Synthesis and electrochemical studies of nickel -diketonate complexes incorporating asymmetric diimine ligands

Article abstract of DOI:10.1071/CH09232

The reaction of ppa^X {(4-X-phenyl)-pyridin-2-ylmethylene-amine; X = H, Me, Et, OMe, F, Cl, Br, and I} with [Ni(β-diketonate) ₂(H₂O)₂] {β-diketonate = 1,3-diphenylpropanedionate (dbm), 2,2,6,6-tetramethyl-3,5-hep

Full text of DOI:10.1071/CH09232

Full Paper
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2010, 63, 75–82
Synthesis and Electrochemical Studies of Nickel β-Diketonate
Complexes Incorporating Asymmetric Diimine Ligands
Phimphaka Harding,A,D David J. Harding,A,D Nitisastr Soponrat,B
Kittiya Tinpun,B Sirirat Samuadnuan,B and Harry AdamsC
AMolecular Technology Research Unit, School of Science, Walailak University, Thasala,
Nakhon Si Thammarat, 80161, Thailand.
BDepartment of Chemistry, Faculty of Science, Taksin University, Songkhla, 90000, Thailand.
CDepartment of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF, UK.
DCorresponding authors. Email: kphimpha@wu.ac.th; hdavid@wu.ac.th
The reaction of ppaX {(4-X-phenyl)-pyridin-2-ylmethylene-amine; X = H, Me, Et, OMe, F, Cl, Br, and I} with [Ni(β-
diketonate)2(H2O)2] {β-diketonate = 1,3-diphenylpropanedionate (dbm), 2,2,6,6-tetramethyl-3,5-heptadionate (tmhd), or
hexafluoroacetylacetonate (hfac)} yields a series of nickel complexes. X-ray crystallography reveals octahedral coordi-
nated nickel centres with a cis arrangement of the β-diketonate ligands. The β-diketonate ligands adopt ‘planar’ or ‘bent’
coordination modes, whereas the aryl ring of the ppaX ligand is twisted with respect to the pyridylimine unit. The
electrochemical behaviour of the complexes reveals quasi-reversible or irreversible one-electron oxidation to Ni(iii) in
the case of the [Ni(tmhd)2(ppaX)] and [Ni(dbm)2(ppaX)] complexes, respectively. The peak potential for oxidation is
dependent on the type of β-diketonate ligand but essentially independent of the substituent, X, on the ppaX ligand. The
[Ni(β-diketonate)2(ppaX)] complexes (X = F, Cl, Br, and I) also undergo ligand based reduction.
Manuscript received: 20 April 2009.
Manuscript accepted: 15 July 2009.
Introduction
difficult to derivatize. In contrast, iminopyridines are easy to pre-
pare and readily modified. Moreover, the different substituents
on the aryl group might be expected to allow subtle changes in
the steric and electronic properties of the ligands, which may in
turn, affect the structure and redox chemistry of the complexes.
A further point is that unlike bipy and phen, iminopyridines
are asymmetric, which may also influence the chemistry of the
system. In the following paper we report the synthesis, struc-
tural characterization, and redox chemistry of a series of novel
[Ni(β-diketonate)2(ppaX)] complexes.
Metal β-diketonates represent an important class of complexes
and have been extensively studied due to their ease of synthesis,
ready modification, and multiple applications.[1–3] In the case
of divalent metal ions, the [M(β-diketonate)2] complexes are
able to coordinate additional ligands forming octahedral metal
complexes.[4] The nature of the chelating ligands can have a
significant effect on the properties of the complexes and there-
fore their subsequent application.Thus, chelating alkyl diamines
are used to synthesize volatile precursors for the preparation of
metal-oxide thin films[5,6] whereas organic radicals may be used
to construct single molecule magnets.[7–10] However, in much
of the reported literature on such octahedral metal-β-diketonate
adducts only acac or hfac ligands (acac = acetylacetonate,
hfac = hexafluoroacetyl-acetonate) are used with the larger
dbm and tmhd ligands (dbm = 1,3-diphenylpropanedionate,
tmhd = 2,2,6,6-tetramethylheptanedionate) remaining poorly
represented.
While metal-β-diketonate adducts have found many applica-
tions, to date little research has been concerned with the redox
chemistry of these systems.[11–13] However, recent studies in our
group have shown that the complexes, [Ni(β-diketonate)2(L)]
(β-diketonate = dbm, tmhd; L = bipy, phen), which incorporate
the less widely used dbm and tmhd ligands and diimines are
electrochemically active oxidizing to rare Ni(iii) species.[14] In
an attempt to develop this area of chemistry we have undertaken
a course of research into the chemistry of [M(β-diketonate)2(L)]
complexes. The bipyridine and phenanthroline ligands used
in this preliminary study, while commercially available, are
Results and Discussion
Synthesis and Characterization
The synthesis of the (4-X-phenyl)-pyridin-2-ylmethylene-amine
(ppaX) ligands, where X = H (1), Me (2), Et (3), OMe (4), F (5),
Cl (6), Br (7), and I (8), was achieved by a simple condensation
reaction between pyridine-2-carboxaldehyde and the appropri-
ate substituted aniline in diethyl or diisopropyl ether (Scheme 1).
While many of these ligands have been reported previously,[15,16]
we found that in most cases the reported procedure did not give
the expected ppaX cleanly. Instead considerable quantities of the
starting materials remained. Hannon et al. recently reported the
use of molecular sieves in an improved preparation of ppaH, to
remove the water produced during the course of the reaction.[17]
We therefore added molecular sieves to the reaction mixture and
found that this simple addition significantly increased yields,
purity, and also reduced reaction times. The molecular sieves
are readily removed by filtration once the reaction is complete.
The ligands have been characterized by IR, UV-vis, and 1H NMR
© CSIRO 2010
10.1071/CH09232
0004-9425/10/010075

76
P. Harding et al.
H
N
H
O
H2N
ϩ
X
N
X
N
Scheme 1. Synthesis of ppaX ligands.
R
R
R
R
Ar
R
R
O
H
O
O
O
O
H
N
O
O
ϩ
Ni
Ni
O
N
N
X
N
R
R
Scheme 2. Synthesis of [Ni(β-diketonate)2(ppaX)] complexes.
Table 1. Selected bond lengths [Å] and angles [◦] of 10, 12, and 14
spectroscopy. IR spectroscopy of the ligands revealed a medium
intensity imine stretch between 1623 and 1626 cm−1 in line
with those for previously reported ppaX compounds.[15–17] The
1H NMR spectra were recorded in CDCl3 showing a singlet
between 8.58 and 8.68 ppm for the imino proton confirming the
formation of the desired ppaX ligands. The peaks for the pyridyl
and phenylene groups are assigned on the basis of their split-
ting patterns, coupling constants, and intergration values and
are typical of such iminopyridine ligands.
