Ring opening complexation of nickel(II) and copper(II) by 2-phenyl-2-(2-pyridyl)imidazolidine: Synthesis, spectra and X-ray crystal structures

Article abstract of DOI:10.1016/j.poly.2008.04.028

The cyclic structure of 2-phenyl-2-(2-pyridyl)imidazolidine (1) derived from the condensation of 1,2-diaminoethane and 2-benzoylpyridine has been confirmed by X-ray crystallography. Reaction of (1) with salts of nickel(II) and copper(II) leads to metal in

Full text of DOI:10.1016/j.poly.2008.04.028

Polyhedron 27 (2008) 2379–2385
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Ring opening complexation of nickel(II) and copper(II) by
2-phenyl-2-(2-pyridyl)imidazolidine: Synthesis, spectra
and X-ray crystal structures
b
b
Sanaa M. Emam a,1, Patrick McArdle a, , James McManus , Mary Mahon
*
a Chemistry Department, National University of Ireland, Galway, Ireland
b Chemistry Department, University of Bath, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
The cyclic structure of 2-phenyl-2-(2-pyridyl)imidazolidine (1) derived from the condensation of 1,2-
diaminoethane and 2-benzoylpyridine has been confirmed by X-ray crystallography. Reaction of (1) with
salts of nickel(II) and copper(II) leads to metal induced ring opening and the formation of complexes con-
taining the tridentate ligand (L). The formulae of the complexes derived from NiX2 and CuX2 are [NiL2]X2
and [CuLY]X2 (X=ClO4À, Y = H2O, CH3CN and N3À). Crystal structures were obtained for (1), [NiL2][ClO4]2,
[CuL(CH3CN)][ClO4]2, [CuL(H2O)][NO3]2 and [CuLN3][ClO4].
Received 7 February 2008
Accepted 10 April 2008
Available online 4 June 2008
Keywords:
Schiff base
Azide
Ó 2008 Elsevier Ltd. All rights reserved.
X-ray crystal structure
DFT calculations
Nickel(II)
Copper(II) complexes
1. Introduction
2. Experimental
Schiff base ligands have played an important role in our under-
standing of the coordination chemistry of transition metal ions and
Schiff base complexes have a broad range of applications including,
enzyme inhibition [1], anti-microbial action [2] and catalytic activ-
ity when encapsulated in zeolite Y [3]. In this paper, the imidazo-
line (1), the result of a disfavoured 5-Endo-Trig cyclization [4], is
reacted with nickel and copper salts to yield tridentate complexes.
The structures of the complexes which could be crystallized and
analysed by X-ray diffraction are discussed. Prompted by reports
of the use of DFT calculations in modeling nickel and copper com-
plexes, with similar and greater complexity than those described
here [5,6], it has been found that while calculations for the nickel
system reproduced the details of the crystallographic results the
copper results were less satisfactory.
2.1. Chemicals and materials
2-Benzoylpyridine and 1,2-diaminoethane (from Sigma–Aldrich
and BDH) were used without further purification. Sodium azide
(Sigma–Aldrich), Ni(ClO4)26H2O (Sigma–Aldrich), Cu(ClO4)26H2O
(Aldrich), Ni(NO3)26H2O (Merck) and Cu(NO3)24H2O (Riedel de-
Haen) were used as received. All other chemicals and solvents were
AR grade and used as received. Ethanol was dried prior to use.
2.2. Instrumentation
Elemental analyses (carbon, hydrogen and nitrogen) were car-
ried out on a Perkin–Elmer 240 CHN elemental analyzer. IR spectra
were measured on a Perkin–Elmer Spectrum One Diamond-ATR-
FT-IR instrument spectrometer, UV–Vis spectra were recorded
using a Varian Cary 50 spectrometer using 1 cm quartz cuvettes.
1H and 13C NMR spectra were recorded on a JEOL ECX-400 NMR
spectrometer at room temperature with tetramethylsilane as
internal reference. Magnetic moments were measured on a Sher-
wood Scientific magnetic susceptibility balance at room tempera-
ture. The diamagnetic corrections were calculated by using
Pascal’s constants and Hg[Co(SCN)4] was used as a calibrant. Molar
conductivities were measured using freshly prepared 10À3 M solu-
tions in nitromethane, acetonitrile and dimethylformamide at
* Corresponding author.
E-mail address: p.mcardle@nuigalway.ie (P. McArdle).
Permanent address: Chemistry Department, Faculty of Science, El-Menoufia
1
University, Shebin El-Kom, Egypt.
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.04.028

2380
S.M. Emam et al. / Polyhedron 27 (2008) 2379–2385
room temperature, using a Jenway 4310 conductivity meter
and the cell constant was calibrated with 0.01 M KCl solution.
Melting points were measured using a Gallenkamp melting point
apparatus.
