Synthesis and characterisation of ammonium mediated assembly of two neutral nickel(II) Schiff base fragments

Article abstract of DOI:10.1016/j.ica.2011.08.026

The 1:2 condensation of o-phenelenediamine and o-vanilline yields a compartmental N₂O₄ ligand N,N′-(1,2-Phenylene)- bis(3-methoxysalicylideneimine) [H₂L]. When nickel(II) thiocyanate is added to the methanol solution of H<

Full text of DOI:10.1016/j.ica.2011.08.026

Inorganica Chimica Acta 378 (2011) 303–306
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Note
Synthesis and characterisation of ammonium mediated assembly of two
neutral nickel(II) Schiff base fragments
⇑
Mithun Das, Shouvik Chattopadhyay
Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata 700 032, India
a r t i c l e i n f o
a b s t r a c t
The 1:2 condensation of o-phenelenediamine and o-vanilline yields a compartmental N2O4 ligand N,N0-
(1,2-Phenylene)-bis(3-methoxysalicylideneimine) [H2L]. When nickel(II) thiocyanate is added to the
methanol solution of H2L, followed by addition of ammonium thiocyanate, an unusual nickel(II) com-
pound, [NH4(NiL)2SCN]ꢀH2O (1), is separated out in which an ammonium ion is sandwiched between
two neutral square planner NiL moieties. Hydrogen bonding interactions are observed among the ammo-
nium ion, NiL moieties, the thiocyanate anion and the water of crystallization. The compound is charac-
terized by C, H, N analysis, UV–VIS and IR spectroscopy, room temperature magnetic susceptibility
measurement and X-ray crystal diffraction study. The compound crystallizes in monoclinic space group
P21/n with a = 13.8636(7) Å, b = 14.0267(7) Å, c = 22.2715(10) Å and b = 94.301(3)°.
Article history:
Received 5 April 2011
Received in revised form 9 July 2011
Accepted 11 August 2011
Available online 22 August 2011
Keywords:
Nickel(II)
Ammonium
Schiff base
N2O4 ligand
Crystal structure
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
three compounds use nickel salen to trap ammonium ion. No
report of the preparation of 3d/ammonium compounds with
Current research in the field of supramolecular chemistry has
shown that small building blocks can lead, through self-assembly
processes, to large, well-defined structures, which are held to-
gether by non-covalent interactions such as hydrogen bonds
[1,2]. In the design and synthesis of multidentate ligands compe-
tent of participating in complicated molecular structures upon
complexation, in pre-arranged manners, with transition metals,
have also been done successfully [3–5]. Many examples of these
types of ligands were provided by the Salen family of Schiff bases,
which coordinate to various kinds of transition and typical metals
to give stable compounds, some of which are frequently used as
catalysts [6–8], models of metalloenzymes [9,10], NLO materials
[11,12] and building blocks for interlocked molecules [13]. Transi-
tion metal compounds of tetradentate Schiff bases can also act as
chelating agents towards both transition [14–18] and non-transi-
tion metal ions [19–22] including alkali [23–28] and alkaline earth
metals [29,30]. Among them, investigation on the compounds con-
taining the alkali metal/ammonium ions is of utmost interest in
connection with a more comprehensive view of the chemistry of
do cations and with the influence of positive charges on the elec-
tronic properties of the transition-metal centre.
salphen 1:2 condensation product of o-phenylenediamine and
salicylaldehyde or substituted salphen is found in the literature,
probably due to the relative instability of the compounds caused
by the enhanced rigidity imposed to ligand by the o-phenelenedi-
amine moiety. Our attempts with H2L [N,N0-(1,2-Phenylene)-bis
(3-methoxysalicylideneimine)] furnished for the first time,
ammonium sandwiched compound with such sterically strained
ligand. X-ray crystal structure determination of it has established
the structure. Herein, we report the facile synthesis, spectroscopic
characterisation, and magnetic property of [NH4(NiL)2SCN]ꢀ
H2O (1).
2. Experimental
Nickel(II) thiocyanate was prepared following the method re-
ported in the literature [34]. All other starting materials were com-
mercially available, reagent grade, and used as purchased without
further purification.
2.1. Synthesis
Interestingly, reports of the preparation of 3d/ammonium ion
compounds are relatively scanty and best to our knowledge, only
three such compounds are found in the literature [31–33]. All the
2.1.1. Preparation of the ligand (H2L)
The ligand H2L was synthesized by refluxing a methanol solu-
tion of o-phenylenediamine (108 mg, 1 mmol) and o-vanilline
(304 mg, 2 mmol) in 1:2 molar ratios for 1 h. It was not isolated
and used directly for the preparation of the compound.
⇑
Corresponding author.
E-mail address: shouvik.chem@gmail.com (S. Chattopadhyay).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.08.026

