Diphenyl(dipyrazolyl)methane complexes of Ni: Synthesis, structural characterization, and chromotropism of NiBr2 derivatives

Article abstract of DOI:10.1021/ic070093m

The reaction of NiBr₂ with the bidentate ligand diphenyl(dipyrazolyl)methane (dpdpm) gives the pentacoordinated complexes [(dpdpm)Ni(μ-Br)Br]₂ (1), [(dpdpm)NiBr₂(H ₂O)] (2a), and [(dpdpm)NiBr(H₂O)₂]Br (2b), or the octahedral complexes [(dpdpm)NiBr(H₂O)₂(CH ₃CN)]Br (3), [(dpdpm)₂NiBr₂] (4), and [(dpdpm)₂NiBr(H₂O)]Br (5). All of these complexes are paramagnetic, both in the solid state and in solution, and have been characterized by spectroscopic (IR, NMR, and UV-vis-NIR) and X-ray diffraction studies. The unoccupied coordination site in the pentacoordinated compounds allows long-range interactions, in the solid state, between the Ni center and a Ph substituent of the dpdpm ligand. These weak interactions are replaced by Ni-solvent interactions, both in the solid state and in solution, facilitating the interconversion of these compounds under various reaction conditions and leading to interesting solvato-, vapo-, and thermochromic properties. UV-vis-NIR spectroscopy has been used to study these phenomena. Absorption spectra for the room-temperature methanol or acetonitrile solutions of the pentacoordinate or octahedral compounds show three main bands in the region of 350-1000 nm that represent spin-allowed (d-d) transitions from the ground state ³A_2g to the excited states ³T_2g, ³T_1g(³F), and ³T_1g( ³P). A weak shoulder was also detected on the middle peak in most spectra (700-800 nm), representing the spin-forbidden ³A_2g → ¹Eg transition. On the other hand, the spectra of high-temperature CH₂Cl₂ or acetone solutions of all complexes show four main bands at ca. 490, 650-660, 860, and 1000 nm, in addition to a shoulder on the first or second band.

Full text of DOI:10.1021/ic070093m

Inorg. Chem. 2007, 46, 7621−7632
Diphenyl(dipyrazolyl)methane Complexes of Ni: Synthesis, Structural
Characterization, and Chromotropism of NiBr2 Derivatives
Natalie Baho and Davit Zargarian*
De´partement de Chimie, UniVersite´ de Montre´al, C. P. 6128, Succursale Centre-Ville,
Montre´al, Que´bec, Canada H3C 3J7
Received January 18, 2007
The reaction of NiBr2 with the bidentate ligand diphenyl(dipyrazolyl)methane (dpdpm) gives the pentacoordinated
complexes [(dpdpm)Ni( -Br)Br]2 (1), [(dpdpm)NiBr2(H2O)] (2a), and [(dpdpm)NiBr(H2O)2]Br (2b), or the octahedral
µ
complexes [(dpdpm)NiBr(H2O)2(CH3CN)]Br (3), [(dpdpm)2NiBr2] (4), and [(dpdpm)2NiBr(H2O)]Br (5). All of these
complexes are paramagnetic, both in the solid state and in solution, and have been characterized by spectroscopic
(IR, NMR, and UV
compounds allows long-range interactions, in the solid state, between the Ni center and a Ph substituent of the
dpdpm ligand. These weak interactions are replaced by Ni solvent interactions, both in the solid state and in
solution, facilitating the interconversion of these compounds under various reaction conditions and leading to interesting
solvato-, vapo-, and thermochromic properties. UV vis NIR spectroscopy has been used to study these phenomena.
Absorption spectra for the room-temperature methanol or acetonitrile solutions of the pentacoordinate or octahedral
−vis−NIR) and X-ray diffraction studies. The unoccupied coordination site in the pentacoordinated
−
−
−
compounds show three main bands in the region of 350
−
1000 nm that represent spin-allowed (d
−
d) transitions
3
3
3
3
from the ground state A2g to the excited states T2g, T1g(3F), and T1g(3P). A weak shoulder was also detected on
3
the middle peak in most spectra (700
−800 nm), representing the spin-forbidden A2g
f
1Eg transition. On the
other hand, the spectra of high-temperature CH2Cl2 or acetone solutions of all complexes show four main bands
at ca. 490, 650 660, 860, and 1000 nm, in addition to a shoulder on the first or second band.
−
Introduction
protocols, thereby allowing a fine-tuning of ligand proper-
ties.4 The anionic bis- or tris(pyrazolyl)borates have been
used in the preparation of a wide range of coordination and
organometallic complexes, including species featuring metals
Scorpionate-type poly(pyrazolyl)borate1 and poly(pyra-
zolyl)alkane2 ligands have found wide applications in
coordination, organometallic, and bioinorganic chemistry.3
The increasing interest in these ligands is due to their
generally robust nature and the ease with which their steric
and electronic properties can be modified via simple synthetic
(3) For a few recent reports and reviews on the development of the
coordination chemistry of scorpionate ligands see: (a) Tang, T.; Wang,
Z.; Xu, Y.; Wang, J.; Wang, H.; Yao, X. Polyhedron 1999, 18, 2383.
(b) Sa´nchez, G.; Serrano, L. J.; Pe´rez, J.; Ram´ırez de Arellano, M.
C.; Lo´pez, G.; Molins, E. Inorg. Chim. Acta 1999, 295, 136. (c)
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Chem. 2001, 626, 16. (f) Mattini, D.; Pellei, M.; Pettinari, C.; Skelton,
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H.; Tang, L.-F.; Jia, W.-L.; Wang, J.-T.; Wang, H.-G. Polyhedron
2002, 21, 873. (h) Kla¨ui, W.; Berghahn, M.; Frank, W.; Reiss, G. J.;
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* To whom correspondence should be addressed. Tel: 514-343-2247.
Fax: 514-343-2468. E-mail: zargarian.davit@umontreal.ca.
(1) (a) Trofimenko, S.; Calabrese, J. C.; Thompson, S. J. Inorg. Chem.
1987, 26, 1507. (b) Trofimenko, S. J. A. Chem. Soc. 1970, 92, 5118.
(c) Trofimenko, S.; Calabrese, J. C.; Domaille, P. J.; Thompson, J. S.