10
12
14
Ni–O(1)
Ni–O(2)
Ni–O(3)
Ni–O(4)
Ni–N(1)
Ni–N(2)
O(1)–Ni–O(2)
O(3)–Ni–O(4)
N(1)–Ni–N(2)
βA
2.013(3)
2.005(3)
2.027(3)
2.010(4)
2.090(4)
2.180(4)
89.05(14)
90.58(14)
76.81(16)
2.98
2.0349(12)
2.0135(12)
2.0479(12)
2.0163(12)
2.0812(14)
2.1096(14)
88.93(5)
88.18(5)
78.60(6)
31.94
2.0091(16)
2.0205(17)
2.0165(16)
2.0128(16)
2.091(2)
2.189(2)
90.66(6)
89.29(6)
77.31(8)
16.57
The reaction of [Ni(dbm)2(H2O)2], [Ni(tmhd)2(H2O)2], or
[Ni(hfac)2(H2O)2] with the eight ppaX ligands, in CH2Cl2,
THF or acetone affords red, brown, and yellow solids of the
octahedral complexes [Ni(dbm)2(ppaX)] {X = H (9), Me (10),
Et (11), OMe (12), F (13), Cl (14), Br (15), and I (16)},
[Ni(tmhd)2(ppaX)] {X = H (17), Me (18), Et (19), OMe (20),
F (21), Cl (22), Br (23), and I (24)}, and [Ni(hfac)2(ppaX)]
{X = H (25), Me (26), Et (27), OMe (28), F (29), Cl (30), Br
(31), and I (32)} (Scheme 2).The red, brown, and yellow colours
of these compounds are in marked contrast with the related
[Ni(β-diketonate)2(L)] (L = bpy, phen) complexes, which are
green[14] and indicative of absorption by the ppaX ligand. The
expected d-d transitions are unfortunately obscured by these
strong UV bands. IR spectroscopy of complexes 9–24 shows a
C=Ostretchfrom1588to1595 cm−1, similartothatreportedfor
the [Ni(β-diketonate)2(L)] (L = bpy, phen) complexes (1582–
1595 cm−1),[14] and indicative of a chelating coordination mode
for the β-diketonate ligand.[18] The C=O stretch for the hfac
compounds, 25–32, is on average 60 cm−1 higher than that
observed for complexes 9–24, consistent with the strong elec-
tron withdrawing effect of the CF3 groups. The imine stretches
of coordinated ppaX ligands which are expected to be between
1580 and 1590 cm−1 are not observed as they masked by the
strong C=O stretch of the β-diketonate ligand.
17.06
22.87
24.72
39.50
1.51
23.99
γB
Intermolecular distancesC
O(1)–H(8)
O(3)–H(8)
2.439
2.615
2.578
2.396
O(3)–H(6)
Aβ is the angle between the plane defined by the carbon and oxygen atoms of
the β-diketonate ligand and the plane defined by the nickel and two oxygen
atoms.
Bγ is the angle between the plane of the pyridylimine unit and the plane of
the substituted phenyl ring.
CNon-bonded metrics and those involving centroids were not included in the
structure refinement, and thus do not have an estimated standard deviation.
Complexes 10, 12, and 14 assume slightly distorted octahe-
dral coordination geometries. The β-diketonate ligands exhibit
a cis arrangement enforced by the chelating ppaX ligand. The
Ni–O bond lengths vary between 2.005 and 2.048 Å for the three
complexes and are similar to other previously reported nickel
β-diketonateadducts, [Ni(dbm)2(en)]{2.009(6), 2.060(7) Å},[19]
and [Ni(dbm)2(phen)] {2.035(1), 2.041(1) Å}.[14]
Crystallographic Studies
The molecular structures of complexes 10, 12, and 14 were deter-
mined by X-ray crystallography (Table 1). The structures of 10
and 12 are shown in Figs 1 and 2, respectively. Crystals of all
complexes were grown by allowing hexane to diffuse slowly
into a concentrated solution of the complex in CH2Cl2 at room
temperature.
The nickel bond to the pyridine of the ppaX ligand of
complexes 10 and 14 is considerably shorter than the bond
to the imine nitrogen, differing by ∼0.1 Å. In contrast, the
Ni–N bond lengths for 12 are different by only 0.03 Å. It is
also interesting to note that in [Cu(ppa2Me,3Me)2]ClO4
and
[16]
[Ru(bipy)2(ppaH)][PF6]2,[17] the imine nitrogen metal bond is

Synthesis and Electrochemical Studies of Nickel β-Diketonate Complexes
77
C39
C40
Ni
R
R
O
O
β
C38
C41
C33
C32
C37
C35
C34
C31
Fig. 3. Schematic diagram showing the angle β between the β-diketonate
and NiO2 planes.
C42
O4
C36
C29
C30
C2
C3
C1
N1
C28
C5
C4
O3
O2
C21
Ni
C6
C12
C11
N2
C7
C27
C26
C8
C25
O1
C13
C22
C10
C9
C20
C14
Fig. 4. Mercury plot showing the CH· · ·O and π-π interactions in
[Ni(dbm)2(ppaCl)] 14. For clarity, only hydrogen atoms involved in inter-
actions are shown.
C15
C16
C23
C24
C43
pyridyl ring of a neighbouring ppaX ligand but is neither
co-planar with, nor perpendicular to, that pyridyl ring.
C19
C17
The β-diketonate ligand is essentially planar and symmet-
ric suggesting that the negative charge is delocalized over the
β-diketonate framework. As noted in other nickel β-diketonate
adducts the nickel centre lies above the plane of the dbm ligand
in a ‘bent’ coordination mode.[14] The extent of this displace-
ment has been determined by calculating the angle between the
plane of the β-diketonate framework and the plane defined by the
nickel and two oxygen atoms (Fig. 3). For complex 12 both dbm
ligands exhibit a ‘bent’ coordination mode, whereas for 10 and
14 only one of the dbm ligands is ‘bent’with the other assuming
a ‘planar’ coordination mode. This is probably the result of the
different substituents on the ppaX ligands.
The complexes are packed into chiral columns with each
column exhibiting the same helicity and adjacent columns of
alternate helicity as shown in Figs 4 and 5. The molecules are
arranged so that the ppaX ligands are positioned above one
another with the substituent alternately pointing ‘in’ and ‘out’.
