Structural characteristics of N,N'-bis(salicylidene)-2,6-pyridinediamine

Article abstract of DOI:10.1016/S0022-2860(96)09608-1

The Schiff base N,N'-bis(salicylidene)-2,6-pyridinediamine has been synthesized and characterized in the solid state and in solution using X-ray analysis, IR, UV/Vis and NMR spectroscopy. Crystal data: C₁₉H₁₅N₃O₂

Full text of DOI:10.1016/S0022-2860(96)09608-1

MOLSTR 9608
Journal of Molecular Structure 406 (1997) 153–158
Structural characteristics of N,NЈ-bis(salicylidene)-2,6-pyridinediamine
a
b
a,
ˇ
N. Galic´ , D. Matkovic´-Calogovic´ , Z. Cimerman *
aDepartment of Chemistry, Laboratory of Analytical Chemistry, Faculty of Science, University of Zagreb, Strossmayerov trg 14,
10 000 Zagreb, Croatia
bDepartment of Chemistry, Laboratory of General and Inorganic Chemistry, Faculty of Science, University of Zagreb, Zvonimirova 8,
10 000 Zagreb, Croatia
Received 30 July 1996; accepted 4 September 1996
Abstract
The Schiff base N,NЈ-bis(salicylidene)-2,6-pyridinediamine has been synthesized and characterized in the solid state and in
solution using X-ray analysis, IR, UV/Vis and NMR spectroscopy. Crystal data: C19H15N3O2, Mr = 317.34, monoclinic, space
3
˚
˚
group P21/c, a = 19.313(5), b = 5.854(2), c = 14.957(6) A, b = 110.45(2)Њ, V = 1584.4(9) A , Z = 4, R = 0.049, Rw = 0.095 for
…
3323 independent reflections with I Ͼ 2j(I). There are two intramolecular hydrogen bonds O–H N between the hydroxyl and
imino groups of 2.564(3) and 2.633(3) A. The enolimino form is found in the solid state and is also the predominant tautomeric
˚
form in solution. A tendency of interconversion to ketoamine has been observed only in rather polar solvents, such as methanol
and methanol/water mixtures and has been found to be very low: tautomeric constants Kt = [ketoamine]/[enolimine] amount to
0.02 and 0.03 in methanol and methanol/water 4/1, respectively. ᭧ 1997 Elsevier Science B.V.
Keywords: N,NЈ-bis(salicylidene)-2,6-pyridinediamine; X-ray crystallography; IR spectroscopy; NMR spectroscopy; UV/Vis
spectroscopy
1. Introduction
amino-3-aminomethylpyridine and 2,3-diaminopyri-
dine, directing attention to their tautomeric equilibria
[5–7]. Some of the synthesized compounds seem to
be promising as analytical reagents [8]. Continuing
our study, we report structural and tautomeric charac-
teristics of N,NЈ-bis(salicylidene)-2,6-pyridinediamine.
The comparison with structurally similar Schiff bases is
made.
Schiff bases of salicylaldehyde with amino- and
aminoalkylpyridines are structurally related to
compounds participating in vitamin B6 chemistry
and are therefore attractive as model systems for the
study of biological equilibria. It was shown that some
compounds of this group possess additional interest-
ing characteristics, like pharmacological activity,
chromic properties and suitability for analytical
application [1–4]. Recently, we have prepared
and characterized Schiff bases of salicylaldehyde
with 2-aminopyridine, 3-aminomethylpyridine, 2-
2. Experimental
2.1. Preparation of the Schiff base
Salicylaldehyde was obtained from Merck, and 2,6-
pyridinediamine was purchased from Fluka. The
* Corresponding author. Fax: +385 1 429643; E-mail: ZCI-
MER@PUBLIC.SRCE.HR
0022-2860/97/$17.00 ᭧ 1997 Elsevier Science B.V. All rights reserved
PII S0022-2860(96)09608-1

154
N. Galic´ et al./Journal of Molecular Structure 406 (1997) 153–158
Table 1
reactants, both dissolved in absolute ethanol, were
mixed in the aldehyde to a diamine ratio 2.25 : 0.9.
