C-ζ), 49.6 (C-2), 60.2 (C-3), 114.0
9), 124.7 (C-9ꢀ), 148.7 (C-10), 151.9 (C-7), 155.1 (C-7ꢀ); 119Sn
NMR (300 MHz, DMSO-d6) δ: −509; MS (FAB) [m/z] (%):
[(M+1)+, 604] (77), [(M-1)+, 602] (72), [(M-nBu)+, 546] (62),
[(M-H, -2nBu)+, 488] (45), [(M-nBu, -C8H7NO2)+, 387] (8),
[(M-OSn(nBu)2)+, 354] (12), [(M-H, -2nBu, -C9H9NO2)+, 325]
(100), [(M-2nBu, -C11H15N2O2)+ 283] (35); IR (KBr, cm−1):
3274 (m, νN-H), 1636 (s, νC N).
(C-10), 120.2 (C-6), 124.0 (C-8), 133.5 (C11), 134.2 (C-9), [(Octyl)2Sn(5-MeO-saldien)] (3c)
167.5 (C-5), 168.3 (C-7); 119Sn NMR (300 MHz, DMSO-d6)
0.5200 g (1.4 mmol) of ligand 1b and 0.506 g (1.4 mmol) of
δ: −502. MS (EI) [m/z] (%): [(M-nOc)+, 542] (38), [(M-H, -
2nOc)+, 428] (5), [(OSn(nOc)2)+, 362] (8), [(M-OSn(nOc)2)+,
293] (20), [(M-C24H40NOSn)+, 177] (100); IR (KBr, cm−1):
3259 (m, νN-H), 1633 (s, νC N).
dioctyltin oxide were allowed to react in toluene, and a brown oil
was obtained (55.3% yield). m.p. 89–90◦C; 1H NMR (300 MHz,
CDCl3) δ: 0.82 (6H, t, J = 7.2, H-θ), 1.07–1.65 (28H, br, H-α,
H-β, H-γ , H-δ, H-ε, H-ζ H-η), 2.17 (4H, s, H-2), 3.72 (6H, s,
-OCH3), 3.73 (4H, s, H-3), 6.52 (2H, t, J = 2.1, H-8), 6.74 (2H,
d, J = 2.7, H-11), 6.85–6.93 (2H, m, H-9), 8.01 (2H, s, H-5).
13C NMR (75 MHz, CDCl3) δ: 14.1 (C-θ), 22.6 (C-β, C-η),
26.1 (C-δ), 29.2(C-ε), 29.3 (C-α), 31.8 (C-γ , C-ζ), 49.7 (C-2),
55.9 (-OCH3), 59.8 (C-3), 114.8 (C-8), 117.6 (C-6), 118.3.0 (C-
11), 119.3 (C9), 152.0 (C-10), 155.2 (C-7), 165.9 (C-5). 119Sn
NMR (300 MHz, CDCl3) δ: −490. MS (FAB) [m/z] (%):[M+,
715] (3), [(M-OSn(nOc)2)+, 354] (5); IR (KBr, cm−1): 3427 (m,
νN-H), 1635 (s, νC N).
[(Ph)2Sn(saldien)] (2d)
0.539 g (1.73 mmol) of ligand 1a and 0.500 g (1.73 mmol)
of diphenyltin oxide were allowed to react in methanol and
1
a yellow solid was obtained (82.5% yield). m.p. ≥300◦C; H
NMR (300 MHz, CDCl3) δ: 2.99 (4H, t, J = 5.4, H-2), 3.71
(4H, t, J = 5.7, H-3), 6.54 (2H, t, J = 7.2, H-8), 6.85 (2H, t,
J = 7.5, H-11), 6.94 (2H, t, J = 7.8, H-10), 7.06–7.39 (6H, m,
H-9, H-m, H-p), 7.50–7.66 (4H, m, H-o), 8.35 (2H, s, H-5);
13C NMR (75 MHz, CDCl3) δ: 41.1 (C-2), 57.6 (C-3), 113.7
(C-10), 120.1 (C-6), 123.2 (C-8), 127.8 (C-m), 128.2 (C-p),
133.8 (C-11), 134.1 (C-9), 135.0 (C-o), 135.4 (C-i), 168.8 (C-
7), 170.0 (C-5); 119Sn NMR (300 MHz, DMSO-d6) δ: −518;
MS (FAB) [m/z] (%): [(M+1)+, 584] (54), [(M)+, 583] (35),
[(M-1)+, 582] (50), [(M-Ph)+, 506] (22), [(M-H, -2Ph)+, 428]
(10), [(M-Ph, -C7H5NO)+, 387] (5), [(M-OSn(Ph)2)+, 293] (9),
[(M-C19H15NO2Sn)+, 175] (17); IR (KBr, cm−1): 3245 (m, νN-
H), 1629 (s, νC N).