(15 cm3) of NaN3 (1.2 g, 0.016 mol). The reaction mixture was stir-
red for 4 h and a buff precipitate formed. This was left to stand for
24 h and then stirred for 2 h, filtered and the filtrate was dissolved
in hot acetonitrile filtered concentrated and allowed to cool to
room temperature yielding yellowish brown micro crystals. These
crystals were dissolved in DMF and re-crystallized by vapour diffu-
sion of diethyl ether from an adjacent container. This afforded dark
brown crystals (melting point 195 °C) which were not suitable for
crystallography. Anal. Calc. for C17H22N10ONi: C, 46.28; H, 5.02; N,
31.75. Found: C, 45.35; H, 4.08; N, 33.91%. KM (S cm2 molÀ1) in
DMF: 23.0. IR (cmÀ1): t(N–H) 3312, 3247, 3153; t(N3) 2020;
t(C@N) 1650; t(C@C), t(C@N)py, d(N–H), 1589, 1570. UV–Vis
(DMF. kmax): 690, 522, 463 nm. leff (BM): 3.30.
2.3. Synthesis of 2-phenyl-2-(2-pyridyl)imidazolidine (1)
The ligand 2-phenyl-2-(2-pyridyl) imidazolidine was prepared
using a slight variation of the procedure reported in the literature
[7]. An anhydrous ethanol solution (15 cm3) of 2-benzoylpyridine
(8.0 g, 0.04 mol), was treated dropwise with 1,2-diaminoethane
(2.62 g, 0.05 mol) in the same solvent (5.0 cm3) with constant stir-
ring and the mixture was then heated under reflux for 16 h. The
yellow solution was concentrated under reduced pressure, cooled
and the formed faint yellow precipitate filtered. The product was
re-crystallized from n-hexane giving almost colourless crystals,
melting point is (83–85 °C). Anal. Calc. for C14H15N3L: C, 74.63; H,
6.7; N, 18.67. Found: C, 74.81; H, 6.47; N, 18.46%. IR (Diamond
ATR cmÀ1): t(N–H) 3320, 3247 (broad); t(C@N) 1620, 1538,
1567, t(C@C) 1490 1448, 1425. 1H NMR data in CDCl3 at 298 K: d
(ppm): 8.73 d(1) (H6); 8.5 t(1) (H4); 7.95 m(1) (H5); 7.69 d(1)
(H3); 7.57–7.42 m(5) (H13–H17); 3.05 m(2) (H10); 2.99 m(2)
(H11); 2.82 br(2) (H 7, 9).13C NMR in CDCl3: d (ppm): 163.3
(C-2); 150.2 (C6); 144.2 (C12); 136.7 (C4); 128.28 (C14, 16);
127.1 (C13, 17); 122.1 (C15); 85.9 (C8); 46.3(C10,11); UV–Vis
(CH3CN): kmax 290, 275 and 252 nm.
2.4.3. [Cu(L)(CH3CN)][ClO4]2 (4)
To a stirred solution of (1) (1.0 g, 0.004 mol) in absolute ethanol
(6 cm3), a solution of Cu(ClO4)2 Á 6H2O (1.6 g, 0.004 mol) in acetoni-
trile (3 cm3) was added dropwise with constant stirring. The colour
changed from yellow to green and then to blue as the copper per-
chlorate solution was added. The reaction mixture was stirred for
5 h at room temperature and a blue precipitate formed. It was iso-
lated by filtration, washed with a mixture of ethanol and acetoni-
trile and dried under vacuum. Crystals grown from acetone
solution were of poor quality however crystallization from a mix-
ture of acetonitrile and ethanol afforded a blue needles of suitable
quality for X-ray crystallography. Melting point 200 °C. Anal. Calc.
for C16H18N4O8Cl2Cu: C, 36.34; H, 3.34; N, 10.59. Found: C,36.11;
H, 3.19; N, 10.59%. KM (S cm2 molÀ1 in CH3CN) and CH3NO2: 270
and 133. IR (cmÀ1): t(N–H) 3300, 3255, 3158; t(C@N) 1636;
2.4. Preparation of metal complexes, L= (1)
2.4.1. [Ni(L)2][ ClO4]2 (2)
t(C@C), t(C@N)py, d(N–H) 1598, 1580; t(ClO4) 1053. UV–Vis
To a stirred solution of (1) (1.0 g, 0.004 mol) in acetonitrile
(7 cm3), a solution of Ni(ClO4)2 Á 6H2O (1.6 g, 0.004 mol) in the
same solvent (7 cm3) was added dropwise with constant stirring.
The solution colour changed from yellow to a dark red. The reac-
tion mixture was stirred at room temperature for 3 h and left to
stand overnight. Evaporation of the solvent left a toffee like resi-
due. This was dissolved in warm methanol from which red crystals
were obtained. Anal. Calc. for C28H30N6Cll2NiO8 (2): C, 47.48; H,
4.23; N, 11.86. Found: C, 47.49; H, 4.07; N, 12.21%. KM
(XÀ1 cm2 molÀ1) in CH3CN and CH3NO2: 275 and 156. IR (Diamond
ATR cmÀ1): t(N–H) 3342, 3293 (broad, m); 1646 t(C@N); 1595,
1580 t(C@C), t(C@N)py, d(N–H), t(ClO4) 1070; UV–Vis (CH3CN;
kmax):784, 531, 464 nm. leff (BM): 3.34.
