Syntheses, crystal structures and chromotropic properties of Nickel(II) mixed ligand complexes containing N-methyl-1,4-diazacycloheptane and various β-diketonates

Article abstract of DOI:10.1016/j.poly.2006.11.003

Six complexes, Ni(medach)(dike)X, have been newly obtained, where medach = N-methyl-1,4-diazacycloheptane, dike = a β-diketonate such as benzoylacetonate (bzac), dibenzoylmethanate (dibm), X = BPh₄^-, NO₃^- or dike: Ni(medach)(bzac)(NO₃) (1a), Ni(medach)(dibm)(NO₃) (2a), Ni(medach)(bzac)(BPh₄) (1b), Ni(medach)(dibm)(BPh₄) (2b), Ni(medach)(bzac)₂ (1c), Ni(medach)(dibm)₂ (2c). X-ray single crystal structures of the complexes 1a, 2a, 1b and 2c have been determined and the structures of the complexes Ni(medach)(acac)(NO₃) (3a) and Ni(medach)(acac)BPh₄ (3b) (acac = acetylacetonate), reported previously, have also been clarified. In the cases of the tetraphenylborate and the nitrate complexes, two types of solvatochromism due to the donor and the acceptor interactions were observed in organic solvents. These spectral behaviors will be discussed in relation to the complex geometry and the donor and acceptor properties of the solvents, and also compared to those of the corresponding complexes containing a linear diamine such as N,N,N′,N′-tetramethylethylenediamine (tmen), Ni(tmen)(dike)X.

Full text of DOI:10.1016/j.poly.2006.11.003

Polyhedron 26 (2007) 1570–1578
www.elsevier.com/locate/poly
Syntheses, crystal structures and chromotropic properties of
Nickel(II) mixed ligand complexes containing
N-methyl-1,4-diazacycloheptane and various b-diketonates
a
a
a
b
a,
*
Fumiko Murata , Machiko Arakawa , Akiko Nakao , Keiichi Satoh , Yutaka Fukuda
a
Department of Chemistry, Faculty of Science, Ochanomizu University, 2-1-1 Otsuka, Bunkyo-ku, Tokyo 112-8610, Japan
b
Department of Chemistry, Faculty of Science, Niigata University, 8050 Igarashi-ninomachi, Niigata 950-2181, Japan
Received 16 May 2006; accepted 2 November 2006
Available online 11 November 2006
Abstract
Six complexes, Ni(medach)(dike)X, have been newly obtained, where medach = N-methyl-1,4-diazacycloheptane, dike = a b-diketo-
ꢀ
nate such as benzoylacetonate (bzac), dibenzoylmethanate (dibm), X ¼ BPh4ꢀ, NO3 or dike: Ni(medach)(bzac)(NO3) (1a), Ni-
(medach)(dibm)(NO3) (2a), Ni(medach)(bzac)(BPh4) (1b), Ni(medach)(dibm)(BPh4) (2b), Ni(medach)(bzac)2 (1c), Ni(medach)(dibm)2
(2c). X-ray single crystal structures of the complexes 1a, 2a, 1b and 2c have been determined and the structures of the complexes Ni-
(medach)(acac)(NO3) (3a) and Ni(medach)(acac)BPh4 (3b) (acac = acetylacetonate), reported previously, have also been clarified. In
the cases of the tetraphenylborate and the nitrate complexes, two types of solvatochromism due to the donor and the acceptor interac-
tions were observed in organic solvents. These spectral behaviors will be discussed in relation to the complex geometry and the donor and
acceptor properties of the solvents, and also compared to those of the corresponding complexes containing a linear diamine such as
N,N,N0,N0-tetramethylethylenediamine (tmen), Ni(tmen)(dike)X.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Keywords: Nickel complexes; Cyclic diamine; b-Diketonate; Solvatochromism; Mixed ligand complexes
1. Introduction
will appear with characteristic properties such as chromo-
tropic and catalytic ones [3]. In accordance with this rule,
a number of mononuclear mixed ligand complexes can be
prepared using N,N,N0,N0-tetramethylethylenediamine
(tmen) as the diam and b-diketonates (dike), M(tmen)-
The synthesis of mixed ligand complexes is not a trivial
procedure because the formation of homoleptic ligand com-
plexes must be suppressed [1]. In the case of a diamine
(diam), nitrogen-donor atoms of the ligand with bulky sub-
stituents prevent the stabilization of homoleptic bis- or tris-
diamine complexes, [M(diam)2]n+ or [M(diam)3]n+, but the
ligand forms a bridging dinuclear l-hydroxo-complex,
[(diam)M(OH)2M(diam)]n+ [2]. On the other hand, a ter-
nary complex has been formed with a suitable combination
of ligands, i.e., a sterically demanding ligand (L, the diamine
in this case) and a slim one (L0, a b-diketonate in this case),
the corresponding heteroleptic ligand complex, [MLL0]n+
ꢀ
(dike)X (X ¼ BPh4ꢀ, ClO4ꢀ, NO3 or dike) [4]. Mixed
ligand Ni(II) complexes with b-diketonate and N-alkylated
ethylenediamines show a number of interesting properties
including solvatochromism or thermochromism [5].
