Structural and spectral studies of N-(3-hydroxypyridine-2-yl)-5- hydroxysalicylideneimine and its dimethyltin(IV) complex

Article abstract of DOI:10.1016/j.molstruc.2004.06.023

N-(3-hydroxypyridine-2-yl)-5-hydroxysalicylideneimine(HOC₆H ₃OHCH=NC₅H₃NOH) (1) and its dimethyltin(IV) complex (Me₂Sn(OC₆H₃OHCH=NC₅H ₃NO)) (2) were prepared and characterized by ¹H-NMR, IR, mass spectroscopy and single crystal X-ray diffraction method. The complex (2) crystallizes in the space group C₂/c with cell dimensions a=20.841(2), b=10.646(2), c=13.206(2)?, β=105.95(1)° with Z=8,V=2817.3(6)?³. Molecular structure has been determined by standard methods and refined by full-matrix least squares (on F²) to R value of 0.036. The studied tin(IV) complex exhibits the strongly distorted square-pyramidal geometry around tin atom. In the solid state, each distorted square-pyramidal Me₂Sn(OC₆H₃OHCH=NC ₅H₃NO) unit is connected to the others via dual use of hydrogen bonds and π-π interactions. The tautomeric effect of ligand was discussed besides the coordination geometry of the complex (2).

Full text of DOI:10.1016/j.molstruc.2004.06.023

Journal of Molecular Structure 705 (2004) 107–112
www.elsevier.com/locate/molstruc
Structural and spectral studies of N-(3-hydroxypyridine-2-yl)-5-
hydroxysalicylideneimine and its dimethyltin(IV) complex
a
b,
a
b
¨ ¨
S.G. Oztas , E. Sahin , N. Ancın , S. Ide , M. Tuzun
a
¨
˙
*
,
,
aDepartment of Chemistry, Ankara University, 06100, Ankara, Turkey
bDepartment of Physics, Faculty of Engineering, Hacettepe University, 06532, Ankara, Turkey
Received 23 March 2004; revised 15 June 2004; accepted 17 June 2004
Available online 19 July 2004
Abstract
N-(3-hydroxypyridine-2-yl)-5-hydroxysalicylideneimine(HOC6H3OHCHyNC5H3NOH) (1) and its dimethyltin(IV) complex (Me2-
Sn(OC6H3OHCHyNC5H3NO)) (2) were prepared and characterized by 1H-NMR, IR, mass spectroscopy and single crystal X-ray
diffraction method. The complex (2) crystallizes in the space group C2=c with cell dimensions a ¼ 20:841ð2Þ; b ¼ 10:646ð2Þ;
3
˚
˚
c ¼ 13:206ð2Þ A, b ¼ 105:95ð1Þ8 with Z ¼ 8; V ¼ 2817:3ð6Þ A . Molecular structure has been determined by standard methods and refined
by full-matrix least squares (on F2Þ to R value of 0.036. The studied tin(IV) complex exhibits the strongly distorted square-pyramidal
geometry around tin atom. In the solid state, each distorted square-pyramidal Me2Sn(OC6H3OHCHyNC5H3NO) unit is connected to the
others via dual use of hydrogen bonds and p–p interactions. The tautomeric effect of ligand was discussed besides the coordination
geometry of the complex (2).
q 2004 Elsevier B.V. All rights reserved.
Keywords: Tin(IV) complex; Self assembly; Hydrogen bonding; p–p interaction
1. Introduction
In recent years considerable research activity has been
aimed toward generating new supramolecular entities
having desired structural network by self-assembling of
metal ions utilising their preference for different coordi-
nation geometry, choice of suitable ligands, and intermo-
lecular interactions such as hydrogen bonding and p–p
interaction [31–36]. Such species are of immense interest
due to their physical properties and potential utilization as
molecule based metals, magnetic materials, optical and
thermal switches, and probes for DNA structures [37–40].
