Metal transition complexes of tridentate Schiff base ligands derived from 2-hydrazinopyridine: synthesis, spectroscopic characterization and X-ray structures

Article abstract of DOI:10.1007/s11243-019-00317-3

Mononuclear complexes of 1-(pyridin-2-ylmethylidene)-2-(pyridin-2-yl)hydrazine (HL¹) and 1-(pyridin-2-yl)-2-(1-(pyridin-2-yl)ethylidene)hydrazine (HL²), [Mn(HL¹)(Cl₂)(H₂O)] (1), [Zn(HL¹)(CH₃COO)₂]·(H₂O)₃ (2), [Mn(HL²)₂]·(ClO₄)₂ (3) and [Cu(HL²)(NO₃)₂(H₂O)] (4) were synthesized and characterized by physicochemical and spectroscopic methods and X-ray structure determination. The mononuclear compounds 1, 2 and 4 contain one ligand molecule per metal atom while the manganese (II) atom in compound 3 is coordinated to two ligand molecules. Both ligands coordinated to the transition metal center in?a tridentate fashion through two N_pyridyl atoms and one N_imino atom. The chloride and acetate anions coordinate in monodentate manner, respectively, in complex 1 and in complex 2. In complex 3, the perchlorate groups remain uncoordinated. In complex 4, the nitrate anions act in unidentate fashion. The molar conductance value indicates that the complexes obtained from HL¹ are non-electrolytes while those obtained from HL² are 2:1 electrolytes in DMF solutions. The X-ray structures reveal octahedral geometry for complexes 1, 3, 4 and trigonal bipyramidal environment for 2.

Full text of DOI:10.1007/s11243-019-00317-3

Transition Metal Chemistry
https://doi.org/10.1007/s11243-019-00317-3
Metal transition complexes of tridentate Schiꢀ base ligands derived
from 2‑hydrazinopyridine: synthesis, spectroscopic characterization
and X‑ray structures
Amar Diop1 · Mamou Sarr1 · Mayoro Diop1 · I1brahima Elhadj Thiam · Aliou Hamady Barry2
1
·
Simon Coles3 · James Orton3 · Mohamed Gaye
Received: 24 January 2019 / Accepted: 15 March 2019
©
Springer Nature Switzerland AG 2019
Abstract
Mononuclear complexes of 1-(pyridin-2-ylmethylidene)-2-(pyridin-2-yl)hydrazine (HL ) and 1-(pyridin-2-yl)-2-(1-(pyridin-
1
2
1
1
2
2
-yl)ethylidene)hydrazine (HL ), [Mn(HL )(Cl )(H O)] (1), [Zn(HL )(CH COO) ]·(H O) (2), [Mn(HL ) ]·(ClO ) (3) and
2
2
3
2
2
3
2
4 2
2
[
Cu(HL )(NO ) (H O)] (4) were synthesized and characterized by physicochemical and spectroscopic methods and X-ray
3
2
2
structure determination. The mononuclear compounds 1, 2 and 4 contain one ligand molecule per metal atom while the
manganese (II) atom in compound 3 is coordinated to two ligand molecules. Both ligands coordinated to the transition metal
center in a tridentate fashion through two N
atoms and one N
atom. The chloride and acetate anions coordinate in
imino
pyridyl
monodentate manner, respectively, in complex 1 and in complex 2. In complex 3, the perchlorate groups remain uncoordi-
nated. In complex 4, the nitrate anions act in unidentate fashion. The molar conductance value indicates that the complexes
1
2
obtained from HL are non-electrolytes while those obtained from HL are 2:1 electrolytes in DMF solutions. The X-ray
structures reveal octahedral geometry for complexes 1, 3, 4 and trigonal bipyramidal environment for 2.
Introduction
scientists to increase their interest in biomimetic processes.
The involvement of transition metal centers in biological
processes depends on several parameters such as the degree
of oxidation [12] and the number of coordinations in the
complex [13]. Schiꢀ bases in the presence of carboxylate,
perchlorate or nitrate anions can react with transition metal
ions to generate a wide range of coordination types with
widely varying architectures [14, 15]. Polydentate ligands
containing both hard donor sites and soft donor sites are
designed to provide special topological structures [16, 17].