Although macrocyclic polyamines are best characterized
as chelating agents for transition metal ions [6], cyclic
diamines have not been fully studied. The six-membered-
ring diamine, piperazine, does not form chelated complexes
with the smaller transition metal (3d) ions such as
copper(II) and nickel(II) [7]. The seven-membered-ring
diamine, 1,4-diazacycloheptane (dach), and the eight-
membered-ring diamine, 1,5-diazacyclooctane (daco), were
examined as chelating agents for nickel(II) and copper(II),
*
Corresponding author. Tel./fax: +81 3 5978 5291.
E-mail address: fukuda@cc.ocha.ac.jp (Y. Fukuda).
0277-5387/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2006.11.003

F. Murata et al. / Polyhedron 26 (2007) 1570–1578
1571
which are normally stable planar chelates, [M(L)2]X2 [8].
Recently, dach and daco have been alkylated with ethylene
sulfide to give a derivative with pendant arms, and then
coordinated to the metal [9]. However, the related cyclic
diamines have not been studied extensively for mixed che-
late complex systems.
Ni(medach)(dibm)NO3 (2a). Anal. Calc. for C21H25N3-
O5Ni: C, 54.92; H, 5.46; N, 9.14. Found: C, 55.06; H,
5.50; N, 9.17%. leff: 3.02 B.M.
2.2.2. Chelates of the tetraphenylborate,
[Ni(medach)(dike)]BPh4
In this work, we have obtained new mixed complexes
with the medach ligand and some kinds of b-diketonates
(dike), Ni(medach)(dike)X, and have determined their crys-
tal structures and the equilibrium constants between a
square-planar structure and an octahedral one with coordi-
nated strong donor solvent molecules [10].
The crude nitrate compounds (1 mmol) were dissolved
in DCE, and sodium tetraphenylborate (1.5 mmol) was
added with stirring and then filtered. During the procedure,
the color of the solution changed from green to reddish-
orange. The crude crystals obtained were recrystallized
from DCE to yield orange crystals. They were all diamag-
netic. Yield: 70–85%.
2. Experimental
Ni(medach)(bzac)BPh4 (1b). Anal. Calc. for C40H43N2-
O2BNi: C, 72.14; H, 6.63; N, 4.33. Found: C, 73.54; H,
6.63; N, 4.29%.
2.1. Materials and instrumentation
Ni(medach)(dibm)BPh4 (2b). Anal. Calc. for C45H45N2-
O2Ni: C, 75.51; H, 6.55; N, 3.96. Found: C, 75.55; H, 6.34;
N, 3.92%.
Nickel(II) nitrate hexahydrate, nickel(II) sulfate hexahy-
drate, N-methyl-1,4-diazacycloheptane (medach), acetylac-
etone (Hacac), benzoylacetone (Hbzac), dibenzoylmethane
(Hdibm), anhydrous sodium carbonate, sodium tetra-
phenylborate and N,N,N0,N0-tetramethylethylenediamine
were purchased from Wako Chemical Co. Ltd. and used
without further purification. As the solvents used for spec-
tral measurements 1,2-dichloroethane (DCE), dimethyl-
sulfoxide (DMSO), acetone (ACO) and nitromethane
(NM) were used without further purification, all of the sol-
vents were of guaranteed grade for spectral measurements.
Elemental analyses were performed on a Perkin–Elmer
2.2.3. Chelates of the ternary bis-diketonate,
[Ni(medach)(dike)2]
NiSO4 Æ 6H2O was dissolved in a small amount of water
and a chloroform solution containing an equimolar
amount of medach and two molar amounts of Hdike was
added to it in a separatory funnel. Then sodium carbonate
was added to the mixture with shaking. After standing for
a minute, the chloroform layer was separated from the
aqueous solution and evaporated. The crude crystals
obtained were recrystallized from DCE to yield bluish-
green crystals. Yield: 70–85%.