After adding a few drops of piperidine, the reaction
mixture was refluxed for 2 h on a water bath. The
separated orange crystals of the bis Schiff base were
recrystallized from the system dichloromethane/
methanol 1/1 (m.p. 186–189 ЊC, elemental analysis
for C19H15N3O2: calculated; C 71.91, H 4.76,
N 13.24%; found: C 72.07, H 4.78, N 13.48%).
Crystal data and structure refinement
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C19H15N3O2
317.34
295
Monoclinic
P21/c
19.313(5)
5.854(2)
14.957(6)
110.45(2)
1584.4(9)
4
1.330
0.89
˚
a (A)
˚
b (A)
˚
c (A)
b (deg)
Volume (A )
3
˚
2.2. Spectroscopy
Z
Density (calculated) (g cm−3
)
m(Mo Ka) (cm−1
F(000)
)
UV/Vis spectra were taken on a Varian Cary 3
spectrometer with a 2 nm slit width. IR spectra of
liquid samples and of KBr discs were recorded with
a Perkin Elmer 783 spectrometer at 2 cm−1 resolution.
NMR spectra were recorded on a Varian XL Gemini
300 spectrometer using tetramethylsilane as internal
standard. The digital resolution was 0.01 ppm. In
solvents containing water hydrolysis of Schiff bases
took place, hence spectra were recorded in a very
short time or extrapolated to zero time.
664
Crystal size (mm)
v range for data collection (deg)
Index ranges
0.063 × 0.435 × 0.600
2.25–30.00
−14 Յ h Յ 0, −8 Յ k Յ 0,
−19 Յ l Յ 21
4061
3290 [I Ͼ 2j(I)]
v–2v
235
No. of collected reflections
No. of independent reflections
Scan type
No. of parameters
Final R indices
R = 0.0488, wR = 0.0949
0.0045(10)
0.123 and −0.157
Extinction coefficient
Largest diff. peak and hole (e A
−3
˚
)
2.3. Crystal structure determination
structure solution, refinement and molecular graphics
computing were performed on an IBM PC/AT com-
patible microcomputer using SHELXS-86 [9],
SHELXL-93 [10], ORTEP92 [11] and PLUTON
[12] programs. Scattering factors were those from
the SHELXL-93 program. Atomic coordinates are
given in Table 2.
A list of structure factors, anisotropic thermal para-
meters, hydrogen atom coordinates and least-squares
planes tables are available as deposited supplementary
data (The tables are deposited with the B.L.L.D. as
Supplementary Publication No. SUP26576 (13
pages).)
X-ray data were collected at room temperature on
the Philips PW1100 diffractometer (upgraded by
STOE) using graphite-monochromatized Mo Ka
˚
radiation (l = 0.71073 A). Unit cell dimensions
were obtained by least-squares refinement of 25
reflections (21.5 Ͻ 2v Ͻ 35.3Њ). The unit cell para-
meters and details of data collection are given in
Table 1. Standard reflections monitored every 90 min
indicated no significant change in intensities. No
absorption correction was applied. The structure was
solved by direct methods. Full-matrix least-squares
refinement on F2 converged ((shift/esd)max = 0.001)
at R = ∑lF0l − lFcl/∑lF0l = 0.049, wR = {∑[w(F20 −
F2c)2]/∑[w(F02)2]}1/2 = 0.095 (for F2 Ͼ 2j(F2), w = 1/
[j2(F20) + (0.0599P)2] where P = (F02 + 2F2c)/3, S =
{∑[w(F20 − Fc2)2]/(Nobs − Nparam)}1/2 = 1.117. Aniso-
tropic Uij were used for all non-hydrogen atoms and
isotropic for hydrogen atoms. Hydrogen atoms posi-
tions were calculated using stereochemical criteria
3. Results and discussion
The solid state structure N,NЈ-bis(salicylidene)-2,6-
pyridinediamine determined by X-ray diffraction is
shown in Fig. 1. Bond lengths and angles are given
in Table 3. Crystal packing of the molecules is shown
in Fig. 2.