304
M. Das, S. Chattopadhyay / Inorganica Chimica Acta 378 (2011) 303–306
Table 1
bond lengths and bond angles are shown in Tables 2 and 3,
respectively.
Crystal data and refinement details.
Formula
C45H42N6Ni2O9S
960.30
Formula weight
Crystal size (mm)
Temperature (K)
Crystal system
Space group
a (Å)
0.2 ꢂ 0.2 ꢂ 0.2
293
3. Results and discussion
monoclinic
P21/n
13.8636(7)
14.0267(7)
22.2715(10)
90
3.1. Synthesis
b (Å)
c (Å)
The ligand was prepared by the 1:2 condensation of the o-phen-
ylenediamine with o-vaniline in methanol following the literature
method [37]. The ligand was then refluxed with a mixture of nick-
el(II) thiocyanate and ammonium thiocyanate to prepare com-
pound 1, where an ammonium ion is stacked between two NiL
units and the charge is satisfied by the thiocyanate (Scheme 1).
In absence of the ammonium thiocyanate, a different compound
NiL was formed, the structure of which is reported elsewhere
[38]. The compound can also be prepared by stirring a methanol
solution of NiL with ammonium thiocyanate. Ammonium ion med-
iated assembly of neutral Ni(II) Schiff base compound is not very
common in the literature. No examples of this these types of com-
pounds are found in the literature with H2L or any compartmental
Schiff bases.
a
(°)
b (°)
94.301(3)
90
4
1.477
0.984
1992
65663
10025
5649
582
0.057
0.1174 and 0.2185
0.0614 and 0.1913
c
(°)
Z
dcalc (g cmꢁ3
)
l
(mmꢁ1
F(000)
)
Total reflections
Unique reflections
Observed data [I > 2
No. of parameters
Rint
R1, wR2 (all data)
R1, wR2 [I > 2r(I)]
r
(I)]
2.1.2. Preparation of compound [NH4(NiL)2SCN]ꢀH2O (1)
methanol solution (10 ml) containing Ni(SCN)2ꢀ4H2O
A
3.2. Spectroscopic and magnetic properties
(247 mg, 1 mmol) and NH4SCN (76 mg, 1 mmol) was added to a
methanol solution (20 ml) of the ligand, H2L (1 mmol) under reflux.
Red crystalline compounds started to separate immediately. Red
pallet-like single crystals of 1, suitable for X-ray diffraction, were
obtained from acetonitrile solution. Yield: 340 mg (70.81%, based
on Ni(II) salt). Anal. Calc. for C45H42N6Ni2O9S: C, 56.28; H, 4.41;
N, 8.75. Found: C, 56.3; H, 4.4; N, 8.7%. UV/Vis (DMF): kmax(nm)
In the IR spectrum of compound 1, distinct band due to the azo-
methine (C@N) group at 1603 cmꢁ1 is customarily noticed [39–41].
A broad band around 3460 cmꢁ1 is assigned to the OH stretching
vibration of the water molecule, which is involved in hydrogen
bonding [42]. The electronic spectrum shows one absorption band
in the visible region at 486 nm. A lack of any electronic transition
at longer wavelengths indicates a large crystal-field splitting and
is consistent with the square planar geometry of Ni(II) compounds
[43]. However, there are many high intensity absorption bands in
the UV region indicating LMCT transitions.
(emax
,
dm3 molꢁ1 cmꢁ1) = 486
(986),
Magnetic
moment
diamagnetic.
2.2. Physical measurements
Room temperature magnetic susceptibility measurement
shows that the compound is diamagnetic, thereby indicating the
presence of magnetically non-couple square planer nickel(II) ions.
Elemental analysis (carbon, hydrogen and nitrogen) was
performed using a Perkin–Elmer 240C elemental analyzer. IR
spectrum in KBr (4500–500 cmꢁ1) was recorded using a Perkin–
Elmer RXI FT-IR spectrophotometer. Electronic spectrum in DMF
(1200–350 nm) was recorded in a Hitachi U-3501 spectrophotom-
eter. The magnetic susceptibility measurement was done with an
EG and PAR vibrating sample magnetometer, model 155 at room
temperature and diamagnetic corrections were made using
Pascal’s constants.
Table 2
Coordination environment around Ni(II).
Ni(1)–O(2)
Ni(1)–O(3)
Ni(1)–N(1)
Ni(1)–N(2)
Ni(2)–O(6)
Ni(2)–O(7)
Ni(2)–N(3)
Ni(2)–N(4)
1.847(3)
1.843(3)
1.842(4)
1.846(4)
1.845(3)
1.844(3)
1.849(4)
1.839(4)
2.3. X-ray crystallography
Single crystals having suitable dimensions were used for data
collection by means of a ‘Bruker SMART APEX II’ diffractometer
equipped with graphite-monochromated Mo
Ka radiation
Table 3
(k = 0.71073 Å) at 293 K. The structure was solved by direct meth-
ods and refined by full-matrix least squares on F2, using the
SHELX-97 package [35]. Non-hydrogen atoms were refined with
anisotropic thermal parameters. The H atoms of the water mole-
cule of crystallization and that of ammonium ion were located by
difference Fourier maps and were kept at fixed positions. Other
hydrogen atoms were placed in their geometrically idealized
positions and constrained to ride on the atoms to which they are
attached. Empirical absorption corrections were carried out with
the ABSPACK program [36]. The structure was refined to R1 = 0.0614
Selected bond angles around Ni(II).
O(2)–Ni(1)–O(3)
O(2)–Ni(1)–N(1)
O(3)–Ni(1)–N(2)
N(1)–Ni(1)–N(2)
O(2)–Ni(1)–N(2)
O(3)–Ni(1)–N(1)
O(6)–Ni(2)–O(7)
O(6)–Ni(2)–N(3)
O(7)–Ni(2)–N(4)
N(3)–Ni(2)–N(4)
O(6)–Ni(2)–N(4)
O(7)–Ni(2)–N(3)
84.40(13)
95.18(14)
94.62(16)
85.87(17)
178.06(14)
177.77(13)
83.96(13)
178.42(16)
178.48(14)
85.54(17)
95.44(15)
95.09(15)
and wR2 = 0.1913, for 5649 reflections with I > 2r(I). The crystallo-
graphic and refinement data are summarized in Table 1. Selected

