Synthesis and characterization of nickel(II) complexes of 14-membered hexaaza macrocyclic ligands "3,10-dialkyl-dibenzo-1,3,5,8,10,12-hexaazacyclotetradecane" produced by the in situ one-pot template reaction of formaldehyde and 1,2-phenylenediamine with alkyl or benzyl amine in the presence of the nickel(II) ion

Article abstract of DOI:10.1016/j.poly.2005.12.026

New square-planar Ni(II) complexes of 14-membered hexaaza macrocyclic ligands {dibenzo-1,3,5,8,10,12-hexaazacyclotetradecane, [Ni(Bzo₂[14]aneN₆)](ClO₄)₂ (1); 3,10-dimethyl-, [Ni(Me₂Bzo₂[14]aneN₆)](ClO₄)₂ (2); 3,10-diethyl-, [Ni(Et₂Bzo₂[14]aneN₆)](ClO₄)₂ (3); 3,10-dibutyl-, [Ni(Bu₂Bzo₂[14]aneN₆)](ClO₄)₂ (4); 3,10-dibenzyl-, dibenzo-1,3,5,8,10,12-hexaazacyclotetradecane [Ni((benzyl)₂Bzo₂[14]aneN₆)](ClO₄)₂ (5); [Ni(Bzo₂[14]aneN₆)](PF₆)₂ (6); [Ni(Me₂Bzo₂[14]aneN₆)](PF₆)₂ (7); [Ni(Et₂Bzo₂[14]aneN₆)](PF₆)₂ (8); [Ni(Bu₂Bzo₂[14]aneN₆)](PF₆)₂ (9); [Ni((benzyl)₂Bzo₂[14]aneN₆)](PF₆)₂ (10); [Ni(Bzo₂[14]aneN₆)Cl₂] (11); [Ni(Me₂Bzo₂[14]aneN₆)Cl₂] (12); [Ni(Et₂Bzo₂[14]aneN₆)Cl₂] (13); [Ni(Bu₂Bzo₂[14]aneN₆)Cl₂](14); [Ni((benzyl)₂Bzo₂[14]aneN₆)Cl₂] (15); [Ni(Bzo₂[14]aneN₆)(NCS)₂] (16); [Ni(Me₂Bzo₂[14]aneN₆)(NCS)₂] (17); [Ni(Et₂Bzo₂[14]aneN₆)(NCS)₂] (18); [Ni(Bu₂Bzo₂[14]aneN₆)(NCS)₂] (19); [Ni((benzyl)₂Bzo₂[14]aneN₆)(NCS)₂] (20)} have been prepared by the in situ one-pot template synthesis (IOPTS) of formaldehyde and 1,2-phenylenediamine with alkyl amine or benzyl amine in the presence of the nickel(II) ion. The complexes of the hexaaza macrocycle have been characterized by elemental analyses, IR, FAB, UV-Vis and ¹H NMR spectroscopy, conductometric and magnetic measurements. The nickel(II) complexes {[Ni(R₂Bzo₂[14]aneN₆)](ClO₄)₂ (1-5) and [Ni(R₂Bzo₂[14]aneN₆)](PF₆)₂ (6-10)} have square-planar coordination geometry in the solid state and in nitromethane. The spectra of all complexes show that the four secondary nitrogen atoms are coordinated to the nickel(II) ion. Synthesis, characterization and solution behavior of the nickel(II) complexes of hexaaza macrocycle (1-6) are reported. The stereochemistry around the metal ions in the {[Ni(R₂Bzo₂[14]aneN₆)(NCS)₂] and "[Ni(R₂Bzo₂[14]aneN₆)Cl₂]}" complexes is octahedral.

Full text of DOI:10.1016/j.poly.2005.12.026

Polyhedron 25 (2006) 2127–2134
www.elsevier.com/locate/poly
Synthesis and characterization of nickel(II) complexes of
14-membered hexaaza macrocyclic ligands
‘‘3,10-dialkyl-dibenzo-1,3,5,8,10,12-hexaazacyclotetradecane’’
produced by the in situ one-pot template reaction of formaldehyde
and 1,2-phenylenediamine with alkyl or benzyl amine in the
presence of the nickel(II) ion
*
Masoud Salavati-Niasari , Fatemeh Davar
Department of Chemistry, University of Kashan, Kashan, P.O. Box 87317-51167, Iran
Received 8 November 2005; accepted 21 December 2005
Available online 21 February 2006
Abstract
New square-planar Ni(II) complexes of 14-membered hexaaza macrocyclic ligands {dibenzo-1,3,5,8,10,12-hexaazacyclotetradecane,
[Ni(Bzo2[14]aneN6)](ClO4)2 (1); 3,10-dimethyl-, [Ni(Me2Bzo2[14]aneN6)](ClO4)2 (2); 3,10-diethyl-, [Ni(Et2Bzo2[14]aneN6)](ClO4)2 (3);
3,10-dibutyl-, [Ni(Bu2Bzo2[14]aneN6)](ClO4)2 (4); 3,10-dibenzyl-, dibenzo-1,3,5,8,10,12-hexaazacyclotetradecane [Ni((benzyl)2Bzo2[14]-
aneN6)](ClO4)2 (5); [Ni(Bzo2[14]aneN6)](PF6)2 (6); [Ni(Me2Bzo2[14]aneN6)](PF6)2 (7); [Ni(Et2Bzo2[14]aneN6)](PF6)2 (8); [Ni(Bu2-
Bzo2[14]aneN6)](PF6)2 (9); [Ni((benzyl)2Bzo2[14]aneN6)](PF6)2 (10); [Ni(Bzo2[14]aneN6)Cl2] (11); [Ni(Me2Bzo2[14]aneN6)Cl2] (12);
[Ni(Et2Bzo2[14]aneN6)Cl2] (13); [Ni(Bu2Bzo2[14]aneN6)Cl2] (14); [Ni((benzyl)2Bzo2[14]aneN6)Cl2] (15); [Ni(Bzo2[14]aneN6)(NCS)2]
(16); [Ni(Me2Bzo2[14]aneN6)(NCS)2] (17); [Ni(Et2Bzo2[14]aneN6)(NCS)2] (18); [Ni(Bu2Bzo2[14]aneN6)(NCS)2] (19); [Ni((benzyl)2-
Bzo2[14]aneN6)(NCS)2] (20)} have been prepared by the in situ one-pot template synthesis (IOPTS) of formaldehyde and 1,2-phenylen-
ediamine with alkyl amine or benzyl amine in the presence of the nickel(II) ion. The complexes of the hexaaza macrocycle have been
characterized by elemental analyses, IR, FAB, UV–Vis and 1H NMR spectroscopy, conductometric and magnetic measurements.
