Synthesis and characterization of tin complexes [Sn(L)Hal4] (L = N-alkyl-(pyridin-2-yl)aldimine; Hal = Cl, Br): A structural study

Article abstract of DOI:10.1016/j.poly.2012.11.022

The reactions of the ligands N-methyl-(pyridin-2-yl)aldimine (a), N-ethyl-(pyridin-2-yl)aldimine (b), and N-benzyl-(pyridin-2-yl)aldimine (c) with SnCl₄ and SnBr₄ led to the formation of compounds [Sn{(C₅H₄N)HCNMe}Cl₄] (1), [Sn{(C ₅H₄N)HCNMe}Br₄] (2), [Sn{(C₅H ₄N)HCNEt}Cl₄] (3), [Sn{(C₅H₄N)HCNEt} Br₄] (4), [Sn{(C₅H₄N)HCNBn}Cl₄] (5), and [Sn{(C₅H₄N)HCNBn}Br₄] (6) in good yields. All the compounds were characterized by ¹H, ¹³C{ ¹H}, and ¹¹⁹Sn{¹H} NMR, vibrational IR-Raman spectroscopy, elemental analyses, and X-ray diffraction analysis. The structural studies confirmed the formation of the respective six-coordinate tin complexes as a result of the chelation of the iminic and pyridinic nitrogen atoms of the ligands towards the tin atom; the Sn-N distances were shortened as the Lewis acid character at the tin atom was increased. In all the molecular structures the tin atom displayed a distorted octahedral local geometry.

Full text of DOI:10.1016/j.poly.2012.11.022

Polyhedron 50 (2013) 418–424
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and characterization of tin complexes [Sn(L)Hal4] (L = N-alkyl-
(pyridin-2-yl)aldimine; Hal = Cl, Br): A structural study
Edmundo Guzmán-Percástegui, Carlos A. Reyes-Mata, Diego Martínez-Otero, Noemí Andrade-López,
⇑
José G. Alvarado-Rodríguez
Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Hidalgo, km. 4.5 Carretera Pachuca-Tulancingo, Col. Carboneras, C.P. 42184, Mineral de la Reforma,
Hidalgo, Mexico
a r t i c l e i n f o
a b s t r a c t
Article history:
The reactions of the ligands N-methyl-(pyridin-2-yl)aldimine (a), N-ethyl-(pyridin-2-yl)aldimine (b), and
N-benzyl-(pyridin-2-yl)aldimine (c) with SnCl4 and SnBr4 led to the formation of compounds [Sn{(C5H4N)
HC@NMe}Cl4] (1), [Sn{(C5H4N)HC@NMe}Br4] (2), [Sn{(C5H4N)HC@NEt}Cl4] (3), [Sn{(C5H4N)HC@NEt}Br4]
(4), [Sn{(C5H4N)HC@NBn}Cl4] (5), and [Sn{(C5H4N)HC@NBn}Br4] (6) in good yields. All the compounds
were characterized by 1H, 13C{1H}, and 119Sn{1H} NMR, vibrational IR-Raman spectroscopy, elemental
analyses, and X-ray diffraction analysis. The structural studies confirmed the formation of the respective
six-coordinate tin complexes as a result of the chelation of the iminic and pyridinic nitrogen atoms of the
ligands towards the tin atom; the Sn–N distances were shortened as the Lewis acid character at the tin
atom was increased. In all the molecular structures the tin atom displayed a distorted octahedral local
geometry.
Received 14 August 2012
Accepted 19 November 2012
Available online 29 November 2012
Keywords:
Tin compounds
X-ray crystal structures
Schiff base
Intermolecular interactions
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
data and antitumor activity have been carried out; consequently,
it has been concluded that biologically active complexes have
Polydentate Schiff ligands play an important role in coordina-
tion chemistry owing to their ease of synthesis by means of con-
densation reactions under mild conditions and their outstanding
ability to bind a vast variety of metallic atoms [1]. Within the wide
diversity of organic compounds which can be prepared by this
route, the coordination of N-substituted-aldimine-based ligands
via the pyridinic and the iminic nitrogen atoms provides a valuable
and versatile tool in organometallic [2] and supramolecular syn-
thesis [3]. As a result, this has led to the formation of several metal
complexes displaying remarkable applications; for example, some
complexes containing transition metals such as Ni [4,5], Pd [6,7],
Mo [8], and Cu [9] exhibit interesting catalytic activity in diverse
polymerization reactions. In this sense, in the last decades new
developments in the chemistry of these ligands have been ex-
tended to main group elements; what is more, an increasing atten-
tion has been devoted to the synthesis of organotin halide
octahedral complexes derived from the coordination of polyden-
tate N-donor Schiff bases and organotin(IV) moieties in view of
their antibacterial [10,11], antifungal [12], and in vitro antitumor
activity [13,14].
Sn–N bond lengths near 2.4 Å [16]. This fact suggests that dissoci-
ation of ligands is an important step in their mechanism of action.
In this regard, it has been usually assumed that the organic frag-
ment would facilitate the transport of the complex across cell
membranes, while the antitumor activity would be accomplished
via a dissociation mechanism of the organotin(IV) moieties [17].
These achievements have encouraged new research work in the
design, synthesis and structural study of novel octahedral organo-
tin and tin halide complexes systematically substituted. Since the
biochemical activity of organotin(IV) Schiff-base complexes seems
to be greatly influenced by structural features and because the
mechanism of the activity requires gaining a greater insight in
the understanding of structure, herein we describe the synthesis,
characterization, structural study and coordination behavior of
six tin(IV) halide complexes of Schiff bases derived from N-substi-
tuted-(pyridin-2-yl)aldimine ligands with SnCl4 and SnBr4.
2. Experimental
2.1. Materials and physical methods
As the activity of many of these compounds has been associated
to their structural features [15], attempts to correlate structural
All the starting reagents were of analytical grade and used with-
out further purification. Solvents were dried by standard methods
and distilled prior to use. 2-Pyridinecarboxaldehyde, methylamine,
ethylamine, benzylamine, SnCl4 and SnBr4 were purchased from
⇑
Corresponding author.