For this, both the synthesis of the ligand and that of the
complex must be controlled [18, 19]. In this context, the
Schiꢀ bases 1-(pyridin-2-ylmethylidene)-2-(pyridin-2-yl)
Although largely explored, the coordination chemistry of
metal transition remains very interesting owing to the vari-
ability of the structures [1–3] and the possibility of applica-
tions in industries [4–6] of the complexes synthesized in
this kind of chemistry. According to the metal center used,
several degrees of oxidation, [7, 8] diꢀerent coordination
numbers and original geometries that are not always eas-
ily predicted can be observed. The involvement of transi-
tion metal ions in various important biological processes
[
9–11] increases the interest of chemists in coordination
chemistry. The examples provided by nature encourage
1
hydrazine (HL ) [20, 21] which provide three soft-donating
N atoms from two pyridine rings and one imino nitrogen
atom were used together with metal transition salts to yield
metal transition complexes in which acetate and nitrate ani-
ons can act with hard oxygen-binding sites. The synthetic
procedures adopted are essential for yielding complexes with
*
Mohamed Gaye
mlgayeastou@yahoo.fr
1
2
3
Department of Chemistry, University Cheikh Anta Diop,
BP 5192, Dakar, Fann, Senegal
1
2
peculiar structure. The two organic molecules HL and HL
Department of Chemistry, University de Nouakchott,
Nouakchott, Mauritanie
(
1-(pyridin-2-yl)-2-(1-(pyridin-2-yl)ethylidene)hydrazine)
can adopt two conꢁguration types of E and Z [22]. In the
E conꢁguration, the ligand oꢀers a terpyridine-like coordi-
nation environment [23, 24] in which the relative position
UK National Crystallography Service, School of Chemistry,
Faculty of Engineering and Physical Sciences, University
of Southampton, Southampton SO17 1BJ, UK
Vol.:(0
1
123456789)
3

Transition Metal Chemistry
−
1
−1
of the nitrogen atoms allows for the formation of stable
M
cm ) 290 (1.1), 310 (1.0), 330 (2.9), 360 (1.1). IR
−
1
ꢁ
ve-membered metallo-cycles after the coordination of the
(cm in DMSO): 3204, 1635, 1600, 1571, 1293, 765.
2
1
three soft nitrogen binding sites to the same metal atom. The
HL The same procedure used for the synthesis of HL
1
2
ligand HL was used in our previous attempts to prepare
was repeated for the synthesis of HL ; 2-acetylpyridine was
used instead of 2-pyridinecarbaldehyde. On cooling, a yel-
new mono- and binuclear complexes. We used a one-pot
synthesis method for the synthesis of dinuclear lanthanide
complexes [25–27] and a heptacoordinated Mn(II) complex
low powder was aꢀorded (80%). Melting point: 54 °C. δ
H
(250 MHz, DMSO-d ): 11.2 (1H, s, H–N–N); 6.6-8.8 (8H,
6
[
28]. Continuing our study in coordination chemistry of the
mult, H-Py); 1.1 (3H, s, CH -C=N). δ (250 MHz, DMSO-
3
C
behavior of this ligand and its homolog in which the acidic
d ): 13.8 (CH ); 109.5 (C ), 113.5 C ), 124.0 (C ), 126.3
6 3 Ar Ar Ar
2
proton is substituted by a methyl group (HL ), mononuclear
(C ), 136.1 (C ), 138.5 (C ), 145.2 (C=N), 148.4 (C ),
Ar Ar Ar Ar
complexes of manganese, copper and zinc are prepared and
characterized by spectroscopic methods and X-ray diꢀrac-
tion analysis.
149.1 (C ), 153.9 (C ), 155.9 (C ). UV–Vis (λ, nm) (ε,
Ar
Ar
Ar
−
1
−1
M
cm ) 294 (1.0), 312 (1.1), 332 (2.9), 358 (1.0). IR
−
1
(cm ): 3230, 3230, 1651, 1600, 1569, 1287, 768.
Synthesis of complexes (1–4)
Experimental section
1
To a solution of 1 mmol of the desired ligand (HL or
2
Starting materials and instrumentations
HL ) in 10 mL of ethanol was added a solution of 1 mmol
2
+
2+
−
−
of the MX .nH O (M = Mn and X = Cl , ClO
,
2
2
4
2
+
2+
−
2+
2+
Commercially available 2-pyridincarbaldehyde, 2-acetylpyr-
idine, 2-hydrazinopyridine and metals transition salts were
purchased from Aldrich and used without further puriꢁca-
tion. The analyses for carbon, hydrogen and nitrogen were
carried out using a LECO CHNS-932 instrument. The IR
spectra were recorded on a Perkin Elmer Spectrum Two
n = 4; M = Cu and X = NO , n = 3; M = Zn and
3
−
X=CH COO , n=2). The mixture was stirred under reꢂux
3
for 60 min, and the resulting solution was ꢁltered oꢀ and the
ꢁltrate was kept at 298 K. Upon keeping ethanol solutions
for 3 days, colored crystals suitable for X-ray diꢀraction
were aꢀorded.