[(Ph)2Sn(5-MeO-saldien)] (3d)
0.6428 g (1.73 mmol) of ligand 1b and 0.500 g (1.73 mmol)
of diphenyltin oxide were allowed to react in methanol, and a
yellow solid was obtained (78.8% yield). m.p. 255–258◦C; 1H
NMR (300 MHz, CDCl3) δ: 2.98 (4H, t, J = 5.7, H-2), 3.73
(6H, s, H-OCH3), 3.76 (4H, s, H-3), 6.55 (2H, s, H-8), 6.74
(2H, d, J = 2.4, H-11), 6.87–7.19 (6H, m, H-9, H-m, H-p),
7.36–7.67 (4H, m, H-o), 8.31 (2H, s, H-5). 13C NMR (75 MHz,
CDCl3) δ: 49.7 (C-2), 55.9 (-OCH3), 59.7 (C-3), 119.3 (C-10),
114.8 (C-8), 117.7 (C-6), 118.4 (C-11), 119.3 (C-10), 122.7
(C-m), 125.2 (C-p), 128.3(C-o), 148.8 (C-i), 152.0 (C-9), 155.2
(C-7), 169.0 (C-5); 119Sn NMR (300 MHz, CDCl3) δ: −504.
MS (FAB) [m/z] (%):[(M+, 643] (2), [(M-CH3, -O-CH3)+, 597]
(10), [(M-Ph)+, 566] (7), [(M-CH3, -O-CH3, -Ph)+, 520] (30),
[(M- 2O-CH3, -Ph)+, 504] (18) [(M-H, -2Ph)+, 488] (8), [(M-
Ph, -C8H7NO2)+, 417] (2), [(M-OSn(Ph)2)+, 354] (85), [(M-H,
-2Ph, -C9H9NO2)+, 325] (33); IR (KBr, cm−1): 3323 (m, νN-H),
1636 (s, νC N).
[(Me)2Sn(5-MeO-saldien)] (3a)
0.6100 g (1.64 mmol) of ligand 1b and 0.270 g (1.64 mmol)
of dimethyltin oxide were allowed to react in methanol, and
a yellow solid was obtained (71.67% yield). m.p. 235–238◦C;
13C NMR CP-MAS (75 MHz) δ: 2.4 (Sn-CH3), 16.6 (Sn-CH3),
50.3 (C-2), 54.8 (-OCH3), 59.7 (C-3), 113.4 (C-8), 121.2 (C-
11), 124.1 (C-6, C-10), 148.4 (C-9), 163.3 (C-7), 167.8 (C-5);
MS (FAB) [m/z] (%): [M+, 519] (2), [(M-CH3, -C8H7NO2)+,
355] (5); IR (KBr, cm−1): 3255 (m, νN-H), 1634 (s, νC N).