E-mail address: jgar@uaeh.edu.mx (J.G. Alvarado-Rodríguez).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.11.022

E. Guzmán-Percástegui et al. / Polyhedron 50 (2013) 418–424
419
Aldrich and used as supplied. Ligands N-methyl-(pyridin-2-
7.10. Found: C, 24.28; H, 2.38; N, 6.74%. IR: 1653
336
1H, H5, JH5—119=117 = 26.89, JH5–H4 = 5.42, JH5–H3 = 1.82, JH5–
m
(C@N(imine)),
yl)aldimine (a), N-ethyl-(pyridin-2-yl)aldimine (b) and N-benzyl-
pyridin-2-yl)aldimine (c) ligands were prepared as reported [18].
Melting points of the compounds were determined on a Mel-Temp
II instrument and are reported without correction. Elemental anal-
yses were recorded on a Perkin Elmer Series II CHNS/O Analyzer
2400. The IR spectra (4000–400 cmꢀ1) were recorded on a Per-
kin-Elmer System 2000 FT-IR spectrometer as either KBr pellets
m
(Sn–Cl). 1H NMR [400 MHz, (CD3)2CO, 20 °C]: d = 9.45 (ddd,
3
4
5
3
Sn
4
3
H2 = 1.00 Hz), 9.33 (td, 1H, H6, JH6—119=117 = 111.61, JH6–H7 = 1.42,
Sn
3
4
4JH6–H2 = 0.91 Hz), 8.69 (td, 1H, H3, JH3–H4,H2 = 7.70, JH3–H5 = 1.60,
3
4
5JH3—119=117 = 7.70 Hz), 8.53 (ddd, 1H, H2, JH2–H3 = 7.70, JH2–
H4 = 1.31, JH2–H5 = 0.91, JH2—119=117 = 7.43 Hz), 8.33 (ddd, 1H, H4,
Sn
5
4
Sn
3
3
4
4
JH4–H3 = 7.82, JH4–H5 = 5.40, JH4–H2 = 1.31, JH4—119=117 = 8.12 Hz),
Sn
or CsI films. The Raman spectra in solid state (4000–100 cmꢀ1
)
4.30 (qd, 2H, H7, 3JH7—119=117 = 32.62, 3JH7–H8 = 7.20, 4JH7–
Sn
were recorded on a Perkin-Elmer Spectrum GX NIR FT-RAMAN
spectrometer with 10–280 mW laser power and 4 cmꢀ1 resolution.
NMR studies were carried out on a Varian VNMRS 400 instrument.
Standard references were used: TMS and SnMe4. All the spectra
were acquired at room temperature (20 °C).
H6 = 1.42 Hz), 1.59 (t, 3H, H8, 3JH8–H7 = 7.20 Hz). 13C{1H}
[100 MHz, (CD3)2CO, 20 °C]: d = 158.4 (C6), 146.3 (C5), 145.3 (C3),
140.2 (C1), 132.3 (C2), 131.8 (C4), 51.2 (C7), 15.5 (C8). 119Sn{1H}
NMR [149 MHz, (CD3)2CO, 20 °C]: d = ꢀ559.0.
2.2.4. [Sn{(C5H4N)HC@NCH2CH3}Br4] (4)
2.2. General synthesis of tetrahalogenate tin(IV) complexes [Sn(L)Hal4]
b (300 mg, 2.24 mmol), dichloromethane (25 mL), SnBr4
(1–6)
(980 mg, 2.24 mmol). Yellow solid. Yield: 77% (992 mg). M.p.:
172 °C (dec.). Anal. Calc. for C8H10Br4N2Sn: C, 16.78; H, 1.76; N,
A ligand L (L = a–c) was dissolved in dichloromethane and mag-
netically stirred for 10 min; then, the tin halide was added at once.
The mixture was stirred overnight and the resulting precipitate
was filtered, washed thoroughly with dichloromethane and recrys-
tallized from a mixture 1:1 of either acetone–hexane or acetoni-
trile–chloroform mixtures for compounds 1–4 and 5–6,
respectively.
4.89. Found: C, 16.95; H, 1.64; N, 4.65%. IR: 1649
209
(Sn–Br). 1H NMR [400 MHz, (CD3)2CO, 20 °C]: d = 9.63 (ddd,
1H, H5, JH5—119=117 = 29.08, JH5–H4 = 5.40, JH5–H3 = 1.42, JH5–
m(C@N(imine)),
m
3
4
5
3
Sn
4
3
H2 = 0.70 Hz), 9.29 (td, 1H, H6, JH6—119=117 = 98.95, JH6–H7 = 1.40,
Sn
3
4
4JH6–H2 = 0.91 Hz), 8.74 (td, 1H, H3, JH3–H4,H2 = 7.70, JH3–H5 = 1.52,
3
4
5JH3—119=117 = 7.62 Hz), 8.58 (ddd, 1H, H2, JH2–H3 = 7.68, JH2–
H4 = 1.38, JH2–H5 = 0.77 Hz), 8.40 (ddd, 1H, H4, JH4–H3 = 7.77, JH4–
Sn
5
3
3
4
4
H5 = 5.40, JH4–H2 = 1.42, JH4—119=117 = 6.70 Hz), 4.39 (qd, 2H, H7,
Sn
4
3
2.2.1. [Sn{(C5H4N)HC@NCH3}Cl4] (1)
3JH7—119=117 = 31.82, JH7–H8 = 7.20, JH7–H6 = 1.42 Hz), 1.71 (t, 3H,
Sn
3
a
(100 mg, 0.83 mmol), dichloromethane (25 mL), SnCl4
H8, JH8–H7 = 7.20 Hz). 13C{1H} [100 MHz, (CD3)2CO, 20 °C]:
2
4
(0.097 mL, 0.83 mmol). Compound 1 was obtained as a very pale
yellow solid. Yield: 77% (243 mg). M.p.: 196 °C (dec.). Anal. Calc.