The nickel(II) complexes {[Ni(R2Bzo2[14]aneN6)](ClO4)2 (1–5) and [Ni(R2Bzo2[14]aneN6)](PF6)2 (6–10)} have square-planar coordina-
tion geometry in the solid state and in nitromethane. The spectra of all complexes show that the four secondary nitrogen atoms are coor-
dinated to the nickel(II) ion. Synthesis, characterization and solution behavior of the nickel(II) complexes of hexaaza macrocycle (1–6)
are reported. The stereochemistry around the metal ions in the {[Ni(R2Bzo2[14]aneN6)(NCS)2] and ‘‘[Ni(R2Bzo2[14]aneN6)Cl2]}’’ com-
plexes is octahedral.
Ó 2006 Elsevier Ltd. All rights reserved.
Keywords: Template synthesis; Hexaazacyclotetradecane; Nickel(II); Macrocycle; 14-Membered
1. Introduction
and lively topic of coordination chemistry of synthetic
macrocycles originated during the 1960s with high yield
syntheses of ligands, in which the Ni(II) ion was employed
as a templating agent [1]. The design and synthesis of poly-
aza macrocycles have attracted increasing interest in recent
years because of the possible relevance of these compounds
as models in bioinorganic chemistry, catalysis extractions
In situ one-pot template synthesis (IOPTS) lies at the
heart of macrocyclic chemistry. In particular, the rich
*
Corresponding author. Tel.: + 98 361 5555333; fax: +98 361 5552935.
E-mail address: salavati@kashanu.ac.ir (M. Salavati-Niasari).
0277-5387/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.12.026

2128
M. Salavati-Niasari, F. Davar / Polyhedron 25 (2006) 2127–2134
of metal ions from solution and the activations of small
molecules gave impetus to this endeavour [2–27]. The syn-
thesis of organic substrates that preferentially interact with
particular metal ions is of fundamental importance to
many areas of chemistry [28–32]. For example, condensa-
tion between carbonyl and amine has played an important
role in the development of synthetic macrocyclic ligands
[33–43]. Usually such syntheses are carried out in the pres-
ence of a suitable metal ion, which serves to direct the steric
course of the reaction preferentially towards cyclic rather
than oligomeric or polymeric products.
The coordination geometry and properties of most tran-
sition metal complexes with 14-membered hexaaza macro-
cyclic ligands containing amine have been studied [1–43].
However, most of them contained tetraaza macrocyclic
ligands, and 14-membered macrocyclic ligands containing
six nitrogen atoms with a phenylene group’s macrocyclic
framework have not been reported yet. We have been inter-
ested in the synthesis of various types of polyaza macrocy-
clic complexes containing amino alkyl groups from in situ
one-pot template synthesis (IOPTS). Metal template con-
densation reactions often provide selective routes towards
products that are not obtainable in the absence of metal
ions. Especially, template reactions involving formaldehyde
and amines facilitate the preparation of saturated polyaza
multidentate macrocyclic and macropolycyclic complexes.
Metal template condensation reactions involving amines
and formaldehyde have been employed in the preparation
of various saturated polyaza macrocyclic complexes [1–43].
In this paper, we report the synthesis, characterization
and properties of the new nickel(II) complexes of dibenzo-
1,3,5,8,10,12-hexaazacyclotetradecane, [Ni(Bzo2[14]aneN6)]-
(ClO4)2 (1); 3,10-dimethyl-, [Ni(Me2Bzo2[14]aneN6)](ClO4)2
(2); 3,10-diethyl-, [Ni(Et2Bzo2[14]aneN6)](ClO4)2 (3); 3,10-
dibutyl-, [Ni(Bu2Bzo2[14]aneN6)](ClO4)2 (4); 3,10-dibenzyl-,
dibenzo-1,3,5,8,10,12-hexaazacyclotetradecane [Ni((benzyl)2-
Bzo2[14]aneN6)](ClO4)2 (5); [Ni(Bzo2[14]aneN6)](PF6)2 (6);
[Ni(Me2Bzo2[14]aneN6)](PF6)2 (7); [Ni(Et2Bzo2[14]aneN6)]-
(PF6)2 (8); [Ni(Bu2Bzo2[14]aneN6)](PF6)2 (9); [Ni((ben-
zyl)2Bzo2[14]aneN6)](PF6)2 (10); [Ni(Bzo2[14]aneN6)Cl2]
(11); [Ni(Me2Bzo2[14]aneN6)Cl2] (12); [Ni(Et2Bzo2[14]-
aneN6)Cl2] (13); [Ni(Bu2Bzo2[14]aneN6)Cl2] (14); [Ni((ben-
zyl)2Bzo2[14]aneN6)Cl2] (15); [Ni(Bzo2[14]aneN6)(NCS)2]
(16); [Ni(Me2Bzo2[14]aneN6)(NCS)2] (17); [Ni(Et2Bzo2-
[14]aneN6)(NCS)2] (18); [Ni(Bu2Bzo2[14]aneN6)(NCS)2]
(19) and [Ni((benzyl)2Bzo2[14]aneN6)(NCS)2] (20) are given
in Schemes 1 and 2.
2. Experimental
2.1. Materials and measurements
Safety note. Caution! Perchlorate salts of metal com-
plexes are potentially explosive and due care must be
employed when handling them. In particular, such com-
pounds should never be heating as solids. All chemicals
and solvents used in the syntheses were of reagent grade
and were used without further purification. For the spec-
troscopic measurements, water was distilled and organic
solvents were purified according to the literature method
[44]. For electrochemical experiments, high-purity aceto-
nitrile was obtained from Aldrich Chemical Co. and
˚
dried over 4 A molecular sieves. Electronic absorption
spectra were obtained with a Shimadzu UV–Vis scanning
2+
R
H
Complex
[Ni(H2Bzo[14]aneN6](ClO4)2
Number
1
Me
Et
Bu
Benzyl
H
[Ni(Me2Bzo[14]aneN6](ClO4)2
[Ni(Et2Bzo[14]aneN6](ClO4)2
[Ni(Bu2Bzo[14]aneN6](ClO4)2
[Ni((Benzyl)2Bzo[14]aneN6](ClO4)2
[Ni(H2Bzo[14]aneN6](PF6)2
2
3
4
5
6
H
H
N
N
N
R
N
N
R
Ni
N
Me
Et
Bu
Benzyl
[Ni(Me2Bzo[14]aneN6](PF6)2
[Ni(Et2Bzo[14]aneN6](PF6)2
[Ni(Bu2Bzo[14]aneN6](PF6)2
[Ni((Benzyl)2Bzo[14]aneN6](PF6)2
7
8
9
10
H
H
R
H
X
Cl
Complex
[Ni(H2Bzo[14]aneN6Cl2]
Number
11
Me
Et
Bu
Benzyl
H
Me
Et
Bu
Benzyl
Cl
Cl
Cl
Cl
NCS
NCS
NCS
NCS
NCS
[Ni(Me2Bzo[14]aneN6Cl2]
[Ni(Et2Bzo[14]aneN6Cl2]
[Ni(Bu2Bzo[14]aneN6Cl2]
[Ni((Benzyl)2Bzo[14]aneN6Cl2]
[Ni(H2Bzo[14]aneN6](NCS)2]
[Ni(Me2Bzo[14]aneN6(NCS)2]
[Ni(Et2Bzo[14]aneN6(NCS)2]
[Ni(Bu2Bzo[14]aneN6(NCS)2]
[Ni((Benzyl)2Bzo[14]aneN6(NCS)2]
12
13
14
15
16
17
18
19
20
H
H
X
N
N
R
N
N
R
Ni
N
N
X
H
H
Scheme 1.