[(Bu)2Sn(5-MeO-saldien)] (3b)
[(Me)2Sn(5-NO2-saldien)] (4a)
0.746 g (2.0 mmol) of ligand 2a and 0.500 g (2.0 mmol) of
1.217 g, (3.03 mmol) of ligand 1c and 0.500 g (3.03 mmol)
dibutyltin oxide were allowed to react in methanol, and a yellow of dimethyltin oxide were allowed to react in methanol, and a
solid was obtained (65.35% yield). m.p. 194–197◦C; 1H NMR yellow solid was obtained (92% yield) m.p. >300◦C: 1H NMR
(300 MHz, CDCl3) δ: 0.61 (6H, s, J = 7.14, H-δ), 0.90–1.66 (300 MHz, DMSO-d6) δ: 0.25 (3H, s, Sn-CH3), 0.77 (3H, s,
(12H, br, H-α, H-β,H-γ ), 2.99 (4H, s, H-2), 3.73 (6H, s, -OCH3), Sn-CH3), 2.63 (2H, J = 11.55, H-2), 3.13 (2H, d, J = 12.09,
3.77 (4H, s, H-3), 6.53 (2H, s, H-8), 6.74 (2H, d, J = 2.4, H-11), H-2), 3.53 (2H, d, J = 13.2, H-3), 3.84 (2H, t, J = 12.66, H-
6.85–6.92 (2H, m, H-9), 8.02 (2H, s, H-5); 13C NMR (75 MHz, 3), 6.62 (2H, d, J = 9.33, H-8), 6.01 (2H, dd, J = 3.0, 9.3,
CDCl3) δ:13.6 (C-δ), 26.3 (C-γ ), 28.2 (C-α, C-β), 55.9 (C-2), H-9), 8.24 (2H, d, J = 3.0, H-11), 8.38 (2H, s, H-5); 13C NMR
56.1 (C-2ꢀ), 59.8 (C-3), 60.2 (C-3ꢀ), 114.8 (C-8), 116.3 (C-8ꢀ), (75 MHz, DMSO-d6) δ: 9.2 (Sn-CH3). 15.2 (Sn-CH3), 49.0
117.6 (C-11), 118.3 (C-11ꢀ), 118.9 (C-6), 119.3 (C-6ꢀ), 122.0 (C- (C-2), 58.4 (C-3), 119.5 (C-8), 123.7 (C-6), 128.9 (C-9), 132.7

DIORGANOTIN (IV) HEPTACOORDINATED COMPLEXES
1147
TABLE 1
Infrared data for ligands 1a–1c and complexes 2a–4d
ν N-H
ꢀν (N-H)
ν C N
ꢀν
(C N) (cm−1
ν Sn-C
ν Sn-O
ν Sn-N
Compound
(cm−1
)
(cm−1
)
(cm−1
)
)
(cm−1
)
(cm−1
)
(cm−1
)
1a
2a
2b
2c
2d
3056
3198
3259
3262
3245
—
1632
1638
1633
1634
1629
—
+5
+1
+2
−3
—
—
579
—
453
457
458
457
+142
+203
+206
+189
637
636
639
639
569
a
a
1b
3a
3b
3c
3d
3005
3255
3274
3255
3245
—
1632
1634
1636
1635
1629
—
+2
+4
+3
−3
—
—
—
a
+250
+269
+250
+240
561
436
a
a
667
665
562
552
416
451
a
1c
4a
4b
4c
4d
3062
3255
3257
3254
3252
—
1657
1644
1639
1638
1636
—
—
—
569
—
+193
+195
+192
+190
−13
−18
−17
−21
640
642
641
645
460
457
458
461
565
a
a
aBands not assigned.
(C-11), 134.5 (C-10), 167.0 (C-7), 174.2 (C-5); 119Sn NMR
(300 MHz, DMSO-d6) δ: −502; MS (EI) [m/z] (%): [M+, 550]
(5), [(M-CH3)+, 534] (2); IR (KBr, cm−1): 3255 (m, νN-H),
1644 (s, νC N).
7.5, H-8), 8.09 (2H, d, J = 3.0, H-9), 8.12 (2H, d, J = 2.4,
H-11), 8.16 (2H, s, H-5); 13C NMR (75 MHz, CDCl3) δ: 14.0
(C-θ), 14.1 (C-θꢀ), 22.6 (C- ζ, C- ζꢀ), 25.7 (C-δ), 25.7 (C-δꢀ),
28.9 (C-β), 29.0 (C-βꢀ), 29.3 (C-η,C-ηꢀ), 31.0 (C-γ ), 31.7 (C-
α), 31.8 (C-αꢀ), 32.7 (C-γ ꢀ), 33.5 (C-ε), 35.1 (C-εꢀ), 49.1 (C-2),
59.6 (C-3), 118.4 (C-8), 124.1 (C-6), 129.1 (C-9), 132.4 (C-11),
135.4 (C-10), 166.9 (C-7), 174.0 (C-5); 119Sn NMR (300 MHz,
CDCl3) δ: −522. MS (EI) [m/z] (%):[(M-H, -nOc)+, 631] (3),
[(M-H, -2nOc)+, 518] (2), [M-OSn(nOC)2)+, 384] (5), [(M-
2Oc, -C9H8N3O3)+, 312] (20), [(HSn(OH)nOc), 251] (70); IR
(KBr, cm−1): 3254 (m, νN-H), 1638 (s, νC N).