for C7H8Cl4N2Sn: C, 22.09; H, 2.12; N, 7.36. Found: C, 23.25; H,
d = 157.0 (C6, JC6—119 = 16.8 Hz), 145.3 (C3, JC3—119 = 4.6 Hz),
S
n
S
n
145.2 (C5, 2JC5—119 = 7.7 Hz), 139.0 (C1), 132.1 (C2,
Sn
3JC2—119 = 7.8 Hz), 132.0 (C4, 3JC4—119 = 12.2 Hz), 50.3 (C7,
Sn
Sn
2.28; N, 6.35%. IR: 1658
[400 MHz, (CD3)2CO,
3JH5—119=117 = 28.40,
H2 = 0.80 Hz), 9.32 (dq, 1H, H6, JH6—119=117 = 108.04, JH6–
H7 = 1.70 Hz), 8.70 (ddd, 1H, H3, JH3–H4 = 8.00, JH3–H2 = 7.60, JH3–
m
(C@N(imine)), 334
m
(Sn–Cl). 1H NMR
2JC7—119 = 18.0 Hz), 15.6 (C8). 119Sn{1H} NMR [149 MHz, (CD3)2CO,
Sn
20 °C]:
d = 9.44
(ddd,
1H,
H5,
20 °C]: d = ꢀ1209.7.
3JH5–H4 = 5.60,
4JH5–H3 = 1.52,
5JH5–
Sn
4
3
2.2.5. [Sn{(C5H4N)HC@NCH2(C6H5)}Cl4] (5)
Sn
3
3
4
c
(300 mg, 1.53 mmol), dichloromethane (25 mL), SnCl4
3
5
H5 = 1.54, JH3—119=117 = 7.69 Hz), 8.54 (ddd, 1H, H2, JH2–H3 = 7.51,
(0.178 mL, 1.53 mmol). Compound 5 was obtained as beige solid.
Yield: 89% (621 mg). M.p.: 243 °C. Anal. Calc. for C13H12Cl4N2Sn:
C, 34.18; H, 2.65; N, 6.13. Found: C, 34.10; H, 2.52; N, 5.91%. IR:
Sn
4
5
4
JH2–H4 = 1.11, JH2–H5 = 0.82, JH2—119=117 = 7.74 Hz), 8.34 (ddd, 1H,
Sn
H4,
3JH4–H3 = 7.80,
3JH4–H5 = 5.34,
4JH4–H2 = 1.33,
4
4JH4—119=117 = 7.97 Hz), 3.93 (d, 3H, H7, JH7—119=117 = 32.10, JH7–
1650
m
(C@N(imine)), 329
m
(Sn–Cl). 1H NMR [400 MHz, (CD3)2CO,
3
Sn
Sn
H6 = 1.72 Hz). 13C{1H} [100 MHz, (CD3)2CO, 20 °C]: d = 159.4 (C6,
20 °C]: d = 9.52 (ddd, 1H, H5, JH5—119=117 = 28.15, JH5–H4 = 5.40,
3
3
Sn
2JC6—119 = 23.8 Hz), 146.5 (C5, JC5—119 = 20.3 Hz), 145.3 (C3,
4JH5–H3 = 1.42, 5JH5–H2 = 0.71 Hz),
9.03
(td,
1H,
H6,
2
Sn
Sn
4
4
4JC3—119 = 5.3 Hz), 140.1 (C1), 132.3 (C2, JC2—119 = 14.1 Hz),
3JH6—119=117 = 107.67, JH6–H7 = 1.80, JH6–H2 = 0.80 Hz), 8.70 (td, 1H,
3
Sn
Sn
Sn
3
4
3
2
5
131.7 (C4, JC4—119 = 12.2 Hz), 43.3 (C7, JC7—119 = 19.0 Hz).
H3, JH3–H4,H2 = 7.70, JH3–H5 = 1.40, JH3—119=117 = 7.72 Hz), 8.55
Sn
Sn
Sn
119Sn{1H} [149 MHz, (CD3)2CO, 20 °C]: d = ꢀ555.9.
(ddd, 1H, H2, JH2–H3 = 7.60, JH2–H4 = 1.30, JH2–H5 = 0.81 Hz), 8.37
3
4
5
(ddd, 1H, H4, 3JH4–H3 = 7.70, 3JH4–H5 = 5.38, 4JH4–H2 = 1.39,
3
4
2.2.2. [Sn{(C5H4N)HC@NCH3}Br4] (2)
4JH4—119=117 = 6.81 Hz), 7.59 (dd, 2H, H9, JH9–H10 = 7.70, JH9–
Sn
a
(100 mg, 0.83 mmol), dichloromethane (25 mL), SnBr4
H11 = 1.60 Hz), 7.54–7.42 (m, 3H, H10–H11), 5.46 (d, 2H, H7,
(365 mg, 0.83 mmol). Pale yellow solid. Yield: 59% (275 mg).
M.p.: 198 °C (dec.). Anal. Calc. for C7H8Br4N2Sn: C, 15.05; H, 1.44;
N, 5.02. Found: C, 17.01; H, 1.71; N, 4.59%. IR: 1655
201
(Sn–Br). 1H NMR [400 MHz, (CD3)2CO, 20 °C]: d = 9.57 (dd,
1H, H5, JH5—119=117 = 29.26, JH5–H4 = 5.40, JH5–H3 = 1.50 Hz), 9.22
3JH7—119=117 = 21.09, 4JH7–H6 = 1.80 Hz). 13C{1H} [100 MHz, (CD3)2CO,
Sn
20 °C]:
d = 159.0
(C6,
2JC6—119 = 24.4 Hz),
146.4
(C5,
Sn
4
m
(C@N(imine)),
2JC5—119 = 20.6 Hz), 145.2 (C3, JC3—119 = 5.5 Hz), 140.2 (C1),
Sn
Sn
m
134.2 (C8), 132.4 (C2, 3JC2—119 = 14.4 Hz), 132.2 (C4,
Sn
3
4
3
3JC4—119 = 12.5 Hz), 131.2 (C9), 130.0 (C10), 129.8 (C11), 57.9
Sn
Sn
3
(m, 1H, H6, JH6—119=117 = 93.52 Hz), 8.69 (td, 1H, H3, JH3–
(C7). 119Sn{1H} NMR [149 MHz, (CD3)2CO, 20 °C]: d = ꢀ560.4.
