Effect of the β-diketonate ligand on the spin states of [Ni(β-dkt)2(NH2-quin) complexes

Article abstract of DOI:10.1016/j.poly.2011.08.014

Three new complexes [Ni(β-dkt)₂(NH₂-quin) {β-dkt = 2,2,6,6-tetramethylheptane-3,3-dionate (tmhd) 1, hexafluoroacetylacetonate (hfac) 2, 1,3-diphenylpropanedionate (dbm) 3} have been prepared by reacting [Ni(β-dkt)₂(H₂O) ₂ with 8-aminoquinoline (NH₂-quin). [Ni(tmhd) ₂(NH₂-quin) is found to be solvatochromic exhibiting a square planar geometry in CH₂Cl₂, acetone, and acetonitrile with the tmhd ligand acting unusually as a counteranion while in THF and DMSO the complex is octahedral. In contrast, 2 and 3 are octahedral in all solvents. Single crystal X-ray diffraction studies reveal octahedral nickel centres with a cis arrangement of the β-diketonates. The molecular packing consists of hydrogen bonded dimers which in the case of 2 and 3 are connected to one another via π?π and C-H?π interactions, respectively. Cyclic voltammetry shows 1 and 3 oxidise irreversibly at 0.46 and 1.17 V, respectively.

Full text of DOI:10.1016/j.poly.2011.08.014

Polyhedron 30 (2011) 2740–2745
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Polyhedron
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Effect of the b-diketonate ligand on the spin states
of [Ni(b-dkt)2(NH2-quin)] complexes
a
b
Darunee Sertphon a, David J. Harding a, , Phimphaka Harding , Harry Adams
⇑
a Molecular Technology Research Unit, School of Science, Walailak University, Thasala, Nakhon Si Thammarat 80161, Thailand
b Department of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Three new complexes [Ni(b-dkt)2(NH2-quin)] {b-dkt = 2,2,6,6-tetramethylheptane-3,3-dionate (tmhd) 1,
hexafluoroacetylacetonate (hfac) 2, 1,3-diphenylpropanedionate (dbm) 3} have been prepared by react-
ing [Ni(b-dkt)2(H2O)2] with 8-aminoquinoline (NH2-quin). [Ni(tmhd)2(NH2-quin)] is found to be solvato-
chromic exhibiting a square planar geometry in CH2Cl2, acetone, and acetonitrile with the tmhd ligand
acting unusually as a counteranion while in THF and DMSO the complex is octahedral. In contrast, 2
and 3 are octahedral in all solvents. Single crystal X-ray diffraction studies reveal octahedral nickel cen-
tres with a cis arrangement of the b-diketonates. The molecular packing consists of hydrogen bonded
Received 18 June 2011
Accepted 10 August 2011
Available online 18 August 2011
Keywords:
Nickel(II) b-diketonates
Square planar-octahedral geometries
Solvatochromism
X-ray crystallography
Cyclic voltammetry
dimers which in the case of 2 and 3 are connected to one another via
respectively. Cyclic voltammetry shows 1 and 3 oxidise irreversibly at 0.46 and 1.17 V, respectively.
p
ꢀꢀꢀ
p
and C–Hꢀ ꢀ ꢀ
p interactions,
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
solid state and either high spin or low spin (S = 0) in solution
depending on the solvent.
The control of spin states remains a considerable challenge in
chemistry and is important because of the potential application that
such compounds may have as molecular switches and devices [1–3].