Continuing our previous study [41] here we report the
synthesis and characterization of a potentially tridentate
ONO donor Schiff base which is a N-salicylidene-2-
aminopyridine derivative. We also describe the synthesis,
properties and solid state structure of a tin(IV) complex of
the Schiff base ligand. Structural formula for the ligand
(HOC6H3OHCHyNC5H3NOH) (1) depicted in its Schiff
base form is given in Scheme 1 in which intramolecular
hydrogen bonding occurs.
The coordination chemistry of some tridentate ONO and
ONS donor Schiff bases has been described [1–4]. The
Schiff bases of salicylaldehyde with aminopyridines are
well-known class of predominantly thermochromic com-
pounds which have attracted a lot of interest from chemists
for a long time [5–14]. It has been found that a series of
N-salicylidene-2-aminopyridine derivatives show thermo-
chromism [15,16]. It can be said that the driving force for
the observed planarity of these derivatives is the intramo-
lecular hydrogen bond, which locks the salicylideneimine
group in the planar configuration. Organotin(IV) complexes
of deprotonated Schiff bases are known [17–21]. The
chemistry of organotin(IV) complexes of Schiff bases has
stemmed from the reported biocidal [22–26] and anti-
tumour [27–29] activities of organotin(IV) complexes and
the behaviour of Schiff bases as models for biological
systems [30].
The diorganotin(IV) complex formulated as Me2-
Sn(OC6H3OHCHyNC5H3NO) (2) is prepared by conden-
sing (CH3)2SnCl2 with the ligand.
*
Corresponding author. Tel.: þ90-312-297-6763; fax: þ90-312-299-
2037.
E-mail address: ertan@hacettepe.edu.tr (E. Sahin).
,
0022-2860/$ - see front matter q 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2004.06.023

¨
108
S.G. Oztas et al. / Journal of Molecular Structure 705 (2004) 107–112
,
Table 1
Summary of the crystal data, details of data collection and structure
determination
Empirical formula
Formula weight
Crystal system
Space group
C14H14N2O3Sn
376.96
monoclinic
C2=c (No:15)
Scheme 1. Structure of the Schiff base.
˚
a (A)
˚
b (A)
˚
c (A)
20.841(2)
10.646(1)
13.206(1)
105.95(1)
2817.3(6)
2. Experimental
b (8)
3
˚
V (A )
2.1. Preparation of the ligand
Z
8
Dcalc (Mg m23
)
1.777
1.822
1488
The solution of 2-amino-3-hydroxypyridine (1.0 mmol)
was added to the solution of 5-hydroxysalicylaldehyde
(1.0 mmol) in methanol. The reaction mixture was cooled in
an ice bath and orange powder was obtained. The isolated
compound was re-crystallized from dichloromethane–
methanol mixture.
Absorption coefficient m (mm21
)
Fð000Þ
Index ranges
224 # h # 25, 0 # k # 13
216 # l # 0
umax (8)
Reflections collected
26.3
3006
Reflections observed ½I . 2sðIÞꢀ
Refinement on F2
No. of parameters
R½F2 . 2sðF2Þꢀ
1930
2.2. Synthesis of the complex
2758
181
0.036
A hot methanol solution of the Schiff base (1.0 mmol)
was added the solution of dimethyl tin(IV)dichloride
(1.0 mmol) in methanol. The mixture was heated and the
colour of the solution changed from orange to red. It was left
standing at room temperature for 1 day. The red powder
filtered off and recrystallized in 2-propanol.
RwðF2Þ
0.078
where P ¼ ðF02 þ 2Fc2Þ=3
2
W ¼ 1=½s2ðF02Þ þ ð0:0302PÞ þ 7:4634Pꢀ
Goodness-of-fit on F2
1.029
Largest difference peak and hole (eA23
)
0.55, 20.55
1
Various studies were carried out with these similar
systems in order to establish the existence of intramolecular
hydrogen bonding stabilizing one of the tautomeric forms
[47–48].
The 1H-NMR spectra of the ligand and its complex were
recorded DMSO at 400 MHz using two-dimensional (2D)
NMR techniques and all proton signals were completely
assigned (Table 2).