Inorg. Chem. 1989, 28, 1091. (d) Paulo, A.; Correia, J. D. G.; Santos,
I. ReV. Inorg. Chem. 1998, 5, 57. (e) Uehara, K.; Hikichi, S.; Akita,
M. J. Chem. Soc., Dalton Trans. 2002, 3529. (f) Santi, R.; Romano,
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10.1021/ic070093m CCC: $37.00
Published on Web 08/01/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 18, 2007 7621

Baho and Zargarian
in their less common oxidation states such as Pd(IV)5,6 and
Pt(IV).5,7 In contrast, the neutral bis- and tris(pyrazolyl)-
alkanes appear to be less suitable for the preparation of
complexes featuring strong-field co-ligands such as hydride,
alkyls, aryls, etc.8 As a result, poly(pyrazolyl)alkanes have
had less impact in organometallic chemistry, particularly in
the case of late transition metals of the first row such as
nickel for which no organometallic complex has been
reported.9,10
Our interest in the chemistry of organonickel complexes11
has prompted us to explore the structures and reactivities of
nickel complexes based on poly(pyrazolyl)alkanes. Our initial
studies focused on the reactions of Ni(NO3)2 with the ligands
bis- and tris(3,5-dimethylpyrazolyl)methane (bpm* and
tpm*),12 bis(pyrazolyl)propane (bpp),13 and diphenyl(dipyra-
zolyl)methane (dpdpm).14 The complexes arising from these
reactions are octahedral species featuring mono- and/or
bidentate nitrate ligands. Our results to date show that these
compounds cannot serve as suitable precursors for the
preparation of organometallic species, but many of them
exhibit interesting solvato-, vapo-, and thermochromic
properties, owing to the labile coordination of the nitrate
ligand.14 Indeed, literature reports show that several nickel
complexes featuring polydentate amine or imine-type ligands
display solvato- and thermochromic behavior arising from
displacement of labile ligands by solvent molecules or
counterions. In the case of coordination complexes, solva-
tochromism refers to changes in the electronic absorption
spectra due to weak dipole interactions or hydrogen bonds
with solvent molecules or a strong and specific interaction
between the solvent and the metal center.15 Solvato- and
thermochromism can also involve various types of structural
isomerism such as monomer-dimer equilibria, some ex-
amples of which have been reported for [Ni(L-L)Cl2]2
wherein L-L is a bidentate, N-based ligand.16
As a continuation of our earlier studies,12-14 we are
investigating the structures and chromotropic properties of
complexes arising from the reactions of other nickel(II) salts
with poly(pyrazolyl)alkane ligands. The present report
describes the synthesis, structural characterization, and
solvato-, vapo-, and thermochromic behavior of the NiBr2
derivatives of dpdpm, namely, [(dpdpm)Ni(µ-Br)Br]2 (1),
[(dpdpm)NiBr2(H2O)] (2a), [(dpdpm)NiBr(H2O)2]Br (2b),
[(dpdpm)NiBr(H2O)2(CH3CN)]Br (3), [(dpdpm)2NiBr2] (4),
and [(dpdpm)2NiBr(H2O)]Br (5). Complexes featuring the
dpdpm ligand have been reported for Cu,17 Mo,18 Ag,19 and
Pd.10c
Results and Discussion
Synthesis of the Complexes. The outcome of the reaction
between NiBr2 and dpdpm depends on a few parameters,
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7622 Inorganic Chemistry, Vol. 46, No. 18, 2007

Diphenyl(dipyrazolyl)methane Complexes of Ni
Scheme 1
Scheme 2
Interestingly, recrystallizing the dark green solid from
acetone/hexane gave light green crystals identified as the
cationic bis(aquo) species 2b. Finally, overnight stirring of
a 1:1 mixture of NiBr2 and dpdpm in acetonitrile at room
temperature gave a dark green solution; removal of the
solvent produced a dark green powder (crude yield 85%),
which was recrystallized from acetonitrile/Et2O to give lime
green crystals of the octahedral species 3.
It is noteworthy that, under appropriate recrystallization
conditions, all of the new products mentioned above can be
derived from a common species obtained from the 1:1
reaction of NiBr2 and dpdpm in acetone at room temperature,
as shown in Scheme 2. Thus, allowing Et2O vapors to diffuse
into concentrated acetone solutions of the dark green solid
at 25-30 °C and with minimum exposure to humid air gave
brown crystals that were identified by X-ray diffraction
studies as 1. Alternatively, recrystallization from acetone/
Et2O solutions at lower temperatures (<20 °C) resulted in
the formation of dark green crystals that were identified by
X-ray diffraction studies as the mono(aquo) compound 2a.
Recrystallization attempts at around 0 °C gave blue crystals,
presumably an octahedral bis(aquo) adduct, but we were
unable to characterize this compound because of the poor
quality of the crystals obtained. Finally, recrystallization of
the dark green solid from acetonitrile gave lime green crystals
that were identified as 3.
including the metal/ligand ratio, the reaction temperature,
the coordinating ability of the solvent, and the degree of
residual moisture present in the reaction medium. Thus,
refluxing a 1:1 mixture of NiBr2 and dpdpm in dried and
distilled acetone for 18 h gave a brown suspension, which
was filtered to give a brown solid identified as the dimeric
species 1 (crude yield 79%, Scheme 1). In contrast, carrying
out the reaction in untreated MeOH at room temperature gave
a dark green solid (crude yield 83%) that provided, after
recrystallization from acetone/Et2O, dark green crystals
identified as the monomeric, mono(aquo) compound 2a.
These mono(dpdpm) derivatives can also interconvert
under various experimental conditions (Scheme 2). For
instance, allowing brown crystals of 1 to stand overnight in
the (green) mother liquor, unprotected from ambient atmo-
sphere, turned them into light green crystals that were
Scheme 3
Inorganic Chemistry, Vol. 46, No. 18, 2007 7623

Baho and Zargarian
Figure 1. ORTEP view of complex 1. Thermal ellipsoids are shown at
30% probability.
Figure 4. ORTEP view of complex 3. Thermal ellipsoids are shown at
30% probability. The Br- counterion has been omitted for clarity.
Figure 2. ORTEP view of complex 2a. Thermal ellipsoids are shown at
30% probability.
Figure 5. ORTEP view of complex 4. Thermal ellipsoids are shown at
30% probability.
