Synthesis and characterization of new addition compounds of bis(2-hydroxyaryloximato) nickel(II) with α-diimines: Crystal and molecular structure of [Ni(saox)2phen]·H2O

Article abstract of DOI:10.1016/S0277-5387(99)00253-3

A series of new addition compounds of bis(2-hydroxyaryloximato) nickel(II), [Ni(ox)₂], with an α-diimine (enR), under the general formula [Ni(ox)₂enR], were synthesized and characterized. The IR and electronic excitation spectra indicate that the bidentate coordination mode of the ligands consists with the chromophore NiN₄O₂. The octahedral environment around nickel(II) was confirmed by an X-ray structure analysis of [1,10-phenanthroline-bis(2-hydroxy-benzaldoximato)nickel(II)], [Ni(saox)₂phen]·H₂O. The equatorial plane, which encompasses the nickel atom, is formed by four nitrogen atoms, two coming from the phenanthroline molecule and two from the two molecules of the 2-hydroxybenzaldoxime (salicylaldoxime). In the apical positions lie the two deprotonated phenolic oxygen atoms of the two salicylaldoxime ligands. The thermal stability and decomposition mode were studied in nitrogen using the technique of thermogravimetry (TG/DTG). Mass spectrometry was also used, and possible fragmentation patterns are given and discussed. Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(99)00253-3

Polyhedron 18 (1999) 3441–3450
www.elsevier.nl/locate/poly
Synthesis and characterization of new addition compounds of
bis(2-hydroxyaryloximato) nickel(II) with a-diimines
Crystal and molecular structure of [Ni(saox)2phen]?H2O
1
*
Maria Lalia-Kantouri , Antonis Hatzidimitriou, Monir Uddin
Department of Chemistry, Laboratory of Inorganic Chemistry, Aristotle University, P.O. Box 135, Thessaloniki GR-54006, Greece
Received 25 May 1999; accepted 31 August 1999
Abstract
A series of new addition compounds of bis(2-hydroxyaryloximato) nickel(II), [Ni(ox)2], with an a-diimine (enR), under the general
formula [Ni(ox)2enR], were synthesized and characterized. The IR and electronic excitation spectra indicate that the bidentate
coordination mode of the ligands consists with the chromophore NiN4O2. The octahedral environment around nickel(II) was confirmed by
an X-ray structure analysis of [1,10-phenanthroline-bis(2-hydroxy-benzaldoximato)nickel(II)], [Ni(saox)2phen]?H2O. The equatorial
plane, which encompasses the nickel atom, is formed by four nitrogen atoms, two coming from the phenanthroline molecule and two from
the two molecules of the 2-hydroxybenzaldoxime (salicylaldoxime). In the apical positions lie the two deprotonated phenolic oxygen
atoms of the two salicylaldoxime ligands. The thermal stability and decomposition mode were studied in nitrogen using the technique of
thermogravimetry (TG/DTG). Mass spectrometry was also used, and possible fragmentation patterns are given and discussed.
Elsevier Science Ltd. All rights reserved.
1999
Keywords: Nickel(II) complexes; 2-Hydroxyaryloximes; a-Diimines; Crystal structure; Spectroscopy; Thermal behaviour
1. Introduction
coordination numbers exceeding four when forming bonds
with nitrogen or oxygen donor atoms. While this tendency
is strong in the case of the ligands bipy and phen, leading
to the formation of cationic octahedral complexes [8–10],
with the 2-hydroxyaryloxime (ox) ligands, nickel(II) forms
neutral complexes, [Ni(ox)2], of square–planar geometry
[3,11–13].
The analytical and biological importance of 2-hydroxy-
oximes and their chelates with some ions of 3d transition
metals are well known [1–4], as well as the chelates with
bidentate heterocyclic nitrogenous bases such as a-
diimines [5]. Research interest for the latter compounds is
enhanced in the case of the ligands 2,29-bipyridyl (bipy)
and 1,10-phenanthroline (phen) after the discovery of their
photoredox and catalytic properties [6,7]. Because of the
less-flexible nature of a-diimines, the steric effects are
usually severe, resulting in different coordination numbers
and unusual geometries for the metal ions. These effects
usually affect the spectroscopic and other significant
properties of the coordination compounds.
The Lewis acidity of the [Ni(ox)2] chelates renders them
susceptible to nucleophilic attack and addition compounds
can be obtained. While unidentate ligands, such as
pyridine, may impose tetragonal distortion by occupying
trans positions [Ni(ox)2(py)2] [14], structural requirements
of bidentate Lewis bases, such as a-diimines, dictate
occupancy of cis positions. It has not been reported,
however, in the literature any nickel(II) compound with
mixed-ligands a-diimine and 2-hydroxyaryloxime, al-
though there are mentioned complexes of nickel(II) and
zinc(II) with phenanthroline and 1-(2-pyridylazo)-2-naph-
thol5(PAN), a compound that coordinates similarly with
salicylaldoxime, under the formula [M(phen)(PAN)] [15].