[(Bu)2Sn(5-NO2-saldien)] (4b)
0.806 g (2.0 mmol) of ligand 1c and 0.50 g (2.0 mmol) of
dibutyltin oxide were allowed to react in methanol, and a yellow
1
solid was obtained (84.3% yield), m.p. 100◦C (dec). H NMR
(300 MHz, CD2Cl2) δ: 1.76 (3H, t, J = 7.2, H-δ), 0.81 (3H, t, J =
7.2, H-δ) 0.89–1.61 (12H, m, H-α, H-β, H-γ ), 2.81–3.13 (2H,
m, H-2), 3.58 (2H, dd, J = 2.4, 14.4, H-3), 3.89 (2H, t, J = 13.8,
H-3), 6.79 (2H, d, J = 9.2, H-8), 8.08 (2H, dd, J = 3.0, 9.15,
H-9), 8.11 (2H, d, J = 2.7, H-11), 8.17 (2H, s, H-5); 13C NMR
(75 MHz, CDCl3) δ: 13.4 (C-δ), 13.8 (C-δꢀ), 25.6 (C-γ ), 26.1
(C-γ ꢀ), 27.9 (C-α), 28.2 (C-αꢀ), 30.6 (C-β), 34.9 (C-βꢀ), 49.3
(C-2), 59.8 (C-3), 120.0 (C-8), 124.0 (C-6), 129.2 (C-9), 129.7
(C-11), 132.3 (C-10), 143.4 (C-7), 166.8 (C-5). 119Sn NMR
(300 MHz, CDCl3) δ: −523. MS (EI) [m/z] (%): [(M-Bu)+,
576] (52), [(M-H, -2Bu)+, 518] (10), [(M-Bu, -C6H4NO2)+,
454] (15), [(M-OSn(nBU)2)+ 384] (11), [(M-Bu,-C9H9N3O2,
-NO2)+, 339] (22); IR (KBr, cm−1): 3257 (m, νN-H), 1639 (s,
νC N).
[(Ph)2Sn(5-NO2-saldien)] (4d)
0.6428 g (1.73 mmol) of ligand 1c and 0.500 g (1.73 mmol)
of diphenyltin oxide were allowed to react in methanol, and a
yellow solid was obtained (88% yield). m.p. >300◦C; 1H NMR
(300 MHz, DMSO-d6) δ: 2.74 (2H, t, J = 2.1, H-2), 2.9 (2H, d,
J = 10.8, H-2), 3.71 (2H, d, J = 13.5, H-3), 4.15 (2H, t, J = 6.0,
H-3), 6.57 (2H, d, J = 9.3, H-8), 7.20–7.26 (6H, m, H-m, H-p),
TABLE 2
ꢀG= and coalescence temperature Tc
Complex
ꢀG= (kcal.mol−1
)
Tc (◦C)
[(Octyl)2Sn(5-NO2-saldien)] (4c)
2c
3b
3c
3d
17.2
16.6
16.0
14.0
17.5
7.5
0.555 g (1.38 mmol) of ligand 1c and 0.506 g (1.38 mmol) of
dioctyltin oxide were allowed to react in toluene, and a yellow
−5.0
solid was obtained (73.7% yield), m.p. 100–102◦C; H NMR
1
−30.0
(300 MHz, CDCl3) δ: 0.91–1.25 (34H, m, H-α, H-β, H-γ , H-δ,
H-ε, H-ζ-H-η,H-θ), 2.84–3.37 (2H, m, H-2), 3.6 (2H, d, J =
13.2, H-3), 3.97 (2H, t, J = 13.2, H-3), 6.87 (2H, dd, J = 2.7,
4b
4c
19.0
23.4
118.0
115.0