Ni(medach)(bzac)2 (1c). Anal. Calc. for C26H32N2O4Ni:
C, 63.03; H, 6.51; N, 5.66. Found: C, 62.68; H, 6.66; N,
5.63%. leff for 1c Æ DCE: 2.66 B.M.
Ni(medach)(dibm)2 (2c). Anal. Calc. for C36H36N2O4Ni:
C, 69.81; H, 5.86; N, 4.52. Found: C, 69.72; H, 5.89; N,
4.39%. leff: 3.20 B.M.
2400 II CHN analyzer. Infrared spectra (400–4000 cmꢀ1
)
were measured with a Perkin–Elmer FT-IR SPECTRUM
2000 using KBr disks. Electronic spectra of the complexes
in solution were observed with Shimadzu UV-3100PC UV–
VIS Scanning Spectrophotometer using 10 mm quartz cells
and concentrations between 1.0 · 10ꢀ3 and 5.0 · 10ꢀ3 mol
dmꢀ3, except where mentioned differently in the text. Mag-
netic susceptibility measurements were performed by the
Faraday method with a Shimadzu Torsion Magnetometer
MB-100 at room temperature. Electric conductances of the
solutions were measured with a Conductivity Outfit Model
AOC-10 (Denki-Kagaku-Keiki Co. Ltd.) at 25 0.2 ꢁC.
2.3. Equilibrium constants
The equilibrium constants (logb) defined by Eq. (1) have
been determined by a spectrophotometric method (calcula-
tion by a least-square method using the data sets from the
electronic spectra at constant temperature, 25 0.2 ꢁC).
All spectral data, as a function of the total concentrations
of the reactants, were computer-fitted to the appropriate
equation, depending on the model to be tested. As a result,
the equilibrium constants for each species (logb) and the
molar extinction coefficients (ecalc) for each species in the
solution were calculated. The number of points used for
the calculation of equilibrium constants was 12 from each
data set, which were picked up at every 10 nm wavelength
in the range of 530–420 nm.
2.2. Syntheses of chelates
2.2.1. Chelates of the nitrate, [Ni(medach)(dike)NO3]
To an ethanol solution of Ni(NO3)2 Æ 6H2O (5 mmol in
30 cm3 of ethanol), a mixture of the appropriate b-diketone
(5 mmol) and anhydrous sodium carbonate (2.5 mmol) was
added. The ligand, medach (5 mmol in 10 cm3 of ethanol)
was added dropwise to the metal-solution with vigorous
stirring. After the reaction was complete, the green solution
was filtered and concentrated using a rotary evaporator.
The crude crystals obtained were recrystallized from
DCE to yield bluish-green crystals. Yield: 70–85%.
Ni(medach)(bzac)NO3 (1a). Anal. Calc. for C16H23N3-
O5Ni: C, 48.52; H, 5.85; N, 10.61. Found: C, 48.54; H,
5.88; N, 10.62%. leff: 3.12 B.M.
b
½NiðdiamÞðdikeÞꢁþ þ 2S !½NiðdiamÞðdikeÞS2ꢁþ
ð1Þ
2
b ¼ ½NiðdiamÞðdikeÞS2ꢁþ = ½NiðdiamÞðdikeÞꢁþ½Sꢁ

1572
F. Murata et al. / Polyhedron 26 (2007) 1570–1578
The solvent ligand (S = DMSO) was added to a DCE solu-
tion of the respective complex, [Ni(diam)(dike)]BPh4.
dike), which are classified into three types: i.e., type
a = nitrate complexes, type b = tetraphenylborate com-
plexes and type c = ternary bis-diketonate complexes, and
the numbers of the complexes, 1, 2 and 3, mean benzoyl-
acetonate, dibenzoylmethanate and acetylacetonate,
respectively. Magnetic data of these complexes at room
temperature are listed in the experimental section, which
show the tetraphenylborate complexes are diamagnetic,
and the nitrate and bis-dike complexes have values of
nearly 3.0 B.M. These data mean that: (a) the Ni(II) coor-
dination geometry in the tetraphenylborate complexes is
square-planar with a N2O2 donor set (type b), and (b)
those of the nitrate complexes (type a) and the ternary
bis-dike complexes (type c) are octahedral with a N2O4
donor set.
Among these complexes we obtained six good single
crystals for X-ray diffraction analysis, complexes 1a, 2a,
3a, 1b, 3b and 2c, whose crystal structures have been deter-
mined. For two acac-complexes, 3a and 3c, which were pre-
viously reported [10], the structures are clarified in this
work. The ORTEP plots of complexes 1a, 1b and 2c as
examples are depicted in Figs. 1–3, with the atom number-
ing scheme. Selected bond distances and angles are given in
Table 2.