Recently, mixed-ligand complexes of nickel, cobalt and
copper with bipyridine or phenanthroline and the amino
Spectroscopic and structural studies of nickel(II) che-
lates revealed the tendency of this metal ion to achieve
*Corresponding author. Tel.: 130-31-997-844; fax: 130-31-997-844.
E-mail address: lalia@chem.auth.gr (M. Lalia-Kantouri)
1Permanent address: Department of Chemistry, University of Chittagong,
Chittagong, Bangladesh.
0277-5387/99/$ – see front matter
PII: S0277-5387(99)00253-3
1999 Elsevier Science Ltd. All rights reserved.

3442
M. Lalia-Kantouri et al. / Polyhedron 18 (1999) 3441–3450
by physico–chemical methods and spectroscopic (IR,
electronic, MS) studies. Their structures were verified by
X-ray diffraction analysis of a representative complex, the
hydrated compound [phenanthroline-bis(2-hydroxyben-
zaldoximato) nickel(II)], [Ni(saox)2phen]?H2O, while their
thermal stability was investigated in nitrogen atmosphere
by thermogravimetric studies. The compounds prepared,
their elemental analyses and some physico–chemical data
are listed in Table 1.
2. Experimental
Fig. 1. Structural formulas of the 2-hydroxyaryloximes.
acid L-phenylalanine (donor atoms O, N), as well as the
X-ray study of the complex [Cu(phen)(H2O)(amino
acid)]ClO4 [16] have been reported. It is also worthwhile
to mention the formation and structural characterization of
a copper(II) addition compound with bipyridine and a
tridentate Schiff base, derived from the condensation of
2-hydroxypropiophenone-salicylhydrazide (donor atoms N,
O and O9), [Cu(bipy)(Schiff base)] [17].
For a better understanding of the bonds and structure of
mixed-ligand compounds with 2-hydroxyoximes and a-
diimines, we here report the synthesis of a series of new
nickel(II) addition compounds with a-diimines (enR), such
as bipyridine or phenanthroline and 2-hydroxyaryloximes
(ox), such as 2-hydroxybenzaldoxime (salicylaldoxime,
Hsaox) and its derivatives (Fig. 1). The resultant octahed-
ral nickel(II) compounds [Ni(ox)2enR], were characterized
2.1. Synthesis and physical methods
The synthesis of 2-hydroxyaryloximes (ox) was
achieved employing literature methods [18,19]. Fig. 1
illustrates the oximes used in this work, which are: 2-
hydroxybenzaldoxime or salicylaldoxime (Hsaox); 2-hy-
droxyphenyl,
1-ethanoneoxime
or
2-hydroxy-
acetophenoneoxime (Hapox); 2-hydroxyphenyl, 1-prop-
anoneoxime or 2-hydroxypropiophenoneoxime (Hppox);
2-hydroxy-5-methyl-phenyl, 1-ethanoneoxime or 2-hy-
droxyacetophenoneoxime (Hmpox); 2-hydroxyphenyl, 1-
benzophenoneoxime or 2-hydroxybenzophenoneoxime
(Hbpox); and 2-hydroxyphenyl-4-methoxy, 1-ben-
zophenoneoxime
zophenoneoxime (Hopox).
The a-diimines (enR), 2,29-bipyridine (bipy) and 1,10-
or
2-hydroxy-4-methoxy-ben-
Table 1
Elemental analyses and physico–chemical data of the addition compounds [Ni(ox)2enR]
a/a
Compound
Colour
Yield
62
M.P. (8C)a
C%
H%
N%
meff (mB)
1
[Ni(saox)2bipy]?H2O
Yellowish
227–229
56.58
(57.03)b
58.72
(58.98)
58.24
(58.54)
62.10
(62.32)
60.26
(60.11)
61.45
(61.75)
61.82
(62.07)
61.53
(61.75)
67.24
4.52
(4.39)
4.25
(4.18)
5.03
(4.91)
4.19
(4.48)
4.77
(5.04)
4.67
(4.84)
4.69
(4.84)
4.28
(4.84)
4.19
10.81
(11.13)
10.25
(10.62)
10.24
(10.54)
10.29
(10.42)
9.68
(10.06)
9.41
(9.64)
10.13
(10.38)
9.34
(9.64)
8.96
(9.22)
8.24
(8.47)
7.53
(7.84)
7.21
3.08
2
[Ni(saox)2phen]?H2O
[Ni(apox)2bipy]
Brownish–yellow
Brownish–yellow
Brownish–yellow
Yellowish
67
65
61
75
65
64
61
69
58
63
60
222–224
.300
3.14
3.06
3.11
3.04
3.08
3.01
3.03
3.19
3.07
3.02
3.06
3
4
[Ni(apox)2phen]
254–256
197–199
227–229
194–196
187–189
231–233
214–216
202–204
234–236
5
[Ni(ppox)2bipy]?H2O
[Ni(ppox)2phen]?H2O
[Ni(mpox)2bipy]
6
Brownish–yellow
Yellowish
7
8
[Ni(mpox)2phen]
Yellowish
9
[Ni(bpox)2bipy]
Yellowish
(67.57)
68.42
(68.75)
63.38
(63.60)
64.41
(4.41)
4.11
(4.25)
4.45
(4.77)
4.32
10
11
12
[Ni(bpox)2phen]
Brownish–yellow
Yellowish
[Ni(opox)2bipy]?H2O
[Ni(opox)2phen]?H2O
Brownish–yellow
(64.78)
(4.62)
(7.58)
a Decomposition.
b Calculated values in parentheses.