The interaction principally involved here is between a C–H group
from the phenyl ring of the ppaX ligand and a coordinated oxy-
gen atom from the dbm ligand. The structure of 12 is slightly
different revealing a further interaction from the imino C–H to
the same oxygen atom. As a result of the stacking of the ppaX
ligands, the dbm ligands are also stacked in columns. As might
be expected, this leads to π-π interactions between two adja-
cent dbm phenyl rings (centroid-centroid 3.653 and 3.651 Å for
10 and 14, respectively). The absence of this interaction in the
structure of 12 once again seems to stem from the extra space
needed to accommodate the ppaOMe ligand and the subsequent
‘bent’ coordination mode of both dbm ligands which preclude
this interaction. Surprisingly, the π-π interaction is not replaced
by any face to edge CH-π interactions.
C18
Fig. 1. ORTEP diagram of [Ni(dbm)2(ppaMe)] 10. The thermal ellipsoids
are drawn to 50% probability level. Hydrogen atoms are omitted for clarity.
C22
C24
C27
C21
C26
C23
C2
C20
C3
C4
C19
C18
O2
C1
N1
C25
O1
C28
C16
C17
Ni
C29
C33
C5
C6
C30
C32
C12
N2
C7
O4
C11
O3
C15
C10
O5
C34
C8
C13
C31
C43
C42
C9
C14
C36
C35
C37
C41
C38
C39
C40
Fig. 2. ORTEP diagram of [Ni(dbm)2(ppaOMe)] 12. The thermal ellipsoids
are drawn to 50% probability level. Hydrogen atoms are omitted for clarity.
shorter than the pyridine nitrogen metal bond.The reason for this
difference remains unclear. The phenyl ring in all the complexes
is twisted with respect to the pyridylimine unit. Interestingly,
the angle for 12 is 39.5◦, whereas those of 10 and 14 are 22.9◦
and 24.0◦, respectively. By comparison [Cu(ppa2Me,3Me)2]ClO4
and [Ru(bipy)2(ppaH)][PF6]2 exhibit angles of 69◦ and 45◦,
respectively.[16,17] The phenyl ring is positioned above the
Electrochemical Studies
The redox properties of the complexes 9–32 were studied by
cyclic voltammetry (CV) in CH2Cl2 at 25◦C (Table 2). The CVs
of 13, 21, and 29 are shown in Fig. 6 as representative examples.
Complexes 9–16 exhibit an irreversible oxidation wave, whereas

78
P. Harding et al.
(a)
5 µA
Ϫ1
Ϫ2
Ϫ1.5
Ϫ0.5
E [V]
0
0.5
1
1.5
(b)
Fig. 5. Mercury plot showing the CH· · ·O interactions in
[Ni(dbm)2(ppaOMe)] 12. For clarity, only hydrogen atoms involved in
interactions are shown.
5 µA
Table 2. Electrochemical data of [Ni(β-diketonate)2(ppaX)]
complexesA
Ϫ2
Ϫ1.5
Ϫ1
Ϫ0.5
E [V]
0
0.5
1
1.5
Complex
Oxidation process
Eoꢀ/Ep [V]B
Reduction process
(c)
Ep [V]
9
0.67 (I)
0.66 (I)
0.66 (I)
0.66 (I)
0.68 (I)
0.72 (I)
0.68 (I)
0.70 (I)
0.33
0.32
0.31
0.32, 0.97 (I)
0.35
0.35
–
–
–
–
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
5 µA
−1.94 (I)
−1.84 (I)
−1.85 (I)
−1.83 (I)
–
Ϫ2
Ϫ1.5
Ϫ1
Ϫ0.5
E [V]
0
0.5
1
1.5
–
–
–
Fig. 6. Cyclic voltammogram of (a) [Ni(dbm)2(ppaF)] 13, (b)
[Ni(tmhd)2(ppaF)] 21, and (c) [Ni(hfac)2(ppaF)] 29.All potentials are versus
−2.09 (I)
−2.01 (I)
−1.98 (I)
−2.00 (I)
−1.76 (I)
−1.79 (I)C
−1.69 (I)
−1.74 (I)
−1.73 (I)C
−1.57 (I)
−1.61 (I)
−1.61 (I)
[FeCp2]0/+
.
0.36
0.37
–
–
–
–
–
–
–
The peak potentials for oxidation of 9–16 are between 0.32
and 0.37V more positive than those of 17–24. It is clear that the
tmhd ligands are considerably more electron donating than
the dbm ligands, presumably as a result of the inductive effect of
thet-butylgroupsonthetmhdligands.Thehfacligandsalsohave
a significant effect on the peak potential for oxidation with no
oxidation observed within the solvent window, with the excep-
tion of 32. This is consistent with the findings of Villamena
et al., in which the oxidation potential for [Ni(hfac)2(2-pyBN)]
(2-pyBN = N-tert-butyl-α-(2-pyridyl)nitrone) is observed at
1.80V (versus Ag/AgCl).[11]
0.58 (I)
AAll measurements were performed at 298 K, in dried and degassed CH2Cl2
0.1 M [NBun4][PF6] solution; scan rate 100 mV s−1; calibrated with [FeCp2],
and reported relative to the [FeCp2]0/+ couple.
BFor an irreversible (I) process the oxidation peak potential, (Ep)ox, is given.
CUncalibrated as the compound reacts with [FeCp2].
In contrast to the considerable effect that the β-diketonate
ligand has on the peak potential for oxidation, the different
ppaX ligands result in only minor changes in the peak poten-
tial for oxidation. A similar insensitivity to the substituent has
been observed in a series of Cu(i) compounds, [Cu(ppaX)2]ClO4
(X = F, Cl, Br, and I).[16] It is possible that the substituent on the
ppaX ligand is simply too remote to significantly affect the peak
potential for oxidation. Moreover, the twist between the phenyl
ring and the pyridylimine unit seen in the solid state will reduce
the degree of conjugation between the rings, thereby limit-
ing the effect of the substituent on the oxidation potential.
However, in the case of [Ni(tmhd)2(ppaOMe)] a second irre-
versible oxidation is also observed, although whether this is
metal-based or ligand-based remains unclear. Further spectro-
electrochemical studies are currently underway to determine the
nature of this second oxidation and will be reported in a later
publication.
those of 17–24 undergo quasi-reversible oxidation, albeit only at
scan rates above 200 mV s−1. Comparison with the related cobalt
complexes [Co(β-diketonate)2(L)] (β-diketonate = dbm, tmhd,
L = bpy, phen), which oxidize between −0.15 and 0.06V (ver-
sus [FeCp2]0/+) to give the isolable Co(iii) cations, suggest that
the oxidation is to Ni(iii) and, as such, represent rare examples
of Ni(iii) species (P. Harding and D. J. Harding, unpubl. data).As
expected the [Ni(β-diketonate)2(ppaX)] complexes are oxidized
atpotentialsverysimilartotheanalogous[Ni(β-diketonate)2(L)]
(β-diketonate = dbm, tmhd; L = bpy, phen) complexes.[14] This
is unsurprising given the structural similarity between the lig-
ands. Attempts to chemically oxidize the complexes have thus
far proved unsuccessful.