M. Salavati-Niasari, F. Davar / Polyhedron 25 (2006) 2127–2134
2129
H
CH2
H
H
2 N
N
H
N
N
H
2 N
2
N
N
N
H2
2RNH2
R
2HCHO
2+
2+
Ni
Ni
2+
N
Ni
N
R
H2C
N
H
H
H
H
2 N
N
2
2
N
H2
H
H
H
H
N
N
N
H2C
N
N
N
R
N
N
2HCHO
2+
R
H
N
2+
Ni
Ni
R
N
N
H
N
R
CH2
H
H
H
R= H, Me, Et, Bu, Benzyl
Scheme 2.
spectrophotometer (Model 2101 PC), FTIR spectra with
a Shimadzu Varian 4300 spectrophotometer, NMR spec-
tra with a Varian Mercury 300 NMR spectrometer, and
conductance measurements with a Metrohm Herisau
conductometer E 518. The elemental analysis (carbon,
hydrogen and nitrogen) of the complexes was obtained
from Carlo ERBA Model EA 1108 analyzer. Magnetic
moments were calculated from magnetic susceptibility
data obtained by using a Johnson Matthey MK-1 mag-
netic susceptibility balance. The electrochemical data was
obtained in acetonitrile with 0.1 M (n-Bu)4NClO4 as sup-
porting electrolyte. The working electrode was a plati-
num disk, the auxiliary electrode was a coiled platinum
wire and the reference electrode was Ag|AgClO4 (0.1 M
in CH3CN), which showed +0.24 V versus SCE. Atomic
absorption spectra (AAS) were recorded on a Perkin–
Elmer 4100-1319 spectrophotometer. FAB mass spectra
were recorded on a Kratos MS50TC spectrometer.
2.3. Preparation of [Ni(Me2Bzo2[14]aneN6)](ClO4)2 (2)
This compound was prepared by a method similar to
that for the preparation of [Ni(H2Bzo2[14]aneN6)](ClO4)2
except that methylamine (84.20 mmol, 10.47 ml) was used
instead of ammonia. (Yield: ꢀ54%; FAB mass (m/z): 484
([M À ClO4]+)). Anal. Calc. for 2: Ni, 10.05; C, 37.01; H,
4.49; N, 14.39. Found: Ni, 9.92; C, 36.88; H, 4.38; N,
14.55%.
2.4. Preparation of [Ni(Et2Bzo2[14]aneN6)](ClO4)2 (3)
This complex was prepared by a method similar to that
for [Ni(H2Bzo2[14]aneN6)](ClO4)2 except that 50% ethyla-
mine (8.72 ml, 84.20 mmol) was used instead of ammonia.
(Yield: ꢀ57%; FAB mass (m/z): 513 ([M À ClO4]+)). Anal.
Calc. for 3: Ni, 9.59; C, 39.24; H, 4.94; N, 13.73. Found:
Ni, 9.47, C, 39.08; H, 4.81; N, 13.84%.
2.2. Preparation of [Ni(H2Bzo2[14]aneN6)](ClO4)2 (1)
2.5. Preparation of [Ni(Bu2Bzo2[14]aneN6)](ClO4)2 (4)
To a stirred methanol solution (100 ml) of Ni(ClO4)2 Æ
6H20 (15.38 g, 42.07 mmol) was slowly added 1,2-pheny-
lenediamine (9.11 g, 84.20 mmol), 36% formaldehyde
(15 ml) and 25% ammonia (6.30 ml, 84.20 mmol). The mix-
ture was heated at reflux for 24 h until a dark solution
resulted. The solution was cooled to room temperature
and filtered to remove nickel hydroxide. The deep yellow
crystals were filtered, washed with methanol, and air-dried.
The crystals were recrystallized from hot water. (Yield:
ꢀ46%; FAB mass (m/z): 456 ([M À ClO4]+)). Anal. Calc.
for 1: Ni, 10.56; C, 34.56; H, 3.99; N, 15.12. Found: Ni,
10.41; C, 34.40, H, 3.81; N, 15.24%.
This complex was prepared by a method similar to that
for [Ni(H2Bzo2[14]aneN6)](ClO4)2 except that iso-butyl-
amine (8.36 ml, 84.20 mmol) was used instead of ammonia.
(Yield: ꢀ44%; FAB mass (m/z): 568 ([M À ClO4]+)). Anal.
Calc. for 4: Ni, 8.79; C, 43.14; H, 5.73; N, 12.58. Found:
Ni, 8.66; C, 43.02; H, 5.60; N, 12.65%.
2.6. Preparation of
[Ni((benzyl)2Bzo2[14]aneN6)](ClO4)2 (5)
This complex was prepared by a method similar to that
for [Ni(H2Bzo2[14]aneN6)](ClO4)2 except that benzylamine

2130
M. Salavati-Niasari, F. Davar / Polyhedron 25 (2006) 2127–2134
(9.20 ml, 84.20 mol) was used instead of ammonia. (Yield:
ꢀ41%; FAB mass (m/z): 638 ([M À ClO4]+)). Anal. Calc.
for 5: Ni, 7.97; C, 48.94; H, 4.66; N, 11.42. Found: Ni,
7.81; C, 48.81; H, 4.53; N, 11.55%.
was allowed to stand at room temperature, and then the
deep pink precipitate formed was filtered, washed with a
1:2 mixture of water and methanol, and dried in a vacuum.