M. Lalia-Kantouri et al. / Polyhedron 18 (1999) 3441–3450
3443
phenanthroline (phen) were purchased from Aldrich, while
hexahydrated NiCl2 was procured from Fluka in extra pure
grade. Solvents for preparation and physical measurements
of ‘extra pure’ or ‘spectro grade’, were obtained from
Merck and used without further purification.
squares. Crystallographic data and other pertinent infor-
mation are given in Table 2. All data were corrected for
Lorentz and polarization effects.
The nickel position was detected by direct methods
using the SHELXS-86 program [20], while subsequent
calculations were performed employing the CRYSTALS
program [21]. All non-hydrogen atoms were refined aniso-
tropically. In the final stages of the refinement, the
DIFABS method [22] was used for an absorption correc-
tion, the reflections were reweighted and an overall
isotropic extinction parameter introduced. Final refinement
was continued until the sum of the shift/esd (estimated
standard deviation) ratio was less than 0.01. All hydrogen
atoms were found but only the positions of them belonging
to the methyleno and the hydroxyl groups of the oxime
were refined. The rest of the atomic hydrogens were
positioned geometrically, their positions recalculated after
each refinement cycle. The figures of the clinographic
projections were produced with the CAMERON program
[23].
2.2. Synthesis of the addition compounds [Ni(ox)2enR]
A solution of 4 mmol of 2-hydroxyaryloxime and 2
mmol of a-diimine in 25 ml of warm EtOH, which became
slightly basic with 1 ml aqueous 15% NaOH, was added
dropwise to a solution of 2 mmol of NiCl2?6H2O (0.476 g)
in 15 ml of water. The solution turned darker after 5 h
continuous stirring and a yellowish solid formed. The
precipitate was washed with ethanol and ether and dried in
vacuo. The newly prepared Ni(II) addition compounds are
crystalline powders, stable in air and insoluble in almost
all organic solvents.
2.3. Physical measurements
Stoichiometric analyses (C, H, N) were performed on a
Perkin-Elmer 240B elemental analyzer. Molar conduc-
tivities were measured in DMF solutions employing a
WTW conductivity bridge and a calibrated dip type cell.
Magnetic susceptibility measurements on powdered sam-
ples were performed at 258C employing the Faraday
3. Results and discussion
The reaction of Ni21 with an a-diimine (enR) and the
anions of 2-hydroxyaryloxime (ox) leads, under proper
conditions, to the formation of yellowish crystalline prod-
ucts. Their elemental analyses and the absence of electrical
conductivity in DMF solutions indicate neutral com-
pounds, with general formula [Ni(ox)2enR], while their
magnetic moments (meff5|3.1 mB; Table 1) corroborate
with octahedral coordination [24,25].
The successful isolation of these compounds depends on
the concentration of the two ligands, the stereoelectronic
factors of the a-diimines and the oximes, the formation of
hydrogen bonds and on the pH in which the oxime can be
deprotonated (usually a slightly basic environment). How-
ever, it appears that the stereochemistry of the a-diimines
outweigh the importance of concentration and constitutes
the determining factor for the composition of the newly
prepared addition compounds, [Ni(ox)2enR]. For instance,
replacement of the oxime Hsaox with the bulkier Hopox
does not alter the preparation process significantly. On the
contrary, after the replacement of the a-diimine phen with
2,9-dimethyl-1,10-phenanthroline (neocuproin, ncup) or
with 2,29-dipyridylamine (dpamH) the isolation of the
corresponding addition compounds [Ni(ox)2ncup] and
[Ni(ox)2dpamH] is not possible.
method on
a home-built balance calibrated against
Hg[Co(SCN)4]. Diamagnetic corrections were estimated
from Pascal’s constants. Infrared spectra were recorded on
a Perkin-Elmer 1600 FT-IR spectrometer with a range
4000–200 cm21 calibrated against polystyrene. Electronic
spectra in DMSO solution were measured on a Shimatzu
160A spectrophotometer using 10-mm Teflon stoppered
quartz cells. The solid-state electronic spectra were ob-
tained from Nujol mulls. Mass spectra were run at 70 eV
on an RMU-6L Hitachi Perkin-Elmer double-focusing
mass spectrometer, using probe insertion for the samples.