(CH3CN; kmax): 606, 412 nm. leff (BM): 1.75.
2.4.4. [CuL(N3)][NO3] (5)
An ethanolic solution (12 cm3) of Cu(NO3)26H2O (2.2 g,
0.01 mol) was added dropwise to ethanolic solution (10 cm3) of
(1) (1.0 g, 0.0044 mol) with continuous stirring. The reaction mix-
ture was stirred for one hour and the solution changed colour to a
greenish-blue. To this NaN3 (1.2 g, 0.02 mol) in hot methanol
(15 cm3) was added slowly with constant stirring. The colour chan-
ged immediately and a brown precipitate formed. The reaction
mixture was stirred for 3 h. at room temperature, the precipitate
was filtered, washed with few drops of ethanol and dried under
vacuum. This precipitate was disgraded (as it proved to be a mix-
ture). The green filtrate was concentrated using a rotary evaporator
and kept at 4 °C in a fridge for several weeks. Unusual dark green
spherical pseudo-crystals (unsuitable for crystallography) were
isolated, washed with few drops of ethanol and dried under vac-
uum. Melting point 115 °C. Anal. Calc. for C14H15N7O3Cu: C, 42.8;
H, 3.84; N, 24.96. Found: C, 42.32; H, 3.10; N, 25.09%. KM
(S cm2 molÀ1) in CH3CN and CH3NO2: 128 and 68. IR (cmÀ1):
t(N–H) 3292, 3244, 151; t(N3) 2042; t(C@N) 1660, 1636; t(C@C),
t(C@N)py, d(N–H) 1594, t(NO3) 1411. UV–Vis (CH3CN; kmax): 614,
518 nm. leff (BM): 1.74.
The red crystals were re-crystallized from a chloroform metha-
nol mixture to give a second crop of red crystals of formula
C28H30N6Cll2NiO8 Á CHCl3 which were suitable for crystallography.
2.4.2. [Ni(L)(N3)2DMF] (3)
The ligand (1) (1.0 g, 0.004 mol) was dissolved in absolute eth-
anol (5 cm3) and a solution of Ni(ClO4)26H2O (1.6 g, 0.004 mol) in
ethanol (7 cm3) was added drop-wise with constant stirring. The
yellow colour of the solution changed to a dark red with the forma-
tion of a semi-solid mass. Rapid stirring for one hour led to the for-
mation of a solid which was treated with a hot methanolic solution
NH2
+
N
N
N
NH
H2N
HN
O
N
H2N
(1)
Scheme 1.

S.M. Emam et al. / Polyhedron 27 (2008) 2379–2385
2381
2.4.6. [CuL(N3)][ClO4] (7)
A blue methanolic solution (7 cm3) of Cu(ClO4)2 Á 6H2O (1.6 g,
0.004 mol) was added dropwise to a methanolic solution (7 cm3)
of L (0.5 g, 0.002 mol) with continuous stirring. The mixture was
stirred for 20 min and then NaN3 (0.6 g, 0.01 mol) in aqueous
methanol (10 cm3, 1:1) was added slowly with a constant stirring.
The blue colour of the reaction mixture changed to dark brown
with the formation of green precipitate. This was filtered off
washed with methanol and dried. It was re-crystallized from hot
acetonitrile to give blue crystals which were suitable for crystallog-
raphy. Its melting point is 175 °C. Anal. Calc. for C14H15N6O4ClCu
(7): C, 39.07; H, 3.51; N, 39.53. Found: C,39.27; H, 2.99; N,
19.45%. (KM S cm2 molÀ1) in CH3CN CH3NO2: 153 and 104. IR
(cmÀ1): t(N–H) 3317, 3264, 3148; t(C@N) 1649; 1598, 1585;
t(ClO4) 1096. UV–Vis (CH3CN; kmax): 611, 513 nm. leff (BM): 1.80.
Fig. 1. ORTEX diagram of C14H15N3, L (1) with 40% probability ellipsoids.
2.4.7. [Cu2(L)2(Pyz)][ClO4]4 CH3CN Á (H2O)0.5 (8)
To a solution of (1) (1.0 g, 0.004 mol) in C2H5OH (10 cm3) was
added solution of Cu(ClO4)26H2O (3.3 g, 0.004 mol) in water
(5 cm3). The solution colour changed from yellow to blue and the
reaction mixture was then stirred for 30 min. at room temperature.
To this pyrazine (1.4 g, 0.02 mol) in water (5 cm3) was added
slowly with constant stirring. After stirring at room temperature
for 5 h the solution was allowed to stand and a precipitate was fil-
tered, washed with ethanol and dried under vacuum over P2O5. It
was crystallized from a mixture of CH3CN and CH3OH (1:3) by slow
vapour diffusion of diethyl ether from an adjacent container giving
dark violet crystals which were not suitable for X-ray crystallogra-
phy. Melting point 140 °C. Anal. Calc. for C34H38N9O16.5Cl4Cu2 (8):
C, 36.93; H, 3.46; N, 11.49. Found (>250 °C): C, 37.12; H, 3.36, N,
10.54%. KM (S cm2 molÀ1) in CH3CN: 507. IR (cmÀ1): t(O–H) 3567,
3407; t(N–H) 3316, 3260, 3140; t(C@N) 1649; t(C@C), t(C@N)py
2.4.5. [CuL(H2O)][NO3]2 (6)
The filtrate remaining after the filtration of (5) was left to stand
at room temperature for several weeks and a precipitate formed.