2.4. X-ray crystallography
The measurements for complex 3a were made on a
DIP2030K automated diffractometer with graphite-
˚
monochromatic Mo Ka radiation (k = 0.71073 A) at 298 K.
The measurements for complexes 1a, 2a, 1b, 3b, and 2c
were made on a MXC03K automated diffractometer with
graphite-monochromatic Mo Ka radiation (k = 0.71073
˚
A) at 298 K. The unit cell parameters were determined by
the least square method using 22 well-centered reflections
for all the complexes. The reflections were corrected for
Lorentz and Polarization effects but not for absorption.
Every structure was solved by the direct method SIR92
[11], and was refined by full matrix least-square techniques
SHELXS-97 [12]. All non-hydrogen atoms were refined with
anisotropic thermal parameters. Hydrogen atoms were
included in calculated positions and refined with isotropic
thermal parameters. Crystallographic data and refinement
parameters are detailed in Table 1.
3. Results and discussion
3.1. Synthesis and structure of the complexes,
Ni(medach)(dike)X
3.1.1. Structure of [Ni(medach)(bzac)NO3] (1a, type a)
Complex 1a crystallizes in the monoclinic space group
P21/c. The nickel atom is coordinated to give an octahedral
geometry with two N atoms of the bidentate medach
ligand, two O atoms of the bidentate bzac ligand and
We obtained eight mixed ligand complexes of theꢀgen-
eral formula Ni(medach)(dike)X (X ¼ NO3ꢀ, BPh4 or
Table 1
Crystallographic data
1a
2a Æ DCE
C23H29N3O5NiCl2 C11H21N3O5Ni
557.12 334.02
3a
1b
3b Æ ACO
2c
Empirical formula
Formula weight
Crystal dimensions
Crystal system
Space group
C16H23N3O5Ni
C40H43BN2O2Ni
653.32
C38H47BN2O3Ni
649.30
C36H36N2O4Ni
619.40
396.09
0.50 · 0.30 · 0.25 0.40 · 0.35 · 0.30
0.35 · 0.25 · 025 0.35 · 0.30 · 0.20 0.35 · 0.30 · 0.20 0.40 · 0.25 · 0.20
monoclinic
triclinic
monoclinic
monoclinic
triclinic
monoclinic
ꢀ
ꢀ
P21/c
P1
P21/c
P21/c
P1
C2/c
T (K)
298
298
298
298
298
298
˚
a (A)
11.026(4)
13.818(5)
14.865(9)
90
127.66(6)
90
1793.0(15)
4
1.467
8.230(4)
11.940(10)
13.54(2)
92.00(10)
105.71(5)
95.97(5)
1271.(2)
2
13.1740(10)
15.3210(10)
7.7830(10)
90
106.894(3)
90
1503.1(2)
4
1.476
17.953(7)
10.790(3)
18.666(4)
90
109.61(2)
90
3406.(2)
4
1.274
9.712(3)
13.411(4)
13.50(2)
94.23(5)
91.37(5)
95.31(2)
1745.(2)
2
22.920(10)
8.876(5)
18.160(10)
90
119.37(5)
90
3219.(3)
4
1.278
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Dc (Mg mꢀ3
)
1.456
1.125
˚
k (A)
0.71073
1.11
0.71073
1.01
0.71073
1.31
0.71073
0.61
0.71073
0.59
0.71073
0.64
l (mmꢀ3
)
Reflections collected
4475
6090
3344
8501
7699
3932
Independent reflections 3858
5839
3166
8241
7402
2816
Reflections used
3741 (I > 2r)
4919 (I > 3r)
0.070
0.135
3043 (I > 2r)
0.0468
0.1349
1.038
5366 (I > 3r)
0.064
0.085
4657 (I > 3r)
0.055
0.074
2256 (I > 2r)
0.0901
0.2437
1.097
Ra
Rw
0.0529
0.1559
1.028
b
S (fit on F)
1.349
1.644
1.337
P
P
a
R ¼ kF oj ꢀ jF ck= jF oj.
P
P
2
2 1=2
b
R ¼ ½ð wðkF oj ꢀ jF ckÞ = jF oj Þ
.

F. Murata et al. / Polyhedron 26 (2007) 1570–1578
1573
Fig. 1. ORTEP diagram of the complex [Ni(medach)(bzac)NO3] (1a).
Thermal ellipsoids are at 50% probability.
Fig. 3. ORTEP diagram of the complex [Ni(medach)(dibm)2] (2c).