The thermogravimetric curves TG/DTG were recorded
on a Perkin-Elmer model TGA 7 thermal analyzer. Sam-
ples of |1.5 mg were heated in platinum crucibles, in
nitrogen atmosphere, within the temperature range 40–
9808C. The heating rate was 108C min21. X-ray powder
diffraction analyses of the final residues were made with a
Phillips PW 1130/00 X-ray diffractometer, using Cu Ka
radiation.
2.4. X-ray crystallography
The coordination mode of the ligands in the addition
compounds was studied using spectroscopic methods. The
X-ray diffraction study of [Ni(saox)2phen]?H2O provided
evidence regarding the geometry around the Ni(II) ion, the
configuration of the ligands and the existence of strong
hydrogen bonds formed between the 2-hydroxyoxime
ligands of the addition compounds.
The X-ray data were measured on an Enraf-Nonius
CAD4 automatic X-ray diffractometer employing graphite-
filtered Mo Ka radiation (l50.71070 A). Unit cell
parameters and orientation matrix of the crystal
[Ni(saox)2phen]?H2O were obtained from the setting an-
gles of 25 reflections (125u5158) and refined by least-
˚

3444
M. Lalia-Kantouri et al. / Polyhedron 18 (1999) 3441–3450
Table 2
Crystal data and experimental details for the structural study of [Ni(saox)2phen]?H2O
Formula
[C26H20N4O4Ni]?H2O
Molecular mass, Mr
529.19
Crystal parameters
Crystal shape
Crystal size (mm)
Crystal system
Yellowish prisms
0.4230.5330.47
Monoclinic
Space group
C2/c
Reflections for cell measurement (8)
25 with 12#u #15
Unit-cell dimensions
˚
a (A)
7.880(1)
26.755(2)
11.172(1)
90
97.96(1)
90
2332.8(4)
4
1.829 (calculated)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
3
˚
Vc (A )
Molecules per cell
Dx (Mg m23
)
Measurement of intensity data
Instrument
Radiation, wavelength
Monochromator
CAD4-F
Mo Ka, l50.71069 A
Graphite
˚
Scan mode
v/2u
Scan speed (8 min21
v range (8)
)
2.5 (min.); 20.1 (max.)
2.3–26.3
Reflections measured
Independent reflections
Reflections observed
Parameters refined
Indices limits
2540
2367
1744 reflected [I $ 2s(I)]
174
2 9 # h # 9, 0 # k # 33, 0 # l # 13
F(000)
968
Refinement
R 5 o(uFou 2 uFcu)/ouFou
w 5 1/s(Fo)
0.0370
Rw 5 [o w(uFou 2 uFcu)2 /o w(uFou2]1 / 2
Refinement method
0.0412
Full-matrix least-squares on F2
3.1. Description of the structure of [Ni(saox)2 phen]?H2O
formed by four nitrogen atoms, two coming from the
phenanthroline molecule N(2), N(2a) at a distance of
2.093(2) A and two from the two molecules of 2-hydroxy-
˚
The unit cell comprises four nickel atoms, each in an
octahedral environment created by one phenanthroline
molecule and two anions of the 2-hydroxybenzaldoxime
ligand. The position parameters of [Ni(saox)2phen]?H2O
reveal two separate entities: The addition compound
[Ni(saox)2phen], and the water molecule that does not
interact with the central metal ion.
benzaldoxime (salicylaldoxime) N(1), N(1a) at a distance
˚
of 2.045(2) A. The four nitrogen atoms that define the
equatorial plane hN(1), N(1a), N(2), N(2a)j and expressed
by the equation h7.064x26.290z521.572j present a slight
deviation from it, smaller than the error for N(2) and
˚
N(2a), equal to 0.05(7) A, while the nickel atom lies
exactly on it. The two deprotonated phenolic oxygen atoms
of the two salicylaldoxime ligands O(1) and O(1a) lie in
the apical positions at a distance of 2.061(2) A, while the
O(1)–Ni–O(1a) angle is 171.2(1)8. The molecular struc-
ture of the compound [Ni(saox)2phen]?H2O is depicted in
Fig. 2, and the interatomic distances and bond angles are
given in Table 3.
The phenanthroline ligand is planar and its plane, which
encompasses the nickel atom, is nearly parallel to the
Each molecule of [Ni(saox)2phen] is generated by
symmetry from the asymmetric unit when rotated around
the C2 axis of the compound passing through the nickel
atom and overlying the phenanthroline C2 axis.