˚
(d(Csp2–H) = 0.97, d(Car–H) = 0.93 A) and con-
strained to ride on their parent C atoms; the two H
atoms of the hydroxyl groups were allowed to ride on
the O atoms and rotate about the C–O bonds. The
The planarity of the salicylideneamino moieties is

155
N. Galic´ et al./Journal of Molecular Structure 406 (1997) 153–158
Table 2
Atomic coordinates and equivalent isotropic displacement para-
2
˚
meters (A ); Ueq is defined as one third of the trace of the orthogo-
nalized Uij tensor
x
y
z
Ueq
O1
O2
C1
C2
C3
C4
C5
C6
C7
N1
C8
C9
C10
C11
C12
N2
0.4023(1)
0.0499(1)
0.4552(1)
0.5276(2)
0.5835(2)
0.5685(2)
0.4967(1)
0.4390(1)
0.3642(1)
0.3090(1)
0.2373(1)
0.1801(2)
0.1094(2)
0.0970(2)
0.1572(1)
0.2269(1)
0.1423(1)
0.1944(2)
0.1799(1)
0.2370(2)
0.2236(2)
0.1519(2)
0.0948(2)
0.1077(2)
0.8394(3)
0.3713(2)
0.066(1)
0.071(1)
0.045(1)
0.057(1)
0.062(1)
0.060(1)
0.049(1)
0.040(1)
0.044(1)
0.045(1)
0.041(1)
0.049(1)
0.056(1)
0.050(1)
0.041(1)
0.041(1)
0.045(1)
0.045(1)
0.041(1)
0.056(1)
0.066(1)
0.068(1)
0.065(1)
0.051(1)
−0.1676(4)
0.6872(4)
0.7397(5)
0.5903(5)
0.3857(5)
0.3314(5)
0.4795(4)
0.4212(4)
0.5543(3)
0.4938(4)
0.6354(4)
0.5834(5)
0.3924(5)
0.2623(4)
0.3075(3)
0.0728(3)
−0.0544(4)
−0.2461(4)
−0.3882(5)
−0.5750(5)
−0.6255(5)
−0.4905(5)
−0.2994(5)
−0.1141(2)
0.3743(2)
0.4282(2)
0.4318(2)
0.3816(2)
0.3297(2)
0.3237(2)
0.2646(2)
0.2531(1)
0.1925(2)
0.1936(2)
0.1360(2)
0.0790(2)
0.0803(2)
0.1371(1)
0.0172(1)
0.0112(2)
−0.0537(2)
−0.0568(2)
−0.1162(2)
−0.1731(2)
−0.1727(2)
−0.1132(2)
N3
C13
C14
C15
C16
C17
C18
C19
Fig. 2. Packing of the molecules of N,NЈ-bis(salicylidene)-2,6-
pyridinediamine in the unit cell.
are of the atoms C6 and C11 which deviate by
0.031(2) and 0.025(2) A from their least-squares
planes.