Synthesis and Electrochemical Studies of Nickel β-Diketonate Complexes
79
Hc
Hd
of completeness. All other chemicals were purchased from
Fluka Chemical Co. and used as received. Infrared spec-
tra were recorded on a Perkin–Elmer Spectrum One infrared
He
N
Hf
Hg
spectrophotometer as KBr discs, in the range 400–4000 cm−1
.
Hb
Electronic spectra were recorded in CH2Cl2 on a Unicam UV300
UV-Visiblespectrometer. Elementalanalyseswerecarriedouton
a Eurovector EA3000 analyzer. 1H NMR spectra were recorded
on a Bruker 300 MHz FT-NMR spectrometer at 298 K in CDCl3
with SiMe4 added as an internal standard. Hydrogen atoms are
labelled according to Fig. 7. ESI-MS were carried out on a
Bruker Daltonics 7.0TApex 4 FTICR Mass Spectrometer. Elec-
trochemical studies were carried out using a PalmsensPC Vs
2.11 Potentiosat in conjunction with a three electrode cell. The
auxiliary electrode was a platinum rod and the working elec-
trode was a platinum disc (2.0 mm diameter). The reference
electrode was a Ag–AgCl electrode (2 M LiCl). Solutions were
5 × 10−4 mol dm−3 in the test compound and 0.1 mol dm−3 in
[NBun4][PF6] as the supporting electrolyte. Under these condi-
tions, Eoꢀ for the one-electron oxidation of [FeCp2] added to the
test solutions for internal calibration is 0.52V.
N
X
Ha
Hf
Hg
Fig. 7. Hydrogen labels of the ppaX ligands.
In addition to the metal-based oxidation noted above, the
complexes also undergo irreversible reduction. In the case of the
complexes with dbm or tmhd ligands, only when X = F, Cl, Br,
and I, are reduction peaks observed. Given the absence of any
reduction peaks for the other complexes; i.e. where X = H, Me,
Et, and OMe; it seems likely that these reductions are ligand
based. Despite this, the reductions show considerable variation,
with differences between the hfac and dbm complexes being
on average 235 mV, whereas those between the dbm and tmhd
complexes are 155 mV. The reason for this variation may be
the result of the differing degrees of π-backbonding from the
metal centre to the ppaX ligand. Thus, the [Ni(tmhd)2(ppaX)]
compounds are the most electron rich, resulting in considerable
π-backbonding and are therefore, the most difficult to reduce.
Conversely, the [Ni(hfac)2(ppaX)] complexes are the most elec-
tron poor, resulting in minimal π-backbonding, making the ppaX
ligand easier to reduce. It is also noteworthy that when X = F the
complexes are more difficult to reduce by ∼0.1V than for [Ni(β-
diketonate)2(ppaX)] (β-diketonate = dbm, tmhd, hfac; X = Cl,
Br, I). A final point of interest is that 25–28 also exhibit irre-
versible reduction waves.Whether this results from the reduction
of the hfac or ppaX ligands remains unclear.
Synthesis
Synthesis of (Phenyl)-pyridine-2-ylmethylene-amine
(ppaH) 1
To a solution of aniline (274 µL, 3 mmol) in diethylether
(10 mL) over molecular sieves, was added pyridine-2-
carboxaldehyde (266 µL, 3 mmol). The yellow solution was
stirred overnight. The solution was filtered and the molec-
ular sieves washed with CH2Cl2 (5 mL). The solvent was
removed under vacuum, yielding a bright yellow oil (0.273 g,
50%). νmax(CH2Cl2)/cm−1 1630 (νC=N). λmax(CH2Cl2)/nm
(log ε/M−1 cm−1) 236 (4.07), 278 (3.82), 318 (3.50). δH = 8.70
1
1
(1H, d, JHH 4.8, Ha), 8.58 (1H, s, He), 8.19 (1H, d, JHH 7.8,
Hd), 7.79 (1H, m, 1JHH 7.8, Hc), 7.35 (3H, m, Hf , Hb), 7.20 (3H,
m, Hg, HH).
Conclusions
In conclusion, we have prepared
a series of [Ni(β-
Ligands 2–8 were synthesized using the same procedure.
Analytical and spectroscopic data are given for each compound.
diketonate)2(ppaX)] complexes and have shown that the ppaX
ligands are convenient alternatives to substituted bipyridine or
phenanthroline ligands. The crystal structures reveal octahe-
dral coordinated nickel centres, with the β-diketonate ligands
exhibiting both ‘bent’and ‘planar’bidentate coordination modes
dependent upon the type of ppaX ligand present.The aryl rings of
the ppaX ligands are found to be non-coplanar with the pyridyl-
imine unit, the degree of twisting dependent on the substituent,
X.The complexes are irreversibly or quasi-reversibly oxidized to
Ni(iii) in the case of [Ni(dbm)2(ppaX)] and [Ni(tmhd)2(ppaX)],
respectively. With the exception of [Ni(hfac)2(ppaI)] the hfac
complexes show no oxidation processes.The [Ni(tmhd)2(ppaX)]
complexes are more easily oxidized by ∼350 mV than the
[Ni(dbm)2(ppaX)] complexes indicating that the β-diketonate
ligand has a significant effect on the redox potential. In con-
trast, the ppaX ligands have only a very minor effect on the redox
potential with a difference of ∼50 mV between the various ppaX
ligands.
Synthesis of (4-Methylphenyl)-pyridine-2-ylmethylene-
amine (ppaMe) 2
Yellow crystalline solid (0.360 g, 62%). νmax(KBr)/cm−1
1625 (νC=N). λmax(CH2Cl2)/nm (log ε/M−1 cm−1) 234 (4.23),
280 (4.12), 324 (4.00 sh). δH = 8.71 (1H, d, 1JHH 6.3, Ha), 8.62
(1H, s, He), 8.19 (1H, d, 1JHH 7.8, Hd), 7.80 (1H, m, 1JHH 7.8,
Hc), 7.35 (1H, m, 1JHH 6.3, Hb), 7.24 (4H, m, Hf , Hg), 2.36 (3H,
s, CH3).