M. Das, S. Chattopadhyay / Inorganica Chimica Acta 378 (2011) 303–306
305
Scheme 1. Synthesis of compound 1.
Fig. 1. View of compound 1 with 20% ellipsoid probability. Only the relevant hydrogen atoms are shown.
3.3. Structure description
good agreement with those found previously in similar compounds
[31,38]. The two Ni atoms are both four-coordinated in an approx-
imately square-planar geometry constructed by two imine N
atoms and two phenolate O atoms from Salen-type Schiff base li-
gand (H2L). Sum of the different angles around the Ni(1) and
The structure of 1, as shown in Fig. 1, shows that ammonium
ion is surrounded by two molecules of NiL moieties. The mean val-
ues of the bond lengths and angles in the [NiL] moieties are in fairly

306
M. Das, S. Chattopadhyay / Inorganica Chimica Acta 378 (2011) 303–306
Table 4
cam.ac.uk/data_request/cif. Supplementary data associated with
this article can be found, in the online version, at doi:10.1016/
j.ica.2011.08.026.
Hydrogen bond distances (Å) and angles (°).
D–HꢀꢀꢀA
D–H
DꢀꢀꢀA
HꢀꢀꢀA
D–HꢀꢀꢀA
N(6)–H(101)ꢀꢀꢀN(5)
N(6)–H(103)ꢀꢀꢀO(3)
N(6)–H(100)ꢀꢀꢀO(6)
N(6)–H(100)ꢀꢀꢀO(7)
N(6)–H(102)ꢀꢀꢀO(1)
N(6)–H(102)ꢀꢀꢀO(2)
O(9)–H(106)ꢀꢀꢀO(5)
1.02(7)
0.62(5)
1.07(7)
1.07(7)
0.75(5)
0.75(5)
0.99(7)
2.940(8)
2.973(7)
2.966(6)
2.920(6)
2.962(7)
2.944(6)
3.160(8)
1.95(7)
2.42(5)
2.38(7)
1.86(7)
2.27(5)
2.37(6)
2.21(7)
162(6)
150(6)
113(4)
171(6)
154(5)
135(5)
163(5)
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Appendix A. Supplementary data
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CCDC 805838 contains the supplementary crystallographic data
for this paper. The data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via http://www.ccdc.