In each molecule of [Ni(saox)2phen], the nickel atom is
surrounded by the six donor atoms from the ligands. The
arrangement of the atoms in the ensuing NiN4O2 chromo-
phore describes a distorted octahedral structure. The
equatorial plane, which encompasses the nickel atom, is
˚

M. Lalia-Kantouri et al. / Polyhedron 18 (1999) 3441–3450
3445
˚
2.045 and 2.061 A, respectively), are appreciably longer
than those reported for the corresponding square–planar
complexes [Ni(ox)2] [3,11–13]. Each of the two saox2
ligands is bonded through the oxime nitrogen atom and the
deprotonated phenolic oxygen forming a six-membered
chelate ring with the metal ion. The phenyl ring of the
oxime ligand and the coordinated oxygen atom are nearly
coplanar with slight deviations from planarity, while the
N(2) and O(2) atoms lie above and below the plane,
˚
respectively, with deviations of 0.06(8) and 0.08(8) A. The
formed mean plane hequation 22.880x121.041y2
4.944z56.272j shows an almost perpendicular arrange-
ment to both the phenanthroline plane and the coordination
plane, forming with each of them dihedral angles of
86.0(7) and 96.1(7)8, respectively.
It is worth mentioning that rather strong intramolecular
hydrogen bonds are observed between the phenolic oxy-
gen, O(1), of one saox2 ligand and the oximic hydrogen
H(10a) of the second saox2 ligand hO(1)–O(2a)52.656(6)
˚
˚
A, O(1)–H(10a) . . . O(2a)51.75(2) A, O(1)–H(10a)–
O(2a)5116(1)8j. The existence of these hydrogen bonds
has a profound effect on the values observed for the
oximic hydroxyl group in the vibrational spectrum, as can
be seen later. Besides, the distances H(11)–O(1)51.98(2)
Fig. 2. CAMERON diagram and atom labelling scheme of
[Ni(saox)2phen]?H2O.
˚
˚
equatorial coordination plane forming a dihedral angle of
A and O(1)–O(3)53.02(3) A, where H(11) and O(3) are
atoms belonging to the water molecule, suggest a weak
intermolecular hydrogen bonding interaction [29].
3.4(8)8. In the rigid nickel–diimine entity, the intraligand
˚
distance N(2)–N(2a) of 2.686(4) A and the bite angle of
79.8(1)8 are similar to reported values of chelated poly-
cyclic diimines [10]. The Ni–N(phen) bond lengths are
˚
3.2. Infrared spectra
equidistant (2.093 A, due to symmetry reasons) and similar
to the values reported for other a-diimine complexes in
comparable structures [26–28].
The oximic coordination bond lengths of the octahedral
compound under investigation (Ni–N(1) and Ni–O(1)5
A plethora of discrete bands appears in the IR spectra of
the new addition compounds. The bands may be classified
as those originating from the 2-hydroxyoxime, those
emanating from the a-diimine, those emanating from
crystal water and those due to the bonds formed between
nickel(II) and ligating atoms. A list of the most relevant
infrared frequencies of the nickel(II) compounds is given
in Table 4. The origin of the bands may be deduced by
comparison with the spectra of the [Ni(ox)2] and
Ni(enR)X2 or [Ni(enR)3]21 compounds of known struc-
ture.
The anionic character of the 2-hydroxyoxime ligands
and their bidentate coordination mode through the nitrogen
atom and the phenolic oxygen are inferred from the
positions and the shifts observed in the IR bands of the
studied addition compounds, compared to the bands of the
free ligands and the bis(2-hydroxyoxime) complexes as
described elsewhere [3,30–33].
Table 3
˚
Selected interatomic distances (A) and bond angles (8) of
[Ni(saox)2phen]?H2O
Ni(1)–O(1)
Ni(1)–N(1)
Ni(1)–N(2)
O(1)–C(2)
O(2)–N(1)
N(1)–C(7)
C(1)–C(7)
2.061(2)
2.045(2)
2.093(2)
1.329(3)
1.397(3)
1.272(4)
1.458(4)
O(1)–Ni(1)–O(1a)
O(1)–Ni(1)–N(1)
O(1a)–Ni(1)–N(1)
N(1)–Ni(1)–N(1a)
O(1)–Ni(1)–N(2)
O(1a)–Ni(1)–N(2)
N(1)–Ni(1)–N(2)
N(1a)–Ni(1)–N(2)
N(2)–Ni(1)–N(2a)
Ni(1)–O(1)–C(2)
Ni(1)–N(1)–O(2)
Ni(1)–N(1)–C(7)
O(2)–N(1)–C(7)
Ni(1)–N(2)–C(8)
Ni(1)–N(2)–C(12)
C(2)–C(1)–C(7)
C(6)–C(1)–C(7)
O(1)–C(2)–C(1)
O(1)–C(2)–C(3)
N(1)–C(7)–C(1)
171.2(1)
86.96(8)
86.94(9)
91.6(1)
90.85(8)
95.88(8)
173.52(9)
94.33(8)
79.8(1)
127.7(2)
115.3(2)
130.7(2)
113.9(2)
129.0(2)
112.6(2)
124.1(3)
116.0(3)
124.1(3)
119.3(2)
123.9(2)
The band observed in some of the new nickel(II)
compounds at |3440 cm21 is indicative of the vibration
n(OH), which is due to the non-coordinated water mole-
cule. Bands typical of a-diimines are abound in the IR