3
Sn
4
5
H4,H2 = 7.77, JH3–H5 = 1.54, JH3—119=117 = 7.72 Hz), 8.54 (d, 1H, H2,
Sn
3JH2–H3 = 7.71 Hz), 8.36 (ddd, 1H, H4, JH4–H3 = 7.81, JH4–H5 = 5.42,
2.2.6. [Sn{(C5H4N)HC@NCH2(C6H5)}Br4] (6)
3
3
4
4
3
JH4–H2 = 1.21 Hz), 3.92 (d, 3H, H7, JH7—119=117 = 32.60, JH7–
c (300 mg, 1.53 mmol), dichloromethane (25 mL), SnBr4 (670 mg,
1.53 mmol). Beige solid. Yield: 70% (680 mg). M.p.: 239 °C. Anal. Calc.
for C13H12Br4N2Sn: C, 24.61; H, 1.91; N, 4.41. Found: C, 25.16; H,
Sn
H6 = 1.72 Hz). 13C{1H} (100 MHz, (CD3)2CO, 20 °C): d = 158.1 (C6,
2JC6—119 = 17.2 Hz), 145.4 (C5), 145.3 (C3), 139.0 (C1), 132.1 (C2,
Sn
3JC2—119 = 12.7 Hz), 131.9 (C4, JC4—119 = 7.8 Hz), 42.6 (C7).
1.90; N, 4.07%. IR: 1649
m
(C@N(imine)), 206
(Sn–Br). 1H NMR
d = 9.65 (ddd, 1H, H5,
m
3
Sn
Sn
119Sn{1H} NMR [149 MHz, (CD3)2CO, 20 °C]: d = ꢀ1206.1.
[400 MHz,
(CD3)2CO,
20 °C]:
3
4
5
3JH5—119=117 = 29.62, JH5–H4 = 5.40, JH5–H3 = 1.42, JH5–H2 = 0.71 Hz),
Sn
2.2.3. [Sn{(C5H4N)HC@NCH2CH3}Cl4] (3)
8.85 (td, 1H, H6, 3JH6—119=117 = 93.22, 4JH6–H7 = 1.80, 4JH6–H2 = 0.80 Hz),
Sn
3
4
5
b
(100 mg, 0.75 mmol), dichloromethane (25 mL), SnCl4
8.68 (td, 1H, H3, JH3–H4,H2 = 7.70, JH3–H5 = 1.40, JH3—119=117
=
Sn
(0.087 mL, 0.75 mmol). Yellow solid. Yield: 74% (219 mg). M.p.:
170 °C (dec.). Anal. Calc. for C8H10Cl4N2Sn: C, 24.34; H, 2.55; N,
7.80 Hz), 8.54 (ddd, 1H, H2, 3JH2–H3 = 7.60, 4JH2–H4 = 1.40,
5JH2–H5 = 0.70 Hz), 8.39 (ddd, 1H, H4, JH4–H3 = 7.70, JH4–H5 = 5.41,
3
3

420
E. Guzmán-Percástegui et al. / Polyhedron 50 (2013) 418–424
Table 1
Collection data and refinement parameters for compounds 1–6.
1
2
3
4
5
6
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
C7H8Cl4N2Sn
380.64
293(2)
orthorhombic
Pna21
14.3901(3)
9.17622(18)
9.34778(18)
90
C7H8Br4N2Sn
558.48
295(2)
orthorhombic
Pna21
14.7587(6)
9.3690(4)
9.7874(4)
90
C8H10Cl4N2Sn
394.67
295(2)
monoclinic
P21/n
8.6653(3)
15.9215(5)
9.7194(3)
90.330(3)
1340.91(8)
4
C8H10Br4N2Sn
572.51
295(2)
monoclinic
P21/n
8.8202(2)
16.4530(3)
10.0408(2)
90.7023(9)
1457.00(5)
4
C13H12Cl4N2Sn
456.74
293(2)
C13H12Br4N2Sn
634.58
293(2)
monoclinic
P21/n
9.3178(6)
17.9554(11)
10.7817(8)
91.976(6)
1802.8(2)
4
triclinic
ꢀ
P1
7.1091(2)
9.1933(3)
13.1180(4)
87.881(2)
837.02(4)
2
b (Å)
c (Å)
b (°)
V (Å3)
1234.34(4)
4
2.899
1353.35(10)
4
13.665
Z
Absorption coefficient (mmꢀ1
F(000)
)
2.673
760
12.697
1048
2.155
444
10.275
1176
728
1016
h range (°)
3.11–26.50
16350
2570
99.9
2570/1/134
1.054
3.01–26.48
10755
2764
99.9
2764/1/133
1.020
3.14–26.05
21285
2645
99.9
2645/0/141
1.080
3.06–26.05
20968
2871
99.9
2871/0/141
1.053
2.93–26.36
17265
3411
99.9
3411/0/181
1.069
2.95–26.37
19270
3689
99.9
3689/0/182
1.024
Reflections collected
Unique reflections
Completeness to h
Data/restraints/parameters
GOF on F2
Final indices [I > 2
R1 and wR2 indices all data
Largest residuals (e Åꢀ3
r
(I)]
0.0183, 0.0456
0.0194, 0.0465
0.238 and ꢀ0.224
0.0289, 0.0621
0.0365, 0.0654
0.377 and ꢀ0.595
0.0192, 0.0395
0.0257, 0.0424
0.269 and ꢀ0.444
0.0244, 0.0505
0.0337, 0.0537
0.374 and ꢀ0.654
0.0295, 0.0683
0.0392, 0.0740
0.744 and ꢀ0.378
0.0381, 0.0713
0.0650, 0.0807
1.503 and ꢀ1.003
)
4
3
4
3
JH4–H2 = 1.39, JH4—119=117 = 6.82 Hz), 7.61 (dd, 2H, H9, JH9–
Sn
4
4
2
H10 = 7.70, JH9–H11 = 1.50 Hz), 7.54–7.45 (m, 3H, H10–H11), 5.51
5
(d, 2H, H7, 3JH7—119=117 = 19.72, 4JH7–H6 = 1.80 Hz). 13C{1H}
1
H
SnHal4
Sn
N
6
2
H
R
[100 MHz, (CD3)2CO, 20 °C]: d = 156.5 (C6, JC6—119 = 16.9 Hz),
Sn
Hal
Hal
N
N
CH2Cl2
R
144.4 (C5), 144.3 (C3), 138.1 (C1), 133.0 (C8), 131.7 (C2,
Sn
N
3JC2—119 = 7.7 Hz), 131.3 (C4, JC4—119 = 12.7 Hz), 130.4 (C9), 129.2
3
Sn
Sn
Hal
(C10), 129.1 (C11), 56.1 (C7). 119Sn{1H} NMR [149 MHz, (CD3)2CO,
Hal
20 °C]: d = ꢀ1201.3.
