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T. Sedaghat et al. / Chinese Chemical Letters 23 (2012) 1355–1358
7
4
8
6
5
9
Br
5
6
6
H
N
H
N
H
N
1
3
1
3
1
3
4
5
N
N
N
2
2
2
4
MeO
O
H
O
H
O
H
b
HO
HO
HO
H2La
H2Lb
Fig. 1. Structure of Schiff base ligands.
H2Lc
(R = Ph, Bu and Me) with corresponding Schiff base in presence of NEt3 in 1:1:2 molar ratio in methanol. 1, 2 and 3
were obtained after stirring for 3 h, while 4 and 5 were refluxed for 5 and 3 h, respectively. The complexes SnMe2Lb
(6) and SnMe2Lc (7) have been also prepared as literature [12,13] for antibacterial tests.
1
In the H NMR spectra of H2La the signal of CH N and OH protons were appeared as doublet supporting the
location of the hydrogen atom on the nitrogen atom and HCNH coupling. It indicates the keto-amine tautomeric form
of H2La is dominating in solution; while H2Lb and H2Lc are in phenol–imine form [12]. In the 1H NMR spectra of the
complexes, the complete absence of the signals due to the phenolic protons suggests deprotonation of ligands and
1
coordination of corresponding anionic groups to tin. In the H NMR spectra of complexes appearance of satellites
around azomethine proton signal due to 3J(119Sn–1H) coupling indicates the ligation of azomethine nitrogen to tin. The
1H NMR spectrum of SnMe2La shows a singlet at low frequency (0.86 ppm) for SnMe2 protons accompanied by
satellites with 2J(119Sn–1H) larger than uncomplexed SnMe2Cl2 (68.7 Hz) indicates the higher coordination number of
tin [14]. Substituation of 2J(119Sn–1H) in the Lockhart–Manders equation [15], gives a value of 129.28 for Me–Sn–Me
angle in 5. The 119Sn{1H}NMR spectra of 1–5 show one sharp singlet significantly at À422.0, À433.7, À444.4,
À235.9 and À153.6 ppm, respectively. These chemical shifts are at lower frequency than that of the original SnPh2Cl2
(À32 ppm), SnBu2Cl2 (122 ppm) and SnMe2Cl2 (+137 ppm) [14]. On the basis of the chemical shift ranges proposed
empirically for organotin(IV) derivatives [16–18], the coordination number of tin is five for 5 in noncoordinating
solvent (CDCl3). However the 119Sn signal for 1–4 in coordinating solvent (DMSO) lies at lower frequency than that
for five-coordinated complexes of phenyltin and butyltin derivatives, since the solvent molecules coordinate to tin,
shifting the signal to the region corresponding to hexacoordinated species [19] or it may be because of a dimeric
structure retains in solution. In the IR spectra of all complexes the azomethine C N band which appears at 1617–
1625 cmÀ1 in free ligands, considerably shifts to the lower wavenumber (1591–1602 cmÀ1) because the imine
nitrogen is involved in coordination to the tin atom. The appearance of new bands in the IR spectra of the synthesized
complexes in the region 443–449 and 513–548 cmÀ1, which may be assigned to n(Sn–N) and n(Sn–O), respectively,
supports the bonding of nitrogen and oxygen to the tin [5,9,20]. Presence of both nsym(Sn–C) and nasym(Sn–C) at 517
and 572 cmÀ1, respectively, in the IR spectrum of 5 is consistent with a nonlinear Me–Sn–Me configuration.
The X-ray diffraction measurements for 4 were made on a STOE IPDS-IIT diffractometer with graphite
monochromated Mo-Ka radiation. Cell constants and an orientation matrix for data collection were obtained by least-
squares refinement of the diffraction data from 5839 unique reflections. Data were collected at a temperature of 120(2)
K to a maximum 2u value of 58.308. The numerical absorption coefficients, m, for Mo-Ka radiation are 1.198 mmÀ1
.
Fig. 2 shows the molecular structure of SnBu2La. This complex was crystallized in the monoclinic unit cell contains
two molecules. The Schiff base behaves as tridentate dibasic ligand via imine nitrogen and two oxygen atoms. The
geometry around the tin atom is distorted octahedral. The O, N, O-tridentate ligand is in a mer orientation to the tin
octahedron. The two n-butyl substitutents are trans to each other, allowing the intermolecular coordination of the O2
˚
with another tin to build a dimeric species. The SnÁ Á ÁO2 bond distance (2.729 A) is longer than the sum of the covalent
’
radii of the tin and oxygen (2.10 A), but significantly shorter than the sum of the van der Waal s radii of these atoms
˚
˚
(3.68 A). The dimeric assembly occurs via the formation of a Sn2O2 four-membered ring. The Sn–OÁ Á ÁSn–O torsion
angle is zero and show evidence of coplanarity. Therefore the tin environment is six coordinate and the pyridine atom
has no participation in coordination to tin. The coordination part of ligand forms six and five membered chelate rings.
These chelate rings are nearly planar as the torsion angles are small, Sn–O1–C1–C10 (À10.38), Sn–O2–C13–C12
(4.08), Sn–N1–C11–C10 (À6.68) and Sn–N1–C12–C13 (À2.88). The OÁ Á ÁSn bonding occurs with the oxygen atom at
Sedaghat, Tahereh