´
1148
A. CORTES-LOZADA ET AL.
TABLE 3
Crystallographic data and structure refinement for 2a, 2d, and 4b
2a
2d
4b
Empirical Formula
C20H25N3O2Sn.CH2Cl2
C30H29N3O2Sn.CHCl3
701.62
C26H35N5O6Sn.CH2Cl2
Formula weight (g mol−1
)
543.05
0.42 × 0.15 × 0.10
Colorless
Orthorhombic
Pna21
717.21
0.39 × 0.26 × 0.19
Yellow
Crystal size (mm)
Color
Crystal system
Space group
a (Å)
0.41 × 0.13 × 0.12
Yellow
Monoclinic
P 21/n
12.971(2)
15.372(2)
15.490(3)
90
91.002(8)
90
3079.1(9)
4
Monoclinic
Cc
18.7754(17)
11.0172(10)
16.7238(15)
90
113.9690(10)
90
3161.0(5)
4
11.3340(11)
16.7424(16)
12.4653(12)
90
90
90
2365.4(4)
4
1.525
b (Å)
c (Å)
α (◦)
β (◦)
γ (◦)
V (Å3)
Z
ρ (g cm−3
)
1.513
1.507
No. of collected reflections
24937
25040
12756
No. of independent reflections (Rint)
No. of observed reflections
4316 (0.0606)
4316
5679 (0.0448)
5679
5734 (0.0358)
5734
No. of parameters
265
392
375
Ra
Rbw
GOF
0.957
1.050
0.906
FIG. 1. Conformational equilibrium and dissociation-association processes of complexes [(nBu)2Sn(5-R-saldien)].

DIORGANOTIN (IV) HEPTACOORDINATED COMPLEXES
1149
TABLE 4
Selected bond lengths (Å), bond angles and torsion angles (◦) for complexes 2a, 2d, and 4b
2a
2d
4b
Bond lengths
Sn(2)-O(1)
Sn(2)-O(3)
Sn(2)-N(11)
Sn(2)-N(14)
Sn(2)-N(17)
Sn(2)-C(25)
Sn(2)-C(26)
2.156 (3)
2.145 (3)
2.480 (4)
2.592 (4)
2.526 (4)
2.111 (5)
2.119 (5)
2.129 (2)
2.131 (2)
2.422 (2)
2.561 (3)
2.512 (2)
2.154 (3)
2.198 (6)
2.204 (3)
2.473 (4)
2.506 (4)
2.495 (4)
2.112 (9)
Sn(2)-C(31)
2.139 (3)
Sn(2)-C(29)
2.138 (9)
Bond angles
O(1)Sn(2)-O(3)
78.5 (1)
74.0 (1)
67.1 (2)
66.0 (2)
75.2 (2)
91.7 (2)
90.8 (2)
91.9 (2)
82.8 (2)
89.87 (8)
171.2 (2)
76.2 (1)
77.7 (1)
68.8 (1)
64.5 (1)
73.3 (1)
95.9 (1)
94.5 (1)
85.2 (1)
88.5 (1)
88.8 (1)
75.05 (2)
75.11 (2)
68.11 (3)
68.25 (2)
74.69 (2)
93.4 (2)
89.9 (2)
94.65 (8)
87.4 (3)
O(3)-Sn(2)-N(11)
N(11)-Sn(2)-N(14)
N(14)-Sn(2)-N(17)
N(17)-Sn(2)-O(1)
C(25)-Sn(2)-O(1)
C(25)-Sn(2)-O(3)
C(25)-Sn(2)-N(11)
C(25)-Sn(2)-N(14)
C(25)-Sn(2)-N(17)
C(25)-Sn(2)-C(26)
C(25)-Sn(2)-C(31)
C(25)-Sn(2)-C(29)
C(26)-Sn(2)-O(1)
C(26)-Sn(2)-O(3)
C(26)-Sn(2)-N(11)
C(26)-Sn(2)-N(14)
C(26)-Sn(2)-N(17)
C(31)-Sn(2)-O(1)
C(31)-Sn(2)-O(3)
C(31)-Sn(2)-N(11)
C(31)-Sn(2)-N(14)
C(31)-Sn(2)-N(17)
C(29)-Sn(2)-O(1)
C(29)-Sn(2)-O(3)
C(29)-Sn(2)-N(11)
C(29)-Sn(2)-N(14)
C(29)-Sn(2)-N(17)
Torsion angles
84.53 (9)
173.2 (1)
175.3 (4)
94.6 (2)
96.6 (2)
85.4 (2)
88.4 (2)
85.9 (2)
89.9 (1)
90.93 (0)
91.7 (1)
84.8 (1)
88.2 (1)
90.3 (2)
94.0 (2)
83.92 (7)
87.8 (3)
93.74 (7)
Sn(2)-O(3)-C(4)-C(5)
Sn(2)-O(3)-C(4)-C(9)
Sn(2)-N(11)-C(10)-C(9)
Sn(2)-O(1)-C(24)-C(19)
Sn(2)-O(1)-C(24)-C(23)
Sn(2)-N(17)-C(18)-C(19)
N(11)-C(12)-C(13)-N(14)
N(14)-C(15)-C(16)-N(17)
−142.98 (0.38)
39.64 (0.64)
−19.54 (0.72)
−31.74 (0.77)
151.39 (0.40)
11.89 (0.83)
56.74 (0.62)
−58.60 (0.65)
171.67 (0.23)
−7.74 (0.51)
0.68 (0.46)
48.30 (0.34)
−134.06 (0.22)
−12.96 (0.40)
60.39 (0.33)
−43.20 (0.36)
−157.44 (0.34)
24.23 (0.75)
−10.48 (0.70)
21.37 (0.81)
−160.05 (0.36)
−9.93 (0.65)
−52.90 (0.59)
54.26 (0.56)