Figure 6. ORTEP view of complex 5. Thermal ellipsoids are shown at
30% probability. The Br- counterion has been omitted for clarity.
Figure 3. ORTEP view of complex 2b. Thermal ellipsoids are shown at
30% probability. The Br- counterion has been omitted for clarity.
Formation of the pentacoordinated compounds 1, 2a, and
2b from the 1:1 reactions with NiBr2 is in contrast to the
exclusive formation of octahedral products from the 1:1
reactions of Ni(NO3)2 with dpdpm (cf. (dpdpm)Ni(η2-NO3)2,
(dpdpm)Ni(η2-NO3)(η1-NO3)(NCMe).14 Using a 2:1 dpdpm/
NiBr2 ratio gave only octahedral species. Thus, stirring a
methanol mixture of NiBr2 and 2 equiv of dpdpm at room
temperature and under nitrogen produced a green mixture
that was filtered and evaporated to give a green solid;
recrystallization of this solid from CH2Cl2/Et2O under a
nitrogen atmosphere gave green crystals that were identified
by X-ray diffraction studies as the complex 4 (Scheme 3).
When complex 4 was exposed to humidity, both in the solid
identified as 2b. The latter compound was also obtained by
allowing the mono(aquo) species 2a to stand in ambient
atmosphere for 2 days or more, while dissolving 2a in CH3-
CN gave the octahedral species 3. On the other hand, heating
solid samples of 2b or 3 to ca. 100 °C or placing them under
reduced pressure converts these compounds to 1. In the case
of 2a, both heating and reduced pressure were needed to
convert this compound to 1. As will be mentioned later, the
interconversion of complexes 1, 2a, and 2b can be affected
by controlling the temperature of their acetone solutions,
whereas dissolving complex 1 in CH3CN generates complex
3 (vide infra).
7624 Inorganic Chemistry, Vol. 46, No. 18, 2007

Diphenyl(dipyrazolyl)methane Complexes of Ni
Table 1. Crystallographic Data for 1, 2a, 2b, and 3
1
2a
2b‚H2O
3‚CH3CN
formula
Mw
C38H32N8Ni2Br4
1037.78
C19H18N4NiBr2O
536.90
C19H20N4NiBr2O2· H2O
572.94
C19H20N4Br2NiO2·(C2H3N)
637.03
cryst color
cryst dimens, mm3
symmetry
space group
a, Å
light brown
0.21 × 0.12 × 0.09
triclinic
green dark
0.24 × 0.21 × 0.09
monoclinic
P21/n
9.8267(5)
14.4774(7)
14.1184(7)
90
93.890(2)
90
2003.93(17)
4
green
green
0.46 × 0.23 × 0.15
0.96 × 0.24 × 0.18
triclinic
triclinic
P1h
P1h
P1h
8.9395(6)
9.1559(6)
11.8205(8)
84.166(3)
81.795(3)
84.779(3)
949.76(11)
1
10.012(10)
10.8995(10)
11.3825(10)
79.529(10)
65.182(10)
73.380(10)
1077.589(17)
2
9.41210(10)
10.3895(2)
14.6092(2)
81.2430(10)
79.5330(10)
66.8230(10)
1286.28(3)
2
b, Å
c, Å
R, deg
â, deg
γ, deg
vol, Å3
Z
D
calcd, g cm-1
1.814
1.780
1.766
1.645
diffractometer
Bruker AXS
SMART 2K
100(2)
Bruker AXS
SMART 2K
100(2)
Bruker AXS
SMART 2K
100(2)
Bruker AXS
SMART 2K
100(2)
T, K
λ
1.5418
6.480
ω scan
512
1.5418
6.203
ω scan
1064
1.5418
5.881
ω scan
572
1.5418
4.990
ω scan
640
µ, mm-1
scan type
F(000)
θ
max, (deg)
h, k, l
72.06
72.02
72.84
72.77
-11 e h e 11
-10 e k e 11
-14 e l e 14
3192
multiscan
SADABS
0.33, 0.67
0.0499, 0.1566
-12 e h e 12
-17 e k e 17
-17 e l e 17
3833
multiscan
SADABS
0.33, 0.68
0.0327, 0.0837
-12 e h e 12
-13 e k e 12
-13 e l e 13
4048
multiscan
SADABS
0.40, 0.68
0.0288, 0.0753
-11 e h e 11
-12 e k e 13
-17 e l e 18
4743
multiscan
SADABS
0.70, 0.72
0.0303, 0.0763
reflns used (I > 2σ(I))
abs correction
T (min, max)
R [F2 > 2σ(F2)],
R
w (F2, all)
GOF
1.127
1.071
1.102
1.071
Table 2. Crystallographic Data for 4 and 5
4‚2CH2Cl2
state and in solution, it hydrolyzed readily to its mono(aquo)
derivative, the blue complex 5. Moreover, heating solutions
or solid samples of 5 or placing them under vacuum gave
back the dibromo species 4. Longer exposures of 4 to
ambient humidity produced another blue compound that was
insoluble and has not been identified.
5
formula
Mw
C38H32N8NiBr2.2(CH2Cl2)
989.06
C38H34Br2N8NiO
837.26
cryst color
cryst dimens,
mm3
green
0.3 × 0.3 × 0.2
blue
0.28 × 0.13 × 0.03
symmetry
space group
a, Å
b, Å
c, Å
orthorhombic
P212121
12.8738(5)
16.6019(7)
19.5642(8)
90
90
90
4181.4(3)
4
1.571
monoclinic
P21/n
13.0397(2)
16.3398(2)
16.8061(2)
90
107.6370(10)
90
3412.49 (8)
4
Solid-State Structures. Suitable crystals of 1, 2a, 2b, 3,
4, and 5 for X-ray diffraction studies were obtained by vapor
diffusion of Et2O or hexane into solutions of these complexes
in acetone (1, 2a, and 2b), acetonitrile (3), and dichlo-
romethane (4 and 5). All six sets of diffraction data resulted
in fairly accurate structures for the complexes studied, as
reflected in the R values of ca. 0.0289-0.0499. The ORTEP
diagrams of these complexes are shown in Figures 1-6,
crystallographic data are tabulated in Tables 1 and 2, and
bond distances and angles are in Tables 3 and 4.