This was isolated by filtration, and washed with few drops of eth-
anol and crystallized from methanol solution and dark blue crys-
tals were grown by slow vapour diffusion of diethyl ether from
an adjacent container which were suitable for X-ray crystallogra-
phy. Melting point 135 °C. Anal. Calc. for C14H17N5O7Cu (6): C,
39.03; H, 3.97; N, 16.25. Found: C, 38.49; H, 4.01; N, 15.23%. KM
(S cm2 molÀ1) in CH3CN and CH3NO2: 141 and 50. IR (cmÀ1):
t(O–H) 3400–2327; t(N–H) 3293, 3240,3135; t(C@N) 1645; 1597,
1585; t(NO3) 1411. UV–Vis (CH3CN; kmax): 648, 516 nm. leff
(BM): 1.76.
Table 1
Crystal data and structure refinement parameters
Compound
(1)
(2)
(4)
(6)
(7)
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C
14H15N3
C29H31Cl5N6NiO8
827.56
298(2)
0.71069
monoclinic
P21/c
C16H18Cl2CuN4O8
528.78
150(2)
0.71073
orthorhombic
Pbca
C14H17CuN5O7
430.87
298(2)
0.71069
monoclinic
P21/c
C14H15ClCuN6O4
430.31
150(2)
0.71073
monoclinic
C2/c
225.29
298(2)
0.71069
monoclinic
C2/c
16.690(2)
5.796(1)
24.465(3)
95.25(2)
2356.7(6)
8
1.270
15.097(2)
25.636(3)
18.197(2) c = 90°
90.74(2)
7042.1(15)
8
1.561
0.987
3392
7.14000(10)
22.8780(2)
25.5040(3)
8.486(2)
24.6030(8)
8.2460(3)
17.1500(7)
106.7130(10)
3332.4(2)
8
1.715
1.507
1752
b (Å)
c (Å)
23.617(3)
8.7509(9)
92.130(10)
1752.6(5)
4
1.633
1.296
884
b (°)
Volume (Å3)
Z
4166.05(8)
8
1.686
1.358
2152
Density (calculated) (Mg/m3)
Absorption coefficient (mmÀ1
F(000)
)
0.078
960
Crystal size (mm)
h Range for data collection (°)
Index ranges
0.55 Â 0.42 Â 0.26
1.67–20.34
À16 6 h 6 15;
À5 6 k <= 5;
À23 6 l 6 23
4312
0.47 Â 0.38 Â 0.21
1.57–20.52
À14 6 h 6 14;
À23 6 k <= 24;
À17 6 l 6 17
22309
0.40 Â 0.20 Â 0.10
3.56–27.46
À9 6 h 6 9;
À29 6 k 6 29;
À33 6 l 6 33
58203
0.47 Â 0.41 Â 0.26
1.72–20.43
À7 6 h <= 7;
À22 6 k 6 22;
À8 6 l 6 8
6763
0.10 Â 0.05 Â 0.05
4.98–27.47
À31 6 h <= 31;
À8 6 k 6 10;
À22 6 l 6 21
11733
Reflections collected
Independent reflections [R(int)]
Reflections observed (>2r)
Data completeness
1137 [0.0361]
1091
0.977
6869 [0.0367]
6306
0.972
4751 [0.0732]
3514
0.997
1639 [0.0528]
1566
0.941
3679 [0.0781]
2583
0.964
Absorption correction
Data/restraints/parameters
Goodness-of-fit on F2
none
1137/0/157
1.066
none
6869/0/883
1.036
none
4751/2/307
1.028
none
1639/0/245
1.094
none
3679/2/243
1.022
Final R indices [I > 2r(I)]
R1 = 0.0363
wR2 = 0.1029
R1 = 0.0387
wR2 = 0.1046
0.130 and À0.136
R1 = 0.0656
wR2 = 0.1743
R1 = 0.0706
wR2 = 0.1786
1.158 and À0.811
R1 = 0.0377
wR2 = 0.0846
R1 = 0.0619
wR2 = 0.0948
0.419 and À0.457
R1 = 0.0467
wR2 = 0.1247
R1 = 0.0523
wR2 = 0.1410
0.781 and À0.474
R1 = 0.0437
wR2 = 0.0843
R1 = 0.0784
wR2 = 0.0987
0.365 and À0.467
R indices (all data)
Largest difference peak and hole (e ÅÀ3
)

2382
S.M. Emam et al. / Polyhedron 27 (2008) 2379–2385
Table 2
Table 3
Selected bond lengths (Å) and angles (°) for (1)