−
1
1
spectrophotometer (4000–400 cm ). UV–Vis spectra were
Complex 1 [Mn(HL )(Cl )(H O)]. Green crystals yield:
2
2
−
3
recorded in methanol solution concentration of 10 M at
5 °C, and wavelength was reported in nm using a Perkin
Elmer Lambda 365 UV/Vis spectrophotometer. The molar
75%. Anal. calc. for C H Cl MnN O: C, 38.6; H, 3.5; N,
11 12 2 4
2
16.1%. Found: C, 38.6; H, 3.5; N, 16.4%.
1
Complex 2 [Zn(HL )(OAc) ].(H O) . Yellow crystals
2
2
3
−
3
conductance of 10 M solution of the metal complex in
DMF was measured at 25 °C using a WTW LF-330 con-
ductivity meter with a WTW conductivity cell. Room-tem-
perature magnetic susceptibility of the powdered sample
was measured using a Johnson Matthey scientiꢁc magnetic
yield: 60%. Anal. calc. for C H N O Zn: C, 41.3; H, 5.1;
15 22 4 7
N, 12.9%. Found: C, 41.4; H, 5.0; N, 12.8%.
2
Complex 3 [Mn(HL ) ].(ClO ) . Orange crystals yield:
2
4 2
80%. Anal. calc. for C H Cl MnN O : C, 42.5; H, 3.6; N,
2
4
24
2
8
8
16.5%. Found: C, 42.6; H, 3.4; N, 16.4%.
2
susceptibility balance (calibrant Hg[Co(SCN) ]).
Complex 4 [Cu(HL )(NO ) (H O)]. Green crystals yield:
4
3 2
2
4
5%. Anal. calc. for C H CuN O : C, 34.5; H, 3.4; N,
12 14 6 7
Synthesis of ligands
20.1%. Found: C, 34.4; H, 3.5; N, 20.0%.
1
HL The Schiꢀ base ligand 1-(pyridin-2-yl)-2-(pyridin-
X‑ray crystallography
1
2
-ylmethylene)hydrazine (HL ) was synthesized as fol-
lows: 2-Hydrazinopyridine (1.0913 g, 10 mmol) in 20 mL of
ethanol was added to a solution of 2-pyridinecarbaldehyde
Diꢀractometer: Rigaku AFC12 goniometer equipped with an
enhanced sensitivity (HG) Saturn724+detector is mounted
at the window of an FR-E + Superbright Mo-Kα rotating
anode generator (λ=0.71075 Å) with VHF Varimax optics
(100 µm focus). Powder X-ray diꢀraction was carried out
using a Bruker D2 Phaser with a LYNXEYE detector and
Cu-Kα radiation (1.5405 Å). Cell determination, data collec-
tion, data reduction, cell reꢁnement and absorption correc-
tion: CrysAlisPro 1.171.39.34b. [29]. Gaussian absorption
correction was applied. Structure solution and reꢁnement
were performed using SHELXT [30] and SHELXL-2014/7
[31]. All hydrogen atoms were added in calculated positions
and reꢁned in riding mode on the parent atom. Molecular
(
1.0711 g, 10 mmol) dissolved in 25 mL of methanol. The
resulting mixture was stirred under reꢂux during 30 min.
After cooling, the solution was completed to 100 mL with
ethanol and stored in the refrigerator. Ten milliliters of this
solution was evaporated to dryness, and the NMR spectrum
of the resulting liquid was recorded. δ (250 MHz, DMSO-
H
d ): 11.2 (1H, s, H–N–N); 8.5 (1H, d, J 4.7 Hz, H-Py); 8.1
6
(
1H, s, H–C=N); 6.8-8.5 (8H, mult, H–Py). δ (250 MHz,
C
DMSO-d ):106.5 (C ), 115.5 (C ), 118.8 (C ), 122.9
6
Ar
Ar
Ar
(
C ), 136.4 (C ), 138.0 (C ), 139.2 (C=N), 147.8 (C ),
Ar
Ar
Ar
Ar
1
49.2 (C ), 154.3 (C ), 156.7 (C ). UV–Vis (λ, nm) (ε,
Ar
Ar
Ar
1
3

Transition Metal Chemistry
graphics were generated using ORTEP-3 [32]. The crystal
and reꢁnement data are summarized in Table 1. Crystal-
lographic data for the structures reported in this paper have
been deposited within the Cambridge Crystallographic Data
Centre with the CCDC numbers: 1889247-1889250. The
data can be obtained free of charge on application to the
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
slow evaporation for yielding crystals suitable for X-ray
diꢀraction.