R, deg
â, deg
γ, deg
vol, Å3
Z
D
calcd, g cm-1
1.630
diffractometer
Bruker AXS
SMART 2K
100(2)
Bruker AXS
SMART 2K
100(2)
T, K
Complex 1 possesses a crystallographically imposed center
of symmetry. On the basis of the low value of the structural
index τ in each complex,20 the coordination geometry around
the Ni centers in 1 (0.17), 2a (0.02), and 2b (0.08) can be
characterized as lightly distorted square pyramidal. In
comparison to 1, the closely related dimeric species [(bpp)-
Ni(µ-Br)Br]2 displays a less distorted square pyramidal
structure (τ ≈ 0.04),13 whereas [(bpm*)Ni(µ-Cl)Cl]2 shows
a much greater distortion toward a trigonal bipyramidal
λ
1.5418
5.579
ω scan
1992
1.5418
3.925
ω scan
1696
µ, mm-1
scan type
F(000)
θ
h, k, l
max, (deg)
72.03
72.93
-15 e h e 15
-20 e k e 20
-24 e l e 24
8071
-16 e h e 16
-19 e k e 20
-20 e l e 20
5030
reflns used
(I > 2σ(I))
abs correction
multiscan
SADABS
multiscan
SADABS
T (min, max)
0.67, 1.00
0.0357, 0.0759
0.58, 0.92
0.0383, 0.0941
(20) Addison, A. W.; Rao, T. N.; Reedijk, J; van Rijn, J.; Verschoor, G.
C. J. Chem. Soc., Dalton Trans. 1984, 1349. The strcutural index τ is
determined from the equation τ ) (â - R)/60, wherein â and R are,
respectively, the largest basal angles (â > R). The τ values for perfectly
square pyramidal and trigonal bipyramidal structures are 0 and 1,
respectively.
R [F2 > 2σ(F2)],
R
w (F2, all)
GOF
1.054
0.925
Inorganic Chemistry, Vol. 46, No. 18, 2007 7625

Baho and Zargarian
Chart 1
Table 3. Selected Structure Parameters for Complex 1, 2a, 2b, and 3a
Table 4. Selected Structure Parameters for Complex 4 and 5a
1
2a
2b
3
4
5
(X2 ) Br2)
(X2 ) O1)
Ni-Br1
2.4387(7)
2.4804(8)
2.5433(8)
-
-
2.047(4)
2.064(4)
100.63(9)
155.82(10) 161.93(6)
93.62(10) 100.06(5)
92.36(10)
85.44(14)
-
-
-
-
2.4595(4)
2.4757(4)
2.4779(4)
-
-
2.0317(16)
2.0077(17)
2.0254(18)
2.0316(19)
2.5681(4)
Ni-Br2
-
-
Ni-Br1
2.5971(4)
2.6476(4)
2.0740(19)
2.0949(19)
2.1031(17)
2.0835(18)
87.84(7)
91.74(7)
178.34(7)
93.41(7)
92.76(7)
86.69(7)
94.94(5)
175.74(6)
89.73(5)
2.6146(7)
2.106(2)
2.116(3)
2.074(3)
2.061(3)
Ni-Br2A
-
Ni-X2
Ni-O1
2.0571(16)
2.0984(15)
Ni-N11
Ni-O2
-
2.0640(15)
2.0766(17)
2.0857(17)
94.03(5)
-
175.49(5)
-
Ni-N21
Ni-N11
2.0546(19)
2.0420(19)
97.61(6)
Ni-N31
Ni-N21
Ni-N41
2.076(3)
N11-Ni-Br1
N11-Ni-Br2
N21-Ni-Br1
N21-Ni-Br2
N11-Ni-N21
N11-Ni- O1
N11-Ni- O2
N21-Ni-O1
N21-Ni- O2
96.58(5)
N11-Ni-N21
N11-Ni-N31
N11-Ni-N41
N21-Ni-N31
N21-Ni-N41
N31-Ni-N41
N11-Ni-Br1
N21-Ni-Br1
N31-Ni-Br1
N41-Ni-Br1
N11-Ni-X2
N21-Ni-X2
N31-Ni-X2
N41-Ni-X2
X1-Ni-X2
84.49(11)
95.84(11)
176.84(11)
100.39(11)
93.16(11)
86.65(11)
94.26(8)
169.51(8)
90.10(8)
87.67(8)
88.56(10)
87.23(10)
171.52(11)
89.22(10)
82.33(7)
-
96.79(5)
94.00(6)
83.83(8)
85.67(7)
-
87.87(7)
86.31(6)
89.05(6)
174.83(7)
88.76(6)
89.43(7)
-
91.87(7)
161.39(8)
165.91(7)
89.75(8)
-
160.72(7)
-
N11-Ni- Br2A 90.29(10)
N21-Ni- Br2A 166.07(10)
-
-
-
84.55(5)
86.05(5)
84.13(5)
176.75(5)
95.54(5)
-
-
O1-Ni-Br1
O1-Ni-Br2
O2-Ni-Br1
O1-Ni-O2
Br1-Ni-Br2
-
97.33(5)
97.24(5)
86.75(4)
-
-
90.98(5)
-
-
-
-
102.02(7)
89.98(5)
87.92(7)
-
-
86.00(7)
103.55(3)
100.430(1)
-
-
-
-
-
-
-
-
-
-
92.827(13)
Br1-Ni-Br2A 100.21(3)
-
-
-
-
-
-
-
-
-
-
a Bond lengths in Å and bond angles in deg.
Br2-Ni-Br2A
Ni-Br2-NiA
Ni-N1
N11-Ni-N1
N21-Ni-N1
N1-Ni-Br1
N1-Ni-O1
N1-Ni-O2
86.11(2)
93.89(2)
-
-
The differences in the ligand architecture also give rise to
a different conformation of the metallacycle formed by the
chelating bis(pyrazole) moiety in the pentacoordinated spe-
cies. Thus, the methylene moiety displays a Cl‚‚‚H-C
interaction in [(bpm*)Ni(µ-Cl)Cl]2 and an agostic-type
Ni‚‚‚H-C interaction in [(bpp)Ni(µ-Br)Br]2 (Chart 1). The
bridging CR2 moiety in our dpdpm compounds 1, 2a, and
2b points toward the Ni center (Figure 7) to allow a long-
range interaction between a CdC bond of a Ph substituent
and the Ni center with the following Ni-C distances (in
Å): 3.34 and 3.63 in 1, 3.04 and 3.13 in 2a, 3.02 and 3.23
in 2b. An examination of space-filling representations of the
solid-state structures of these complexes indicates that steric
considerations alone can justify the longer Ni-Ph distances
in the dimeric species 1.22
Complexes 3, 4, and 5 display slightly distorted octahedral
geometries, the cis and trans bond angles are in the range
84-100° and 171-176° in 3, 84-96° and 176-178° in 4,
and 82-100° and 170-177° in 5 (Tables 3 and 4). An
important structural difference between these octahedral
species and the above-discussed pentacoordinated compounds
is the conformation of the 6-membered ring formed by the
coordination of the chelating dpdpm ligand to the Ni center.