Synthesis of (4-Ethylphenyl)-pyridine-2-ylmethylene-
amine (ppaEt) 3
Dull orange oil (0.375 g, 59%). νmax(CH2Cl2)/cm−1 1630
(νC=N). λmax(CH2Cl2)/nm (log ε/M−1 cm−1) 234 (4.10), 280
(4.03), 324 (3.93 sh). δH = 8.73 (1H, d, 1JHH 4.8, Ha), 8.68 (1H,
s, He), 8.24 (1H, d, 1JHH 7.8, Hd), 7.85 (1H, m, 1JHH 7.5, Hc),
7.23 (5H, m, Hb, Hf , Hg), 2.69 (2H, q, 1JHH 7.2, CH2), 1.23 (3H,
t, 1JHH 7.2, CH3).
Experimental
General Remarks
Synthesis of (4-Methoxyphenyl)-pyridine-2-ylmethylene-
amine (ppaOMe) 4
All reactions were conducted in air using HPLC grade solvents.
[Ni(tmhd)2(H2O)2], [Ni(hfac)2(H2O)2], and [Ni(dbm)2(H2O)2]
were prepared by literature methods.[1,20] Although the ppaX
ligands are known, our synthesis differs from that previously
reported and thus, their syntheses are included in the interests
Light orange solid (0.423 g, 67%). νmax(KBr)/cm−1 1626
(νC=N). λmax(CH2Cl2)/nm (log ε/M−1 cm−1) 238 (4.11), 286
1
(4.01), 340 (4.08). δH = 8.70 (1H, d, JHH 7.2, Ha), 8.65 (1H,
s, He), 8.20 (1H, d, 1JHH 7.8, Hd), 7.81 (1H, dd, 1JHH 8.1, 7.8,

80
P. Harding et al.
Hc), 7.36 (3H, m, Hb, Hg), 6.94 (2H, m,1JHH 8.7, Hf ), 3.83 (3H,
s, CH3).
νmax(KBr)/cm−1 1595 (νC=O). λmax(CH2Cl2)/nm (log ε/
M
−1 cm−1) 248 (4.63), 358 (4.51).
Synthesis of [Ni(dbm)2(ppaEt)] 11
Synthesis of (4-Fluorophenyl)-pyridine-2-ylmethylene-
amine (ppaF) 5
Brown-yellow solid (acetone/n-hexane) (0.115 g, 64%)
Bright yellow crystalline solid (0.491 g, 82%). νmax(KBr)/
cm−1 1627 (νC=N). λmax(CH2Cl2)/nm (log ε/M−1 cm−1) 236
(Found: C 73.5, H 5.1, N 4.0. Calc. for C44H36N2NiO4:
C 73.9, H 5.1, N 3.9%). m/z (ESI) 701 (100%, [M-
dbm− + ppaEt]+), 491 (28%, [M-dbm−]+). νmax(KBr)/cm−1
1595 (νC=O). λmax(CH2Cl2)/nm (log ε/M−1 cm−1) 246 (4.45),
284 (4.23 sh), 356 (4.48).
1
(3.91), 282 (3.91), 318 (3.75 sh). δH = 8.80 (1H, d, JHH 4.8,
Ha), 8.60 (1H, s, He), 8.20 (1H, d, 1JHH 7.8, Hd), 7.85 (1H, dd,
1
1JHH 7.5, 7.8, Hc), 7.38 (1H, dd, JHH 7.5, 4.8, Hb), 7.31 (2H,
dd, 1JHH 8.1, 7.9, Hf ), 7.09 (2H, dd, 1JHH 7.9, 8.1, Hg).
Synthesis of [Ni(dbm)2(ppaOMe)] 12
Synthesis of (4-Chlorophenyl)-pyridine-2-ylmethylene-
Brown-yellow solid (acetone/n-hexane) (0.122 g, 68%)
(Found: C 72.2 H 5.0, N 3.9. Calc. for C43H34N2NiO5:
C 72.0 H 4.8, N 3.9%). m/z (ESI) 493 (100%, [M-
dbm−]+). νmax(KBr)/cm−1 1595 (νC=O). λmax(CH2Cl2)/nm
(log ε/M−1 cm−1) 250 (4.60), 282 (4.21 sh), 358 (4.54).
amine (ppaCl) 6
Paleyellowcrystallinesolid(0.452 g, 70%). νmax(KBr)/cm−1
1624 (νC=N). λmax(CH2Cl2)/nm (log ε/M−1 cm−1) 238 (4.12),
280 (4.09), 320 (3.95 sh). δH = 8.80 (1H, d, 1JHH 5.1, Ha), 8.66
(1H, s, He), 8.30 (1H, d, 1JHH 8.1, Hd), 7.89 (1H, dd, 1JHH 8.1,
7.8, Hc), 7.44 (1H, dd, 1JHH 5.1, 7.8, Hb), 7.30 (2H, d, 1JHH 8.7,
Hf ), 7.01 (2H, d, 1JHH 8.7, Hg).
Synthesis of [Ni(dbm)2(ppaF)] 13
Brown-yellow microcrystals (CH2Cl2/n-hexane) (0.222 g,
59%) (Found: C 71.2, H 4.6, N 4.2. Calc. for C42H31FN2NiO4:
C 71.5, H 4.4, N 4.0%). m/z (ESI) 481 (100%, [M-
dbm−]+). νmax(KBr)/cm−1 1595 (νC=O). λmax(CH2Cl2)/nm
(log ε/M−1 cm−1) 246 (4.66), 284 (4.33 sh), 356 (4.53).
Synthesis of (4-Bromophenyl)-pyridine-2-ylmethylene-
amine (ppaBr) 7
Brown solid (0.596 g, 76%). νmax(KBr)/cm−1 1623 (νC=N).
λmax(CH2Cl2)/nm (log ε/M−1 cm−1) 232 (4.12), 280 (4.12), 324
(3.97 sh). δH = 8.73 (1H, d, 1JHH 4.8, Ha), 8.62 (1H, s, He), 8.21
(1H, d, 1JHH 7.5, Hd), 7.86 (1H, t, 1JHH 7.5, 6.9, Hc), 7.53 (2H,
d, 1JHH 7.8, Hf ), 7.42 (1H, dd, 1JHH 6.9, 4.8, Hb), 7.18 (2H, d,
1JHH 7.8, Hg).