In the case of Ni(II), square planar complexes have an S = 0 spin state
while octahedral complexes have an S = 1 spin state. Thus, a change
in spin state can be affected simply by coordination of additional li-
gands to the square planar complex [4,5]. Of particular relevance to
this paper is the [Ni(b-dkt)(N–N)]+ (b-dkt = b-diketonate, N–
N = bulky diamine) series prepared by Fukuda and co-workers
who found the use of a bulky diamine allowed isolation of the square
planar species [6–8], previously known only with diphosphines
[Ni(b-dkt)(P–P)]+ [9], while at the same time permitting access to
the octahedral complex in donor solvents. Tanaka and co-workers
have also reported square planar complexes [Ni(Py(Bz)2)(tmhd)]PF6
2. Results and discussion
2.1. Synthesis and IR spectroscopic studies of [Ni(b-dkt)2(NH2-quin)]
The addition of NH2-quin to a solution of [Ni(b-dkt)2(H2O)2]
yields the expected [Ni(b-dkt)2(NH2-quin)] {b-dkt = 2,2,6,6-tetra-
methylheptane-3,3-dionate (tmhd) 1, hexafluoroacetylacetonate
(hfac) 2, 1,3-diphenylpropanedionate (dbm) 3} complexes in mod-
erate to excellent yield as blue-green or green solids (Scheme 1 and
Table 1). Interestingly, while all the solids are green the reaction
mixture in the case of 1 was red-purple suggesting that complex
in solution and that in the solid state were different a fact later con-
firmed by UV–Vis spectroscopy (vide infra). IR spectroscopy reveals
an NH stretch between 3286 and 3436 cmꢁ1 consistent with the
presence of a coordinated amino group from the NH2-quin ligand.
Further bands between 1645 and 1582 cmꢁ1 are typical of chelating
b-diketonate ligands with the position dependent on the substitu-
ent groups on the b-diketonate ligand and similar to those reported
for [Ni(b-dkt)2(N–N)] (N–N = diamine, diimine) [11–13].
{Py(Bz)2 = N,N-bis(benzyl)-N-[(2-pyridyl)methyl]amine;
tmhd =
2,2,6,6-tetramethyl-heptane-3,5-dionate} this time with a tertiary
amine–imine ligand [10]. In both instances, the complexes exhibit
solvatochromism and thermochromism. While the physical proper-
ties of these compounds have been well studied the redox chemistry
of these systems and the effect this may have on the change in spin
states is poorly understood [11,12]. In this paper we explore a new
series [Ni(b-dkt)2(NH2-quin)] (NH2-quin = 8-aminoquinoline), in
which unusually [Ni(tmhd)2(NH2-quin)] is high spin (S = 1) in the
2.2. Electronic spectra of [Ni(b-dkt)2(NH2-quin)] 1–3 in coordinating
and non-coordinating solvents
The unusual colour of the reaction mixture for 1 led us to inves-
tigate the electronic spectra of 1–3 in a variety of different solvents
(Table 2). In the case of 2 and 3 there are low intensity peaks above
⇑
Corresponding author. Tel.: +66 75 672094; fax: +66 75 672004.
E-mail address: hdavid@wu.ac.th (D.J. Harding).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.08.014

D. Sertphon et al. / Polyhedron 30 (2011) 2740–2745
2741
Scheme 1. Synthesis of [Ni(b-dkt)2(NH2-quin)] 1–3.
Table 1
and acetonitrile the solution is red-purple and there is an intense
band between 525 and 528 nm consistent with a four-coordinate
square planar nickel centre and assigned to a 1A1g ? 1A2g transition
[14]. However, in strong donor solvents such as DMSO or THF the
solution becomes green and bands at 550 and 672 nm are observed
indicative of an octahedral nickel centre suggesting coordination of
the solvent molecules (Fig. 1). Interestingly, solvatochromic Ni(II)
complexes typically require non-coordinating anions such as BPh4
or PF6 and when coordinating anions such as nitrate are present
the complex is invariably six coordinate [6–8,10]. In this system
the second tmhd ligand acts as a counteranion in all complexes
and is to the best of our knowledge unprecedented. It is possible
that the larger tmhd ligand is better able to stabilize the four coor-
dinate complex compared with the hfac and dbm ligands, although
electronic effects may also be important as the hfac and dbm li-
gands would be expected to make the nickel centre more electron
poor thus favouring an octahedral geometry.
Physical and IR spectroscopic data for [Ni(b-dkt)2(NH2-quin)] 1–3.
a
Compound
Yield
(%)
Colour
IR (cmꢁ1
)
mNH
mCO
mCN
[Ni(tmhd)2(NH2-
quin)] 1
[Ni(hfac)2(NH2-quin)] 80
2
[Ni(dbm)2(NH2-
quin)] 3
34
Green
3339(m) 1582(s) 1420(s)
3286(m) 1645(s) 1489(s)
3436(m) 1595(s) 1478(s)
Blue-
green
Green
66
a
In KBr.