a - c
1 6
-
119Sn{1H}
(ppm)
2.3. X-ray crystallography and structure solution
R
R
Hal
Compounds 1–4 were successfully recrystallized from a 1:1
acetone–hexane mixture whereas 5 and 6 were crystallized from
a 1:1 acetonitrile–chloroform solution. Single crystals of suitable
quality were glued on a glass fiber. X-ray diffraction data of 1–6
compounds were collected at room temperature on an Oxford Dif-
fraction Gemini CCD diffractometer with graphite-monochromated
a
b
c
Me
Et
1
2
3
4
5
6
Me
Me
Et
Cl
Br
Cl
Br
Cl
Br
−555.9
−1206.1
−559.0
Bn
Et
−1209.7
−560.4
Mo Ka radiation (k = 0.71073 Å). Data were integrated, scaled,
Bn
Bn
sorted, and averaged using the CrysAlis software package [19].
An analytical numeric absorption correction using a multifaceted
crystal model was applied by using the CrysAlis software. The
structures were solved by direct methods, using SHELXTL NT Version
5.10 and refined by full-matrix least squares against F2 [20]. The
displacement parameters of non-hydrogen atoms were anisotrop-
ically refined. The positions of the hydrogen atoms were kept fixed
with a common isotropic displacement parameter. The collection
data details are collected in Table 1.
−1201.3
Scheme 1. Synthesis of compounds 1–6.
Table 2
Selected vibration frequencies (cmꢀ1) for ligands a–c and compounds 1–6.
a
b
c
1
2
3
4
5
6
R
Hal
Me
–
Et
–
Bn
–
Me
Cl
Me
Br
Et
Cl
Et
Br
Bn
Cl
Bn
Br
3. Results and discussion
C@N(iminic) 1634 1650 1647 1658 1655 1653 1649 1650 1649
Sn–Hal 334 201 336 209 329 206
–
–
–
3.1. Synthesis
The reaction of the aldiminic ligands a–c dissolved in dichloro-
methane with the corresponding tin tetrahalide compound at
room temperature gave the corresponding coordination com-
pounds 1–6 with yields ranging from 59% to 89%, Scheme 1; the
numbering scheme for the NMR assignment is also showed. All
compounds are soluble in acetone, insoluble in low-polar solvents
as chloroform and dichloromethane; they experience dissociation
in solvents with high dielectric constant as dimethylsulfoxide
and methanol.
3.2. Vibrational spectroscopy
The analyses of the FT-IR spectra revealed the formation
of the complexes owing to the shift of the C@N(iminic) stretching
band of free ligands upon reaction with tin(IV) halides,
indicating the participation of the aldiminic nitrogen atoms in
the coordination to tin (Table 2). These shifts are toward higher

E. Guzmán-Percástegui et al. / Polyhedron 50 (2013) 418–424
421
frequencies; this is similar to that observed for other tin-com-
plexes containing the imino functional group [21]. In addition, this
band is shifted to higher frequencies, seemingly due to an electron
density transfer from the SnHal4 moiety to the ligand, strengthen-
ing the C@N bond; this effect may occur for these ligands when
they coordinate to main-group elements [22,23].
ing from the vibration Sn–Hal (see, for example, the Supplemen-
tary Material, Figure 1S). These values are similar to those found
for analogous tin halide complexes [11].
3.3. NMR spectra
Additionally, the analysis of the Raman spectra in the 350–
NMR spectra of all the compounds were recorded in (CD3)2CO
solutions at 20 °C. The assignment of the signals was carried out
200 cmꢀ1 region revealed the presence of a very strong band aris-
Fig. 1. Molecular structure of compounds 1–6 (40% probability ellipsoids).

422
E. Guzmán-Percástegui et al. / Polyhedron 50 (2013) 418–424
by homonuclear and heteronuclear correlation of two dimensional
experiments (COSY, HSQC and HMBC). The general numbering for
compounds 1–6 is showed in Scheme 1.