spectra of the [Ni(ox)2enR] compounds. Some bands in the
1600–1400 cm21 region, emanating from the pyridyl ring,
a constituent omnipresent in the enR ligands, were masked

3446
M. Lalia-Kantouri et al. / Polyhedron 18 (1999) 3441–3450
Table 4
Vibrational frequencies (n/cm21) for selected absorption bands in the IR spectra and band maxima in the electronic excitation spectra (/mm21) of the
[Ni(ox)2enR] compoundsa
a/a
Compound
n(=N–OH)
n(C–O)
n(N–O)
n(=C–H)
n(Ni–N)
Band IN
Band IIN
n2 /n1
B
(pyridine)
n1
n2
1
2
3
4
5
6
7
8
9
[Ni(saox)2bipy]?H2O
[Ni(saox)2phen]?H2O
[Ni(apox)2bipy]
2987m
2924m
2770m
2769m
2870m
2875m
2857m
2859m
2848m
2858m
2837m
2834m
1333s
1334s
1330s
1325s
1319s
1319s
1320s
1325s
1319s
1313s
1321s
1340s
993, 907
996, 908
1010, 945
1003, 937
985, 928
762s, 720s
846s, 763s
762s, 734s
853s, 762s
759s, 735s
846s, 754s
770s, 736s
849s, 727s
768s, 752s
841s, 754s
771s, 728s
844s, 726s
583m
584m
588m
558m
556m
557m
590m
592m
588m
586m
589m
590m
1.060
1.090
1.080
1.110
1.060
1.090
1.090
1.090
1.090
1.090
1.080
1.070
1.740
1.830
1.790
1.810
1.750
1.800
1.780
1.750
1.830
1.790
1.790
1.720
1.64
1.68
1.66
1.63
1.66
1.65
1.63
1.60
1.68
1.65
1.66
1.61
1025
1300
1137
1017
1007
1110
1010
887
1300
1058
1137
883
[Ni(apox)2phen]
[Ni(ppox)2bipy]?H2O
[Ni(ppox)2phen]?H2O
[Ni(mpox)2bipy]
[Ni(mpox)2phen]
[Ni(bpox)2bipy]
[Ni(bpox)2phen]
[Ni(opox)2bipy]?H2O
[Ni(opox)2phen]?H2O
983, 928
1022, 956
1030, 960
1013, 939
1011, 938
1009, 960
1013, 964
10
11
12
a s5strong, m5medium, N5Nujol.
by the more intense absorptions originating from the 2-
hydroxyoxime ligands, while others were employed to
reaffirm the presence of the a-diimines in the compounds
under consideration. Actually, the intense band at 750620
cm21, ascribed to the rocking vibrations of the pyridyl
C–H bonds, and the band at 870615 cm21, attributable to
the deformation vibrations of the pyridyl C–H bonds
disclosed the occurrence of nitrogenous bases in the
prepared addition compounds.
(Bo 51084 cm21), the exceptions being those found for the
compounds [Ni(saox)2phen]H2O and [Ni(bpox)2bipy] (B5
1300 cm21). The n2 /n1 ratio for a d8 ion in a regular
octahedron is 1.8. The smaller values (1.54–1.68) ob-
served for the compounds under consideration and the B
values mentioned above, are indications of slight distor-
tions of the octahedral symmetry.
In the electronic spectra of the studied compounds in
solution, band II is shifted (|0.2 mm21) towards lower
energy, while band I looses its intensity and becomes
broader, rendering in this way uncertain its position. Based
on these, we could suggest the existence of an equilibrium
between octahedral and square–planar geometry in solu-
tion, resulting in some rearrangements of the ligands
around Ni(II).
3.3. Electronic excitation spectra
The electronic excitation spectra of the addition com-
pounds were studied in the visible and the near-infrared
region, in the solid state (nujol mulls) and in solution
(DMSO). All the spectra in the solid state are of the same
general form and consist of three principal bands. Band I is
observed at about 1.020 mm21 and band II at 1.640 mm21
(Table 4), while band III at |2.65 mm21 suggests an
octahedral arrangement of the ligands around Ni(II) [34].
Accordingly, these bands could be assigned to the spin-
3.4. Mass spectra
In the mass spectra of the nickel addition compounds
under investigation, the molecular ions are not detected,
probably due to their high thermal instability in the
ionization beam. The most prominent mass spectral peaks
are given in tabular form in Table 5, while a representative
spectrum for the compound [Ni(saox)2phen]?H2O is given
in Fig. 3.
In the higher mass-number region, the detected ions
correspond to the fragments Ni(ox)s2;, taking also into
account the relative intensities, including the abundance
ratio of nickel (58Ni:60Ni52.59:1.00). These might be
regarded as direct fragments of the molecular ion,
[Ni(ox)2enR]s;, resulting from the elimination of the a-
diimine molecule. Evidence for this also arises from the
existence of the free base, as can be deduced from the
peaks at m/e 180 and 156, which correspond to the
phenanthroline and dipyridyl molecule, respectively, and
compose the base peak of the mass spectra.