Selected bond lengths (Å) and angles (°) for (2)
N(2)–C(6)
N(3)–C(8)
C(6)–C(9)
C(6)–C(9)
C(1)–C(6)–C(9)
C(6)–N(2)–C(7)
N(3)–C(8)–C(7)
1.466(3)
1.465(3)
1.520(3)
1.520(3)
107.5(2)
103.3(2)
105.9(2)
N(2)–C(7)
N(3)–C(6)
C(1)–C(6)
C(7)–C(8)
C(6)–N(3)–C(8)
N(2)–C(7)–C(8)
C(1)–C(6)–N(2)
1.468(3)
1.480(2)
1.540(3)
1.510(3)
106.1(2)
105.8(2)
109.6(2)
Ni(1)–N(1)
Ni(1)–N(3)
Ni(1)–N(5)
Ni(2)–N(7)
Ni(2)–N(9)
Ni(2)–N(11)
N(1)–Ni(1)–N(2)
N(1)–Ni(1)–N(4)
N(1)–Ni(1)–N(6)
N(7)–Ni(2)–N(9)
N(7)–Ni(2)–N(11)
2.121(5)
2.103(5)
2.016(5)
2.121(5)
2.095(5)
2.017(5)
81.4(2)
92.1(2)
89.5(2)
158.3(2)
101.6(2)
Ni(1)–N(2)
Ni(1)–N(4)
Ni(1)–N(6)
Ni(2)–N(8)
Ni(2)–N(10)
Ni(2)–N(12)
N(1)–Ni(1)–N(3)
N(1)–Ni(1)–N(5)
N(7)–Ni(2)–N(8)
N(7)–Ni(2)–N(10)
N(7)–Ni(2)–N(12)
1.996(5)
2.112(5)
2.093(5)
1.998(5)
2.115(5)
2.088(5)
158.4(2)
100.7(2)
80.5(2)
90.7(2)
91.0(2)
H
H
N
N
M2+
..
N
Fig. 2. Metal induced ring opening of the imadazoline.
d(N–H) 1600, 1567; t(ClO4) 1095, 1043. UV–Vis (CH3CN; kmax):
650, 512 nm. leff (BM): 1.09.
2.5. Crystallography
Reflection data were collected either on a Marresearch image
plate system or on a Nonius kappa CCD system. Data reduction
were carried out using the XDS and DENZO/SCALEPACK packages. respec-
tively [8] The structures was solved by direct methods, SHELXS-97,
and refined by full matrix least squares using SHELXL-97 [9,10]. SHELX
operations were automated using ORTEX which was also used to
obtain the drawings [11]. Hydrogen atoms were included in calcu-
lated positions with thermal parameters 30% larger than the atom
to which they were attached. The non-hydrogen atoms were re-
fined anisotropically. All calculations were performed on a Pen-
tium PC.
Fig. 4. ORTEX diagram of [CuL(CH3CN)][ClO4]2 (4), with 40% probability ellipsoids.
2.6. Calculations
DFT calculations were carried out using PC-GAMESS [12] which
was driven by the molecular modeling software within the OSCAIL
package [13].
Table 4
Selected bond lengths (Å) and angles (°) for (4)
Cu(1)–N(1)
Cu(1)–N(3)
Cu(1)–O(7)
N(1)–Cu(1)–N(3)
N(2)–Cu(1)–N(3)
N(3)–Cu(1)–N(4)
N(2)–Cu(1)–O(7)
N(4)–Cu(1)–O(7)
2.008(2)
1.996(2)
2.391(2)
163.95(9)
80.77(8)
98.98(8)
97.87(9)
87.43(9)
Cu(1)–N(2)
Cu(1)–N(4)
1.957(2)
1.983(2)
83.51(9)
96.37(9)
174.70(8)
92.15(8)
93.20(8)
3. Results and discussion
N(1)–Cu(1)–N(2)
N(1)–Cu(1)–N(4)
N(2)–Cu(1)–N(4)
N(1)–Cu(1)–O(7)
N(3)–Cu(1)–O(7)
3.1. Structure of the ligand
The condensation of 2-benzoyl pyridine and 1,2-diaminoethane
has been reported and the structure of the product assigned as 2-
Fig. 3. ORTEX diagram of the cation of [NiL2][ClO4]2 (2) with 40% probability ellipsoids and hydrogen atoms omitted for clarity.

S.M. Emam et al. / Polyhedron 27 (2008) 2379–2385
2383
Fig. 5. ORTEX diagram of the cation of [Cu(L)(H2O)][(NO3)2] (6), with 40% probability ellipsoids.