Anal. Calc. for 16: Ni, 12.40; C, 45.68; H, 4.69; N, 23.68.
Found: Ni, 12.29; C, 45.55; H, 4.56; N, 23.75%. Anal. Calc.
for 17: Ni, 11.71; C, 47.92; H, 5.23; N, 22.35. Found: Ni,
11.59; C, 47.80; H, 5.11; N, 22.46%. Anal. Calc. for 18:
Ni, 11.09; C, 49.92; H, 5.71; N, 21.17. Found: Ni, 10.91;
C, 49.80; H, 5.58; N, 21.26%. Anal. Calc. for 19: Ni,
10.03; C, 53.34; H, 6.54; N, 19.14. Found: Ni, 9.92; C,
53.21; H, 6.41; N, 19.23%. Anal. Calc. for 20: Ni, 8.98;
C, 58.81; H, 5.24; N, 17.15. Found: Ni, 8.83; C, 58.70; H,
5.12; N, 17.23%.
2.7. Preparation of [Ni(R2Bzo2[14]aneN6)](PF6)2 (6–10)
To an acetonitrile (50 ml) suspension of [Ni(R2Bzo2-
[14]aneN6)](ClO4)2 (0.50 g) was added excess NH4PF6,
and white precipitates of NH4ClO4 were formed. NH4ClO4
was filtered off and the filtrate was concentrated to 25 ml.
Water (25 ml) was added to the solution, and the mixture
was kept in the refrigerator. The yellow precipitates were
filtered, washed with a 6:1 mixture of water and acetoni-
trile, and dried in vacuum. (6, FAB mass (m/z): 502
([M À PF6]+)). Anal. Calc. Ni, 9.07; C, 29.70; H, 3.43; N,
12.99. Found: Ni, 8.94; C, 29.58; H, 3.32; N, 13.04%. (7,
FAB mass (m/z): 530 ([M À PF6]+)). Anal. Calc. Ni, 8.70;
C, 32.02; H, 3.88; N, 12.45. Found: Ni, 8.57; C, 31.90; H,
3.75; N, 12.56%. (8, FAB mass (m/z): 558 ([M À PF6]+)).
Anal. Calc. Ni, 8.35; C, 34.16; H, 4.30; N, 11.95. Found:
Ni, 8.22; C, 34.02; H, 4.18; N, 12.06%. (9, FAB mass
(m/z): 614 ([M À PF6]+)). Anal. Calc. Ni, 7.73; C, 37.97;
H, 5.04; N, 11.07. Found: Ni, 7.60; C, 37.85; H, 4.91; N,
11.13%. (10, FAB mass (m/z): 682 ([M À PF6]+)). Anal.
Calc. Ni, 7.10; C, 43.56; H, 4.14; N, 10.16. Found: Ni,
6.94; C, 43.44; H, 4.03; N, 10.24%.
2.10. Preparation of [Ni(Bzo2[10]aneN4)](ClO4)2 (21)
To a stirred methanol solution (100 ml) of Ni(ClO4)2 Æ
6H20 (15.38 g, 42.07 mmol) were slowly added 1,2-pheny-
lenediamine (9.11 g, 84.20 mmol) and 36% formaldehyde
(30 ml). The mixture was heated at reflux for 24 h until a
dark yellow solution resulted. The solution was cooled to
room temperature and filtered to remove nickel hydroxide.
The dark yellow crystals were filtered, washed with metha-
nol and air-dried. The crystals were recrystallized from hot
water. (Yield: ꢀ58%; FAB mass (m/z): 398 ([M À PF6]+)).
Anal. Calc. for 21: Ni, 11.78; C, 33.77; H, 3.24; N, 11.25.
Found: Ni, 11.61; C, 33.58, H, 3.16; N, 11.37%.
2.8. Preparation of [Ni(R2Bzo2[14]aneN6Cl2)] (11–15)
2.11. Preparation of [Ni((Allyl)2Bzo2[14]aneN6)](ClO4)2
(22)
To a stirred methanol solution (100 ml) of NiCl2 Æ 6H2O
(10.00 g, 42.07 mmol) were slowly added 1,2-phenylenedi-
amine (9.11 g, 84.20 mmol), 36% formaldehyde (15 ml)
and 25% ammonia (6.3 ml, 84.20 mmol). The mixture was
heated at reflux for 24 h until a dark solution resulted.
The solution was cooled to room temperature and filtered
to remove nickel hydroxide. The dark brown crystals were
filtered, washed with methanol and air-dried. The crystals
were recrystallized from hot water. Anal. Calc. for 11: Ni,
13.72; C, 30.18; H, 5.18; N, 19.64. Found: Ni, 13.58; C,
30.08; H, 5.10; N, 19.73%. Anal. Calc. for 12: Ni, 12.87;
C, 47.40; H, 5.75; N, 18.43. Found: Ni, 12.76; C, 47.29;
H, 5.62; N, 18.56%. Anal. Calc. for 13: Ni, 12.13; C,
49.62; H, 6.25; N, 17.36. Found: Ni, 12.01; C, 49.48; H,
6.18; N, 17.45%. Anal. Calc. for 14: Ni, 10.87; C, 53.36;
H, 7.09; N, 15.56. Found: Ni, 10.75; C, 53.22; H, 6.91;
N, 15.64%. Anal. Calc. for 15: Ni, 9.65; C, 56.24; H,
5.63; N, 13.82. Found: Ni, 9.54; C, 26.10; H, 5.48; N,
13.95%.
This compound was prepared by a method similar to
that for the preparation of [Ni(H2Bzo2[14]aneN6)](ClO4)2
except that allylamine ‘‘3-amino-1-propene’’ (84.20 mmol,
4.81 g) was used instead of ammonia. (Yield: ꢀ54%; FAB
mass (m/z): 568 ([M À PF6]+)). Anal. Calc. for 23: Ni,
8.78; C, 39.54; H, 5.13; N, 16.77. Found: Ni, 8.57; C,
39.38; H, 5.01; N, 16.83%.
3. Results and discussion
In situ one-pot template synthesis (IOPTS) of 1,2-pheny-
lenediamine with formaldehyde, in the presence of the
nickel(II) ion, was expected to produce of the mononuclear
14-membered hexaaza macrocycle complex ‘‘[Ni(R2Bzo2-
[14]aneN6)]2+’’. It was observed that the product obtained
from the reactions was largely affected by the molar ratio
of the reactants. The mononuclear hexaaza complex
‘‘[Ni(R2Bzo2[14]aneN6)](ClO4)2 (1–5)’’ was readily pre-
pared as the main product by the reaction of the nickel(II)
ion, 1,2-phenylenediamine, CH2O and amine in a 1:2:4:2
molar ratio. The crude product often contained a small
amount of the 10-membered tetraaza macrocyclic nickel(II)
complex (21) as a by-product (Section 2.10). However, the
mononuclear complex could be readily isolated by frac-
tional recrystallization of the product from ca. 0.05 M
HClO4 aqueous solutions.