The H-NMR spectra were obtained by using DMSO
solvent on a Bruker DPX400 FT-NMR spectrometer with
TMS as internal standard. The infrared spectra were recorded
on a Mattson-1000 FTIR spectrometer using KBr pellets in
the range 4000–400 cm21. A resolution of 4 cm21 was
feasible and 32 pulses were found to be suitable for a
spectrum of acceptable quality. Band locations were found
by means of microprocessor. Mass spectra were recorded
with a Micromass UK PLATFORM II LC-MS spectrometer.
Single crystal of the compound suitable for X-ray analysis
were used for data collection on an Enraf–Nonius CAD4
diffractometer with grafite monochromated Mo Ka
For the ligand, the single proton giving a singlet at 9:34d
does not exchange with D2O, hence may be assigned to the
azomethine proton [41,45,49]. The signal of the CHyN
proton is a singlet which shows the absence of any H–NH
coupling and indicates the phenol-imine tautomer form of
the ligand [41,50]. For the complex, the d value of
azomethine proton resonance is at 9:27d: A change in the
d values of azomethine proton resonance seen on com-
˚
ðl ¼ 0:73071 A) radiation and using an v 2 2u scan. Full-
matrix least-squares refinement method was carried out on F2
of the positional and anisotropic thermal parameters of the
non-hydrogen atoms and of the positional parameters of the
hydrogen atoms, which were assigned fixed isotropic thermal
parameters. SHELXS-97 and SHELXL-97 programs were used
to solve and refine the structures [42]. All molecular diagrams
were drawn with the program ORTEPIII [43]. A summary of
crystal data and refinement results were given in Table 1.
3
plexation and the observed J (Sn–H) coupling involving
the azomethine proton support the ligation of azomethine
nitrogen to tin [21,51].
3. Result and discussion
Schiff base obtained from salicylaldehyde is expected to
exist predominantly as the phenol imine tautomer (I)
(Scheme 2) [44–46].
Scheme 2. Intramolecular hydrogen transfer in the ligand.

¨
S.G. Oztas et al. / Journal of Molecular Structure 705 (2004) 107–112
109
,
In the ligand, the downfield signal of the proton of the
hydroxy group at the salicylaldehyde moiety (OH)b (reson-
ance around 12:88dÞ justifies the existence of intramolecular
hydrogen bonding between hydrogen atom of the hydroxyl
group and imine-nitrogen atom forming a six-membered ring
[52]. The signal at 10:11d is assigned to the (OH)a proton.
This is in agreement with the proton of the hydroxy group at
the pyridine moiety [53]. The other signal at 9:07d belongs to
the proton of the hydroxyl group (OH)c. (OH)a, (OH)b and
1
(OH)c proton signals do exchange with D2O in H-NMR
spectrum of the DMSO-d6 solution. Other protons in the
phenyl and pyridine rings are found in their normal d range.
1
In the H-NMR spectra of the complex, the complete
absence of the signals due to hydroxylic protons (OH)a and
(OH)b suggests deprotonation and coordination of the
phenolic oxygen to the tin centre. The signal observed at
8:91d is assigned to the (OH)c protons. This (OH)c proton
signal does exchange with D2O in NMR spectrum of the
DMSO-d6 solution of the complex. The single proton
resonance which occurs at 0:57d is assigned to the SnMe2
2
protons. The J(119Sn–1H) of the complex has a value of
78.9 Hz, typical of the five-coordinated tin(IV) species [54].
On the basis of the Lockart’s equation;
2
½Me–Sn–Meꢀ ¼ 0:0161 £ ½2Jð119Sn–1HÞꢀ –1:32
£ ½2Jð119Sn 2 1HÞꢀ þ 133:4
The Me–Sn–Me angle is estimated to approximately
1308 which well agree with the angle of 1328 found in the
crystal structure.