Thermal ellipsoids are at 50% probability.
two O atoms of the bidentate NO3 ligand as shown in
Fig. 1. The angles O(1)–Ni(1)–N(3), O(2)–Ni(1)–O(3),
O(4)–Ni(1)–N(2), O(1)–Ni(1)–O(2), O(3)–Ni(1)–O(4), and
N(3)–Ni(1)–N(2) are 173.97ꢁ, 158.68ꢁ, 160.11ꢁ, 91.00ꢁ,
59.92ꢁ and 76.60ꢁ, respectively. The bite angle of the NO3
ligand to the metal center is too narrow and the bond
of the ligand NO3 affects the easy dissociation of the NO3
ligand from the coordination sphere in acceptor or strong
donor solvents. Another structural interest is that the axial
bonds Ni(1)–O(2) and Ni(1)–O(3) are repelled by the cyclic
medach ligand, which means that the angle O(2)–Ni(1)–
O(3) 158.68ꢁ is smaller than the other equatorial trans-
bonds. This interligand repulsion between medach and
the axial donor atoms (NO3) may reflect the another reason
for the weakened coordination ability of the NO3 ligand.
The structures of 2a and 3a show also similar structural
properties as explained in this case of 1a.
˚
˚
lengths of Ni(1)–O(3) 2.167 A and Ni(1)–O(4) 2.173 A are
rather longer than those of the Ni–O(bzac) (Ni(1)–
˚
O(1) = 2.009, Ni(1)–O(2) = 2.003 A). The structural strain
3.1.2. Structure of [Ni(medach)(bzac)]BPh4 (1b, type b)
Complex 1b crystallizes in the monoclinic space group
P21/c. As shown in Fig. 2, the nickel atom is coordinated
with medach and bzac to give a square-planar geometry
and the uncoordinating anion BPh4ꢀ. The N2O2 donor
set from medach and bzac and the central Ni atom are
located on the same plane. If we compare these metal–
ligand bond distances and their bite angles with those of
Table 2
˚
Selected bond lengths (A) and angles (ꢁ) for complexes 1a, 1b and 2c
1a
1b
2c
Ni(1)–O(1)
Ni(1)–O(2)
Ni(1)–N(2)
Ni(1)–N(3)
Ni(1)–O(3)
Ni(1)–O(4)
2.009(3)
2.003(3)
2.093(4)
2.093(3)
2.167(3)
2.173(3)
1.819(3)
1.831(3)
1.936(4)
1.887(4)
Ni(1)–O(3)
Ni(1)–O(4)
Ni(1)–N(2)
2.01(14)
2.05(14)
2.14(14)
O(1)–Ni(1)–O(2) 91.00(11) 95.80(14) O(3)–Ni(1)–O(4)
N(2)–Ni(1)–N(3) 76.60(14) 81.3(2)
88.(6)
Fig. 2. ORTEP diagram of the complex [Ni(medach)(bzac)]+ (1b).
Thermal ellipsoids are at 50% probability.
N(2)–Ni(1)–N0(2) 76.(5)

1574
F. Murata et al. / Polyhedron 26 (2007) 1570–1578
ꢀ
can be seen from the table that the ionization of NO3
the corresponding octahedral nitrate complex 1a, this pla-
nar complex has shorter bond lengths Ni–O(bzac) 1.819
from the complexes in NM is about 10%, which indicates
partial dissociation into the NO3 anion and the cationic
ꢀ
˚
˚
and 1.831 A and Ni–N(medach) 1.936 and 1.887 A and
wider bite angles O(1)–Ni(1)–O(2) 95.80 and N(2)–Ni(1)–
N(3) 81.3ꢁ than those of the octahedral complex. In this
planar complex, the tertiary N-donor of medach coordi-
nates more weakly to the metal center than the secondary
N–M bond. The chelate angle of medach in this square-pla-
nar mixed complex is almost the same as the angle in the
bis-dach square-planar homoleptic complex, [Ni(dach)2]-
Cl2 Æ 2H2O 82.2ꢁ [13]. It means that the chelate angle of
the cyclic dach ligand was determined by the rigid confor-
mation of the ligand and the same metal-ligand bond
length. The crystal structure of 3b show also same geome-
try as 1b.
planar complex, [Ni(medach)(dike)]+. In DCE or ACO,
the nitrate complexes show almost non-electrolytic behav-
ior, which means that the species in solution is the same
as that of the solid state. On the other hand, in a very
strong donor solvent like DMSO, the conductivity data
show that the nitrate complexes are almost 1:1 electrolytes.