Table 5
Selected bond lengths (Å) and angles (°) for (6)
Cu(1)–O(1)
Cu(1)–N(1)
Cu(1)–O(3)
N(1)–Cu(1)–N(2)
N(2)–Cu(1)–N(3)
O(1)–Cu(1)–N(2)
O(3)–Cu(1)–O(6)
1.942(5)
1.994(5)
2.621(6)
84.2(2)
80.8(2)
178.0(2)
173.6(2)
Cu(1)–N(2)
Cu(1)–N(3)
Cu(1)–O(6)
N(1)–Cu(1)–N(3)
O(1)–Cu(1)–N(1)
O(1)–Cu(1)–N(3)
1.948(5)
2.003(5)
2.536(5)
164.9(2)
93.9(2)
101.1(2)
phenyl-2-(2-pyridyl)imidazolidine, (1), using 1H and 13C NMR. It is
reasonable to suggest that the reaction proceeds via initial forma-
tion of the imine and subsequent cyclization as shown in Scheme 1.
Since this is an example of an unfavorable 5-Endo-Trig cycliza-
tion [4], the crystal structure was determined to confirm the
NMR assignment. The X-ray structure of (1) is shown in Fig. 1.
Fig. 6. ORTEX diagram of the cation of [Cu(L)N3][ClO4] (7), with 40% probability
ellipsoids and hydrogen atoms omitted for clarity.
Crystal data are given in Table 1 and selected bond lengths and an-
gles are given in Table 2.
DFT calculations on (1) using B3LYP functionals at the 6-31G*
level suggest that in the gas phase the cyclic structure is more sta-
ble than the open imine form by 13.1 kJ molÀ1. Thus the unfavour-
able 5-Endo-Trig cyclization may in part be possible in this case due
to the higher stability of the cyclic form. If solvent effects are ig-
nored, and if equilibrium was possible, this energy difference
translates to an equilibrium concentration of the cyclic form that
is approximately 5 Â 103 times greater than the imine form. There
is spectroscopic and kinetic evidence that the imine form may have
appreciably higher concentrations in polar solvents [14]. There are
many well established examples of 5-Endo-Trig cyclizations in the
literature [15,16].
Table 6
Selected bond lengths (Å) and angles (°) for (7)
Cu(1)–N(4)
Cu(1)–N(3)
N(1)–C(8)
N(2)–C(7)
N(3)–C(5)
N(5)–N(6)
C(2)–C(3)
C(4)–C(5)
C(6)–C(9)
1.946(3)
2.010(3)
1.494(4)
1.466(4)
1.364(4)
1.162(4)
1.382(5)
1.384(5)
1.491(4)
Cu(1)–N(2)
Cu(1)–N(1)
N(2)–C(6)
N(3)–C(1)
N(4)–N(5)
C(1)–C(2)
C(3)–C(4)
C(5)–C(6)
C(7)–C(8)
1.950(3)
2.033(3)
1.279(4)
1.333(4)
1.204(4)
1.381(5)
1.398(5)
1.498(4)
1.522(5)
N(4)–Cu(1)–N(2)
N(2)–Cu(1)–N(3)
N(2)–Cu(1)–N(1)
C(8)–N(1)–Cu(1)
C(6)–N(2)–Cu(1)
C(1)–N(3)–C(5)
C(5)–N(3)–Cu(1)
N(6)–N(5)–N(4)
173.0(1)
80.5(1)
83.7(1)
107.2(2)
118.8(2)
118.6(3)
113.4(2)
176.6(3)
N(4)–Cu(1)–N(3)
N(4)–Cu(1)–N(1)
N(3)–Cu(1)–N(1)
C(6)–N(2)–C(7)
C(7)–N(2)–Cu(1)
C(1)–N(3)–Cu(1)
N(5)–N(4)–Cu(1)
N(3)–C(1)–C(2)
94.9(1)
101.8(1)
161.1(1)
126.9(3)
114.3(2)
127.9(2)
126.0(2)
122.3(3)
3.2. Ring opening complexation
When (1) was reacted with Cu(II) and Ni(II) salts no complexes
containing the cyclic structure were observed. In every case where
crystal structures were obtained only the open form was observed
in the complexes. This reaction is probably an example of a cationic

2384
S.M. Emam et al. / Polyhedron 27 (2008) 2379–2385
Fig. 7. ORTEX diagram of showing the weak interactions in the crystal structure of (7).
N
3.4. Reaction of (2) with sodium azide
N
N
C6H5
H3C
O
N
When complex (2) was reacted with sodium azide a product of
Cu
formula [Ni(L)(N3)2(DMF)] (3) was isolated. Single crystals suitable
for X-ray crystallography could not be obtained. This formula is as-
signed on the basis of elemental analysis, spectroscopic, magnetic
and conductivity data. In the IR spectrum bands due to azide, DMF
and the Schiff base were all observed. The observed conductivity is
an order of magnitude lower than that observed for (2) in agree-
ment with its covalent formulation.
NEt2
Fig. 8. Structure of (8).
metal induced ring opening reaction. A possible mechanism is
illustrated in Fig. 2.
This mechanism is related to that proposed for the Fe(III) catal-
ysed opening of an imidazolidine ring in the presence of alcohols
[17].
3.5. Reaction of (1) with copper nitrate and acetonitrile in methanol
Treatment of a solution of (1) in methanol with copper perchlo-
rate gave a blue solution from which after addition of acetonitrile
blue crystals of formula [CuL(CH3CN)][ClO4]2 (4) were obtained.