stabilized by intramolecular hydrogen bonds between
the hydroxyl and imino groups, O1H N1 and
˚
…
…
…
˚
O2H N3 of 2.633(3) and 2.564(3) A, respectively
The enolimino character of the molecule is indi-
cated by short bonds N1–C7 of 1.282(3) and N3–
˚
…
…
(H1 N1 1.91(2) A, O1–H N1 147(2)Њ; H2 N3
1.83(2) A, O2–H N3 148(2)Њ). The largest devia-
˚
…
˚
C13 of 1.281(3) A which have a double bond char-
tions from planarity of the salicylideneamino moieties
acter, and C1–O1 of 1.346(3) and C19–O2 of
˚
1.353(3) A which are single bonds. A Cambridge
Structural Database (CSD) search [13] of unsubsti-
tuted and uncoordinated salicylideneamino moieties
in the enolimino form revealed 58 structures and 74
salicylideneamino fragments. They are all nearly
…
planar with OH N intramolecular hydrogen bonds
˚
in the range 2.515 to 2.698 A. The following bond
length ranges and mean values were obtained: NyC
˚
1.223–1.317 (mean 1.280(2) A), NC–Car 1.388–
˚
1.476 (mean 1.448(2) A), C–O 1.320–1.399 (mean
˚
1.352(1) A). The bond lengths in the present structure
are very close to these mean values.
The shift in the tautomeric equilibrium toward the
ketoform in the solid state is possible if strong inter-
molecular hydrogen bonding with the oxygen atom in
Fig. 1. ORTEP92 drawing of N,NЈ-bis(salicylidene)-2,6-pyridine-
diamine with the atom numbering scheme. The thermal ellipsoids
are at the 50% probability level.

156
N. Galic´ et al./Journal of Molecular Structure 406 (1997) 153–158
Table 3
˚
Bond lengths (A) and angles (deg)
O1–C1
O2–C19
C1–C2
C1–C6
C2–C3
C3–C4
C4–C5
C5–C6
C6–C7
C7–N1
N1–C8
C8–N2
1.346(3)
1.353(3)
1.382(3)
1.409(3)
1.376(3)
1.389(4)
1.369(3)
1.389(3)
1.447(3)
1.282(3)
1.411(3)
1.342(3)
1.385(3)
C9–C10
C10–C11
C11–C12
C12–N2
C12–N3
N3–C13
C13–C14
C14–C15
C14–C19
C15–C16
C16–C17
C17–C18
1.371(3)
1.376(4)
1.385(3)
1.343(3)
1.418(3)
1.281(3)
1.446(3)
1.395(3)
1.402(3)
1.375(4)
1.380(4)
1.359(4)
1.397(4)
C8–C9
C18–CI9
O1–C1–C2
O1–C1–C6
C2–C1–C6
C3–C2–C1
C2–C3–C4
C5–C4–C3
C4–C5–C6
C5–C6–C1
C5–C6–C7
C1–C6–C7
N1–C7–C6
C7–N1–C8
N2–C8–C9
N2–C8–N1
C9–C8–N1
C10–C9–C8
C9–C10–C11
118.3(2)
C10–C11–C12
N2–C12–C11
N2–C12–N3
C11–C12–N3
C8–N2–C12
C13–N3–C12
N3–C13–C14
C15–C14–C19
C15–C14–C13
C19–C14–C13
C16–C15–C14
C15–C16–C17
C18–C17–C16
C17–C18–C19
O2–C19–C18
O2–C19–C14
C18–C19–C14
118.4(3)
122.0(2)
119.7(2)
120.1(3)
120.9(3)
119.1(3)
121.5(3)
118.8(2)
120.0(2)
121.3(2)
123.0(2)
121.2(2)
123.1(2)
120.2(2)
116.7(2)
118.9(3)
119.3(3)
123.5(2)
120.1(2)
116.5(2)
116.8(2)
121.3(2)
121.7(2)
117.9(3)
121.0(2)
121.0(3)
121.5(3)
119.4(3)
120.9(3)
120.3(3)
119.2(3)
120.9(3)
119.9(3)
the salicylidenamino group is present. In that case the
hydrogen atom is shifted toward the nitrogen atom
and an intramolecular hydrogen bond of the type
groups around the N1–C8 and C12–N3 bonds. The
dihedral angle between the least-squares plane 1
(defined by atoms C1–C7, O1 and N1) and 2 (N1–