Table 2
UV–Vis spectroscopic data of 1–3.
Complex Solvent kmax/nm (e)
1
CH2Cl2
254 (38 040), 276 (26 080), 315 (4380), 332 (3190),
528 (860), 671sh (170)
Acetone
525 (570), 665 (100)
2.3. Structural studies of [Ni(b-dkt)2(NH2-quin)] 1–3
Acetonitrile 526 (632), 653 (101)
THF
505 (80), 634 (60)
511 (80), 676 (70)
351 (22 400), 616 (12), 672 (6), 797 (4)
252 (45 850), 340 (51 970), 672 (15)
Crystals of 1 were grown by slow evaporation of CH2Cl2/hexane
solution while those of 2 and 3 were grown by allowing a solution
of the complex in CH2Cl2 to diffuse into hexane. The structure of 1
is shown in Fig. 2 as a representative example while selected bond
lengths and angles are given in Table 3. It should noted that the
structure of 1 contains two independent molecules in the asym-
metric unit while that of 3 contains CH2Cl2 as a solvent of crystal-
lization. The structures are all broadly similar with an octahedrally
coordinated Ni centre and cis-coordinated b-diketonate ligands
DMSO
CH2Cl2
CH2Cl2
2
3
600 nm in all solvents typical of d–d transitions for octahedral nick-
el complexes. The band at 672 nm is assigned to the 3A2g ? 3T1g (F)
transition by comparison with [Ni(Py(Bz)2)(tmhd)]PF6 [10]. In con-
trast, 1 clearly exhibits solvatochromism. Thus, in CH2Cl2, acetone
Fig. 1. UV–Vis spectra of [Ni(tmhd)2(NH2-quin)] 1 in CH2Cl2, MeCN, acetone, THF and DMSO.

2742
D. Sertphon et al. / Polyhedron 30 (2011) 2740–2745
Fig. 3. POVRAY diagram of [Ni(hfac)2(NH2-quin)] 2 showing the NHꢀ ꢀ ꢀO hydrogen
bonds.
Fig. 2. POVRAY diagram of [Ni(tmhd)2(NH2-quin)] 1, drawn with 50% ellipsoids.
Only one of the independent molecules and the amino hydrogens are shown for
clarity.
Table 3
Bond lengths and angles for [Ni(b-dkt)2(NH2-quin)] 1–3 (Å, °).
1
1a
2
3
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)
b
2.021(4)
2.032(4)
2.038(4)
2.024(4)
2.122(4)
2.118(5)
89.32(15)
87.50(15)
79.20(17)
22.33
2.025(4)
2.023(3)
2.041(4)
1.994(4)
2.116(4)
2.134(5)
90.08(15)
88.61(15)
77.84(16)
7.11
2.063(14)
2.057(14)
2.053(13)
2.025(14)
2.066(16)
2.079(17)
88.78(6)
90.26(5)
81.08(7)
1.44
2.035(2)
2.022(2)
2.055(2)
2.041(2)
2.083(2)
2.098(2)
90.54(8)
88.79(8)
80.58(9)
22.79
Fig. 4. POVRAY diagram of [Ni(hfac)2(NH2-quin)] 2 showing the
Symmetry code: (i) ꢁx, 1 ꢁ y, 1 ꢁ z.
pꢀ ꢀ ꢀp interactions.
13.51
25.18
6.80
13.24
interactions in which one of the aromatic rings of the NH2-quin li-
gand overlaps with its neighbour {Cg 1ꢀ ꢀ ꢀCg1* = 3.521(4) Å where
Cg1 is the centroid of C11 ? C15,N1 and * = symmetry code = ꢁx,
1 ꢁ y, 1 ꢁ z; see Fig. 4}. The combination of this with the H-bonding
interaction results in formation of a 1D chain. However, in the
enforced by the chelating NH2-quin ligand. The Ni–O bond lengths
vary from 1.994 to 2.063 Å with 1 exhibiting on average the short-
est bonds despite the tmhd ligand having the largest steric bulk. In
contrast, the Ni–N bond lengths are shortest for 2 and longest for 1
with the difference between the average Ni–N bond lengths ca.