´
1150
A. CORTES-LOZADA ET AL.
FIG. 2. Perspective views of molecular structures of complexes 2a, 2d, and 4b. ORTEP (Thermal ellipsoids at 30% probability).
ing ethanol as solvent. The complexes [(Rꢀ)2Sn(5-X-saldien)]
2a–2d, 3a–3d, and 4a–4d were synthesized by reaction of the
pentadentate ligand with the corresponding diorganotin(IV) (in
a 1:1 ratio), as depicted in Scheme 2.
7.41–7.49 (4H, m, H-o), 7.99 (2H, dd, J = 3.0, 9.3, H-9), 8.35
(2H, d, J = 3.0, H-11), 8.79 (2H, s, H-5). 13C NMR (75 MHz,
DMSO-d6) δ: 48.5 (C-2), 58.0 (C-3), 118.2 (C-8), 123.2 (C-6),
127.8 (C-m), 128.2 (C-p), 128.5 (C-9), 132.6 (C-11), 133.1 (C-
o), 134.1 (C-i), 134.5 (C-10) 169.6 (C-7), 173.7 (C-5). 119Sn
NMR (300 MHz, DMSO-d6) δ: −504. MS (FAB) [m/z] (%):
[(M)+, 673] (2), [(M-Ph)+, 596] (2), [(M-Ph, -C10H10N3O2)+,
391] (18), [(M-C8H6N, -OSn)+, 251] (100); IR (KBr, cm−1):
3252 (m, νN-H), 1636 (s, νC N).
FTIR Spectroscopy
The infrared spectra of all of the complexes showed vi-
brational bands in the range of 1629–1639 cm−1 due to the
ν(N C). These bands do not show a significant shift in wave
number with respect to the free Schiff base in the spectra of
RESULTS AND DISCUSSION
The Schiff-base ligands saldienH2, 5-MeO-saldienH2, and 2a–2d and 3a–3d (Table 1). However, it is evident that in com-
5-NO2-saldienH2 were prepared by reaction of the correspond- plexes 4a–4d [(Rꢀ)2Sn(5-NO2-saldien)] the ν (C N) are shifted
ing salicylaldehyde and diethylenetriamine (in a 2:1 ratio) us- 13–21 cm−1 lower with respect to the ligand 1c. This shift could
N
R
H
O
H
N
N
O
- 2 H2O
ethanol
- 2 H2O
NH2
2
+
+
HN
Sn
2
methanol or
methanol/toluene 2:3
or toluene
OH
HO
R'
R'
OH
R' = CH3
n-C4H9
R
R
R = H
n-C8H17
C6H5
OCH3
NO2
1a
1b
R = H,
saldienH2
R = OCH3, 5-MeO-saldienH2
1c R = NO2, 5-NO2-saldienH2
R
CH3
a: R' =
b: R' =
c: R' =
α
γ
N
R'
Sn
R'
δ
δ
β
O
[(R')2Sn(saldien)]
(2a-2d)
α
γ
ε
η
1
[(R')2Sn(5-MeO-saldien)] (3a-3d)
[(R')2Sn(5-NO2-saldien)] (4a-4d)
HN
2
O
6
θ
β
ζ
11
N
10
3
4
o
m
9
5
7
8
p
d: R' =
R
i
SCH. 2. Synthesis of saldienH2 ligands and diorganotin (IV) complexes.