3
allowed excitations from A2g(F) ground state to the
3
3
3
electronic levels T2g(F) (n1), T1g(F) (n2) and T2g(P)
(n3). In most cases, however, the highest energy band is
only poorly resolved because of overlap by the most
intense charge transfer bands. Credence to this arose from
the comparison of the spectra of [Ni(ox)2] complexes,
where two CT bands are observed at |2.60 and |2.70
mm21 [3,12]. Besides, the weak absorption observed as a
shoulder, band IV, at 1.28 mm21 could be assigned to the
3
spin-forbidden transition A2g(F) → 1Eg(F).
The ligand field parameter 10 Dq was taken to be equal
to the energy of the first spin-allowed transition (10 Dq5
˜
v1). The Racah parameter B was calculated by inserting
the n1 and n2 values in simplified forms of the equation for
the d8 systems. The calculated values B (883–1137 cm21
,
In the low mass-number region, the intense peaks are
those corresponding to the released oxime and its daughter
Table 5) were found to be quite close to the free-ion value

M. Lalia-Kantouri et al. / Polyhedron 18 (1999) 3441–3450
3447
Table 5
The most relevant mass spectral peaks of the compounds [Ni(ox)2enR]
a/a
Compound
m/e (R.I.)a
1
[Ni(saox)2bipy]?H2O
50(51), 51(74), 52(56), 58(11), 60(4), 64(26), 76(28), 77(25),
78(71), 91(36), 102(18), 119(19), 137(18), 155(86), 156(100),
177(10), 178(13), 282(11), 284(7), 300(6), 302(4), 312(5), 314(4),
330(37), 332(15)
2
3
[Ni(saox)2phen]?H2O
39(30), 50(15), 51(19), 58(11), 60(7), 64(24), 76(17), 77(17),
91(60), 102(13), 115(15), 119(23), 137(27), 179(40), 180(100),
282(7), 284(5), 300(7), 302(4), 312(6), 314(3), 330(20), 332(9)
39(25), 40(21), 42(26), 58(19), 60(5), 63(22), 65(29), 77(37),
78(42), 91(41), 92(19), 105(65), 119(14), 120(36), 133(24),
134(37), 135(42), 149(19), 150(14), 151(58), 155(53), 156(100),
177(42), 192(74), 193(34), 194(34), 207(7), 208(6), 306(23),
312(16), 326(16), 342(42), 344(17), 358(96), 359(71), 360(28)
51(60), 55(13), 58(44), 60(18), 63(78), 76(94), 77(63), 90(69),
91(82), 92(54), 119(83), 120(69), 146(66), 147(35), 148(80),
149(48), 150(36), 151(46), 152(64), 153(72), 154(74), 165(82),
166(60), 179(89), 180(100), 181(87), 193(48), 201(43), 204(53),
205(54), 206(70), 220(12), 221(16), 238(32), 370(47), 372(18),
386(73), 387(48), 388(63)
[Ni(apox)2bipy]
4
[Ni(ppox)2phen]?H2O
5
6
7
[Ni(mpox)2phen]
[Ni(bpox)2bipy]
[Ni(bpox)2phen]
39(42), 41(39), 42(44), 51(46), 55(60), 56(30), 77(85), 78(59),
91(43), 105(78), 121(80), 147(37), 149(48), 150(11), 152(16),
161(27), 165(29), 179(40), 180(100), 191(24), 204(20), 206(27),
220(7), 222(12), 386(22), 388(16)
40(28), 44(30), 50(28), 51(58), 52(30), 64(12), 77(17), 78(63),
92(4), 101(6), 102(9), 103(11), 152(46), 155(83), 156(100),
157(39), 182(12), 195(6), 196(4), 197(3), 213(30), 252(7),
254(6), 482(12), 484(5)
50(61), 51(71), 52(48), 57(10), 62(49), 63(70), 64(63), 76(61),
77(100), 78(52), 92(54), 93(43), 103(54), 120(40), 121(60),
139(39), 151(37), 152(56), 153(56), 167(66), 179(61), 180(72),
195(71), 196(64), 210(31), 213(50), 252(7), 254(8), 268(4), 270(3),
482(15), 484(7)
8
[Ni(opox)2bipy]?H2O
51(92), 52(68), 63(24), 64(28), 76(41), 77(40), 78(92), 79(46),
101(20), 102(26), 103(29), 104(24), 155(98), 156(100), 157(71),
227(7), 228(6), 243(30), 446(8), 448(3), 542(8), 544(3)
a R.I.5Relative intensity.
fragments following well-known pathways [35–38]. The
decomposition modes of the Ni(ox)s2; ions are in agree-
ment with those reported previously for the [Ni(ox)2]
complexes with the same 2-hydroxyaryloxime ligands
[35,39]. A simplified picture of the main fragmentation
pathway for the studied addition compounds is presented
in Fig. 4.