2.9. Preparation of [Ni(R2Bzo2[14]aneN6)(NCS)2]
(16–20)
To a saturated hot aqueous solution of the perchlorate
salt of the appropriate ‘‘[Ni(R2Bzo2[14]aneN6)](ClO4)2
(R = H, Me, Et, Bu, Benzyl)’’ was added excess KSCN dis-
solved in a minimum amount of hot water. The solution

M. Salavati-Niasari, F. Davar / Polyhedron 25 (2006) 2127–2134
2131
2+
tal analyses and the molecular ion peaks in the mass spectra.
All mass spectra showed molecular ion peaks for the 1:1
metal-to-ligand stoichiometry with no further peaks above
them. A preliminary identification of the metal complexes
was made on the basis of their IR spectra, which exhibited
no bands characteristic of free primary amine, thus support-
ing the proposed macrocyclic skeleton (Scheme 1).
H
H
H
N
N
N
Ni
N
H
The IR spectra of all the complexes (Table 1) showed a
single sharp absorption around ꢀ3230 cmÀ1 which may
possibly arise from a secondary amine, mN–H, although its
position has been found to be lower by 40–60 cmÀ1 than
the analogous metal-free hexaaza ligands [46]. This sug-
gests that the secondary amine nitrogens take part in coor-
dination to the metal ions, which has been further
confirmed by the appearance of bands in the 320–
365 cmÀ1 region in all the complexes, corresponding to
21
The deep yellow complexes ‘‘[Ni(R2Bzo2[14]aneN6)]-
(ClO4)2 (1–5) and [Ni(R2Bzo2[14]aneN6)](PF6)2 (6–10)’’
readily dissolve in polar solvents such as H2O, CH3CN,
mM–N vibrations. A much higher mN–H value (3235 cmÀ1
)
À
CH3NO2 and Me2SO2. However, PF6 salts of the com-
for [Ni{(CH3)2Bzo2[14]aneN6}](ClO4)2 than that (3220
cmÀ1) for [Ni{(CH3)2[14]aneN6}](ClO4)2 [57], indicates
that the Ni–N interaction in 2 is much stronger than in
the [Ni{(CH3)2[14]aneN6}](ClO4)2 complex. The absorp-
tion bands in the 2850–3050 and 1400–1450 cmÀ1 regions
observed in the complexes may reasonably correspond to
CH stretching and CH bending vibrational modes. How-
ever, a medium intensity band at 280–290 cmÀ1 may unam-
biguously be assigned to the M–Cl stretching mode in
complexes 11–15.
plexes readily dissolve in nitromethane and water. The
nickel(II) complexes are extremely stable in the solid state
and in solution and are relatively stable against ligand dis-
sociation even in highly acidic solutions. [Ni(R2[14]-
aneN6)]2+ react with excess KSCN in aqueous solution to
form tetragonal complexes [Ni(R2[14]aneN6)(NCS)2],
whose IR spectra (Table 1) show that the nitrogen atoms
of the NCSÀ ligands are coordinated to the Ni(II) ion [45].
The molecular formulae of the complexes ‘‘[Ni(R2Bzo2-
[14]aneN6)](ClO4)2, [Ni(R2Bzo2[14]aneN6)](PF6)2, [Ni(R2-
Bzo2[14]aneN6)Cl2] and [Ni(R2Bzo2[14]aneN6)(NCS)2]’’
have been assigned on the basis of the results of their elemen-
The molar conductance values of 1–10 (ꢀ240 XÀ1 molÀ1
cm2), measured in water, correspond to 1:2 electrolytes.
Table 1
Spectral and conductance data for 14-membered hexaaza macrocyclic nickel(II) complexes
IR (cmÀ1
)
Electronic spectra, kmax (nm (e, MÀ1 cmÀ1))
KM
leff
(MB)
a
Complex
(XÀ1 cm2 MÀ1
)
MeNO2 MeCN
H2O
In 3.0 M DMSO
NaCl
aqueous
solution
[Ni(H2Bzo2[14]aneN6)](ClO4)2
[Ni((CH3)2Bzo2[14]aneN6)](ClO4)2
[Ni(Et2Bzo2[14]aneN6)](ClO4)2
[Ni(Bu2Bzo2[14]aneN6)](ClO4)2
[Ni((Allyl)2Bzo2[14]aneN6)](ClO4)2
mN–H 3240
mN–H 3235
mN–H 3232
mN–H 3225
mN–H 3227
441 (56) 450 (39) 454 (51) 447 (53)
441 (55) 451 (40) 455 (52) 447 (54)
442 (56) 452 (40) 456 (52) 448 (53)
442 (67) 452 (39) 457 (67) 449 (53)
443(67) 452 (39) 458 (67) 450 (54)
440 (56) 449 (39) 453 (52) 445 (53)
442 (57) 451 (36) 453 (50) 446 (54)
441 (55) 450 (35) 456 (51) 446 (52)
443 (56) 453 (35) 456 (52) 447 (53)
443 (67) 453 (36) 457 (67) 450 (52)
441 (57) 450 (35) 454 (52) 446 (54)
250
248
240
236
230
234
258
256
248
245
237
18
15
14
12
10
16
13
12
10
À0.08
À0.09
À0.09
À0.10
À0.11
À0.12
À0.10
À0.11
À0.12
À0.12
À0.13
2.82
2.83
2.84
2.82
2.83
2.83
2.84
2.82
2.83
[Ni((benzyl)2Bzo2[14]aneN6)](ClO4)2 mN–H 3245
[Ni(H2Bzo2[14]aneN6)](PF6)2
[Ni((CH3)2Bzo2[14]aneN6)](PF6)2
[Ni(Et2Bzo2[14]aneN6)](PF6)2
[Ni(Bu2Bzo2[14]aneN6)](PF6)2
[Ni((benzyl)2Bzo2[14]aneN6)](PF6)2
[Ni(H2Bzo2[14]aneN6)Cl2]
[Ni((CH3)2Bzo2[14]aneN6)Cl2]
[Ni(Et2Bzo2[14]aneN6)Cl2]
[Ni(Bu2Bzo2[14]aneN6)Cl2]
[Ni((benzyl)2Bzo2[14]aneN6)Cl2]
[Ni(H2Bzo2[14]aneN6)(NCS)2]
[Ni((CH3)2Bzo2[14]aneN6)(NCS)2]
[Ni(Et2Bzo2[14]aneN6)(NCS)2]
[Ni(Bu2Bzo2[14]aneN6)(NCS)2]
mN–H 3239
mN–H 3235
mN–H 3232
mN–H 3226
mN–H 3243
mN–H 3255
mN–H 3253
mN–H 3250
mN–H 3245
mN–H 3248
mN–H 3258; mC@N 2052; mC@S 785
mN–H 3256; mC@N 2052; mC@S 784
mN–H 3255; mC@N 2049; mC@S 784
mN–H 3257; mC@N 2047; mC@S 783
506
506
507
508
504
497
496
496
495
490
[Ni((benzyl)2Bzo2[14]aneN6)(NCS)2] mN–H 3261; mC@N 2050; mC@S 787
9
2.82
a
In DMSO solution.