DIORGANOTIN (IV) HEPTACOORDINATED COMPLEXES
1151
indicate that the Sn-N bonds in 4a–4d are stronger than those signals for the methylene groups split into an ABCD system for
of compounds 2a–2d and 3a–3d.
the non-equivalent hydrogen atoms, and eventually the signals
It is reported that vibrational bands associated with Sn-O coalesced at 17.5, 7.5, −5.0, and −30◦C for 2c, 3b, 3c, and
bonds are in the range of 450–650 cm ,
−1 [26,27] whereas the bands 3d, respectively, as shown in Table 2. The corresponding ꢀG=
corresponding to Sn-N bonds are under 500 cm−1, and bands values of the fluxional process of each complex were calculated
related to Sn-C bonds display values above 500 cm−1. In our using the Eyring[29] equation and are in the range of 14–24 kcal.
study, we could assign most of the vibrational bands of Sn-O,
NMR experiments at variable temperature for complexes
which are in the range of 561–579 cm−1; the vibrational bands 4b–4c showed an ABCD system from −90 to 100◦C, which
of Sn-N appeared from 416 to 461 cm−1, whereas the bands of vanished above 100◦C, turning into broad signals. This behav-
Sn-C are above 600 cm−1
.
ior reveals that the energy associated with this process is higher
than that observed for the other complexes. In this case, the NO2
group could be influencing the acid character of the Sn atom,
Mass Spectrometry
The monomeric structures of the complexes were estab- leading to stronger Sn-N bonds. For complexes 4a and 4d, the
lished by mass spectrometry, which showed the molecular ABCD system remains in the NMR spectra even at 130◦C.
ions for most of the complexes and similar fragmentation
The 13C NMR spectra of 2c, 3d, and 4d showed signals
patterns were observed for all of the complexes. In the first corresponding to two equivalent halves of the molecules. How-
stage, loss of an alkyl or aryl group attached to the tin ever, the 13C NMR of complexes 2b and 3b displayed signals
atom was observed to form an [M+-R] atom, which corre- for all carbons on the ligand, but only four carbons from the
sponds to the base peak for almost all of the complexes. Frag- butyl substituents attached to the tin atom. This indicates that
ment ions representing [R-C6H3CH N-CH2-CH2-NH-CH2- the butyl groups are magnetically equivalent, which could be a
CH2O-Sn-O]+ and [(R-C6H3CH N-CH2-CH2-NH-CH2-CH2- consequence of a different conformation. Apparently, the two
O]+ were also detected.
organic substituents bonded to metallic center adopt the equa-
torial positions and the oxygen atoms the axial (Figure 1). The
13C NMR spectra of complexes 4a–4c showed signals for eight
carbons from the ligand. In this case, the substituents attached
to the tin atom exhibited different signals due to their different
magnetic environments.
NMR Spectroscopy
The evidence for the formation of heptacoordinated tin
species was provided by 119Sn, 1H, and 13C NMR spectroscopy.
The 119Sn NMR spectra showed signals in the range of −490 to
−618 ppm, which are typical for heptacoordinated tin atoms.[28]
The coordination of the nitrogen atoms to the metallic center,
in connection with the simultaneous formation of Sn-O bonds,
accounted for the pentagonal bipyramidal geometry.
X-Ray Crystallography
The molecular structures of complexes 2a, 2d, and 4b were
established by X-ray crystallography.
1
The H NMR spectra of all of the complexes showed that
Compounds 2a and 2d are isomorphous to those described
the H-2 and H-3 protons are shifted to high frequencies with previously, which were crystallized as solvates. Details of the
respect to the free ligands, which could be associated with the crystal data and a summary of the data collection parameters of
coordination of the nitrogen atoms to the metallic center.
the complexes are given in Table 3. Selected bond lengths and
The complexes 2a, 2b, and 2d have been described in the bond angles are listed in Table 4. Examination of the molecular
literature. However, they were obtained by a different synthetic structures of the three complexes reveals that they are isostruc-
route using organotinchlorides and triethyl amine or KOH as a tural with pentagonal-bipyramidal (PBP) geometries (Figure 2).