0.05 Å. The difference is probably due to the more electron with-
drawing CF3 groups of the hfac ligand which makes the metal cen-
tre more electron poor and hence shortens the Ni–N bond. Similar
Ni–O and Ni–N bond lengths are found in [Ni(Py(Bz)2)(tmhd)(-
NO3)] [10]. In the case of 1 and 3, the nickel centre lies slightly
above the plane of one of the b-diketonate ligands in a ‘bent’ coor-
dination mode, while the other b-diketonate ligand exhibits a ‘pla-
nar’ coordination mode [11,12]. A similar ‘planar’ coordination
mode is found for both hfac ligands in 2 consistent with the smaller
steric bulk of the hfac ligand.
There are two sets of N–HꢀꢀꢀO interactions between the amino
protons of the NH2-quin ligand and the coordinated O atoms of
the b-diketonate forming discrete dimers (Fig. 3). Similar interac-
tions are also found in [Ni(dbm)2(dmae)] (dmae = dimethylamino-
ethylamine) and appear to be a feature of these types of compounds
[11]. Interestingly, in 1 the H-bonds are virtually identical differing
by only 0.01 Å, while in 2 and 3 the difference is 0.43–0.49 Å (Table
S1). The reason for this striking difference is unclear. In addition to
structure of 3 this interaction is replaced by two C–Hꢀ ꢀ ꢀ
p interac-
tions between a hydrogen atom on the NH2-quin ligand and the
aromatic rings of the dbm phenyl group thereby forming a square
{C3–H3ꢀꢀꢀ
p (C19 ? C24) 2.587 Å, see Fig. 5}. This change in the type
of interaction may be due to the larger bulk of the dbm ligand com-
pared with the hfac ligand.
2.4. Electrochemical studies of [Ni(b-dkt)2(NH2-quin)] 1–3
The complexes 1–3 have been studied by cyclic voltammetry
(CV) in dry CH2Cl2 under inert conditions and reveal irreversible
one-electron oxidation for complexes 1 and 3 while in the case
of 2 there is no oxidation observed within the solvent window.
The CVs of [Ni(tmhd)(NH2-quin)][tmhd] 1 and [Ni(dbm)2(NH2-
quin)] 3 are shown in Fig. 6. The cyclic voltammogram of the
dbm complex 3 is similar to that of other [Ni(dbm)2(N–N)] (N–
N = phen and bipy) complexes with an oxidation potential of
1.17 V. Although the previously reported [Ni(tmhd)2(N–N)] (N–
N = diimine ligands) complexes exhibit reversible oxidation waves
H-bonding interactions, the structure of
2
also has
pꢀ ꢀ ꢀp

D. Sertphon et al. / Polyhedron 30 (2011) 2740–2745
2743
Fig. 5. POVRAY diagram of [Ni(dbm)2(NH2-quin)] 3 showing the C–Hꢀ ꢀ ꢀ
p
interactions. Symmetry code: (i) ꢁ1 ꢁ x, 2 ꢁ y, 1 ꢁ z.
Fig. 6. Cyclic voltammogram of [Ni(tmhd)(NH2-quin)][tmhd] 1 and [Ni(dbm)2(NH2-quin)] 3 at scan rate 100 mV/s.
at ca. 0.85 V the oxidation potential for the tmhd complex 1 is
much lower at 0.46 V and irreversible consistent with the square
planar geometry of complex 1 in an inert solvent such as CH2Cl2
[11,12]. As noted in the introduction the lack of other redox studies
on such systems makes further comparison difficult.
prepared by literature methods [15,16]. All other chemicals were
purchased from Fluka Chemical Company and used as received.
Elemental analyses and ESI-MS were carried out by the staff of
the School of Chemistry, University of Bristol, UK. Elemental anal-
yses were carried out on a Eurovector EA3000 analyser. ESI-MS
were carried out on a Bruker Daltonics 7.0T Apex 4 FTICR Mass
Spectrometer.
3. Experimental
3.1. Materials
3.2. Spectroscopy
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
Infrared spectra, as KBr discs, were recorded on a Perkin-Elmer
Spectrum One infrared spectrophotometer in the range

2744
D. Sertphon et al. / Polyhedron 30 (2011) 2740–2745
400–4000 cmꢁ1. Electronic spectra were recorded in HPLC grade sol-
vents on a Shimidzu UV1700 UV–Vis spectrometer between 200 and
900 nm.