Evidently, the occupation of the sixth coordination site
around the Ni center in the octahedral compounds pushes
the Ph substituents of dpdpm toward the equatorial plane,
thereby changing the conformation of the Ni-N-N-C-
N-N ring from a boat conformation observed in the
-
-
-
-
-
-
2.0957(17)
99.52(7)
93.53(6)
90.85(5)
171.25(7)
83.66(7)
a Bond lengths in Å and bond angles in deg.
geometry (τ ≈ 0.50).9j,21 The differences in the overall
geometry of the Ni centers in these closely analogous
pentacoordinated Ni(II) complexes based on bpm*, bpp, or
dpdpm are caused by the differences in the ligand structures,
i.e., the different substituents at the 3- and 5-positions of
the pyrazolyl groups (H, Me) and the different CR2 moieties
bridging them (R ) Ph, Me, H). It is also interesting to note
that the axial site in all complexes adopting lightly distorted
square pyramidal structures (1, 2a, 2b, and [(bpp)Ni(µ-Br)-
Br]2) is occupied by a Br atom, whereas in the compound
[(bpm*)Ni(µ-Cl)Cl]2 that shows major trigonal distortions
the axial site is occupied by the pyrazolyl N. This may, of
course, be related to the substantial difference in the relative
sizes of Cl and Br atoms.22
(21) A number of other dinickel species with similar structural motifs have
also been reported, including [(dab)NiBr2]2 (dab ) N,N′-di-t-butyl-
diazabutadiene; τ ≈ 0.12; Jameson, G. B.; Oswald, H. R.; Beer, H.
R. J. Am. Chem. Soc. 1984, 106, 1669) and [(dmp)NiBr2]2 (dmp )
bis(2,9-dimethyl-1,10-phenanthroline; τ ≈ 0.40; Butcher, R. J.; Sinn,
E. Inorg. Chem. 1977, 16, 2334).
(22) The authors thank one of the reviewers of the manuscript for this
suggestion.
7626 Inorganic Chemistry, Vol. 46, No. 18, 2007

Diphenyl(dipyrazolyl)methane Complexes of Ni
Figure 7. Different perspectives of the ORTEP diagrams for complexes 1, 2a, and 2b showing the long-range Ni-C distances.
pentacoordinated complexes to a half-chair conformation
observed in 3, 4, and 5. The different spatial disposition of
the Ph substituents in the octahedral and pentacoordinated
complexes can be quantified by comparing the angles
between the equatorial coordination plane (defined by the
ligating atoms N11, N21, Br/O/N, Br/O/N) and the chelation
plane defined by the four N atoms of the dpdpm ligand; these
angles have the values of ca. 57° in 1, 47° in 2a, 38° in 2b,
4° in 3, 16° in 4, and 1° in 5.
pyrazolyl group (dpdpm ≈ H2O ≈ η1-ONO2 > CH3CN ≈
η2-O2NO).14
Magnetic Measurements and Spectroscopic Studies.
Magnetic susceptibility measurements using the Gouy method
have established that all the dpdpm compounds investigated
here are paramagnetic in the solid state. Thus, µeff for
pentacoordinated complexes 1, 2a, and 2b were found to be
between 3.2 and 3.4 µB, whereas those of the hexacoordinated
complex 3-5 were ca. 3.3 µB. All of these values are in the
expected range for square pyramidal or octahedral Ni(II)
complexes having two unpaired electrons.23
Apart from the overall geometry of the new complexes
and the conformation of the metallacycles, the Ni-element
bond distances are informative about the relative stabilities
of the various species and the relative trans influence of the
ligands. For instance, the Ni-(µ-Br) distances in complex 1
are much longer than the axial Ni-Br distance (2.48 and
2.54 vs 2.44 Å, ∆Ni-Br > 50 esd). These weak Ni-(µ-Br)
interactions explain why this dimer is susceptible to cleavage
and transformation into monomeric derivatives 2a and 2b
by hydrolysis. Fairly inequivalent distances were also found
for the Ni-Br bonds in 2a (axial < basal; ∆Ni-Br ≈ 40
esd) and the Ni-O bonds in 2b (∆Ni-O ≈ 14 esd). On the
other hand, the two Ni-N distances in 1, 2a, and 2b are
fairly similar to each other (∆Ni-N ≈ 4 esd in 1, ≈ 6 esd
in 2a, and ≈ 3 esd in 2b).
That the paramagnetism of these compounds is maintained
in solution is reflected in 1H NMR spectra displaying broad
and, for the most part, featureless signals that resonated as
far upfield as -160 ppm and as far downfield as 70 ppm.
The broadness of the NMR signals in bis(pyrazolyl)alkane
complexes may also be caused by the dynamic exchange
process involving the flipping of the M-N-N-C-N-N
ring between chair and boat conformations. Moreover, the
1H NMR spectra recorded in CD3CN feature a fairly
broadened residual solvent signal (at 1.94 ppm) in addition
to somewhat broader signals due to the dpdpm ligand (at
6.69, 6.36, and 6.13 ppm). We suspect, therefore, that a
ligand exchange process involving CD3CN molecules and
the dpdpm ligand might be taking place in solution, but no
dpdpm-free complex or species with monodentate dpdpm
has been obtained in the solid state. The IR spectra of the
new complexes contain a large number of absorptions that
serve primarily as fingerprints for this family of complexes.