the same along the series of the 1–6 compounds, when the chloro
ligands were replaced by the bromo ligands, the 119Sn nuclei were
considerably shifted to lower frequencies resulting in chemical
shifts around ꢀ1205 ppm. This trend of chemical shift can be re-
lated to the effect of the heavy atom induced on the tin nucleus
by the bromo ligands [27]. In addition, this shift to lower frequen-
cies may be due to the less electron-withdrawing inductive effect
of the bromo compared to chloro as well as to the possibility of
All the proton signals were found shifted to higher frequencies
when compared to the signals in the corresponding free ligands
(see, for example, the Supplementary Material, Figure 2S). In solu-
tion the pyridinic rings display an ABCD pattern for all six com-
plexes (see the Supplementary Material, Figure 3S). The chemical
shifts of the 2, 3, and 4 protons do not present considerable differ-
ences among the six complexes. The H5 signal was observed as the
most shifted one around 9.65–9.44 ppm. The aldiminic proton H6
displays a signal in the 9.34–8.85 ppm range and was observed
that this proton in compounds 1, 3, and 5 is found at higher fre-
quencies compared to those protons in compounds 2, 4, and 6; this
could be attributed to the enhancement of Lewis acidity on the tin
atom when more electron withdrawing ligands such as chloro
compared to bromo, are attached to it. In addition, due to the nat-
ure of the phenyl group and its diamagnetic ring-current, the H6
proton experiences an even more noticeable upfield shifting in
the 5 and 6 compounds. H6 protons also exhibit 3J(119/117Sn–1H)
satellite couplings with the tin nucleus, evidencing that the ligand
L is bonded to the tin atom in acetone solution. Values for the
3J(119/117Sn–1H) range from 91 to 111 Hz; similar values have been
also observed for other (pyridin-2-yl)aldimine tin complexes [24].
The magnitude of 3J(119/117Sn–1H) might be used to estimate the
strength of N–Sn coordination since the larger constants are found
in the chloro compounds 1, 3, and 5. Finally, the H7 protons also
display signals accompanied by satellite couplings with tin nucleus
(see the Supplementary Material, Figure 4S).
additional
p back-bonding contribution to the Sn–Br bonds which
would shield the nucleus in a greater extent [28].
3.4. X-ray diffraction
The crystal structures of the compounds were determined by
single crystal X-ray diffraction analyses. The molecular drawings
of 1–6 are depicted in Fig. 1 and selected bond lengths, angles
and some relevant structural features are given in Table 3. The
methyl derivatives 1 and 2 crystallized in the orthorhombic system
and same space group, Pna21; the ethyl derivatives 3 and 4 crystal-
lized in the monoclinic system with the same space group P21/n. In
these pairs of compounds the enlargement of cell parameters in 2
and 4 is due to the presence of four larger bromo ligands in com-
parison to the tetrachloro compounds 1 and 3. Benzyl compounds
5 and 6 crystallized in the triclinic and monoclinic systems, respec-
tively; the difference in crystal systems can be attributed to the
conformational freedom of the benzyl groups where the C6–N2–
C7–C8 torsion angles are 75.1(4)° and 11.9(8)° for 5 and 6,
respectively.
All the tin complexes are isostructural and some common as-
pects are observed from the analysis of the crystallographic data.
In all cases an hexacoordination based upon a [SnN2Hal4] core is
observed (Hal = Cl, Br), with similar N–Sn–N bite angles regardless
of the different R groups and halogen ligands. The Sn–N(iminic) and
Sn–N(pyridinic) distances are in the range of 2.220–2.257 and 2.236–
2.274 Å respectively, and they are in general shorter when the exo-
cyclic pendant groups are chloro ligands, suggesting that the coor-
dination of the bidentate Schiff ligand is stronger in 1, 3, and 5.
These averaged distances are also shorter than those reported for
similar compounds derived from the coordination of equivalent
N-substituted-(pyridin-2-yl)aldimine ligands towards nBuSnCl3
and Me2SnCl2 [16,21,24]. From the above, it is observed that the
Sn–N distances are shortened as the Lewis acid character at the
tin atom increases. In addition, it can be noted that the Sn–N dis-
tances are significantly the same in the N-methyl compounds 1
and 2, despite the nature of the halogen atom; a different situation
is observed in the N-ethyl and N-benzyl compounds, where the
Discrete 13C signals for all the individual carbons are identified
in the 13C{1H} NMR spectra. The signals for the aldiminic carbon C6
appeared in the 159.5–156.5 ppm range, the signals for C5 range
from 146.5 to 144.4 ppm and signals for C1 are near 139 ppm.
The signals for C1, C6, and C5 showed a significant shift to low fre-
quencies in all the complexes compared to the resonances in the
free ligands owing to the electron density transfer effect since
these carbons are directly bound to the nitrogen atoms; C1 under-
goes the larger shift (
the remaining carbons are shifted to higher frequencies.
D
ꢁ 16 ppm) indeed. In contrast, signals for
The 119Sn{1H} NMR spectra of compounds 1–6 show only one
sharp resonance confirming the existence of one tin species. The
119Sn chemical shifts for the chloro compounds 1, 3, and 5 span
from ꢀ555 to ꢀ561 ppm (Scheme 1); these chemical shifts are in
the range of hexacoordinate tin species [25]. Nevertheless, even
though the 119Sn chemical shifts are depending on the coordina-
tion number [26] and, in turn, the coordination number must be
Table 3
Selected bond lengths (Å), angles (°), and geometrical parameters of compounds 1–6.
1
2
3
4
5
6
Sn–N(1)
Sn–N(2)
Sn–Hal(1)
Sn–Hal(2)
Sn–Hal(3)
Sn–Hal(4)
N(2)–C(6)
N(1)–Sn–N(2)
Hal(1)–Sn–Hal(2)
Hal(1)–Sn–Hal(4)
Hal(3)–Sn–Hal(1)
Hal(3)–Sn–Hal(2)
Hal(2)–Sn–Hal(4)
Hal(3)–Sn–Hal(4)
C6–N2–C7–C8
Sum of internal angles around Sna
2.236(2)
2.230(2)
2.3665(9)
2.3954(7)
2.3625(7)
2.4122(7)
1.266(4)
73.92(10)
94.14(4)
91.04(3)
99.00(3)
92.55(3)
171.88(3)
92.81(3)
–
2.253(5)
2.244(5)
2.5283(8)
2.5571(6)
2.5154(7)
2.5679(7)
1.264(8)
73.0(2)
91.10(3)
91.10(3)
98.87(3)
92.66(3)
170.89(3)
93.49(3)
–
2.2548(19)
2.220(2)
2.3765(6)
2.3899(6)
2.3691(6)
2.4171(6)
1.276(3)
74.05(8)
93.03(2)
90.90(2)
99.74(2)
92.33(2)
173.47(2)
92.14(2)
100.3(3)
1585.70
2.274(3)
2.241(3)
2.236(3)
2.226(2)
2.3663(9)
2.3872(9)
2.3626(10)
2.4336(8)
1.268(4)
74.47(9)
92.42(3)
91.42(3)
97.63(4)
95.77(4)
170.72(3)
92.09(4)
75.1(4)
2.261(4)
2.257(4)
2.5406(7)
2.5508(8)
2.5208(7)
2.5650(7)
1.258(6)
73.53(16)
93.55(3)
93.96(2)
99.52(3)
94.93(3)
168.12(3)
92.89(3)
11.9(8)
2.5382(4)
2.5777(5)
2.5247(5)
2.5490(5)
1.265(5)
73.49(13)
91.227(15)
93.585(16)
99.466(10)
92.551(17)
172.499(17)
92.329(17)
97.9(5)
1583.99
1581.82
1584.13
1584.40
1578.15
a
The sum of the internal angles for a central atom in an ideal octahedral arrangement equals to 1620°, see text.