Synthesis of [Ni(dbm)2(ppaCl)] 14
Yellow solid (acetone/n-hexane) (0.114 g, 63%) (Found: C
71.2, H 4.7, N 3.9. Calc. for C42H31ClN2NiO4: C 69.9, H 4.3,
N 3.9%). m/z (ESI) 497 (100%, [M-dbm−]+). νmax(KBr)/cm−1
1594 (νC=O). λmax(CH2Cl2)/nm (log ε/M−1 cm−1) 246 (4.61),
358 (4.50).
Synthesis of (4-Iodophenyl)-pyridine-2-ylmethylene-
amine (ppaI) 8
Pale green solid (prepared in i-Pr2O) (0.605 g, 65%).
νmax(KBr)/cm−1 1625 (νC=N). λmax(CH2Cl2)/nm (log ε/
Synthesis of [Ni(dbm)2(ppaBr)] 15
M
−1 cm−1) 242 (4.21), 282 (4.07), 320 (4.00 sh). δH = 8.72 (1H,
Yellow solid (acetone/n-hexane) (0.158 g, 82%) (Found: C
65.9, H 4.0, N 3.9. Calc. for C42H31BrN2NiO4: C 65.8, H 4.1,
N 3.6%). m/z (ESI) 543 (100%, [M-dbm−]+). νmax(KBr)/cm−1
1593 (νC=O). λmax(CH2Cl2)/nm (log ε/M−1 cm−1) 247 (4.66),
355 (4.47).
dd, 1JHH 1.5, 4.8, Ha), 8.58 (1H, s, He), 8.15 (1H, d, 1JHH 8.1,
Hd), 7.96 (1H, ddd, 1JHH 1.5, 7.8, 8.1, Hc), 7.54 (1H, ddd, 1JHH
0.9, 4.8, 7.8, Hb), 7.31 (2H, d, 1JHH 8.4, Hf ), 7.09 (2H, d, 1JHH
8.4, Hg).
Synthesis of [Ni(dbm)2(ppaH)] 9
Synthesis of [Ni(dbm)2(ppaI)] 16
To a lime green suspension of [Ni(dbm)2(H2O)2] (0.135 g,
0.25 mmol) in acetone (10 mL), was added a solution of ppaH
(0.046 g, 0.25 mmol) in acetone (3 mL). The brown orange solu-
tion was stirred overnight then concentrated under vacuum.
n-Hexane (10 mL) was added to precipitate a brown solid, which
was washed with additional n-hexane (2 × 5 mL) and dried under
vacuum, yielding a brown solid (0.106 g, 61%) (Found: C 73.4, H
4.6, N 3.9. Calc. for C42H32N2NiO4: C 73.4, H 4.7, N 4.1%). m/z
(ESI) 463 (100%, [M-dbm−]+). νmax(KBr)/cm−1 1595 (νC=O).
λmax(CH2Cl2)/nm (log ε/M−1 cm−1) 259 (4.84), 277 (4.81), 352
(4.60).
Complexes 10–32 were synthesized by the same gen-
eral procedure using acetone, THF, or CH2Cl2 in the case
of [Ni(dbm)2(H2O)2], [Ni(tmhd)2(H2O)2], and [Ni(hfac)2
(H2O)2], respectively. They were crystallized from the solvents
indicated.
Brown solid (THF/n-hexane) (0.091 g, 44%) (Found: C 61.9,
H 4.2, N 3.2. Calc. for C42H31IN2NiO4: C 62.0, H 3.8, N
3.4%). m/z (ESI) 897 (100%, [M-dbm− + ppaI]+), 589 (85%,
[M-dbm−]+). νmax(KBr)/cm−1 1594 (νC=O). λmax(CH2Cl2)/nm
(log ε/M−1 cm−1) 248 (4.66), 286 (4.28 sh), 354 (4.50).
Synthesis of [Ni(tmhd)2(ppaH)] 17
Brown solid (THF/n-hexane) (0.063 g, 41%) (Found: C 67.8,
H 7.9, N 4.8. Calc. for C34H48N2NiO4: C 67.2, H 8.0, N 4.6%).
m/z (ESI) 605 (37%, [M-tmhd− + ppaH]+), 423 (100%, [M-
tmhd−]+). νmax(KBr)/cm−1 1591 (νC=O). λmax(CH2Cl2)/nm
(log ε/M−1 cm−1) 240 (4.36), 294 (4.28).
Synthesis of [Ni(tmhd)2(ppaMe)] 18
Brown needles (slow evaporation of CH2Cl2) (0.080 g, 52%)
(Found: C 67.0, H 7.9, N 4.4. Calc. for C35H50N2NiO4:
C 67.6, H 8.1, N 4.5%). m/z (ESI) 633 (100%, [M-
tmhd− + ppaMe]+), 437 (88%, [M-tmhd−]+). νmax(KBr)/cm−1
1586 (νC=O). λmax(CH2Cl2)/nm (log ε/M−1 cm−1) 240 (4.46),
272 (4.26 sh), 308 (4.42).
Synthesis of [Ni(dbm)2(ppaMe)] 10
Dull green microcrystals (CH2Cl2/n-hexane) (0.207 g, 55%)
(Found: C 73.5, H 4.9, N 4.1. Calc. for C43H34N2NiO4: C
73.6, H 4.9, N 4.0%). m/z (ESI) 477 (100%, [M-dbm−]+).

Synthesis and Electrochemical Studies of Nickel β-Diketonate Complexes
Synthesis of [Ni(tmhd)2(ppaEt)] 19
81
[M-hfac−]+). νmax(KBr)/cm−1 1654 (νC=O). λmax(CH2Cl2)/nm
(log ε/M−1 cm−1) 247 (4.23), 320 (4.31).
Brown oil (0.066 g, 40%) (Found: C 67.8, H 8.0, N 4.1.
Calc. for C36H52N2NiO4: C 68.0, H 8.2, N 4.4%). m/z
(ESI) 451 (100%, [M-tmhd−]+). νmax(KBr)/cm−1 1591 (νC=O).
λmax(CH2Cl2)/nm (log ε/M−1 cm−1) 240 (4.40), 308 (4.35).
Synthesis of [Ni(hfac)2(ppaOMe)] 28
Deep yellow solid (THF/n-hexane) (0.098 g, 54%) (Found: C
40.3, H 2.4, N 4.3. Calc. for C23H14F12N2NiO5: C 40.3, H 2.1,
N 4.1%). m/z (ESI) 477 (100%, [M-hfac−]+). νmax(KBr)/cm−1
1647 (νC=O). λmax(CH2Cl2)/nm (log ε/M−1 cm−1) 255 (4.27),
325 (4.26).