Solvato- and Thermochromism of the Pentacoordinated
Species. The presence of an “unfilled” coordination site
around the Ni center in the pentacoordinated complexes 1,
2a, and 2b facilitates the interaction of these species with
nucleophiles or coordinating counterions. We have examined
the interaction of these complexes with solvent molecules
of varying nucleophilicities and found a number of interesting
color changes that signal structural changes. Since temper-
Finally, the Ni-N distances trans to Ni-OH2 are some-
what shorter than the corresponding distances trans to Ni-
Br in 2a (2.042(2) vs 2.055(2) Å), 3 (2.077(2) vs 2.086(2)
Å), and 5 (2.061(3) vs 2.074(3) Å), implying that Br has a
greater trans influence than H2O. Moreover, in 4 the Ni-
Nav distance trans to Br is somewhat longer than those trans
from the pyrazolyl group (2.099(2) vs 2.079(2) Å), implying
a slightly greater trans influence for Br. Interestingly, the
Ni-O distance trans to MeCN in 3 is longer than that trans
to the pyrazolyl group (2.098(2) vs 2.064(2) Å), implying a
greater trans influence for MeCN. These observations lead
to the following order of relative trans influence strengths
in these compounds: CH3CN ≈ Br > H2O ≈ dpdpm. It
should be noted, however, that the structural parameters for
the octahedral species arising from the reactions of Ni(NO3)2
with dpdpm have implied a greater trans influence for the
(23) Collinson, S. R.; Schro¨der, M. Nickel: Inorganic and Coordination
Chemistry. In Encyclopedia of Inorganic Chemistry, 2nd ed.; King,
R. B., Ed.; Wiley InterScience: Chichester, 2005; Vol. VI.
Inorganic Chemistry, Vol. 46, No. 18, 2007 7627

Baho and Zargarian
3
3
3
3
3T2g, A2g f T1g(3F), and A2g f T1g (3P),24 although the
bands of the CH3CN spectra are more intense. Interestingly,
the middle bands in these spectra (3A2g f 3T1g) have multiple
maxima that arise from interactions between the allowed and
nonallowed excited states, as described elsewhere.25
The pair wise similarities of the spectra obtained for
MeOH and CH3CN solutions of 1 and 2a indicate that these
compounds have similar structures in these solvents. Indeed,
comparison of the CH3CN spectra to that of complex 3 in
this solvent shows that acetonitrile solutions of 1, 2a, and 3
contain the same species. We conclude, therefore, that
interaction of the Ni center in 1 or 2a with acetonitrile
involves the coordination of CH3CN and H2O to form 3. In
the case of the species generated in MeOH solutions of 1
and 2a, the absence of reliable structural information does
not allow us to determine whether the resulting octahedral
species is a simple MeOH or water adduct26,27 or a compound
arising from the displacement of Br by MeOH or water.28
Heating the MeOH solution of 1 produced a color change,
going from light blue at room temperature to light green at
ca. 60 °C, but the spectra recorded for these solutions do
not show significant changes in the shapes of the bands or
the energy maxima (<5-10 nm). These color changes are
likely due to ligand exchange reactions that cause only minor
modifications in the overall geometry of the complex.
The electronic spectra of 2a in CH2Cl2 and acetone (Figure
10) were quite different from those discussed above. For
instance, the room-temperature spectrum recorded for the
acetone solution showed four main bands at 488, 650, 861,
and 1006 nm; the band at 650 nm features a shoulder at 712
nm. The room-temperature spectrum recorded in CH2Cl2 also
shows four main peaks at 491, 662, 859, and 1002 nm; the
band at 491 nm also shows a shoulder at 560 nm. These
spectra are quite similar, their main difference being the
position of the shoulder band. These observations indicate
that CH2Cl2 and acetone solutions of 2a do not contain
octahedral species. Literature reports show that most pen-
tacoordinated Ni(II) species display three or four bands of
variable intensities.29 On the other hand, computational
studies have indicated that Ni(II) compounds surrounded by
Figure 8. Room-temperature UV-vis-NIR spectra of MeOH solutions
of 1 (1.3 mM) and 2a (2.1 mM).
Figure 9. Room-temperature UV-vis-NIR spectra of CH3CN solutions
of 1 (1.3 mM) and 2a (2.7 mM).
ature variations can also influence metal-ligand interactions
and structural changes, we have also probed the influence
of temperature on the optical properties of these compounds.
Given the similarities of the UV-vis-NIR spectra for
solutions of 2a and 2b in various solvents, we have focused
the present discussion on the spectra for 1 and 2a only.
(26) For a few recent reports on a variety of Ni(II) complexes of (N-N)
donor ligands containing coordinated MeOH see: (a) Sun, Y.-J; Cheng,
P.; Yan, S.-P; Jiang, Z.-H; Liao, D.-Z; Shen, P.-W. Inorg. Chem.
Comm. 2000, 3, 289. (b) Dorta, R.; Shimon, L. J. W.; Rozenberg, H.;
Ben-David, Y.; Milstein, D. Inorg. Chem. 2003, 42, 3160. (c) Casabo´,
J.; Pons, J.; Siddiqi, K. S.; Teixidor, F.; Molins, E.; Miravitlles, C. J.
Chem. Soc., Dalton Trans. 1989, 1401. (d) Makowska-Crzyska, M.
M.; Szajna, E.; Shipley, C.; Arif, A. M.; Mitchell, M. H.; Halfen, J.
A.; Berreau, L. M. Inorg. Chem. 2003, 42, 7472.
(27) Examples of penta- and hexacoordinated Ni(II) complexes with a
coordinated water molecule: (a) Adams, H.; Clunas, S.; Fenton, D.
E. Acta Crystallogr. 2004, E60, m338. (b) Matecka, M.; Rybarczyk-
Pirek, A.; Olszak, T. A.; Malinowska, K.; Ochocki, J. Acta Crystallogr.
2001, C57, 513. (d) Bazzicalupi, C.; Bencini, A.; Duce, C.; Fornasari,
P.; Giorgi, C.; Paoletti, P.; Pardini, R.; Tine`, M. R.; Valtancoli, B.
Dalton Trans. 2004, 463.
(28) It should be recalled, however, that the only crystals obtained from
blue solutions of 2a in MeOH are those of light green 2b, implying
that the octahedral species present in these solutions is a more soluble,
presumably neutral compound such as [(dpdpm)NiBr2(OH2)(L)] (L
) H2O or MeOH).
(29) (a) Larue, B.; Tran, L.-T.; Luneau, D.; Reber, C. Can. J. Chem. 2003,
81, 1168. (b) Sacconi, L.; Nannelli, P.; Nardi, N.; Campigli, U. Inorg.