E. Guzmán-Percástegui et al. / Polyhedron 50 (2013) 418–424
423
Fig. 2. Hal---H hydrogen bonding in 1 and 2 along the twofold screw axis (Hal = Cl, Br).
Sn–N distances are longer in the bromo compounds, reflecting the
steric effects of the larger N-substituents as well as the bromo li-
gands. On the other hand, it is interesting to note that the Sn–
Hal distances can be sorted in two sets. The first set contains the
shortest distances formed by the linking of the tin atom with the
halogen ligands located in the plane of the chelate ring; in the
chloro compounds 1, 3, and 5 the distances range from 2.3625(7)
to 2.3765(6) Å and for the bromo compounds 2, 4 and 6 from
2.5154(7) to 2.5406(7) Å. The second set is formed by the larger
Sn–Hal bond distances perpendicular to that plane ranging from
2.3872(9) to 2.4336(8) and 2.5490(5) to 2.5777(5) Å for the chloro
and bromo compounds, respectively. This effect is also observed
within the series of a small number of examples of tin(IV) tetra-
chloro and tetrabromo compounds derived from the coordination
of N,N0 bidentate ligands where the Hal–Sn distances perpendicular
to the ligand plane are larger than the co-planar ones [29–31]. In
this respect, the coordination geometry at tin atom is described
as distorted octahedral. The greatest deviations from the ideal an-
gles in an octahedral geometry are those for the N(2)–Sn–N(1),
N(1)–Sn–Hal(3) and N(2)–Sn–Hal(1) which range between 73–
75°, 165–169°, and 165–168° respectively; these data reflect the
restricted bite angle of the ligand. Moreover, by means of the anal-
ysis of the sum of internal angles around tin, the distortion from
the ideal octahedral geometry can be estimated, where a value of
1620° is calculated for an ideal octahedral arrangement [32]. The
data are listed in Table 3. Thus, in 6 the tin atom displays the most
distorted geometry from the ideal octahedral arrangement, where
the sum of the angles around Sn is 1578.15° and can be attributed
to the larger steric effect of the bromo ligands and the phenyl
group attached to the iminic nitrogen atom; the other compounds
exhibit similar sum of internal angles data.
Fig. 3. Dimeric intermolecular associations via p---H interactions in 5.
Likewise, the molecules in the structure of 5, besides of the
Cl4---H non-covalent interactions with the iminic H6 proton
[Cl4---H6 (2.796 Å)] displayed, form a centrosymmetric dimeric
association via H---aromatic rings interactions (Fig. 3).
4. Conclusions
Six new tetrahalide tin(IV) complexes have been synthesized
from the reaction of the Schiff bases N-R-(pyridin-2-yl)aldimine
(R = Me, Et, Bn) and SnHal4 (Hal = Cl, Br). On the basis of the spec-
tral and structural evidence the ligands are coordinated to the tin
tetrahalides in a bidentate mode via the pyridinic and the iminic
nitrogen atoms. As a result, the tin atom displays a distorted octa-
hedral geometry in all the complexes which are isomorphic indeed.
The different organic groups attached to the aldiminic nitrogen do
not seem to impact the coordination behavior as the different hal-
ogen substituents around the tin atom do. This is reflected in how
the structural parameters, such as the bond lengths, are affected in
a different way in chloro and bromo derivatives suggesting that the
binding effect is stronger when chloro substituents are present gi-
ven that the Lewis acid character on tin is enhanced.
The hexacoordinate [SnN2Hal4] core in all compounds hinders
any possible intermolecular interaction where the large tin atom
might be involved; a different situation has been observed in the
analogous compounds with smaller coordination numbers like
[Zn{a}Cl2]2 [33], [Cu{c}Cl2]2 [34], and [Hg{c}Cl2]2ꢂHgCl2 [35], where
the coordination of the a and c ligands to Zn(II), Cu(II), and Hg(II)
leads to
l-dichloro dimeric structures. Nevertheless, it is worth
noting that some interesting features remain in structures 1–6
since they display a series of non-covalent interactions Hal---H
as well as H---aromatic interactions offset-stacked parallel-dis-
placed and face-tilted T-shaped [36], exhibiting a variety of motifs
and chains in the crystalline structure. For example, the molecules
in the isostructural compounds 1 and 2 generate a chain motif
through Hal---H non-covalent intermolecular interactions ranging
from 2.797 to 2.917 Å with the iminic H6 and one of the pyridinic
protons; the motifs are related by a twofold screw axis along the
chain in the c direction (Fig. 2). Besides the interactions above
mentioned, the structures also showed relevant Cl3---H7 intermo-
lecular contacts related by a glide plane, generating a different
chain linked via the methyl groups.
Acknowledgments
E.G.P. fully acknowledges CONACYT for his fellowship. This re-
search was supported by CONACyT (Project 83157).