ThesolidstateIRspectraoftheliganddisplaysabroadband
at ,3030 cm21 which may be assigned to O–H stretching
vibration. The free O–H stretching vibrations in phenol are
reported to be a sharp absorption band between 3650–
3584 cm21 ranges [55]. Due to intra- and intermolecular
hydrogen bonding in the Schiff base, this band broadens and
shiftstolowerfrequencies. Inthedimethyltin(IV)complex,the
broad band due to intermolecularly hydrogen bonded OH,
occurs at ,3169 cm21. The CyN stretching vibrations in
ligand and complex are observed at 1639 and 1591 cm21
,
respectively. Lowering of stretching frequency in the complex
indicates the coordination of imine nitrogen to dimethyltin(IV)
moiety. In the spectra of complex, the absorptions at 519 and
534 cm21 are assigned to Sn–O vibration. The band due to
Sn–C stretching is observed at 569 cm21 [21].
In the mass spectra of ligand and complex, molecular ion
peaks are observed at m=e 230, 376, respectively. In the
mass spectra of Schiff base, a peak at 119 can be assigned to
the fragment,
d
It has been shown that the five-membered heteroatomic
ring shows very similar chain-closure in gaseous phase [56].

¨
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S.G. Oztas et al. / Journal of Molecular Structure 705 (2004) 107–112
,
Table 4
˚
Selected geometric parameters (A, 8)
Sn–C14
Sn–C13
Sn–N1
O2–C8
C6–C5
N1–C7
C4–O3
N2–C11
2.083(5)
2.098(6)
2.204(5)
1.317(7)
1.408(7)
1.283(6)
1.383(7)
1.323(7)
Sn–O1
Sn–O2
O1–C1
C6 C7
2.084(4)
2.154(4)
1.329(6)
1.407(7)
1.423(8)
1.446(6)
1.315(7)
C6–C1
N1–C12
C12–N2
C14–Sn–O1
O1–Sn–C13
O1–Sn–O2
C14–Sn–N1
C13–Sn–N1
C1–O1–Sn
C7–N1–C12
C12–N1–Sn
O1–C1–C6
C3–C4–O3
N2–C12–N1
O2–C8–C9
95.3(2)
98.2(2)
C14–Sn–C13
C14–Sn–O2
C13–Sn–O2
O1–Sn–N1
O2–Sn–N1
C8–O2–Sn
C7–N1–Sn
O1–C1–C2
C5–C4–O3
N2–C12–C8
C8–C12–N1
O2–C8–C12
132.7(2)
89.9(2)
92.7(2)
159.5(2)
117.6(2)
108.7(2)
131.1(4)
120.8(5)
112.7(3)
124.8(5)
121.9(5)
119.2(4)
123.5(5)
84.5(2)
75.5(2)
Fig. 1. The molecular structure and atomic labelling scheme of the studied
dimethyltin(IV) complex, Me2 Sn(OC6H3OHCHyNC5H3NO). (Ellipsoids
at 50% probability level).
117.0(3)
126.4(4)
118.2(5)
119.1(6)
125.6(5)
115.2(5)
119.5(5)
In the mass spectra of complex, a peak is observed at m=e
228. This peak can be assigned to the fragment,
The coordination around tin in the complex is defined by
two methyl groups, two oxygen atoms forming a bridge to
phenyl and pyridyl rings through the tin atom and
imino nitrogen atom found in the ligand which is in
phenol-imine form. The metal atom is in a strongly distorted
square-pyramidal geometry. The two methyl groups and
two oxygen atoms constitute the square base and the imino
nitrogen atom occupies the apical position. The following
bond and torsion angles may be given as an evidence
of strongly distorted square-pyramidal conformation.
O1–Sn–O2: 159.5(2), O1–Sn–N1: 84.5(2), O2–Sn–N1:
75.5(2), C14–Sn–N1:117.6(2), C13–Sn–N1: 108.7(2),
C14–Sn–C13: 132.7(2), C14–Sn–O1: 95.3(2), O1–Sn–
C13: 98.2(2), C13–Sn–O2: 92.7(2), C14–Sn–O2: 89.9(2)
and Sn–N1–C7–C6: 4.7(8), Sn–O1–C1–C6: 25.9(8),
Sn–N1–C12–C8: 20.9(5), Sn–O2–C8–C12: 2.9(6)8.