Synthesis of [Ni(tmhd)2(ppaOMe)] 20
Red-brown solid (THF/n-hexane) (0.079 g, 37%) (Found:
C 65.7, H 7.4, N 4.5. Calc. for C35H50N2NiO5: C 65.9,
H 7.9, N 4.4%). m/z (ESI) 665 (100%, [M-tmhd− + ppaOMe]+),
453 (73%, [M-tmhd−]+). νmax(KBr)/cm−1 1592 (νC=O).
λmax(CH2Cl2)/nm (log ε/M−1 cm−1) 242 (4.51), 316 (4.42) 354
(4.31 sh).
Synthesis of [Ni(hfac)2(ppaF)]·0.5C6H14 29
Brown solid (CH2Cl2/n-hexane) (0.131 g, 78%) (Found: C
41.6, H 2.3, N 3.7. Calc. for C25H18F13N2NiO4: C 41.9, H 2.5,
N 3.9%). m/z (ESI) 665 (100%, [M-hfac− + ppaF]+), 465 (27%,
[M-hfac−]+). νmax(KBr)/cm−1 1651 (νC=O). λmax(CH2Cl2)/nm
(log ε/M−1 cm−1) 238 (4.26), 318 (4.45).
Synthesis of [Ni(tmhd)2(ppaF)] 21
Brown needles (slow evaporation of CH2Cl2) (0.048 g, 32%)
(Found: C 65.3, H 7.5, N 4.8. Calc. for C34H47FN2NiO4: C 65.3,
H 7.6, N 4.5%). m/z (ESI) 641 (13%, [M-tmhd− + ppaF]+),
441 (100%, [M-tmhd−]+). νmax(KBr)/cm−1 1591 (νC=O).
λmax(CH2Cl2)/nm (log ε/M−1 cm−1) 238 (4.46), 272 (4.27), 308
(4.45).
Synthesis of [Ni(hfac)2(ppaCl)] 30
Golden brown solid (CH2Cl2/n-hexane) (0.101 g, 58%)
(Found: C 38.5, H 1.7, N 4.2. Calc. for C22H11ClF12N2NiO4:
C 38.3, H 1.6, N 4.1%). m/z (ESI) 481 (100%, [M-
hfac−]+). νmax(KBr)/cm−1 1651 (νC=O). λmax(CH2Cl2)/nm
(log ε/M−1 cm−1) 240 (4.25), 319 (4.38).
Synthesis of [Ni(tmhd)2(ppaCl)] 22
Synthesis of [Ni(hfac)2(ppaBr)] 31
Red-brown solid (THF/n-hexane) (0.068 g, 42%) (Found:
C 63.3, H 7.3, N 4.7. Calc. for C34H47ClN2NiO4: C 63.6,
H 7.4, N 4.4%). m/z (ESI) 675 (13%, [M-tmhd− + ppaCl]+),
457 (100%, [M-tmhd−]+). νmax(KBr)/cm−1 1588 (νC=O).
λmax(CH2Cl2)/nm (log ε/M−1 cm−1) 240 (4.27), 303 (4.24).
Deep yellow solid (CH2Cl2/n-hexane) (0.096 g, 52%)
(Found: C 36.2, H 1.7, N 3.9. Calc. for C22H11BrF12N2NiO4:
C 36.0, H 1.5, N 3.8%). m/z (ESI) 527 (100%, [M-
hfac−]+). νmax(KBr)/cm−1 1651 (νC=O). λmax(CH2Cl2)/nm
(log ε/M−1 cm−1) 319 (4.46), 342 (4.34).
Synthesis of [Ni(tmhd)2(ppaBr)] 23
Synthesis of [Ni(hfac)2(ppaI)] 32
Brown solid (THF/n-hexane) (0.051 g, 29%) (Found: C 59.2,
H6.6, N4.3. Calc. forC34H47BrN2NiO4:C59.5, H6.9, N4.1%).
m/z (ESI) 763 (100%, [M-tmhd− + ppaBr]+), 503 (88%, [M-
tmhd−]+). νmax(KBr)/cm−1 1592 (νC=O). λmax(CH2Cl2)/nm
(log ε/M−1 cm−1) 244 (4.39).
Yellow solid (THF/n-hexane) (0.107 g, 54%) (Found: C 33.6,
H 1.9, N 3.6. Calc. for C22H11F12IN2NiO4: C 33.8, H 1.4, N
3.6%). m/z (ESI) 881 (100%, [M-hfac− + ppaI]+), 573 (82%,
[M-hfac−]+). νmax(KBr)/cm−1 1654 (νC=O). λmax(CH2Cl2)/nm
(log ε/M−1 cm−1) 244 (4.40), 320 (4.41).
Synthesis of [Ni(tmhd)2(ppaI)] 24
Brown solid (THF/n-hexane) (0.091 g, 49%) (Found: C 55.2,
H 6.5, N 3.7. Calc. for C34H47IN2NiO4: C 55.7, H 6.5, N 3.8%).
m/z (ESI) 857 (100%, [M-tmhd− + ppaI]+), 549 (90%, [M-
tmhd−]+). νmax(KBr)/cm−1 1592 (νC=O). λmax(CH2Cl2)/nm
(log ε/M−1 cm−1) 252 (4.50), 276 (4.38).
Crystal Structure Determinations
Crystal data for the structures of 10, 12, and 14 are given in
Table 1. X-ray quality crystals of 10, 12, and 14 were grown
by allowing hexane to diffuse into a concentrated solution of
the complex in CH2Cl2. Crystals were mounted on a glass fibre
using perfluoropolyether oil and cooled rapidly to 150 K for 10
and 12 and 100 K for 14 in a stream of cold nitrogen. All diffrac-
tion data were collected on a Bruker Smart CCD area detector
with graphite monochromated Mo Kα (λ = 0.71073 Å). After
data collection, in each case an empirical absorption correc-
tion (SADABS) was applied,[21] and the structures were then
solved by direct methods and refined on all F2 data using the
SHELX suite of programs.[22] In all cases non-hydrogen atoms
were refined with anisotropic thermal parameters; hydrogen
atoms were included in calculated positions and refined with
isotropic thermal parameters, which were ∼1.2 × (aromatic CH)
or 1.5 × (Me) the equivalent isotropic thermal parameters of
their parent carbon atoms.
10: C43H34N2NiO4, M 701.43, yellow needle, triclinic, space
group P-1, a 9.6344(15), b 11.9506(18), c 16.267(3) Å, α
85.726(12), β 87.747(11), γ 66.802(10)◦, U 1716.6(5) Å3, Z 2,
D 1.357 Mg m−3, µ(MoKα) 0.612 mm−1, F(000) 732, T 150 K,
20118 reflections, 6429 unique (Rint 0.0806), R1 0.0655 (6429
reflections, I >2.0σ(I)), wR2 0.1449, R1 0.1316 (all data), wR2
0.1796 (all data), S 1.008.