N3, C8–C12) is 7.72(5)Њ, and the angle between plane
2 and 3 (C13–C19, O2 and N3) is 1.17(3)Њ. This dif-
ference can only be explained by crystal packing
forces. The planarity and the bond lengths are con-
sistent with the p system delocalization which is
extended over the whole molecule. Bis Schiff bases
of salicylaldehyde with diamines tend to be planar if
the amine part of the molecule is aromatic, as in the
structure of N,NЈ-bis(salicylidene)-p-phenylenedi-
amine [17]. The planarity can be altered by steric
and crystal packing effects. In the structure of N,NЈ-
bis(salicylidene)-o-phenylenediamine one salicylide-
neamino residue is removed from the plane of all other
atoms by 56.8Њ [18]. Steric repulsions of hydrogen
atoms in N,NЈ-bis(salicylidene)-2,3-pyridinediamine
[6] cause the 3-positioned salicylidene moieties in
…
NH O forms. Only three solid state structures were
found with the predominant ketoamine form and in all
of them an additional hydroxyl group was involved in
strong intermolecular hydrogen bonds with the keto
oxygen atom [14–16]. The N–C and CyO bond
lengths in these compounds are in the range 1.301–
˚
1.325 and 1.279–1.300 A. In the present crystal struc-
ture no intermolecular hydrogen bonds are possible,
and the molecules are held together only by van der
Waals forces.
The molecule has no elements of symmetry
although there are no significant differences in the
bond lengths and angles of the two chemically identi-
cal parts of the molecule on the two sides of the
central pyridine ring. The deviation from planarity is
caused by slight twisting of the salicylideneamino

157
N. Galic´ et al./Journal of Molecular Structure 406 (1997) 153–158
two crystallographically independent molecules to
Table 5
1
Proton chemical shifts and coupling constants in the H NMR spec-
trum of N,NЈ-bis(salicylidene)-2,6-pyridinediamine dissolved in
dimethylsulfoxide at 50ЊC
be inclined at dihedral angles of 51.1(4) and
51.8(4)Њ to the pyridine ring. When the amine part is
aliphatic the molecule is not planar and the salicyli-
dene moieties are inclined at different angles, e.g.
in N,NЈ-bis(2-hydroxybenzylidene)-2,2-dimethyl-1,3-
propanediamine [19] they are inclined at an angle of
68.7(1)Њ.
Similarly, the mono Schiff bases obtained by con-
densation of salicylaldehyde with 2-aminopyridines
are examples of the nearly planar molecules [20–
22]; steric repulsion of hydrogen atoms cause
deviation from planarity in 2-(3-pyridyliminomethyl)
phenols [23,6]; in 2-(3-pyridylmethyliminomethyl)
phenol [7] there is a methylene group between the N
atom of the imino group and the pyridine ring, and the
benzene and pyridine rings are inclined at 89.9(2)Њ.
The present conformation of the molecule is not
favorable for direct coordination to the metal ion,
but rotations around bonds C6–C7, N1–C8, C12–
N3 and C13–C14 are possible.