3.5. Synthesis of [Ni(tmhd)2(NH2-quin)] 1
To a pale purple solution of [Ni(tmhd)2(H2O)2] (0.9338 g,
2 mmol) in CH2Cl2 (10 cm3) was added 8-aminoquinoline
(0.2884 g, 2 mmol). After stirring for 2 h the red-purple solution
was evaporated to low volume (ca. 2 cm3) and then hexane
(15 cm3) was added. The mixture was allowed to evaporate slowly
3.3. X-ray crystallography
Crystal data and data processing parameters for the structures
of 1, 2 and 3 are given in Tables 3 and 4. X-ray quality crystals of
2 and 3 were grown by allowing hexane to diffuse into a concen-
trated solution of the complex in CH2Cl2 while those of 1 were
grown by slow evaporation of solution of 1 in CH2Cl2/hexane.
Crystals were mounted on a glass fibre using perfluoropolyether
oil and cooled rapidly to 100 K in a stream of cold nitrogen. All
diffraction data were collected on a Bruker APEX II area detector
to yield green crystals 0.3911 g (34%).
m
max(KBr)/cmꢁ1 3339 (
m
NH),
1582 (mCO), 1420 (mC@N). UV–Vis kmax(CH2Cl2)/nm (e
, dm3 molꢁ1
cmꢁ1) 254 (38 040), 276 (26 080), 315 (4380), 332 (3190), 528
(860), 671sh (170). m/z (ESI) 385 [Mꢁtmhd]+. Anal. Calc. for
C31H46N2O4Ni: C, 65.39; H, 8.14; N, 4.92. Found: C, 65.22; H, 8.11;
N, 4.69%.
3.6. Synthesis of [Ni(hfac)2(NH2-quin)] 2
with graphite monochromated Mo K
a (k = 0.71073 Å). After data
collection, in each case an empirical absorption correction (SADABS
)
To
a blue-green solution of [Ni(hfac)2(H2O)2] (0.2574 g,
was applied [17] and the structures were then solved by direct
methods and refined on all F2 data using the SHELX suite of pro-
grams [18]. In all cases non-hydrogen atoms were refined with
anisotropic thermal parameters; hydrogen atoms were included
in calculated positions and refined with isotropic thermal param-
eters which were ca. 1.2 ꢂ (aromatic CH) or 1.5 ꢂ (Me) the equiv-
alent isotropic thermal parameters of their parent carbon atoms.
In the structure of 1 the CH2Cl2 molecule was disordered and this
was modelled by splitting the molecule into two parts. Similar
disorder was found in some of the CF3 groups of 2 which were
also modelled over two positions. X-SEED was used as a graphical
interface with SHELX and pictures were generated using POV-Ray
[19,20].
0.5 mmol) in CH2Cl2 (10 cm3) was added 8-aminoquinoline
(0.0721 g, 0.5 mmol). After stirring for 2 h the deep blue-green
solution was evaporated to low volume (ca. 2 cm3) before hexane
(5 cm3) was added giving a green precipitate. The green solid
was filtered then washed with hexane (2 ꢂ 3 cm3) and air dried
to yield a blue-green microcrystals 0.248 g (80%). X-ray quality
crystals were grown by layering a CH2Cl2 solution with hexane
(10 cm3) leading to blue-green crystals after 2 days.
cmꢁ1 3286 (
NH), 1645 ( CO), 1489 ( C@N). UV–Vis kmax(CH2Cl2)/
nm (
mmax(KBr)/
m
m
m
e
, dm3 molꢁ1 cmꢁ1) 351 (22 400), 616 (12), 672 (6), 797 (4).
m/z (ESI) 409 [Mꢁhfac]+. Anal. Calc. for C19H10N2O4F12Ni: C,
36.99; H, 1.63; N, 4.54. Found: C, 36.72; H, 1.54; N, 4.55%.