2132
M. Salavati-Niasari, F. Davar / Polyhedron 25 (2006) 2127–2134
The observed low molar conductivities recorded (10–20) in
DMSO indicate that these are non-electrolytes in nature.
The overall geometries of all macrocycles have been
deduced on the basis of the observed values of the magnetic
moments and the band positions in the electronic spectra.
The magnetic moments (À0.08 to À0.13 lB) of the
nickel(II) complexes (1–10) measured in the solid state cor-
respond to a square-planar coordination geometry of the
complexes. The diamagnetic nature of the Ni(II) complex
7 has allowed its characterization by NMR spectrometry.
1H NMR spectra of the Ni(II) complexes of 6–10 exhibit
very broad peaks in D2O, CH3CN-d3 and Me2SO-d6, but
sharp resolvable peaks in CH3NO2-d3. This indicates that
a considerable amount of the paramagnetic octahedral
species [Ni(R2Bzo2[14]aneN6)(Solvent)2]2+ exists in the
donating solvents, where as the Ni(II) complexes of
‘‘R2Bzo2[14]aneN6’’ exist primarily as diamagnetic
square-planar species in CH3NO2-d3. The 1H NMR spectra
of the nickel complex ‘‘[Ni{((CH3)2Bzo2[14]aneN6)}]-
(PF6)2’’ gave a singlet at 1.67 ppm corresponding to CH3
from their hydrate, reduce the effective concentration of
free water and thus increase the concentration of square-
planar species [52,53]. The electronic spectra (Table 1) of
the Ni(II) complexes are comparable to other square-
planar tetraaza macrocyclic nickel(II) complexes, indicating
that the hexaaza ligands of this study do not differ signifi-
cantly from the tetraaza ligands with respect to the ligand
field strength [1–43].
The absorption spectra of [Ni((Allyl)2Bzo2[14]aneN6)]-
(ClO4)2 and [Ni(Bu2Bzo2[14]aneN6)](ClO4)2 were recorded
and the results are given in Table 1 along with the spectral
properties of analogous complexes. For aqueous solutions
of the [Ni(R2Bzo2[14]aneN6)]2+ complexes, the e value at
k
max = 441 nm increases from 56 to 67 MÀ1 cmÀ1 as the
alkyl chain length increases from methyl to butyl groups.
Moreover, contrary to [Ni(R2Bzo2[14]aneN6)]2+ (R = H,
Me, Et, Benzyl), both the [Ni(Bu2Bzo2[14]aneN6)]2+ and
[Ni((Allyl)2Bzo2[14]aneN6)]2+ complexes exhibit the same
e value (e = 67 MÀ1 cmÀ1) in nitromethane and water. This
is probably due to the presence of butyl/propylene groups
on the macrocyclic skeleton, which can exert a mechanical
resistance towards the axial coordination and hence both
[Ni((Allyl)2Bzo2[14]aneN6)]2+ and [Ni(Bu2Bzo2[14]aneN6)]2+
complexes seem to exist in the deep yellow, square-planar
form in water and nitromethane. So it can be assumed
that in aqueous solution [Ni(Bu2Bzo2[14]aneN6)]2+ and
[Ni((Allyl)2Bzo2[14]aneN6)]2+ exist in the square-planar
form and the propenyl/propyl groups of these complexes
provide steric hindrance to the incoming water molecules
for coordination [54,55]. The molecular models showed
that the propylene group of [Ni(Bu2Bzo2[14]aneN6)]2+
and [Ni((Allyl)2Bzo2[14]aneN6)]2+ can block the axial posi-
tions for water molecules easily by tending towards the
metal center (Scheme 3).
The 14-membered hexaaza macrocyclic nickel(II) com-
plexes undergo intense color changes due to deprotonation
of the macrocyclic ligand in the presence of amine bases
such as pyridine and Et3N. Similar N–H deprotonations
have been observed with other metal complexes containing
N–H linkages. For the nickel(II) complexes, Et3N is suffi-
ciently basic to facilitate formation of the molecular com-
plexes. For preparation of the deprotonation form of
[Ni(Me2Bzo2[14]aneN6)](ClO4)2, Et3N (0.5 cm3) was added
1
(6H) protons. However, the H NMR spectra of the com-
plexes ‘‘[Ni(R2Bzo2[14]aneN6)](PF6)2’’ showed a multiplet
in the region 7.51–7.70 ppm, corresponding to the phenyl
1
ring protons (8H). The H NMR spectra of all the com-
plexes showed a broad signal at 8.23–8.41 ppm and can
be assigned to secondary amine protons (4H). A singlet
for the complexes at 3.08–3.16 ppm corresponds to CH2
(8H) protons adjacent to nitrogen. However, the spectra
of all the complexes do not show any signal corresponding
to free primary amine protons.