Appendix A. Supplementary data
CCDC 893891, 893892, 893893, 893894, 893895, and 893896
contain the supplementary crystallographic data for 1, 2, 3, 4, 5,

424
E. Guzmán-Percástegui et al. / Polyhedron 50 (2013) 418–424
[15] Z. Rappoport, The Chemistry of Organic Germanium, Tin and Lead Compounds,
vol. 2, John Wiley & Sons, Ltd., England, 2002.
[16] S.G. Teoh, S.B. Teo, L.K. Lee, H.K. Fun, J. Coord. Chem. 33 (1994) 69.
[17] R.P. Irwin, Organometallic Chemistry Research Perspectives, Nova Science
Publishers, New York, 2007.
[18] P. Bamfield, R. Price, R.G.J. Miller, J. Chem. Soc., A (1969) 1447.
[19] Oxford Diffraction, CrysAlis Software System, Version 1.171.33.31, Oxford
Diffraction Ltd., Abingdon, UK, 2009.
[20] SHELXTL, Version 5.10, Bruker AXS, Inc., Madison, WI, USA, 1998.
[21] S.G. Teoh, S.B. Teo, L.K. Lee, Y.L. Chong, E.R.T. Tiekink, Polyhedron 14 (1995)
2275.
and 6, respectively. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: depos-
it@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/
10.1016/j.poly.2012.11.022.
[22] P.H.M. Budzelaar, Eur. J. Inorg. Chem. (2012) 530.
[23] J. Scott, S. Gambarotta, I. Korobkov, Q. Knijnenburg, B. de Bruin, P.H.M.
Budzelaar, J. Am. Chem. Soc. 127 (2005) 17204.
[24] G. Matsubayashi, T. Tanaka, S. Nishigaki, K. Nakatsu, J. Chem. Soc., Dalton
Trans. (1979) 501.
[25] J. Holecek, M. Nadvornik, K. Handlir, J. Organomet. Chem. 241 (1983) 177.
[26] J.B. Lamber, The Multinuclear Approach to NMR Spectroscopy, Kluwer
Academic Publishers, Scotland, 1982.
[27] J. Mason, Multinuclear NMR, Plenum, New York, 1987.
[28] C. Pettinari, F. Marchetti, R. Pettinari, D. Martini, A. Drozdov, S. Troyanov, Inorg.
Chim. Acta 325 (2001) 103.
References
[1] R.W. Layer, Chem. Rev. 63 (1962) 489.
[2] N.E. Borisova, M.D. Reshetova, Y.A. Ustynyuk, Chem. Rev. 107 (2007) 46.
[3] L. Fabbrizzi, A. Poggi, Transition Metals in Supramolecular Chemistry, Kluwer
Academic Publishers, The Netherlands, 1994.
[4] B.K. Bahuleyan, J.H. Kim, H.S. Seo, J.M. Oh, I.Y. Ahn, C.S. Ha, D.W. Park, I. Kim,
Catal. Lett. 126 (2008) 371.
[5] S. Song, T. Xiao, L. Wang, C. Redshawb, F. Wang, W.H. Sun, J. Organomet. Chem.
699 (2012) 18.
[6] R. Chen, J. Bacsa, S.F. Mapolie, Inorg. Chem. Commun. (2002) 724.
[7] H. Zhang, J.E. Enman, M.L. Conrad, M.J. Manning, C.S. Turner, S.L. Wheaton, C.M.
Vogels, S.A. Westcott, Transition Met. Chem. 31 (2006) 13.
[8] A.C. Gomes, S.M. Bruno, S. Gago, R.P. Lopes, D.A. Machado, A.P. Carminatti, A.A.
Valente, M. Pillinger, I.S. Gonçalves, J. Organomet. Chem. 696 (2011) 3543.
[9] G.A. Ardizzoia, S. Brenna, F. Castelli, S. Galli, Inorg. Chim. Acta 362 (2009) 3507.
[10] L.S. Zamudio-Rivera, R. George-Tellez, G. López-Mendoza, A. Morales-Pacheco,
E. Flores, H. Höpfl, V. Barba, F.J. Fernández, N. Cabirol, H.I. Beltrán, Inorg. Chem.
44 (2005) 5370.
[29] N.J. Hill, G. Reeske, J.A. Moore, A.H. Cowley, Dalton Trans. (2006) 4838.
[30] V.N. Zakharov, A.V. Yatsenko, A.L. Kamyshnyi, L.A. Aslanov, Koord. Khim.
(Russ.) (Coord. Chem.) 17 (1991) 789.
[31] B.Z. Momeni, F. Rominger, S.S. Hosseini, Acta Crystallogr., Sect. E 65 (2009)
690.
[32] D.G. Vargas-Pineda, T. Guardado, F. Cervantes-Lee, A.J. Metta-Magana, K.H.
Pannell, Inorg. Chem. 49 (2010) 960.
[33] M. Schulz, M. Klopfleisch, H. Görls, M. Kahnes, M. Westerhausen, Inorg. Chim.
Acta 362 (2009) 4706.
[11] T. Sedaghat, M. Naseh, H.R. Khavasi, H. Motamedi, Polyhedron 33 (2012) 435.
[12] W. Rehman, A. Badshah, S. Khan, L.T. Anh Tuyet, Eur. J. Med. Chem. 44 (2009)
3981.
[13] T.S. Basu Baul, S. Basu, D. de Vos, A. Linden, Invest. New Drugs 27 (2009) 419.
[14] T.A. Kabanos, P. Anastasios, D. Keramidas, D. Mentzafos, U. Russo, A. Terzisb,
J.M. Tsangaris, J. Chem. Soc., Dalton Trans. (1992) 2729.
[34] H.W. Lee, N. Sengottuvelan, H.J. Seo, J.S. Choi, S.K. Kang, Y.I. Kim, Bull. Korean
Chem. Soc. 29 (2008) 1711.
[35] Y.I. Kim, Y.K. Song, S.J. Yun, I.C. Kim, S.K. Kang, Acta Crystallogr., Sect. E 67
(2011) 52.
[36] W.B. Jennings, B.M. Farell, J.F. Malone, Acc. Chem. Res. 34 (2001) 885.