Chem. 1965, 4, 943.
Figures 8 and 9 show the UV-vis-NIR spectra of 1 and
2a in MeOH (blue) and CH3CN (lime green), respectively.
It is noteworthy that these spectra display the characteristic
spectral pattern for octahedral Ni(II) compounds. Thus, all
of these spectra contain the allowed d-d transitions 3A2g f
(24) (a) Landry-Hum, J.; Bussie`re, G.; Daniel, C.; Reber, C. Inorg. Chem.
2001, 40, 2595. (b) Bussie`re, G.; Beaulac, R.; Cardinal-David, B.;
Reber, C. Coord. Chem. ReV. 2001, 219-221, 509.
(25) Very similar “weak shoulders” have been observed in the absorption
spectra of many octahedral Ni(II) complexes, including [Ni(NH3)6]2+
.
For a discussion of this phenomenon, including detailed analyses of
these transitions based on Tanabe-Sugano diagrams and modern
theoretical models, see : (a) Bussie`re, G.; Reber, C. J. Am. Chem.
Soc. 1998, 120, 6306. (b) Triest, M.; Bussie`re, G.; Be´lisle, H.; Reber,
C. J. Chem. Ed. 2000, 77, 670. Available at http://jchemed.chem.wis-
c.edu/jcewww/articles/JCENi/JCENi.html. (c) Bussie`re, G.; Reber, C.;
Neuhauser, D.; Walter, D. A.; Zink, J. I. J. Phys. Chem. A 2003, 107,
1258. (d) Nolet, M.-C.; Beaulac, R.; Boulanger, A.-M.; Reber, C. Struc.
Bonding 2004, 107, 145. (e) Gonza´lez, e.; Rodrigue-Witchel, A.;
Reber, C. Coord. Chem. ReV. 2007, 251, 351.
7628 Inorganic Chemistry, Vol. 46, No. 18, 2007

Diphenyl(dipyrazolyl)methane Complexes of Ni
Figure 10. Room-temperature UV-vis-NIR spectra of 2a in CH2Cl2
(8.7 mM) and acetone (8.3 mM).
Figure 11. Variable-temperature UV-vis-NIR spectra for a 6.5 mM
solution of 2a in acetone.
weak-field ligands arranged in a square pyramidal geometry
(C4V idealized symmetry, high-spin) should give rise to six
spin-allowed transitions in the UV-vis region.30 We propose
that our observations are consistent with the maintenance of
square pyramidal structure for 2a in acetone and CH2Cl2
solutions, which is reasonable because both of these solvents
have weaker coordinating abilities relative to MeOH and
CH3CN.
The colors of the acetone and CH2Cl2 solutions of 2a and
their temperature-dependence also reveal an interesting
interconversion between 2a and 1. Thus, the CH2Cl2 solution
of 2a is brown, very similar to the color of solid samples of
1, while the room-temperature acetone solution of 2a is
green. Varying the temperature of the acetone solution of
2a caused a color variation from light green (<30 °C) to
dark green (30-40 °C) to brown (40-60 °C). Cooling the
samples to 18 °C regenerated the light green color of the
solution, and repeating this heating-cooling cycle eight times
produced the same observations. The variable-temperature
spectra of an acetone solution of 2a showed a continuous
blue-shift of the shoulder band from ca. 711 nm at -10 °C
to ca. 555 nm at 60 °C (Figure 11). It is noteworthy that the
high temperature acetone spectrum is virtually identical to
the room-temperature CH2Cl2 spectrum of 2a (Figure 12),
and both of these solutions have the same color as the solid
samples of 1. Since 1 can be prepared by dehydration of 2a
or 2b (vide supra), these observations suggest that the
continuous and reversible thermochromism of 2a in acetone
involves its conversion to 1 at high temperatures. Conversion
of complex 2a to 1 can also occur at room temperature in
concentrated CH2Cl2 solutions. Unfortunately, the insufficient
solubility of 1 in CH2Cl2 and acetone prevented us from
recording the spectra of 1 in these solvents, which would
allow us to confirm the conversion of 1 to 2a.
Figure 12. UV-vis-NIR spectra for solutions of 2a (8.7 mM in CH2Cl2
and 6.5 mM in acetone) and acetone solutions of 4 (4.7 mM) and 5 (6.6
mM).
the vapors of benzene, Et2O, or toluene turned the crystals
to brown in less than 2 min. Visual inspection indicated that
the sample had lost its crystallinity; however, exposing this
brown sample to humidity changed it back to green in a very
slow process (many days).
Solvato- and Thermochromism of the Octahedral
Species 4 and 5. In order to determine whether the
coordinatively saturated Ni centers in our octahedral species
can undergo similar solvato- and thermochromic changes,
we examined (visually and by spectroscopy) the colors of
the solutions of the bis(dpdpm) compounds 4 and 5. Since
complex 4 (green) is readily converted to 5 (blue) in the
presence of humidity, both in solution and solid state, the
thermo- and solvatochromism tests were carried out using
dried and distilled solvents and with freshly grown crystals
of these complexes.
Finally, we have briefly studied the effect of solvent vapor
on the pentacoordinated species 2a and 2b. These studies
showed that 2b is readily converted to 1 in the presence of
solvent vapors, whereas 2a did not register important
changes. Thus, exposing a small light green crystal of 2b to
Complexes 4 and 5 give variously colored solutions in
different solvents; in addition, some of these solutions
changed color as a function of temperature. Thus, CH2Cl2
solutions of 4 are dark green at room temperature and pink
at 40 °C. The MeOH solution of 4 turns from turquoise blue
(30) Ciampolini, M. Inorg. Chem. 1966, 5, 35.
Inorganic Chemistry, Vol. 46, No. 18, 2007 7629

Baho and Zargarian
Figure 15. Variable-temperature UV-vis-NIR spectra for 4 in CH3CN
(8.7 mM).
Figure 13. Variable-temperature UV-vis-NIR spectra for 4 in CH2Cl2
(4.7 mM).
Figure 16. Variable-temperature UV-vis-NIR spectra for 5 in CH2Cl2
(6.6 mM).
Figure 14. Variable-temperature UV-vis-NIR spectra for 4 in MeOH
(3.9 mM).