Proton
Chemical shift d
(ppm)
Coupling constant J
(Hz)
H(O)
H(C7,C13
12.91
9.58
8.03
7.82
7.48
7.41
7.03
7.02
J9,10 = J10,11 = 7.7
J2,3 = J17,18 = 7.8
J3,4 = J16,17 = 7.8
J4,5 = J15,16 = 7.9
)
H(C10
)
H(C5,C15
H(C3,C17
H(C9,C11
H(C4,C16
H(C2,C18
)
)
)
)
)
and CCl4 are very similar, containing absorption
bands of enolimine in the range 1610–1620 cm−1
and 1548 cm−1 (CyN), 1285 cm−1 (C–O) and
2740 cm−1 (hydrogen bonded OH) [24–26]. In the
1H NMR spectrum of dimethylsulfoxide solution
taken at 50ЊC (Table 5), the signals of methine and
hydroxy protons appear at 9.58 and 12.91 ppm,
whereas in the CDCl3 solution at 45ЊC the corre-
sponding signals are at 9.48 and 13.34 ppm. Its
shape (singlets) and position (low fields) are charac-
teristic for enolimine with strong intramolecular bond
In non-polar solvents, similarly as in the solid state,
enolimine is the predominant tautomeric form of
Schiff bases of salicylaldehyde with amino- and
aminoalkylpyridines [5–7]. However, Schiff bases
originating from aminoalkylpyridines readily convert
to ketoamines, when changing to polar solvents like
ethanol, methanol or alcohol/water mixtures due to
formation of intermolecular hydrogen bonds [7]. It
has been shown that the tendency to tautomeric inter-
conversion is much less pronounced in the case of
Schiff bases of aminopyridines [6]. Electron
delocalization results in a decrease in imino nitrogen
basicity, followed by a weakening of the intra-
…
OH NyC [6,7]. Decrease in the temperature results
with further downfield shift of these signals (Table 6),
offering additional evidence for presence of intra-
molecular hydrogen bond.
Besides enolimine, no other forms are observable in
the 1H NMR and IR spectra of CCl4, CDCl3 and
(CD3)2SO solutions. Unfortunately, it was not pos-
sible to record IR and NMR spectra in more polar
solvents, because of the insufficient solubility of the
Schiff base. However, further informations about
structural characteristics in solution have been
obtained by UV absorption spectroscopy which has
enabled, due to its sensitivity, recording of spectra
…
molecular H bond OH NyC and reduced tendency
to tautomeric interconversion.
As expected, the IR spectra of N,NЈ-bis(salicyli-
dene)-2,6-pyridinediamine (Table 4) taken in KBr
Table 4
Characteristic IR bands (cm−1
pyridinediamine
) of N,NЈ-bis(salicylidene)-2,6-
Table 6
Dependence of chemical shifts of hydroxy and azomethine protons
on the temperature (solvent CDCl3)
Solvent
KBr
n(OH)
n(CyN)
n(C–N)
n(C–O)
25ЊC
30ЊC
35ЊC
40ЊC
45ЊC
2740vw
1610vs
1548m
1620vs
1548m
1438m
1285s
d(OH)
(ppm)
d(HCyN) 9.51
13.42
13.39
13.38
13.35
13.34
CCl4
2740vw
1435m
1285s
9.50
9.49
9.49
9.48
(ppm)
s, strong; v, very; m, medium; w, weak.

158
N. Galic´ et al./Journal of Molecular Structure 406 (1997) 153–158
Table 7
UV spectral data of N,NЈ-bis(salicylidene)-2,6-pyridinediamine in various solvents and corresponding tautomeric constants
Solvent
UV spectral data in solvent transparent region l (nm) (10−4 e (l mol−1 cm−1))
Kt [ketoamine]/[enolimine]
enolimine
enolimine
ketoamine
Diethylether
277(2.66)
277(2.66)
277(2.66)
278(2.66)
275(2.62)
275(2.58)
372(2.49)
373(2.49)
372(2.49)
371(2.48)
368(2.45)
367(2.40)
Dichloromethane
Tetrachloromethane
Dioxane
Methanol
Methanol/water 4/l
452(0.05)
452(0.10)
0.02
0.03
[9] G.M. Sheldrick, SHELXS-86, Program for the Automatic
Solution of Crystal Structures, University of Go¨ttingen,
Germany, 1986.
[10] G.M. Sheldrick, SHELXL-93, Program for the Refinement
of Crystal Structures, University of Go¨ttingen, Germany,
1993.
[11] I. Vickovic´, ORTEP92, J. Appl. Crystallogr., 27 (1994) 437.
[12] A.L. Spek, PLUTON, Univ. of Utrecht, The Netherlands,
1993.
[13] Cambridge Structural Database, V5.11, Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge, England,
April 1996.