3.5. Thermal behaviour
The thermal behaviour of the six nickel addition com-
pounds under investigation was studied using the simulta-
neous thermogravimetry/derivative thermogravimetry
(TG/DTG) technique, in nitrogen atmosphere over the
temperature range 40–9808C. Representative thermal
curves for [Ni(saox)2bipy]?H2O are given in Fig. 5 and
thermoanalytical data derived from the thermal curves are
presented in Table 6.
The anhydrous studied compounds, after the elimination
of the crystal water molecule in the range 60–1108C,
decompose in three or four stages. Their thermal decompo-
Fig. 3. Mass spectrum of [Ni(saox)2phen]?H2O.

3448
M. Lalia-Kantouri et al. / Polyhedron 18 (1999) 3441–3450
Fig. 4. Possible fragmentation pattern of the [Ni(ox)2enR] compounds.
sition mode does not follow a definite mode, depending on
the oxime ligand. It was quite surprising that the decompo-
sition does not begin with the elimination of the a-diimine
molecule as expected and deduced from the mass spectral
data. It proceeds mostly with rupture of the bonds inside
the first 2-hydroxyoxime ligand, resulting in the elimina-
tion of a nitrile and a phenanthroline molecule, in agree-
ment with the thermal decomposition mode of the
[Ni(ox)2] complexes [39]. The second molecule of the
oxime ligand is subsequently eliminated, with rupture of
the coordination bonds and finally, the a-diimine molecule
is gradually eliminated over the temperature 5008C. In
some cases, the last procedure can be merged, resulting in
the simultaneous elimination of the oxime and the a-
diimine ligands.
Supplementary data
Supplementary data (Tables 1s–7s with crystallographic
data of the compound [Ni(saox2)phen]?H2O and Figs.
1s–2s concerning the unit cell and the excitation spectrum
of it, respectively) are available from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK on request, quoting the deposition number
CCDC 114439.
Acknowledgements
Thanks are due to State Scholarship Foundation (S.S.F.)
Greece for post graduate scholarship of Dr Monir Uddin.
The authors also express their thanks to Prof. C.Kipar-
risides (Chemical Engineering Department, Thessaloniki)
for providing the necessary technical assistance for thermal
In all cases, the intermediates formed are unstable and
undergo further decomposition at higher temperatures,
until the stable NiO is formed at about 9408C, as verified
from the X-ray powder diffraction data.
Fig. 5. Thermoanalytical curves (TG/DTG) of the compound [Ni(saox)2bipy]?H2O.

M. Lalia-Kantouri et al. / Polyhedron 18 (1999) 3441–3450
3449
Table 6
Thermoanalytical data (TG/DTG) for the [Ni(ox)2enR] compounds in nitrogen
Compound
Stage
Temperature
range (8C)
DTG max.
(8C)
Mass loss
(%)
Evolved
moiety formula
Mass calc.
(%)
[Ni(saox)2bipy]?H2O
60–110
110–270
270–420
420–550
550–960
.960
60–110
110–205
205–270
270–440
440–960
.960
150–230
230–345
345–425
425–800
.800
60–110
200–290
290–530
530–900
.900
100–420
420–980
.980
60–110
110–210
210–300
300–650
650–960
.960
76
225
326, 473
3.4
17.8
32.0
H2O
C6H4OH
saox1HCN
3.56
18.41
32.28
1
2
3
770
31.3
15.5
3.6
bipy
NiO
H2O
30.89
14.85
3.4
Residue
[Ni(saox)2phen]?H2O
80
Plateau
240
330, 360
500, 745
1
2
3
8.4
14.0
60.0
14.0
21.7
19.8
13.1
30.8
14.6
3.0
HCNO
C6H5
saox1phen
NiO
C6H4CNO
C6H4CN
2(CH3OH)
bipy
8.13
15.55
59.7
14.18
22.9
19.8
12.4
30.29
14.56
3.1
Residue
1
2
3
[Ni(apox)2bipy]
219
286
376
4
550, 665
Residue
NiO
H2O
[Ni(ppox)2phen]?H2O
80
265
360
1
2
3
16.2
9.2
C6H4OH
C2H5CN
ppox1phen
NiO
Hmpox
L1ox1phen
NiO
H2O
CH3OC6H3CN
PhOH
15.9
9.4
670(br)
58.6
13.0
29.4
57.0
13.6
2.8
18.2
12.6
33.6
22.4
10.4
58.8
12.8
29.1
57.8
13.2
2.5
18.4
13.1
33.9
21.7
10.5
Residue
1
2
[Ni(mpox)2phen]
318
647, 757br
Residue
[Ni(opox)2bipy]?H2O
80
198
272
1
2
3
4
360, 470
670
Hopox
bipy
NiO
Residue
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these measurements.
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