The elemental analysis results are in good agreement
with the calculated values for the four synthesized mono-
nuclear complexes which are non-hygroscopic and sta-
ble in air. The electrolytic nature of the complexes was
−
3
measured in DMF at 10 M. The molar conductivities
1
−1
2
−1
+
44(0)1223-336033 or e-mail: deposit@ccdc.cam.ac.uk.
Λ of the complexes of HL are 26 Ω cm mol for
−
1
2
−1
manganese (II) complex (1) and 5 Ω cm mol for zinc
(
II) complex (2), indicating that they are non-electrolytic
2
Results and discussions
in DMF solutions, while the values of complexes of HL
−
1
2
−1
are 190 Ω cm mol for manganese (II) complex (3)
−
1
2
−1
General studies
and 180 Ω cm mol for copper (II) complex (4) which
are 2:1 electrolytes in DMF solutions [33]. The copper
complex probably dissociates in DMF solution. The val-
ues of the magnetic moment at room temperature for the
three diamagnetic complexes are indicative of the pres-
ence of one metal atom per molecule. In fact, for man-
ganese (II) complexes, the magnetic moment values of
5.69 μ and 5.54 μ for complex (1) and complex (3),
The intention of the reported work was to study the coor-
dination chemistry of ligands isolated from condensation
1
of 2-hydrazinopyridine and 2-formylpyridine (HL ) or
2
2
-acetylpyridine (HL ) which can act as strong chelating
ligand, to produce complexes with transition metal ions
(
Scheme 1). Accordingly, the ethanolic solution of organic
B
B
ligand was treated with transition metal salts in 1:1 molar
ratio. The resulting solution was ꢁltered oꢀ and left under
respectively, are in accordance with the presence of one
manganese (II) atom per molecule [34]. For complex (4)
Table 1 Crystallographic data and reꢁnement parameters for complexes 1–4
Compound
1
2
3
4
Chemical formula
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C H Cl MnN O
342.09
C H N O Zn
435.73
Triclinic
P-1
7.6585(2)
9.9819(2)
12.6480(2)
C H Cl MnN O
678.35
C H CuN O
7
417.83
Monoclinic
1
1
12
2
4
15 22
4
7
24 24
2
8
8
12 14
6
Orthorhombic
Pbca
11.3134(2)
13.4826(2)
18.1982(2)
90
Monoclinic
Cc
12.1531(2)
12.2039(2)
19.1297(4)
90
P2 /n
1
9.1235(1)
13.5827(1)
13.5991(2)
90
α (°)
79.4320(10)
β (°)
γ (°)
V (Å )
90
90
83.103(2)
86.327(2)
942.74(3)
2
1.535
1.35
100(2)
90.705(2)
90
2837.01(9)
4
1.588
0.72
106.121(1)
90
1618.96(3)
4
1.714
1.40
3
2776.05(7)
8
1.637
1.33
100(2)
Z
ρcalc. (g cm−3)
−
1
μ (mm
T (K)
)
100(2)
100(2)
hkl range
−14, 12; −15, 17;
−9, 9; −12, 12; −16, 16
−15, 15; −15, 15; −24, 24
−11, 11; −17, 17; −15, 17
−
23, 23
No. measured reꢂ.
No. independent reꢂ.