Consequently the nitrate complexes are strongly influenced
by the respective (donor and acceptor) properties of thꢀe
solvents for coordination and dissociation of the NO3
ion. These data support the following section on spectral
chromotropic behaviors (Scheme 1).
3.2.2. The nitrate complexes [Ni(medach)(dike)NO3]
(type a)
3.1.3. Structure of [Ni(medach)(dibm)2] (2c, type c)
Complex 2c crystallizes in the monoclinic space group
C2/c. As shown in Fig. 3, the nickel atom is coordinated
to give an octahedral geometry with two N atoms of the
bidentate medach ligand and four O-donor atoms from
two bidentate dibm ligands, forming the non-charged com-
plex. The medach ligand in the structure is disordered and
the structural data is not so well refined. The characteristic
properties of this type of complex in the solid state shows
the plasticity of the non-charged weak intermolecular inter-
action in the case of ternary bis-hexafluoroacetylacetonate
(hfac), [M(tmen)(hfac)2] [14]. Due to the very weak inter-
molecular interaction in this crystal, the diamine (medach)
moiety of the complex can easily move position at the tem-
perature for this X-ray crystal determination. Therefore,
we could not determine the position of medach ligand with
certain accuracy. For the complex 1c, a good single crystal
for X-ray analysis could not be obtained.
Fig. 4 shows the typical electronic absorption spectra of
the nitrate complex 1a in various organic solvents. These
spectra were measured at room temperature in DCE,
NM, ACO and DMSO. In Table 4, all of the spectral data
for the complexes in these solvents are summarized.
The spectra in DCE and ACO have nearly the same pat-
tern, showing two bands corresponding to the similar spec-
tral pattern of octahedral complexes (Eq. (2)). The
anomaly of the spectra is their intensity, which means that
the intensity of the first band, at ca. 10 · 103 cmꢀ1, is nearly
half of that of the second band, 16.5 · 103 cmꢀ1. It is prob-
ably due to the existence of the bidentate nitrate ion, i.e.,
the deformation from a regular octahedral structure and
the smaller four membered chelate ring of the NO3 ligand.
On the other hand, in the case of DMSO although the spec-
tra also show octahedral bands, the spectral profile is differ-
ent from that in DCE, especially the intensity profile is
drastically changed. The electric conductivity data men-
tioned above also support that the complexes in DCE or
ACO are non-charged octahedral with the coordination
of NO3, while those in DMSO are 1:1 electrolytes and
octahedral with the coordination of the solvent molecules
(Eq. (3)). In NM, with intermediate acceptor and poor
donor properties, the nitrate ion is partially dissociated
from the octahedral complex and gives square-planar spec-
tra (Eq. (4)), which shows a new solvatochromism.
3.2. Solvatochromic behavior with the structure change of the
complexes in solution
3.2.1. Electric conductivity data of the chelates in various
solvents
Table 3 gives the electrical conductivity data at room
temperature for the complexes in some organic solvents
with different donor numbers (DN) and acceptor numbers
(AN) [15]. The standard values of 1:1 electrolytes in the
respective solvents are shown in the same table [16]. It
½NiðmedachÞðdikeÞðNO3Þꢁ ! ½NiðmedachÞðdikeÞðNO3Þꢁ ð2Þ
½NiðmedachÞðdikeÞðNO3Þꢁ þ 2DMSO
! ½NiðmedachÞðdikeÞðDMSOÞ2ꢁþ þ NO3
ð3Þ
ð34Þ
ꢀ
Table 3
½NiðmedachÞðdikeÞðNO3Þꢁ ! ½NiðmedachÞðdikeÞꢁþ þ NO
ꢀ
Molar conductivity (ohmꢀ1 cm2 molꢀ1 at 25 0.2 ꢁC)
DCE
NM
DMSO
ACO
Ni(medach)(bzac)NO3 (1a)
Ni(medach)(dibm)NO3 (2a)
Ni(medach)(acac)NO3 (3a)
Ni(medach)(azac)BPh4 (1b)
Ni(medach)(dibm)BPh4 (2b)
Ni(medach)(acac)BPh4 (3b)
Ni(medach)(dibm)2 (2c)
1:1 Electrolytes [16]
0.13
0.07
0.13
11.91
11.04
12.95
0.072
10–24
7.65
7.55
9.26
42.10
44.08
36.45
2.66
23.43
22.91
24.41
11.49
12.96
10.69
0.96
2.13
1.54
1.49
6.31
7.18
3.89
0.003
100–140
3.2.3. The tetraphenylborate complexes
[Ni(medach)(dike)]BPh4 (type b)
Fig. 5 shows the typical electronic absorption spectra of
the tetraphenylborate complex 1b in various organic sol-
vents. These spectra were measured at room temperature
in DCE, NM, ACO and DMSO. In Table 4, all of the
75–95
35

F. Murata et al. / Polyhedron 26 (2007) 1570–1578
1575
+
+
+
N
O
N
N
O
O
-
Inert solvent
-
-
BPh4
BPh4
BPh4
N
O
N
N
O
S
Type b
Strong
donor solvent
O
-
or NO3
Strong donor
solvent
S
O
O
N
N
O
O
Inert solvent
N
O
N
O
N
N
O
O
O
O
Type a
Weak donor
and strong acceptor
solvent
+
N
N
O
O
-
NO3
N
N
O
O
O
N
O
O
O
All solvents
N
O
O
Type c
Scheme 1. Solid structure and solvatochromic behaviors of the complexes in solution.