Synthesis of [Ni(hfac)2(ppaH)]·0.5THF 25
Yellow solid (THF/n-hexane) (0.076 g, 46%) (Found: C 41.3,
H 2.2, N 4.3. Calc. for C24H16F12N2NiO4.5: C 41.7, H 2.3, N
4.0%). m/z (ESI) 447 (100%, [M-hfac−]+). νmax(KBr)/cm−1
1652 (νC=O). λmax(CH2Cl2)/nm (log ε/M−1 cm−1) 243.5 (4.26),
285 (4.36), 315 (4.35).
Synthesis of [Ni(hfac)2(ppaMe)]·0.5CH2Cl2 26
Green-brown solid (CH2Cl2/n-hexane) (0.181 g, 98%)
(Found: C 40.3, H 2.6, N 3.6. Calc. for C23.5H15ClF12N2NiO4:
C 40.0, H 2.1, N 3.9%). m/z (ESI) 657 (100%, [M-
hfac− + ppaMe]+), 461 (26%, [M-hfac−]+). νmax(KBr)/cm−1
1653 (νC=O). λmax(CH2Cl2)/nm (log ε/M−1 cm−1) 242 (4.20),
318 (4.40).
Synthesis of [Ni(hfac)2(ppaEt)] 27
Brown solid (THF/n-hexane) (0.055 g, 31%) (Found: C 42.5,
H 2.5, N 4.2. Calc. for C24H16F12N2NiO4: C 42.2, H 2.4, N
4.1%). m/z (ESI) 685 (100%, [M-hfac− + ppaEt]+), 475 (84%,

82
P. Harding et al.
12: C43H34N2NiO5, M 717.43, yellow plate, triclinic, space
[7] (a) M. H. Dickman, Acta Crystallogr.
C
1997, 53, 1192.
doi:10.1107/S0108270197005945
group P-1, a 9.9252(3), b 11.2859(3), c 17.4359(4) Å, α
73.2240(10), β 86.0220(10), γ 68.8910(10)◦, U 1743.17(8) Å3,
Z 2, D 1.367 Mg m−3, µ(MoKα) 0.607 mm−1, F(000) 748, T
150 K, 23492 reflections, 7901 unique (Rint 0.0318), R1 0.0372
(7901 reflections, I >2.0σ(I)), wR2 0.0922, R1 0.0480 (all data),
wR2 0.0987 (all data), S 1.037.
(b) M. H. Dickman, J. P. Ward, F. A. Villamena, D. R. Crist, Acta
Crystallogr. C 1998, 54, 929. doi:10.1107/S0108270198000730
(c) F. A. Villamena, M. H. Dickman, D. R. Crist, Inorg. Chem. 1998,
37, 1446. doi:10.1021/IC9709741
(d) F. A. Villamena, M. H. Dickman, D. R. Crist, Inorg. Chem. 1998,
37, 1454. doi:10.1021/IC971215L
14: C42H31ClN2NiO4, M 721.85, red needle, triclinic, space
group P-1, a 9.6098(4), b 12.0443(5), c 16.1292(7) Å, α
85.154(2), β 86.882(2), γ 66.725(2)◦, U 1708.34(12) Å3, Z 2,
D 1.403 Mg m−3, µ(MoKα) 0.693 mm−1, F(000) 748, T 100 K,
31160 reflections, 7710 unique (Rint 0.0334), R1 0.0466 (7710
reflections, I >2.0σ(I)), wR2 0.1209, R1 0.0626 (all data), wR2
0.1278 (all data), S 1.094.
[8] (a) R. G. Hicks, M. T. Lemaire, L. K. Thompson, T. M. Barclay, J. Am.
Chem. Soc. 2000, 122, 8077. doi:10.1021/JA001627K
(b)T. M. Barclay, R. G. Hicks, M. T. Lemaire, L. K. Thompson, Inorg.
Chem. 2001, 40, 5581. doi:10.1021/IC010542X
[9] (a) L. M. Field, P. M. Lahti, Inorg. Chem. 2003, 42, 7447.
doi:10.1021/IC0349050
(b) M. Baskett, P. M. Lahti, A. Paduan-Filho, N. F. Oliveira, Jr, Inorg.
Chem. 2005, 44, 6725. doi:10.1021/IC050435T
[10] (a) A. Caneschi, D. Gatteschi, J. Laugier, P. Rey, R. Sessoli, Inorg.
Chem. 1988, 27, 1553. doi:10.1021/IC00282A009
Acknowledgements
(b) A. Caneschi, D. Gatteschi, J. P. Renard, P. Rey, R. Sessoli, Inorg.
Chem. 1989, 28, 2940. doi:10.1021/IC00314A013
(c) D. Luneau, G. Risoan, P. Rey,A. Caneschi, D. Gatteschi, J. Laugier,
Inorg. Chem. 1993, 32, 5616. doi:10.1021/IC00076A032
[11] F. A. Villamena, V. Horak, D. R. Crist, Inorg. Chim. Acta 2003, 342,
125. doi:10.1016/S0020-1693(02)01154-4
[12] S. Kudo, A. Iwase, N. Tanaka, Inorg. Chem. 1985, 24, 2388.
doi:10.1021/IC00209A015
[13] G. M. Denison, A. O. Evans, C. A. Bessel, D. W. Skaf, R. W.
Murray, J. M. DeSimone, J. Electrochem. Soc. 2005, 152, B435.
doi:10.1149/1.2047387
[14] P. Harding, D. J. Harding,W. Phonsri, S. Saithong, H. Phetmung, Inorg.
Chim. Acta 2009, 362, 78. doi:10.1016/J.ICA.2008.03.014
[15] S. Dehghanpour, A. Mahmoudi, Main Group Chemistry 2007, 6, 121.
doi:10.1080/10241220801889025
[16] S. Dehghanpour, N. Bouslimani, R. Welter, F. Mojahed, Polyhedron
2007, 26, 154. doi:10.1016/J.POLY.2006.08.011
[17] A. C. G. Hotze, J. A. Faiz, N. Mourtzis, G. I. Pascu, P. R. A. Webber,
G. J. Clarkson, K. Yannakopoulou, Z. Pikramenou, M. J. Hannon,
Dalton Trans. 2006, 3025. doi:10.1039/B518027A
We gratefully acknowledge the Thailand Research Fund and Walailak Uni-
versity (Grant No. RSA5080007) for funding this research. We also thank
the School of Chemistry, University of Bristol for elemental analysis and
MS services.
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