[14] S.V. Lindeman, M.Yu. Antipin and Yu.T. Struchkov,
Kristallografiya, 33 (1988) 365.
[15] V.G. Puranik, S.S. Tavale, A.S. Kumbhar, R.G. Yerande, S.B.
Padhye and R.J. Butcher, J. Cryst. Spectrosc. Res., 22 (1992)
725.
in polar and non-polar solvents (Table 7). Whereas in
non-polar solvents only the bands of enolimine are
present, in polar solvents additional weak band of
ketoamine emerges at 452 nm. Approximate values
of corresponding tautomeric constants, Kt = [keto-
amine]/[enolimine], estimated on the basis of e values
at 452 nm (ketoamine) and 367–368 nm (enolimine),
amount to 0.02 (methanol) and 0.03 (methanol/water
4/1). Similar values of tautomeric constants have been
obtained for the structurally related 2-(2-pyridyl-
iminomethyl)phenol (Kt amounts to 0.02 in methanol
and 0.09 in methanol/water 4/1), and N,NЈ-bis(sali-
cylidene)-2,3-pyridinediamine (Kt amounts to 0.08 in
methanol and 0.14 in methanol/water 4/1) [7].
The compound studied here shows interesting
properties as analytical reagent for the determination
of metal ions. Preliminary investigations reveal stimu-
lating results for the development of a relevant
spectrofluorimetric method for aluminium.
[16] F. Mansilla-Koblavi, J.A. Tenon, S. Toure, N. Ebby, J.
Lapasset and M. Carles, Acta Cryst. C, 51 (1995) 1595.
[17] N. Hoshino, T. Inabe, T. Mitani and Y. Maruyama, Bull.
Chem. Soc. Jpn., 61 (1988) 4207.
[18] N. Bresciani Pahor, M. Calligaris, P. Delise, G. Dodic, G.
Nardin and L. Randaccio, J. Chem. Soc. Dalton Trans.,
(1976) 2478.
[19] J.P. Corden, W. Errington, P. Moore and M.G.H. Wallbridge,
Acta Cryst. C, 52 (1996) 125.
[20] I. Moustakali-Mavridis, E. Hadjoudis and A. Mavridis, Acta
Cryst. B, 34 (1978) 3709.
[21] C. Escobar and M.T. Garland, Acta Cryst. C, 39 (1983) 1463;
C40 (1984) 889.
[22] A.M. Atria, M.T. Garland, E. Spodine and L. Toupet, Acta
Cryst. C, 47 (1991) 1116.
[23] I. Moustakali-Mavridis, E. Hadjoudis and A. Mavridis, Acta
Cryst. B, 36 (1980) 1126.
[24] R. Herscovitsch, J.J. Charette and E. de Hoffman, J. Am.
Chem. Soc., 95 (1973) 5135.
[25] J.W. Ledbetter, J. Phys. Chem., 81 (1977) 54.
[26] G.C. Percy and D.A. Thornton, J. Inorg. Nucl. Chem., 34
(1972) 3357.
References
[1] R.K. Parashar, R.C. Sharma, A. Kumar and G. Mohan, Inorg.
Chim. Acta, 151 (1988) 201.
[2] E. Hadjoudis, J. Photochem., 17 (1981) 355.
[3] Z. Holzbecher and H.V. van Trung, Collect. Czech. Chem.
Commun., 41 (1976) 1506.
[4] J. Siepak, Polish. J. Chem., 59 (1985) 651.
[5] Z. Cimerman and Z. Stefanac, Polyhedron, 4 (1985) 1755.
[6] Z. Cimerman, N. Galesˇic´ and B. Bosner, J. Mol. Struct., 274
ˇ
(1992) 131.
[7] Z. Cimerman, R. Kiralj and N. Galic´, J. Mol. Struct., 323
(1994) 7.
[8] Z. Cimerman, V. Sinkovic´ and N. Galic´, Euroanalysis VIII,
Edinburgh, 1993.