The structure of a cation from (4) and its contacts to one of the per-
chlorate anions is shown in Fig. 4, crystal data are in Table 1 and
selected bond distances and angles are given in Table 4. The geom-
etry about copper is tetragonally distorted octahedral with metal
nitrogen distances within the square plane close to 2.0 Å and long-
er contacts to the oxygen atoms of symmetry related perchlorate
anions of 2.391(2) and 2.526(2) Å, respectively. The metal nitrogen
bond lengths within the salicylaldimine ligand show the same or-
der observed in the nickel complex (2) above.
3.3. Reaction of (1) with nickel perchlorate (2)
Reaction of (1) with nickel perchlorate led to the isolation of a
red solid. It was characterized by elemental analysis, IR and 1H
and 13C NMR. Crystals grown from a chloroform/methanol mixture
were suitable for X-ray crystallography. The structure of a cation
from the crystal structure of (2) is shown in Fig. 3. Crystal data
are given in Table 1 and selected bond lengths and angles are given
in Table 3. There are two almost identical formula units in the crys-
tallographic asymmetric unit. Each of the ligands in the cation is
tridentate with and the overall geometry is close to octahedral.
Thus within each asymmetric unit there are four examples of nick-
el ligand binding moeties. The nickel–nitrogen distances in all
cases are in order of increasing length; imine, pyridine and primary
amine. For example in Fig. 3 the Ni(1)–N(2), Ni(1)–N(3) and Ni(1)–
N(1) are 1.996(5), 2.103(5) and 2.121(5) Å.
To see if this order of bond lengths was due to crystal packing or
a genuine property of the complex the structure of the cation was
optimized using DFT calculations using B3LYP functionals at the 6-
31G* level [12]. The results while giving slightly longer distances
nevertheless gave the same order of bond lengths; N-i-N(2)
2.040, Ni–N(3) 2.115 and Ni–(N1) 2.183 Å. The bonding to nickel
on the part of the unsaturated nitrogens is clearly stronger than
that of the primary nitrogen. It is possible that a small amount of
strain in the chelate rings is the cause of the shortest Ni–N bond
being to the middle nitrogen. The observed magnetic moment of
3.34 lB is higher that the spin-only value for two unpaired elec-
trons of 2.83 lB however it is within the observed range for octa-
hedral nickel(II) complexes [18,19].
3.6. Reaction of (1) with copper nitrate and sodium azide in ethanol
An ethanolic solution of copper nitrate was reacted with (1) and
sodium azide. On standing for some time tiny green spheres grew
from solution. These spheres did not diffract X-rays and they had
the properties of a glass. The formula [CuLN3][NO3] (5) was as-
signed to this solid on the basis of analytical and spectroscopic
data. Attempts to grow crystals from the filtrate of this reaction
led to the isolation of crystals of [Cu(L)(H2O)][(NO3)2] (6), in which
water had replaced the azide anion. The structure of the cation
from (6) is shown in Fig. 5, crystal data are given in Table 1 and se-
lected bond lengths and angles are given in Table 5. The geometry
about the copper is tetragonally distorted octahedral with longer
contacts to nitrate oxygens. The coordinated water molecule is in-
volved in strong hydrogen bond contacts to nitrate ions, OÁ Á ÁO dis-
tances of 2.739(7) and 2.763(7) Å to O6 and O3, respectively, and
there are contacts from nitrate O7 to N1 of 3.078(7) Å which ex-
tend the hydrogen bond network throughout the lattice.

S.M. Emam et al. / Polyhedron 27 (2008) 2379–2385
2385
When weak interactions are included the stereochemistry of
4. Conclusion
the copper(II) ion is often difficult to describe due to the distortions
resulting from the Jahn–Teller effect. In an extensive review of this
area using structure correlation analysis Murphy and Hathaway
have analysed the range of observed structures and the crystal
structure of (5) lies well within that range [20]. Attempts were
made to model the strongly bonded square planar portion of the
structure using the DFT calculation methods that had been suc-
cessfully applied to the nickel complex above. In the crystal struc-
ture of (6) the copper and the three nitrogen atoms are essentially
planar, with a maximum deviation from least squares plane of
0.02 Å. The oxygen atom is just 0.10 Å above this plane. In the
DFT optimised structure the maximum deviation from the plane
defined by the copper and the three nitrogens is 0.18 Å and the
oxygen is 1.12 Å out of that plane. Attempts to model the complete
[Cu(L)(H2O)][(NO3)2] unit were even less successful. The B3LYP
functional appears to be able to model Cu(II) when the relative
geometry of the ligating atoms is restrained to some extent [5,6].
A recent review of DFT functionals has suggested that B3LYP has
some serious shortcomings and perhaps more advanced function-
als are required for the Cu(II) complexes described here [21].
2-Phenyl-2-(2-pyridyl)imidazolidine reacts with Ni(II) and
Cu(II) salts to give stable complexes containing the tridentate open
form of the ligand. Combined structural and theoretical calcula-
tions show that DFT calculations using the B3LYP functionals at
the 6-31G* level reproduce the geometry of the Ni(II) complexes
but are less successful in modelling the Cu(II) complexes.