Nickel(II) complexes with the 14-membered hexaaza
macrocyclic ligand ‘‘R2Bzo2[14]aneN6’’ exist in aqueous
solution as an equilibrium mixture of a yellow, square-pla-
nar, diamagnetic, low spin species and a blue, octahedral,
paramagnetic, high-spin species. Solutions of hexaaza mac-
rocyclic nickel(II) complexes in coordinating solvents (such
as water, acetonitrile, etc.) show an absorption maximum
at 450 nm, characteristic for square-planar yellow species,
and at 350 and 500 nm, characteristic for blue octahedral
species. Table 1 shows that the molar absorption coefficient
of the ligand field transition band for complexes measured
in water or acetonitrile is smaller than that in nitrometh-
ane, a non-coordinating solvent. These results are quite
similar to those reported for other related polyaza macro-
cyclic complexes, indicating that the complex dissolves in
water or acetonitrile to produce an equilibrium mixture
of square-planar [Ni{R2Bzo2[14]aneN6]2+ and octahedral
trans-[Ni(R2Bzo2-[14]aneN6)(solvent)2]2+; (solvent = H2O
or MeCN) [47–51]. Generally, the ligand structure, nature
of the solvent and concentration of added electrolyte affect
the equilibrium. The molar absorption coefficient of the
2+
N
H
H
N
N
N
Ni
ligand field transition band for [Ni(R2Bzo2[14]aneN6)]2+
,
N
H
H
N
measured in 3.0 M NaCl aqueous solutions, is somewhat
higher than that in pure water (Table 1). A similar result
was also observed in solutions containing NaBr, NaNO3,
or NaClO4. This corresponds to the generally observed
trend that neutral salts such as NaCl, dissolved in water
Scheme 3.

M. Salavati-Niasari, F. Davar / Polyhedron 25 (2006) 2127–2134
2133
to a deaerated solution of 200 mg of [Ni(Me2Bzo2[14]-
aneN6)](ClO4)2 in 15 cm3 of MeCN. The shiny-brown prod-
uct, which began precipitating within minutes, was filtered
after 0.5 h under a N2 atmosphere, washed with anhydrous
EtOH, and dried in a vacuum. IR. (KBr, cmÀ1): 3214 (mN–H).
[Ni(C18H24N6)] (23): Calc.: Ni, 15.18; C, 56.30; H, 6.16; N,
22.08. Found: Ni, 15.32; C, 56.43; H, 6.31; N, 21.94%. The
N–H stretching frequency of this compound, [Ni(C18H24-
N6)], 3214 cmÀ1, is reduced significantly from its dicationic
H
N
-
N
N
R
2+
Ni
R
N
-
N
N
H
precursor, [Ni(Me2Bzo2[14]aneN6)](ClO4)2, 3235 cmÀ1
.
23
Table 2
Cyclic voltammetric data for Ni(II) complexes with 16-membered hexaaza macrocyclesa,b
Complexes
Oxidation potential (V),
[Ni(polyaza)]2+/[Ni(polyaza)]3+
Reduction potential (V)
[Ni(polyaza)]2+/[Ni(polyaza)]+
Ref.
[Ni(H2Bzo2[14]aneN6)](ClO4)2
[Ni((CH3)2Bzo2[14]aneN6)](ClO4)2
[Ni(Et2Bzo2[14]aneN6)](ClO4)2
[Ni(Bu2Bzo2[14]aneN6)](ClO4)2
[Ni((Allyl)2Bzo2[14]aneN6)](ClO4)2
[Ni((benzyl)2Bzo2[14]aneN6)](ClO4)2
1.06
1.07
1.07
1.09
1.10
1.05
À1.50
À1.47
À1.47
À1.45
À1.41
À1.52
this work
this work
this work
this work
this work
this work
+0.93
+0.90
+0.91
À1.55
À1.47
À1.46
[57]
H
H
N
N
N
Ni 2+
N
CH3
H3C
N
N
H
H
H
H
[57]
N
N
N
Ni 2+
N
C2H5
C2H5
N
N
H
H
H
[56,58]
H
N
N
N
2+
N
Ni
H
H
H
+0.94
À1.57
[19]
H
N
N
2+
H3C
N
N
CH3
Ni
N
N
H
H
+0.93
À1.47
À1.30
[19]
H
H
N
N
2+
C2H5
N
N
C2H5
Ni
N
N
H
H
CH3
1.30
[56,59]
H3C
H
CH3
H
N
2+
N
N
N
Ni
H
H
H3C
CH3
CH3
a
Measured in acetonitrile solutions; 0.1 M (n-Bu)4NClO4; vs. SCE.
Redox potential of this work and Ref. [56] were measured against a Ag|Ag+ (0.1 M) reference electrode and converted to the values measured against
b
the SCE by adding +0.24 V.

2134
M. Salavati-Niasari, F. Davar / Polyhedron 25 (2006) 2127–2134
[18] H. Bang, E.J. Lee, E.Y. Lee, J. Suh, M.P. Suh, Inorg. Chim. Acta
Cyclic voltammetry data are summarized in Table 2.
308 (2000) 150.
Table 2 shows that the oxidation and reduction potentials
of the Ni(II) complexes of 1–5 do not differ significantly
from other [14]aneN4 complexes. This suggests that macro-
cycles 1–5 have Lewis basicities and hole size similar to the
[14]aneN4 ligand in spite of the structural differences. A
pronounced shift in oxidation state stability occurs when
there is a change in the macrocyclic ring size. An increase
in ring size promotes the ease of formation of Ni(I), while
rendering the oxidation to Ni(III) more difficult. The differ-
ence between the [(Ni[14]aneN4)]2+ and [Ni((CH3)6[16]1,4,
12-trieneN4)]2+ complexes is 0.3 V. Busch and co-workers
suggested that this difference is primarily due to deviations
from the ideal metal-donor atom distances accompanying
the redox changes [56]. This concept of optimum fit
between the coordinated metal ion and the ‘‘hole size’’ pro-
vided by the macrocyclic ligand is also in accord with the-
oretical conclusions and electronic spectral studies. The
more common effect of ligand unsaturation also favors
the formation of the lower valent states of the complexes
and causes the Ni(II) to Ni(III) process to occur at higher
energy. The effect of the Bzo function on the reduction
reactions of the nickel macrocycles is very pronounced
and the structures containing this moiety form the stable
complexes in lower valence states under the influence of
relatively mild potentials.
[19] M. Salavati-Niasari, H. Najafian, Polyhedron 22 (2003) 2633.
[20] M. Salavati-Niasari, M. Rezai-Adaryani, Polyhedron 23 (2004) 1325.
[21] M. Salavati-Niasari, Polyhedron 24 (2005) 1405.
[22] M. Salavati-Niasari, A. Amiri, Trans. Met. Chem. 30 (2005) 720.
[23] M. Salavati-Niasari, M. Rezai-Adaryani, S. Hydarzadeh, Trans.
Met. Chem. 30 (2005) 445.
[24] M. Salavati-Niasari, Inorg. Chem. Commun. 8 (2005) 174.
[25] M. Salavati-Niasari, Inorg. Chem. Commun. 7 (2004) 963.
[26] M. Salavati-Niasari, Inorg. Chem. Commun. 7 (2004) 698.
[27] M. Salavati-Niasari, F. Davar, Inorg. Chem. Commun. 9 (2005)
175.