2½NiðmedachÞðdikeÞꢁBPh4 þ 2S ! ½NiðmedachÞðdikeÞðSÞ ꢁþ
spectral data for the complexes in these solvents are sum-
marized. In non-coordinated solvents like DCE or NM,
the spectra are similar to those of the square-planar species
reported earlier [17]. Also in an intermediate coordinating
solvent like ACO, they are dissolved as predominantly
square-planar species. This is critically different from simi-
lar complexes with linear chain diamines, such as tmen, in
which the complexes exist as an equilibrium mixture of the
square-planar and octahedral species (Eq. (5)). This is a
characteristic property of the cyclic diamine. In a strong
donor solvent like DMSO, the spectra indicate that the
only species in solution is octahedral (Eq. (6)).
2
þ ½NiðmedachÞðdikeÞꢁþ þ 2BPh4
½NiðmedachÞðdikeÞꢁBPh4 þ 2DMSO
! ½NiðmedachÞðdikeÞðDMSOÞ2ꢁþ þ 2BPh4
ð5Þ
ꢀ
ꢀ
ð6Þ
3.2.4. The ternary bis-diketonato complexes,
[Ni(medach)(dike)2] (type c)
In any kind of solvent, these ternary bis-dike complexes
do not show any solvatochromism, which means the spec-
tra in all of the solvents used are similar and any solvent
coordination could not be observed.
It is noteworthy that the chelates are very soluble in var-
ious organic solvents with high concentrations, which
means that there are weak intermolecular interactions in
the crystal. As already known for the structure of Ni-
(acac)2, the chelate is rather insoluble in organic solvents
and it is not mononuclear but the trinuclear [Ni3(acac)6]
[18], in which each nickel(II) center is octahedral (other
kinds of diketonate chelates also show similar structures).
The homoleptic trinuclear, [Ni3(dike)6] is dissociated into
the heteroleptic mononuclear, [Ni(medach)(dike)2], by the
addition of the diamine (medach) (Eq. (7)).
30
DCE
DMSO
NM
25
20
15
10
5
ACO
½Ni3ðdikeÞ6ꢁ þ 3medach ! 3½NiðmedachÞðdikeÞ2ꢁ
ð7Þ
0
8
10
12
14
16
18
20
22
24
The resultant mononuclear mixed chelates, with very bulky
substituent groups on each diamine and diketonate, show
very high solubility in various organic solvents, which
Wavenumber (×103cm- 1
)
Fig. 4. UV–Vis absorption spectra of [Ni(medach)(bzac)NO3] (1a).

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F. Murata et al. / Polyhedron 26 (2007) 1570–1578
Table 4
Wave numbers (Vmax/·103 cmꢀ1) and molar absorption coefficient (emax/·103 molꢀ1 dm3 cmꢀ1) of the d–d transition band (at 25 ꢁC)
DCE
NM
DMSO
ACO
Ni(medach)(acac)NO3
9.98(12.64)
16.56(18.86)
10.01(10.90)
16.57(16.10)
21.28(21.03)
9.57(12.89)
15.61(7.75)
9.98(12.26)
16.50(17.72)
Ni(medach)(bzac)NO3
Ni(medach)(dibm)NO3
Ni(medach)(bzac)BPh4
Ni(medach)(bzac)BPh4
Ni(medach)(dibm)BPh4
Ni(medach)(dibm)2
10.00(12.74)
16.57(19.35)
10.10(11.66)
16.58(18.52)
9.60(13.23)
15.63(8.78)
10.05(12.43)
16.52(18.95)
10.04(12.71)
16.57(19.83)
10.09(11.54)
16.63(18.05)
9.63(13.37)
15.75(9.59)
10.02(12.21)
16.53(18.61)
21.10(151.7)
21.21(211.0)
21.12(164.4)
21.14(127.9)
21.28(211.7)
21.19(169.6)
9.56(11.15)
15.58(6.33)
21.14(123.9)
21.23(187.2)
21.14(162.1)
9.60(13.18)
15.63(8.26)
9.56(14.13)
15.64(7.94)
9.72(15.17)
9.77(14.58)
9.72(14.30)
9.70(14.14)
16.45(18.15)
16.37(16.87)
16.35(17.34)
16.42(17.89)
DCE
NM
ACO
20
15
10
5
200
DMSO
150
100
50
0
0
8
10
12
14
16
18
20
22
24
Wave number (×103 cm-1)
Fig. 5. UV–Vis absorption spectra of [Ni(medach)(bzac)]BPh4 (1b). The left axis is for DMSO solution and the right axis is for DCE, NM and ACO
solutions.