The distortion is mainly due to the rigidity of chelate
rings, together with the large covalent radius of tin(IV) [21].
These geometric results are in agreement with the results of
similar tin(IV) complexes [4,21,41,51,57–60]. The slight
Besides the above mentioned spectral studies, certain
molecular and crystal structure of the complex was
determined by single crystal X-ray diffraction method. The
molecular structure of the complex is shown in Fig. 1.
Fractional atomic coordinates and equivalent isotropic
displacement parameters are given in Table 3. A list of the
bond lengths and angles for the complex is given in Table 4.
Table 3
Fractional atomic coordinates and equivalent isotropic displacement
2
P P
i
parameters (A ) Ueq ¼ ð8p2=3Þ
j Uijapi apj aiaj
˚
Atom
x=a
y=b
y=c
Ueq
Sn
0.44503(2)
0.5449(2)
0.3574(2)
0.7615(2)
0.18409(4)
0.1331(4)
0.3012(4)
0.3486(4)
0.00104(3)
0.0591(3)
0.0364(2)
0.0511(11)
0.0604(12)
0.0707(15)
O1
O2
O3
20.0422(4)
0.3461(4)
N1
N2
0.4778(2)
0.4368(2)
0.3648(4)
0.5676(5)
0.0798(3)
0.1059(4)
0.0365(11)
0.0465(12)
˚
shortening of Sn–O1: 2.084(4) A respect to the Sn–O2:
˚
2.154(4) A shows the phenol-imine tautomeric form of the
C1
0.5958(2)
0.6571(2)
0.7115(2)
0.7078(3)
0.6500(3)
0.5929(2)
0.5357(3)
0.3628(3)
0.3097(3)
0.3221(3)
0.3859(3)
0.4244(2)
0.4060(3)
0.4428(3)
0.1907(6)
0.1275(5)
0.1796(6)
0.2962(6)
0.3620(5)
0.3130(6)
0.3895(6)
0.4150(6)
0.4977(7)
0.6151(7)
0.6466(6)
0.4559(5)
0.0725(6)
0.1681(6)
0.1262(4)
0.1582(4)
0.2288(4)
0.2725(5)
0.2410(4)
0.1683(4)
0.1414(4)
20.0016(4)
20.0163(5)
0.0306(5)
0.0892(5)
0.0622(4)
0.1009(5)
20.1570(4)
0.0352(12)
0.0385(13)
0.0442(14)
0.0470(15)
0.0419(13)
0.0367(12)
0.0395(13)
0.0419(14)
0.0541(17)
0.063(2)
ligand. This complex and the other two very similar
complexes [Me2Sn(OC6H4CHyNC5H3NO) and Me2-
Sn(OC6H3BrCHyNC5H3NO)] which were studied pre-
viously [41] contain a range of structural types
intermediate between the idealized square-pyramidal (SP)
and trigonal-bipyramidal (TBP) extrems.
C2
C3
C4
C5
C6
C7
C8
To quantify the extent of distortion from either ideal
structure towards the other we have found the t values for
the complexes ðt ¼ ðb 2 aÞ=60; a and b are the two largest
bond angles around the metal atom). For a perfectly
tetragonal geometry t is equal to zero, while it becomes
unity for perfectly trigonal-bipyramidal geometry [61].
C9
C10
C11
C12
C13
C14
0.0567(18)
0.0345(12)
0.0568(17)
0.0502(15)

¨
S.G. Oztas et al. / Journal of Molecular Structure 705 (2004) 107–112
111
,
Fig. 2. The packing diagram of Me2Sn(OC6H3OHCHyNC5H3NO) molecules as projected along b axis. For major clarity, the hydrogen atoms not involved in H
bonds are omitted.