Reꢂections with [I>2σ(I)]
No. of parameters
Rint
16,552
3177
2926
15,746
4241
4162
31,604
6476
6315
18,302
3669
3548
178
267
547
246
0.035
0.029
0.071
1.05
0.028
0.024
0.062
1.07
0.025
0.057
0.159
1.07
0.032
0.025
0.069
1.05
R (F) [I>2σ(I)]
1
2
wR (F )
2
Goodness-of-ꢁt
3
Δρmin;max (e Å )
0.45, −0.32
0.40, −0.32
0.85, −0.76
0.57, −0.42
1
3

Transition Metal Chemistry
Scheme 1 Synthetic scheme for
ligands and complexes prepara-
tion
of copper (II), the magnetic moment value of 1.66 μ
chelation modes of carboxylate ions: Δν for monoden-
tate bonding increases compared to the free anion; Δν
decreases for bidentate chelating; and Δν remains similar
to the free anion for bidentate bridging. In 1985 [37], they
restated these modes of coordination and it seems that
only the unidentate criterion is valid: ν (CO ) higher and
B
is in the range expected for a mononuclear copper (II)
complex [35]. The infrared spectra of the various syn-
thesized compounds were used to determine the differ-
ent coordination modes of organic ligands and transition
metal anions. In all infrared spectra of the complexes, a
as
2
strong shift to low frequencies of the bands attributed to
ν (CO ) lower. In the case of complex (2), the values of
s
2
1
−1 −1
ν
of the free ligands is observed. Indeed, for HL , the
ν (CO )=1587 cm and ν (CO )=1388 cm indicate the
C=N
as 2 s 2
−
1
frequency which was located at 1635 cm has strongly
presence of a monodentate coordinated acetate [38]. In
−
1
shifted to 1605 cm for complex 1. In the infrared spec-
trum of complex (2), a strong and broad band centered at
the case of complex (3), the additional bands at 1070 and
−
1
619 cm clearly reveal non-coordinated perchlorate anion
playing the role of counterion [39]. In the spectrum of
the copper complex (4), bands attributable to coordinated
and uncoordinated nitrate groups are observed. The sharp
−
1
1
586 cm which has obscured the band attributable to
2
C=N is observed. In the case of ligand HL , the band cen-
−
1
−1
−1
tered at 1652 cm is shifted to 1614 cm and 1619 cm ,
−
1
respectively, for complexes (3) and (4). In the IR spec-
and intense band at 1394 cm is attributed to the ionic
−
1
−1
trum of complex 1, additional bands at 3223 cm and
nitrate group while the two bands at 1245 and 1061 cm
−
1
9
07 cm are noted which indicate the presence of coor-
are assigned to ν and ν , respectively. The difference
5
2
dinated water molecules. For compound 2, other charac-
Δν=ν − ν is a criterion for evaluating the coordination
5 2
−
1
teristic bands at 3370, 1586 and 1388 cm , respectively,
mode of the nitrate group. The Δν value increases from
monodentate mode to bidentate mode. In the case of this
attributable to free water molecule, asymmetric vibration
−
−1
and symmetrical vibration of CH COO acetate group are
copper complex, the value Δν = 184 cm indicates the
3
observed. In 1980, Deacon and Phillips [36] established
presence of unidentate nitrate group in complex (4) [40].
criteria on the basis of Δν = ν − ν for assignment of
The UV–Vis spectra of both compounds are recorded
as
s
1
3

Transition Metal Chemistry
in methanol solution in the range of 200–1000 nm. The
Crystal structure descriptions
2
1
UV–Vis spectra of the ligands HL and HL show one
absorption band attributable to the π → π* transition of
the pyridine rings in the range 280–295 nm. Additional
band in the range 310–330 nm which can be attributed to
the n → π* transitions of the C=N chromophore is also
observed. For complexes (1), (2) and (4), high intensity
bands due to LMCT appeared in the range 300–450 nm.
The spectrum of the copper (II) complex (4) shows one
absorption band at 546 nm which may be due to dxz,
Suitable single crystals for X-ray diꢀraction of complexes
1, 2, 3 and 4 were obtained by slow solvent evaporation at
room temperature. Crystal data, collection and reꢁnement
parameters are listed in Table 1. Selected bond lengths and
angles are summarized in Table 2. Hydrogen bond data for
complex are gathered in Table 3. Figures 1, 2, 3 and 4 dis-
play the asymmetric unit of all compounds with main atom
numbering.
2
2
dyz → dx − y transition. This transition band is indica-
tive of copper (II) atom with distorted square pyramidal
geometry as reported in the literature [41].