means the mixed chelates have hydrophobic properties and
weak intermolecular interactions.
stituents at the diamine ligand. On the other hand, an
increase in equilibrium constants of these complexes can
be seen with increasing electron-withdrawing and decreas-
ing electron-releasing effects of the substituent group on
the b-diketonate ligand; dibm > bzac > acac.
3.3. Equilibrium constants
Fig. 6 shows an example of the spectra obtained in the
course of the titration procedure of [Ni(medach)(bzac)]-
BPh4 in DCE solution. The absorption maximum of the
square-planar species decreases on addition of donor sol-
vent, DMSO, and the absorption band of the octahedral
species in the region between 570 and 600 nm increases.
A titration procedure can be used to evaluate formation
constants. Equilibrium constants (logb) according to the
reaction are given in Table 5.
The medach complexes prefer the square-planar geome-
try to the octahedral geometry. The steric hindrance to
axial coordination at the N-donor atoms appears to be
much smaller for tmen complexes than the corresponding
medach complexes.
4. Conclusion
We have obtained six new mixed chelate complexes with
the ligand bzac or dibm as a b-diketonate, medach and
three kinds of monoanion, nitrate, tetraphenylborate or
The d–d band positions and the corresponding molar
absorption coefficients are shifted by a change in the sub-

F. Murata et al. / Polyhedron 26 (2007) 1570–1578
1577
2.5
2
a
1.5
1
0.2
b
0.15
0.1
0.5
0
0.05
0
10
12
14
14
16
16
18
18
20
22
24
10
12
wavenumber (x 103 cm-1)
Fig. 6. Spectral changes of [Ni(medach)(bzac)]BPh4 (1b) with the addition of DMSO ligand: (a) square-planar spectral decrease and (b) octahedral
spectral increase. The initial concentration of the complex in DCE solution was 8.0 · 10ꢀ3 mol dmꢀ3 (initial amount of solution: 20 ml) and the light path
was 1 cm. The solution was titrated with DMSO–DCE solution (8.0 · 10ꢀ1 mol dmꢀ3). Ratios of DMSO/complex are 0, 0.25, 0.50, 0.70, 1.00, 1.35 and
1.85 ((a) spectral curves from top to bottom; (b) those from bottom to top, respectively).
Table 5
Appendix A. Supplementary material
Stability constants (logb) (molꢀ1 dm3)
dike
[Ni(medach)(dike)]BPh4
[Ni(tmen)(dike)]BPh4
CCDC 208117, 212342, 207923, 212341, 208119, and
208118 contain the supplementary crystallographic data
for 1a, 2a, 3a, 1b, 3b, and 2c. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/
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.
2006.11.003.
acac
bzac
dibm
2.32 0.01
3.04 0.01
3.13 0.02
4.50 0.01
5.20 0.02
5.31 0.01
one more b-diketonate, and have determined their crystal
structures. These complexes are classified as three catego-
ries, type a (octahedral with a bidentate nitrate coordina-
tion), type b (square-planar with tetraphenylborate as a
counter anion) and type c (octahedral with two b-diketo-
nate ligands). Type a complexes show solvatochromic
behavior due to the change of acceptor property of the sol-
vents. Type b complexes show another type of solvatochro-
mism due to the change of donor properties of the solvents.
Type c complexes are inert stable octahedral complexes
without any chromotropic behavior in various solvents.
The medach ligand in the mixed chelate [Ni(dike)-
(medach)]+ has a much stronger influence on the axial
coordination of the donor solvents, which means that the
series of the medach mixed ligand system exist as the more
stable square-planar structure in comparison to the com-
plexes of the linear N-alkylated diamines, such as the tmen
analogue.
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Prof. Hiroshi Miyamae of Josai University in Tokyo is
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