3.7. Synthesis of [Ni(dbm)2(NH2-quin)].CH2Cl2
3
3.4. Electrochemistry
Synthesized using the procedure of 2, dark green crystals
recrystallized from CH2Cl2/hexane, 66% yield.
max(KBr)/cmꢁ1
C@N). UV–Vis kmax(CH2Cl2)/nm (
Electrochemical studies were carried out using a palmsensPC Vs
2.11 potentiostat in conjunction with a three electrode cell. The
auxiliary electrode was a platinum rod and the working electrode
was a platinum disc (2.0 mm diameter). The reference electrode
was a Ag–AgCl electrode. Solutions were 5 ꢂ 10ꢁ4 M in the test
m
3436 (
m
NH), 1595 (
m
CO), 1478 (
m
e,
dm3 molꢁ1 cmꢁ1) 252 (45 850), 340 (51 970), 672 (15). m/z (ESI)
449 [MꢁCH2Cl2ꢁdbm]+. Anal. Calc. for C40H32N2O4Cl2Ni: C, 65.43;
H, 4.93; N, 3.82. Found: C, 65.67; H, 4.84; N, 3.99%.
compound and 0.1 M in [NBun4][PF6] as the supporting electrolyte.
0
Under these conditions, Eo for the one-electron oxidation of [Fe(
g
-
4. Conclusions
C5H5)2] added to the test solutions as an internal calibrant is
0.52 V.
In conclusion, we have successfully prepared three novel [Ni(b-
dkt)2(NH2-quin)] complexes which while exhibiting the same octa-
hedral geometry in the solid state, in solution the geometry de-
pends principally upon the type of b-diketonate and in the case
of tmhd on the nature of the solvent. The wide variety of b-diketo-
nate ligands available combined with an easily modifiable amino-
quinoline framework makes this a promising system for further
study in the development of molecular switches.
Table 4
Crystallographic data and structure refinement for complexes 1–3.
Complex
1 tmhd
2 hfac
3 dbm
Chemical formula
Formula weight
Crystal system
Space group
C
31H46N2NiO4 C19H10F12N2NiO4 C40H32Cl2N2NiO4
569.41
triclinic
617.00
triclinic
734.29
triclinic
P1
P1
P1
a (Å)
b (Å)
c (Å)
12.0928(13)
14.8973(17)
19.744(2)
69.521(6)
87.000(6)
69.481(5)
3110.6(6)
2
9.7729(2)
10.2521(2)
12.3288(3)
113.2910(10)
91.5050(10
95.1900(10)
1127.34(4)
2
11.083(3)
11.273(3)
15.259(4)
88.488(14)
70.406(12)
77.383(13)
1750.4(8)
2
Acknowledgements
We gratefully acknowledge the Royal Society of Chemistry for a
JWT Jones Travelling Fellowship and a Research Fund award (both
to DJH) which partially funded this research. A research grant from
Walailak University (Grant No.: WU53204 to PH) is also acknowl-
edged. Finally, we thank the National Science and Technology
Development Agency for a scholarship (awarded to DS).
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g cmꢁ3
)
1.216
0.659
1.818
0.990
1.393
0.751
l
(Mo K
a
) (mmꢁ1
)
T (K)
150(2)
293(2)
293(2)
Reflections collected
Independent
43 823
19 933
15 283
7992, 0.036
Appendix A. Supplementary data
13 878, 0.091 5206, 0.0139
reflections, (Rint
R1, wR2 [I > 2 (I)]
)
r
0.0787,
0.2252
0.1716,
0.2925
0.0363, 0.0909
0.0395, 0.0939
0.0550, 0.1354
0.0776, 0.1503
CCDC 838299, 838300 and 838301 contain the supplementary
crystallographic data for 1, 2 and 3. 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,
R1, wR2 (all data)

D. Sertphon et al. / Polyhedron 30 (2011) 2740–2745
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2745
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.2011.08.014.
[11] P. Harding, D.J. Harding, W. Phonsri, S. Saithong, H. Phetmung, Inorg. Chim.
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Aust. J. Chem. 63 (2010) 75.
[13] K. Nakamoto, in: Infrared and Raman Spectra of Inorganic and Coordination
Compounds: Part B, sixth ed., John Wiley and Sons, New Jersey, 2009, pp. 96–
100.
[14] A.B.P. Lever, Inorganic Electronic Spectroscopy, second ed., Elsevier Science,
Amsterdam, The Netherlands, 1984.
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Chemistry, sixth ed., John Wiley and Sons, New York, 1999, pp. 479–
482.
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