Compound 1 crystallizes in the orthorhombic system with
the space group Pbca. An ORTEP view of the structure is
shown in Fig. 1. In the asymmetric unit, there is a single
Table 2 Selected bond distances [Å] and angles [deg] for complexes 1, 2, 3 and 4
1
2
3
4
Cl1–Mn1
Cl2–Mn1
Mn1–O1
Mn1–N1
Mn1–N3
Mn1–N4
N1–Mn1–N4
O1–Mn1–Cl2
N1–Mn1–Cl2
N3–Mn1–Cl2
N4–Mn1–Cl2
O1–Mn1–Cl1
N1–Mn1–Cl1
N4–Mn1–Cl1
Cl2–Mn1–Cl1
2.5294(5)
2.4132(5)
2.2356(14)
2.2461(16)
2.2501(15)
2.2781(14)
141.22(6)
92.91(4)
105.28(5)
175.70(4)
112.49(4)
174.06(4)
92.64(4)
Zn1–N1
Zn1–N3
Zn1–N4
Zn1–O21
Zn1–O31
2.1639(12)
2.1276(12)
2.1931(12)
1.9714(10)
1.9684(10)
Mn1–N3
Mn1–N24A
Mn1–N21
Mn1–N21A
Mn1–N1
Mn1–N4
Mn1–N23
Mn1–N23A
Mn1–N24
N3–Mn1–N21
N24–Mn1–N4
N21–Mn1–N4
N4–Mn1–N1
N3–Mn1–N23
N1–Mn1–N23
2.222(5)
2.217(16)
2.266(13)
2.305(15)
2.223(5)
2.222(4)
2.308 (13)
2.189(15)
2.180(15)
103.4(3)
99.9(3)
Cu1–N3
Cu1–O41
Cu1–N1
Cu1–N4
Cu1–O21
Cu1–O31
N3–Cu1–N1
N3–Cu1–O41
O21–Cu1–O31
O41–Cu1–O21
O41–Cu1–N4
N1–Cu1–N4
N3–Cu1–O21
O41–Cu1–N1
N4–Cu1–N3
1.9513(11)
1.9583(10)
2.0042(11)
2.0096(12)
2.2721(10)
2.6225(11)
79.97(5)
165.50(5)
168.96(4)
93.78(4)
101.56(5)
159.13(5)
100.01(4)
96.66(4)
O31–Zn1–N3
O21–Zn1–N3
O31–Zn1–N1
O21–Zn1–N1
N3–Zn1–N1
O31–Zn1–N4
O21–Zn1–N4
N3–Zn1–N4
N1–Zn1–N4
120.74(5)
122.96(4)
99.17(5)
101.11(4)
74.27(5)
91.53(4)
101.85(4)
73.50(4)
147.08(5)
93.6(6)
142.56(15)
176.1(4)
109.8(4)
93.79(4)
93.028(17)
79.86(5)
Table 3 Intermolecular and
intramolecular contacts in 1, 2
and 4 (values in Å and deg)
Complex
D—H···A
O1—H1A···Cl1i
D—H
H···A
D···A
D—H···A
1
0.77(3)
0.77(3)
0.95
2.35(3)
2.34(3)
2.36
3.1206(15)
3.1068(15)
2.9607(17)
2.8496(18)
2.9106(16)
2.8636(18)
2.7266(17)
2.8089(18)
2.7453(17)
2.7490(17)
2.7990(16)
2.7409(16)
2.7155(14)
176(2)
178(3)
120.9
ii
O1—H1B···Cl2
iii
2
C6—H6···O31
iv
N2—H2A···O22
0.959(18)
1.896(18)
172.4(16)
156(2)
156(2)
175(2)
174(2)
166(2)
165(2)
168(2)
171(2)
171(2)
O61—H61A···O21
O61—H61B···O51
O41—H41A···O32
O41—H41B···O51
O51—H51A···O61
O51—H51B···O41
N2—H2A···O31
0.77(3)
0.83(3)
0.86(2)
0.85(2)
0.82(2)
0.84(2)
0.86(3)
0.76(2)
0.85(2)
2.19(3)
2.08(3)
1.87(2)
1.96(2)
1.95(2)
1.93(2)
1.95(3)
1.99(2)
1.87(2)
v
vi
vii
4
O41—H41A···O32
O41—H41B···O22
viii
Symmetry codes: (i) −x+1/2, y−1/2, z; (ii) −x, −y+1, −z+1; (iii) −x+1, −y+1, −z+1; (iv) −x+2,
−
−
y+1, −z+1; (v) −x+2, −y, −z; (vi) −x+1, −y, −z; (vii) −x+1, −y+1, −z; (viii) −x+1, −y+1,
z+1
1
3

Transition Metal Chemistry
plan is 359.008° while the angle subtended by the atoms in
apical position (N1–Mn–N4=141.22(6)°) is considerably
diꢀerent of the ideal value of 180°. The octahedral polyhe-
dron is severely distorted. The distances Mn–N are in the
range 2.2461(16)–2.2781(15) Å and are comparable with
the values found for analogous complex dichlorido(2,4,6-
tri-2-pyridyl-1,3,5-triazine)manganese(II) [42]. The Mn–Cl
(
Mn–Cl1 = 2.5294(5) and Mn–Cl2 = 2.4132(5) Å) are the
longest distances while the shortest distance is Mn–O
water
with 2.2356(14) Å. In this compound, there are intermo-
lecular hydrogen bonds involving, respectively, the OH of
one of the coordinated water molecules as donors and the
coordinated chloride atoms as acceptor (O2–H1A…Cl1 and
O2–H1B…Cl2) (Table 3).