Appendix A. Supplementary data
CCDC 677183, 677184, 677185, 677186 and 677187 contain the
supplementary crystallographic data for 1, 2, 4, 6 and 7. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/con-
ts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033, or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.poly.2008.04.028.
References
3.7. Reaction of (1) with copper perchlorate and sodium azide in
methanol
[1] D. Shi, Z. You, C. Xu, Q. Zhang, H. Zhu, Inorg. Chem. Commun. 10 (2007) 404.
[2] C.M. Sharaby, Spectrochim. Acta A 66 (2007) 127.
[3] C. Jin, W. Fan, Y. Jia, B. Fan, J. Ma, R. Li, J. Mol. Cat. A: Chem. 249 (2006) 23.
[4] J.E. Baldwin, J. Chem. Soc., Chem. Commun. (1976) 734.
[5] V. Ruangpornvisuti, Struct. Chem. 18 (2007) 977.
[6] S. Ritimukta, S.I. Gorelsky, L. Basumallick, H.J. Hwang, R.C. Pratt, T.D.P. Stack,
Y. Lu, K.O. Hodgson, B. Hedman, E.I. Solomon, J. Am. Chem. Soc. 130 (2008)
3866.
When the reaction above was repeated using copper perchlo-
rate in methanol solution it was possible to isolate good quality
crystals of the copper azide [Cu(L)N3][ClO4] (7). Crystal data are gi-
ven in Table 1 and selected bond lengths and angles are in Table 6.
The crystal structure of the cation from this salt without the weak-
er interactions which complete the tetragonally distorted octahe-
dral geometry is shown in Fig. 6.
The geometry about the copper is close to square-planar with
N2 showing the greatest deviation from the best plane through
the four nitrogens of 0.15 Å and the copper is 0.04 Å out of the
plane. The tetragonally distorted octahedral geometry about cop-
per is achieved by the addition of two weak interactions involving
highly asymmetric bridging on the part of the azide ligands,
1.946(3) and 2.709(3) and a weak interaction involving a perchlo-
rate anion, 2.774(3) Å (Fig. 7).
There are many reported structures of azide complexes in
which the azide ligand is seen to span the range from mono-den-
tate through semi-bridging to symmetrical bridging. Structure (7)
is close to mono-dentate. The energy difference between mono-
dentate and bridging structures is however small and less than
typical lattice energies. This point is clearly evident in the recently
reported structure of complex (8), depicted in Fig. 8, which Sarker
et al. have described [22,23]. In the reported crystal structure both
symmetrically bridged l-azido and mono-dentate square-planar
geometries are present in the same asymmetric unit.
[7] H. Sharghi, H. Naeimi, Synlett 12 (1998) 1343.
[8] (a) XDS, W. Kabasch, J. Appl. Crystallogr. 21 (1988) 916;
(b) Denzo/Scalepack, Z. Otwinowski, W. Minor, International Tables for
Crystallography, vol. F, Springer, 2001.
[9] G.M. Sheldrick, Acta Crystallogr., Sect. A 46 (1990) 467.
[10] G.M. Sheldrick, SHELXL-97
A Computer Program for Crystal Structure
Determination, University of Gottingen, 1997.
[11] P. McArdle, J. Appl. Crystallogr. 28 (1995) 65.
[12] PC GAMESS program provided by A.A. Granovsky, PC GAMESS version 7.1.5, <http://
classic.chem.msu.su/gran/gamess/index.html>.
[13] P. McArdle, K. Gilligan, D. Cunningham, R. Dark, M. Mahon, CrystEngComm 6
(2004) 303.
[14] J. McManus, M.J. Hynes, unpublished observations.
[15] A. Ishita, O. Tamura, Tetrahedron Lett. 43 (2002) 473.
[16] T. Yamazaki’, S. Hiraoka, J. Sakamoto, T. Kitazume, J. Fluorine Chem. 101 (2000)
309.
[17] V.M. Ugalde-Saldivar, H. Hopfl, N. Farfan, A.R. Toscano, M.E. Sosa-Torres, Inorg.
Chim. Acta 358 (2005) 3545.
[18] C.E. Housecroft, A.G. Sharpe, Inorganic Chemistry, 3rd ed., Pearson, Harlow,
2008, p. 672.
[19] F.A. Cotton, G. Wilkinson, C.A. Murillo, M. Bochmann, Advanced Inorganic
Chemistry, 6th ed., Wiley, New York, 1999. p. 839.
[20] B. Murphy, B. Hathaway, Coord. Chem. Rev. 243 (2003) 237.
[21] Y. Zhao, D.G. Truhlar, Acc. Chem. Res. 41 (2008) 157.
[22] B. Sarkar, M.S. Ray, M.G.B. Drew, C. Lu, A. Ghosh, J. Coord.Chem. 60 (2007)
2165.
[23] F.H. Allen, Acta Crystallogr., Sect. B 58 (2002) 380.