[28] S.-G. Kang, K. Ryu, S.-K. Jung, J. Kim, Inorg. Chim. Acta 293
(1999) 140.
[29] M. Shakir, S.P. Varkey, Polyhedron 14 (1995) 1117.
[30] M.P. Suh, I.S. Kim, B.Y. Shim, D. Hong, T.-S. Yoon, Inorg. Chem.
35 (1996) 3595.
[31] M. Salavati-Niasari, Chem. Lett. 34 (2005) 1444.
[32] M. Salavati-Niasari, Chem. Lett. 34 (2005) 244.
[33] H.-Z. Kou, S. Gao, B.-Q. Ma, D.-Z. Liao, Chem. Commun. (2000)
713.
[34] T.-B. Lu, H. Xiang, R.L. Luck, L. Jiang, Z.-W. Mao, L.-N. Ji, New
J. Chem. 26 (2002) 969.
[35] M. Salavati-Niasari, A. Amiri, J. Mol. Catal. A 235 (2005) 114.
[36] M. Salavati-Niasari, H. Najafian, J. Chem. Res. 9 (2003) 586.
[37] S.V. Rosokha, Y.D. Lampeka, I.M. Maloshtan, J. Chem. Soc.,
Dalton Trans. (1993) 631.
[38] M. Salavati-Niasari, J. Mol. Catal. A 217 (2004) 87.
[39] M. Salavati-Niasari, J. Mol. Catal. A 229 (2005) 159.
[40] M. Salavati-Niasari, J. Mol. Catal. A 245 (2005) 192.
[41] S. Kang, S. Jung, J. Kweon, M. Kim, Polyhedron 12 (1993) 353.
[42] R.W. Hay, J.M. Armstrong, M.M. Hassan, Trans. Metal Chem. 17
(1992) 270.
References
[43] F. Abba, G. De Santis, L. Fabbrizzi, M. Licchelli, A.M.M.
Lanfredi, P. Pallavicini, A. Poggi, F. Ugozzoli, Inorg. Chem. 33
(1994) 1366.
[44] D.D. Perrin, W.L.F. Armarego, D.R. Perrin, Purification of Labo-
ratory Chemicals, 2nd ed., Pergamon Press, Headington Hill Hall,
Oxford, London, England, 1980.
[45] K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 3rd ed., Wiley, New York, 1978, p. 270.
[46] D.H. Cook, D.E. Fenton, Inorg. Chim. Acta 25 (1977) L95.
[47] R.W. Hay, B. Jeragh, G. Ferguson, B. Kaiter, B.L. Rule, J. Chem.
Soc., Dalton Trans. (1982) 1531.
[1] N.F. Curtis, Coord. Chem. Rev. 3 (1968) 3.
[2] M. Shakir, S.P. Varkey, O.S.M. Nasman, Polyhedron 14 (1995) 1283.
[3] V. Goedken, S. Peng, J. Chem. Soc., Chem. Commun. (1973) 62.
[4] D.E. Fenton, P.A. Vigato, Chem. Soc. Rev. 17 (1988) 69.
[5] B.Z. Shan, X.Z. Yu, H.K. Fun, K. Sivakumar, Acta Crystallogr.,
Sect. C 52 (1996) 3035.
[6] M. Shakir, A.K. Mohamed, S.P. Varkey, Z.A. Siddiqi, Trans. Metal
Chem. 21 (1996) 162.
[7] R.W. Hay, J.A. Crayston, T.J. Cromie, P. Lightfoot, D.C.L. Dealwis,
Polyhedron 16 (1997) 3557.
[8] R.W. Hay, A. Dandy, P. Lightfoot, Y.D. Lampeka, Polyhedron 16
(1997) 2777.
[48] R.W. Hay, D.P. Piplani, J. Chem. Soc., Dalton Trans. (1977) 1956.
[49] L. Fabbrizzi, Inorg. Chem. 18 (1977) 438.
[9] R.W. Hay, T.J. Cromie, P. Lightfoot, Trans. Metal Chem. 22 (1997)
510.
[50] A. Anichini, F. Fabbrizzi, F. Paoletti, Inorg. Chem. Acta 24 (1977)
L21.
[10] A. Deblas, G. Desantis, L. Fabbrizzi, M. Licchelli, A.M.M. Lanfredi,
P. Morosini, P. Pallavicini, F. Ugozzoli, J. Chem. Soc., Dalton
Trans. (1993) 1411.
[51] M.P. Suh, B.Y. Shim, T.-S. Yoon, Inorg. Chem. 33 (1994) 5509.
[52] S.-J. Kim, J.-S. Choi, S.-G. Kang, C.-S. Kim, M.P. Suh, Bull.
Korean Chem. Soc. 16 (1995) 217.
[11] N. Sardone, M. Licchelli, Acta Crystallogr., Sect. C 52 (1996) 2713.
[12] R.M. Izatt, J.J. Christensen, Synthetic Multidentate Macrocyclic
Compounds, Academic Press, New York, 1987.
[13] S.V. Rosokha, Y.D. Lampeka, J. Chem. Soc., Chem. Commun.
(1991) 1077.
[14] M.P. Suh, S. Kim, Inorg. Chem. 32 (1993) 3562.
[15] M.P. Suh, W. Shin, H. Kim, C. Koo, Inorg. Chem. 26 (1987) 1846.
[16] L. Fabbrizzi, M. Licchelli, A.M.M. Lanfredi, O. Vassalli, F.
Ugozzoli, Inorg. Chem. 35 (1996) 1582.
[17] D. Anastasi, N.F. Curtis, O.P. Gladkikh, T.J.C. Goode, D.C.
Weatherburn, Aust. J. Chem. 51 (1998) 673.
[53] L. Fabbrizzi, A.M.M. Lanfredi, P. Pallavicini, A. Perotti, A. Taglietti,
F. Ugozzoli, J. Chem. Soc., Dalton Trans. (1991) 3263.
[54] M. Ciampolini, L. Fabbrizzi, M. Licchelli, A. Perotti, F. Pezzini, A.
Poggi, Inorg. Chem. 25 (1986) 4131.
[55] K.V. Gobi, Koichi Tokuda, T. Ohsaka, Electrochim. Acta 43 (1998)
1013.
[56] F.V. Lovecchio, E.S. Gore, D.H. Busch, J. Am. Chem. Soc. 96 (1974)
3109.
[57] M.P. Suh, S.-G. Kang, Inorg. Chem. 27 (1988) 2544.
[58] E.K. Barefield, Inorg. Chem. 11 (1972) 2273.
[59] E.K. Barefield, D.H. Busch, Inorg. Chem. 10 (1971) 108.