Fig. 1 ORTEP plot (30% probability ellipsoids) showing the mol-
ecule structure of the manganese (II) complex of HL1
The X-ray structural determination of compound 2
1
derived from HL reveals a mononuclear neutral zinc (II)
complex which crystallizes in the triclinic system with the
space group P-1. An ORTEP view of the compound for-
1
mulated as [Zn(HL )(CH COO) ](H O) is shown in Fig. 2.
3
2
2
3
The complex is built up as a mononuclear zinc (II), and
the metal atom is linked to three nitrogen atoms from the
organic ligand molecule and to two acetate groups which
act in a monodentate fashion. The coordination geometry
around the zinc (II) atom is best discussed with the trigo-
nality index. In fact, the Addison index [43] τ=(β−α)/60
where β and α are the largest values of the bond angles
around zinc (II) atom can be used to attribute the geometry
of a penta-coordinated metal complex. When the geom-
etry is a perfect square pyramidal τ = 0 and when τ = 1, a
perfect trigonal bipyramidal geometry is obtained. In the
penta-coordinated environment of the zinc (II) atom in our
complex, the τ value of 0.352 is indicative of a distorted
square pyramidal geometry around the metal center. How-
ever, when the modiꢁed index suggested by Konno et al.
[
44], χ=(β + γ+δ − 2α)/180 (which takes into account the
other angles β and α are the largest angles, γ and δ are the
other angles around the metal centers without the donor
atoms deꢁning β) is used, the χ value of 0.750 suggests
that the geometry around the zinc (II) atom is a distorted
trigonal bipyramid. The equatorial plan is occupied by
N3, O21 and O31 with angle values in the close proxim-
ity of the ideal value of 120° (N3–Zn–O31 = 120.74(5)°,
N3–Zn-O21=122.96(4)° and O21–Zn–O31=116.14(5)°).
The value of the sum of the subtended angles is 359.84°.
The apical positions are occupied by N1 and N4 with an
angle N1–Zn–N4 = 147.08(5)° severely deviated from
the ideal value of 180°. The oxygen atom of the acetate
groups is strongly linked to the zinc (II) atom as shown
by the short distance values of Zn1–O21= 1.9714(10) Å
and Zn–O31 = 1.9684(10) Å. These values are in accord-
ance with those found for similar complexes in which the
acetate group acts in unidentate fashion [45]. The dis-
tance Zn–N falls in the range 2.1276(12)–2.1931(12) Å
Fig. 2 ORTEP plot (30% probability ellipsoids) showing the mol-
1
ecule structure of the zinc (II) complex of HL
molecule of complex formed by a manganese (II) atom
1
which is bound to one organic ligand HL , one water mol-
ecule and two chloride anions. The ligand acts in tridentate
fashion through one azomethine and two nitrogen atoms
from pyridine rings. The manganese (II) atom is hexacoor-
dinated, and the geometry around the manganese (II) center
is best described as an octahedral polyhedron. The basal
plane is occupied by O1, N3, Cl1 and Cl2 atoms, the apical
positions being occupied by the two nitrogen atoms from
the pyridine rings. The sum value of the angles in the basal
1
3

Transition Metal Chemistry
Fig. 3 ORTEP plot (30% prob-
ability ellipsoids) showing the
molecule structure of the man-
2
ganese (II) complex of HL
and is comparable with the values found for the complex
polyhedron around the manganese atom is constructed by
2
[
Zn(CH COO) (4-pyao) ] (4-pyao=pyridine-4-aldoxime;
two neutral ligand molecules HL which acts in tridentate
3
2
2
4
-pyamo=pyridine-4-amidoxime [27]. In this compound,
fashion. The manganese (II) atom is coordinated to each of
2
there are intermolecular hydrogen bonds involving, respec-
tively, the NH of the hydrazino moiety of the ligand mol-
ecule and OH of one of the uncoordinated water molecules
as donors and the oxygen atoms of the coordinated acetate
group as acceptors (N2-H…O22 and O51–H…O32). Intra-
molecular hydrogen bonds involving uncoordinated water
molecule are also observed (Table 3).
the two HL ligands through three nitrogen donor atoms.