base.[14a,14b] The 1H NMR spectra of these complexes show the Theequatorial planeconsistsoftwooxygenatomsandtwonitro-
reported patterns for the NH-CH2-CH2-NH moiety. However, gen atoms from the azomethine fragment and the nitrogen atom
the compounds 2c and 3b–3d display single broad signals at of the amine group, whereas the axial positions are occupied
room temperature in their 1H NMR spectra, which indicate the by the two organic groups, with C-Sn-C angles of 171.2(2)◦,
presence of a fluxional process that involves the rupture of N-Sn 173.2(1)◦, and 175.3(4)◦ for 2a, 2d, and 4b, respectively. This
bonds and the inversion of the central nitrogen.[14] The complex structure leads to a distorted geometry around the tin atom. From
3a is not soluble in common organic solvents therefore the the Sn(2)-O(3)-C(4)-C(5) and Sn(2)-O(1)-C(24)-C(23) torsion
solution NMR spectrum could not be recorded. The compounds angles of 2a, 2d, and 4b, it can be deduced that the aromatic
4a–4d displayed ABCD systems at room temperature in their rings are not coplanar. The torsion angles in the compound 2a
1H NMR spectra. This finding could be due to the electron indicate that both aromatic rings are below the equatorial plane
withdrawing effect of the NO2 group, resulting in stronger N- formed by N(11), N(14), N(17), O(1), and O(3).
Sn bonds, which prevent the fluxional process. This observation
is in agreement with the IR spectroscopy results.
However, for 2d, the aromatic ring with carbon atoms C(19)
to C(20) is below the mean plane and the other aromatic ring is
Variable temperature 1H-NMR experiments were performed coplanar to the mean plane formed by the three nitrogens and
for complexes 2c and 3b–3d. Thus, upon cooling to 0, −5, the oxygen. For 4b, one aromatic ring is above and the other is
−20, and −40◦C for 2c, 3b, 3c, and 3d, respectively, the broad below the mean plane formed by N(11), N(14), N(17), O(1), and

´
A. CORTES-LOZADA ET AL.
1152
O(3) (Table 4). For all complexes, the Sn(2)-N(11) and Sn(2)-
N(17) (imine nitrogen) bond lengths are slightly shorter than the
Sn(2)-N(14) (amine-nitrogen) bond length. Furthermore, these
bond lengths are slightly longer than those found for other com-
plexes that contains N3O2 as donor atoms.[15–22] It can be seen
from Table 4 that the Sn(2)-N(14) bond length of 4b is the
shortest in this molecule, and this property could be attributed
to the electronic effect of the nitro substituent. A comparison of
the Sn(2)-N(14), Sn(2)-N(11) and Sn(2)-N(17) bond lengths of
2a and 2d clearly shows that the bond lengths for 2d are slightly
shorter than those of 2a, which indicates that the phenyl group
bonded to the tin atom increases the Lewis acidity of the com-
plex. Additionally, the Sn(2)-O(1) and Sn(2)-O(3) bond lengths
in 4b are slightly longer than the corresponding bonds of 2a and
2d. Analysis of the N(11)-C(12)-C(13)-N(14) and N(14)-C(15)-
C(16)-N(17) torsion angles of 2a, 2d, and 4b reveals that the
five-membered rings formed by the Sn-N-C-C-N atoms adopt a
boat conformation.
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This contribution reveals that the Schiff-base ligands
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diorganotin oxides to yield heptacoordinated complexes, which
exhibit a fluxional process that involves the rupture of N-Sn
bonds and the inversion of the central nitrogen. The electronic
effects of the substituents attached to the aromatic ring of the
Schiff-base ligands account for the ꢀG= values obtained from
12. Chakraborty, J.; Ray, A.; Pilet, G.; Chastanet, G.; Luneau, D.; Ziessel, R.F.;
Charbonnie`re, L.J.; Carrella, L.; Rentschler, E.; El-Fallah, M.S.; Mitra, S.
Synthesis, characterization, magnetism and photoluminescense of a ho-
modinuclear Ln(III)-schiff base family. Dalton Trans. 2009, 10263–10272.
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H.I.; Zamudio-Rivera, L.S. Structural relationship between a host included
chain of spirocyclic water hexamers and bulk water—the role of water clus-
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H.; Beltra´n, H.I.; Zamudio-Rivera, L.S.; Structure and conformational mo-
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1
the variable temperature H NMR, and the fluxional process
requires the most energy when the substituent is a nitro group,
followed by hydrogen, and then methoxy (NO2> H > MeO).
X-ray crystallography of the complexes shows a shortening of
the Sn-N bond distances when more electronegative substituents
are on the ligands.
SUPPLEMENTARY MATERIALS
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data Centre
(CCDC reference numbers; 832861 2a, 832862 2d, 832863 4b).
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acylhydrazones, including the x-ray crystal structure of SnEt2(dapt) [H2dapt
= 2,6-diacetylpyridine bis(2-thenoylhydrazone)]. J. Chem. Soc., Dalton
Trans. 1989, 289–293.
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