˚
t values of Me2Sn(OC6H3BrCHyNC5H3NO), Me2Sn(OC6-
H3OHCHyNC5H3NO) and Me2Sn(OC6H4CHyNC5H3NO)
are found 0.38, 0.44 and 0.46, respectively. In this series the
intramolecular hydrogen bond lengths between C7 and N2
4.545 A. The following unit B is a pair of Me2Sn(OC6H3-
OHCHyNC5H3NO) molecules which are involved in p–p
interactions between the phenyl and pyridyl fragments of
the coordinated ligands. In this unit, the distance between
˚
atoms are 2.735(6), 2.744(7) and 2.765(6) A, respectively.
˚
the two tin atoms is 7.108 A. The interplanar and centroid-
to-centroid distances between the phenyl and pyridyl rings
˚
are 3.477 and 3.916 A, respectively. The corresponding slip
There seems to exist a relation between t values and
intramolecular hydrogen bond lengths. While there is an
increase in the intramolecular hydrogen bond lengths, the
degree of distortion from square-pyramidal towards trigo-
nal-bipyramidal also increases. The dihedral angle between
the plane through the phenyl ring and the plane through the
pyridine ring was defined as 174.0(2)8. C7 atom is also
located on the phenyl plane just like O3 and N1 atoms. O1
angle is 278. These values can be compared with those in the
literature [31,67]. The units of A and B are connected via a
pair of hydrogen bridges which have been formed by
O3· · ·O2 intermoleculer contacts [O3–H3· · ·O2i: 1488,
˚
atom is slightly deviates from the phenyl plane (20.054 A).
The other common planarity for pyridine ring and the
position of O2 atom has been also observed. The deviation
˚
of N1 atom from the pyridine plane is 20.055(4) A.
According to these geometrical results, it may accepted that
the backbone of the molecule is approximately planar. For a
p-stacked arrangement, planarity of the whole molecule is
one of the prerequisites [62–64]. Multidentate ligands with
pyridine groups in general is featured prominently as
building blocks in the design of metal-ligand networks
[31,63–66].
In Fig. 2, the packing diagram of the Me2Sn(OC6H3-
OHCHyNC5H3NO) molecules is shown. In Fig. 3, a chain-
like arrangement of the complex molecules formed by
O3–H3· · ·O2 intermolecular hydrogen bondings and p–p
interactions between the phenyl and pyridyl rings is seen. In
unit A, two Me2Sn(OC6H3OHCHyNC5H3NO) molecules
are connected by two weak intermolecular Sn–O inter-
actions and are coplanar with each other (dihedral angle
between N1_a–O1_a–O2_a and N1_b–O1_b–O2_b
planes is 08). The Sn_a–O1_b distance, which is identical
Fig. 3. Chain-like structure [Me2Sn(OC6H3OHCHyNC5H3NO)] formed by
O3–H3· · ·O2 bonding and p–p interactions. Me atoms are omitted for
clarity.
˚
to Sn_b–O1_a is 3.488 A and the Sn_a–Sn_b distance is

¨
S.G. Oztas et al. / Journal of Molecular Structure 705 (2004) 107–112
,
112
˚
˚
[27] M. Gielen, Metal-based Drugs 1 (1994) 213–220.
[28] A.J. Crowe, Drugs Future 12 (1987) 40.
O3· · ·O2: 2.664(6) A, H3· · ·O2: 1.930 A, i: x þ 1=2; 2y þ
1=2; þz þ 1=2ꢀ giving rise to a chain-like structure.
Intermolecular hydrogen bonds and p–p interactions
together contribute the formation of pairs of chain-like
arrangement of Sn(IV) centers with successive long and
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˚
[32] J.M. Lehn, Angew. Chem. Int. Ed. Engl. 29 (1990) 1304.
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short Sn· · ·Sn distances (4.545 A and 7.108 A).
In summary one-dimensional assembly of tin(IV) poly-
hedra is formed by dual use of hydrogen-bonding and p–p
interaction in the solid state in the complex.
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Acknowledgements
1554.
The authors’ wishes to acknowledge the support of
Ankara University Research Fund (project no:
200110705049).
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