The two nitrogen pyridine atoms and the azomethine atom
are coordinated to the manganese (II) while the N–H atom
of the hydrazino moiety remains uncoordinated. The basal
plan is occupied by N1, N4, N21 and N24 while the api-
cal positions are occupied by N3 and N23. The angles in
the basal plan N1‒Mn‒N4 = 142.44(12), N21‒Mn‒
N24 = 139.9(4)° and the angles between the apical atoms
N3‒Mn‒N23=173.2(3)° are indicative of a severely dis-
torted octahedral polyhedron around the manganese (II)
atom center. This strong distortion can be explained by the
formation of ꢁve-membered ring which deviates the angle
N‒Mn‒N from 90° to 71°. One of the perchlorate anions
2
Compound 3 which is formulated as [Mn(HL ) ](ClO )
2
4 2
crystallizes in the monoclinic crystal system with Cc space
group. In the asymmetric unit, one discrete mononuclear
complex is present with two perchlorate anions. Figure 3
depicts the perspective view of the complex. Selected bond
lengths and angles are listed in Table 2. The coordination
1
3

Transition Metal Chemistry
Fig. 4 ORTEP plot (30% prob-
ability ellipsoids) showing the
molecule structure of the copper
(
II) complex of HL2
−
(
ClO ) is disordered and was constrained to be tetrahedral
around the Cu atom center. The two apical Cu–ONO dis-
4
2
with three sites having occupancies of 0.236(3), 0.221(3)
and 0.543(2). Both atoms of one of the ligand molecules are
disordered with two sites having occupancies of 0.419(4)
and 0.581(4). The chain bridging the two pyridine rings
in the ligand is disordered. The bond lengths in the bridg-
ing chain C–CH = N–NH–C are, respectively, 1.405(12)
and 1.44(3) Å for C–C, 1.328(14) and 1.24(4) Å for C=N,
tances are signiꢁcantly diꢀerent (Cu–O21 =2.2721(10) Å
and Cu–O31 = 2.6265(11) Å while the equatorial Cu–N
and Cu–OH distances are in the range [1.9513 Å–2.0096
2
Å]. The axial elongation is due to the Jahn–Teller distor-
9
tion of the degenerated d electronic ground state. The hard
donor site O31–NO is weakly coordinated to the soft cop-
2
per (II) and can be easily dissociated as observed with the
conductance measurement and the infrared spectroscopy.
Intramolecular hydrogen bond involving the OH of the
coordinated water molecule as donor and an oxygen atom
of the coordinated nitrate group as acceptor (O41–H41A…
O32) is observed. Intermolecular hydrogen bonds involving
the NH of the hydrazine moiety of the ligand as donor and
an oxygen atom of the coordinated nitrate group as accep-
tor (N2–H2A…O31) and the OH of the coordinated water
molecule as donor and an oxygen atom of the nitrate group
as acceptor (O41–H41B…O22) are also observed (Table 3).
1
.37(2) and 1.36(2) Å for N–N and 1.316(9) and 1.326
(
18) Å for N–C. These bonds are slightly longer than those
observed for this ligand in other complexes [27]. This may
be related to the disorder detected for this chain.
X-ray diꢀraction of the copper (II) complex 4 reveals that
the compound crystallizes in the monoclinic system with
space group of P2 /n. The selected bond lengths and angles
1
are listed in Table 2. Figure 4 shows the asymmetric unit
which is composed of one copper (II) atom linked in triden-
tate fashion to the organic ligand via one azomethine and
two nitrogen atoms from pyridine rings, one coordinated
water molecule and two coordinated nitrates acting as uni-
dentate units. The metal center is hexacoordinated, and the
copper (II) atom is in a distorted octahedral environment.
The basal plane is occupied by N1, N3, N4 and O41 atoms,
the apical positions being occupied by O21 and O31 from
the monodentate nitrato ligands. The angles in the basal plan
N1‒Cu‒N3 = 79.87(5)°, N3‒Cu‒N4 = 79.86(5)°, N4‒
Cu‒O41=101.56(5)°, N1‒Cu‒O41=96.66(4)°, N3‒Cu‒
O41=165.50(5)°, N1‒Cu‒N4=159.13(5)° and the angles
between the apical atoms O21‒Cu‒O31 = 168.96(4)° are
indicative of a severely distorted octahedral polyhedron
Conclusion
1
2
The mononuclear complexes of the ligand HL and HL
derived from 2-hydrazinopyridine are synthesized and char-
acterized. The complexes are characterized by elemental
analysis, IR and UV–Vis spectroscopies, magnetic meas-
urements, conductivity study and X-ray diꢀraction analysis.
Both ligands coordinated to transition metal center in triden-
tate fashion to generate mononuclear complex in each case.
1
3

Transition Metal Chemistry
2
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