577 nm) in addition to the emergence of a new shoulder
band at 575 nm.
at 20 °C to light green at 60 °C. The CH3CN solutions of 4
are light green at room temperature or below, becoming dark
green at higher temperatures. Room-temperature solutions
of complex 5 were light blue in both CH2Cl2 and MeOH
but green in CH3CN. Increasing the temperature turned the
CH2Cl2 solution from blue to pink at 40 °C, whereas the
MeOH and CH3CN solutions did not change color upon
heating.
The UV-vis-NIR spectra of various solutions prepared
from crystals of 4 and 5 were recorded to monitor spectral
changes as a function of solvent and temperature. Figures
13-15 show the variable-temperature spectra of 4 in CH2-
Cl2, MeOH, and CH3CN, respectively. Figure 16 shows the
variable temperature spectra recorded for CH2Cl2 solution
of 5 (6.6 mM); the MeOH and CH3CN spectra were very
similar to those of complex 4. The spectra taken at 20 °C
for MeOH and CH3CN solutions of complex 4 show the
expected pattern for octahedral species, implying that 4
generates fairly similar species in these relatively nucleophilic
solvents. Varying the temperature of the MeOH solutions
from -10 to 60 °C caused a red-shift of the 586 nm band
(to 599 nm, Figure 14), whereas the corresponding band in
the CH3CN spectra (Figure 15) showed a blue-shift (591 to
The variable-temperature spectra of 4 and 5 in CH2Cl2
(Figures 13 and 16) registered major changes over a much
narrower range of temperature (-10 to +40 °C), implying
that significant changes take place in the overall structure
of these complexes. It is interesting to note the striking
similarity between the -10 and 40 °C spectra of 4 and 5.
Furthermore, as was mentioned above, at 40 °C the spectral
features are reminiscent of those observed for CH2Cl2
solution of complex 2a at room temperature and those of
the acetone solution at high temperatures. On the basis of
these observations, we propose that heating CH2Cl2 solutions
of the octahedral, bis(dpdpm) complexes 4 and 5 leads to
the dissociation of a dpdpm ligand to form mono(dpdpm)
species. The similarity between the colors of these solutions
and the solid sample of 1 points to the possible formation
of the dimeric structure of 1 in high-temperature solutions
of 4 and 5.
Conclusion
NiBr2 forms pentacoordinated complexes when it is reacted
with 1 equiv of dpdpm in weakly coordinating solvents. This
7630 Inorganic Chemistry, Vol. 46, No. 18, 2007

Diphenyl(dipyrazolyl)methane Complexes of Ni
g, 83% crude yield). X-ray quality single crystals (dark green) were
obtained by slow diffusion of Et2O into a concentrated acetone
solution kept at room temperature. mp ) 234 °C. µeff ) 3.21 µB.
Anal. Calcd for C19H18N4O1NiBr2: C, 42.51; H, 3.38; N, 10.44.
Found: C, 42.96; H, 3.35; N, 10.28%.1H NMR (CDCl3): 69.86
(br), 50.42 (br), 37.94 (br), 6.62 (br), 5.65 (br), 4.45 (br), 3.92 (br),
3.12 (br), 2.2 (br), 1.47 (br) 1.30 (br) 0.089 (br) -130.7 (br)
-150.34 (br), -163.01 ppm (br). IR (KBr, cm-1): 3323 (br),
3150-3033 (w), 1631 (vs), 1516 (w), 1491 (m), 1451 (s), 1434
(m), 1406 (s), 1385(m), 1332 (m), 1314 (s), 1254 (m), 1226 (m),
1198 (s), 1171 (m), 1091 (w), 1080 (w), 1070 (vs), 999 (m), 942
(w), 923 (m), 890 (m),867 (m), 847 (w), 771 (vs), 775 (s), 699 (s),
657 (m), 638(m), 605 (m), 578 (w), 502 (w).
is in contrast to the exclusive formation of octahedral species
from the reaction of Ni(NO3)3 under similar conditions. The
unusual geometry of the NiBr2 derivatives appears to be
stabilized, in the solid state, by long-range Ni-Ph interac-
tions. In contrast, reactions using a 1:2 Ni/dpdpm ratio
give octahedral species with both nitrate and bromide
derivatives.
A common aspect of all Ni-dpdpm complexes prepared
to date is the lability of all Ni-ligand bonds. This is perhaps
the reason why these compounds are not suitable precursors
for organometallic derivatives. It is worth noting, however,
that the facile dissociation of Br- or NO3- bestows interesting
solvato-, vapo-, and thermochromic properties to these
compounds. The results of our studies encourage us to
explore the potential of these complexes in detecting solvent
vapors or anions.
[(dpdpm)NiBr(H2O)2]Br (2b). The procedure used for the
synthesis of 2a was followed. X-ray quality single crystals (light
green) were obtained by slow diffusion of hexane into a concen-
trated acetone solution kept at room temperature. mp > 260 °C.
µeff ) 3.22 µB. Anal. Calcd for C19H20N4O2NiBr2: C, 41.13; H,
1
3.63; N, 10.10. Found: C, 40.63; H, 3.43; N, 9.83%. H NMR
Experimental Section
(CD3OD): 60.81 (br), 39.05 (br), 7.28 (br), 7.12 (br), 6.72 (br),
-140.55 (br), -162 ppm (br). IR (KBr, cm-1): 3395 (br), 3344
(br), 3127-3056 (w), 1631 (s), 1516 (m), 1491 (m), 1450 (s), 1437
(m), 1414 (s), 1385 (m), 1336 (m), 1318 (s), 1257 (m), 1223 (w),
1214 (m), 1198 (m), 1185 (w), 1174 (w), 1104 (m), 1086 (m), 1069
(vs), 1001 (m), 942 (w), 922 (m), 891 (m), 870 (w), 843 (w), 780
(s), 757 (w), 749 (vs), 702 (s), 567 (w), 642 (w), 611 (w), 600 (w),
537 (w), 511 (w).
General. The main ligand used in this study, dpdpm, was
synthesized according to a published procedure.19 Anhydrous NiBr2
was purchased from Sigma-Aldrich, stored in a drybox, and used
without further dehydration. Where necessary, the synthetic ma-
nipulations were carried out in dry and oxygen-free solvents under
an atmosphere of ultrahigh purity nitrogen using standard Schlenk
techniques and a drybox. The elemental analyses (C, H, and N)
were performed in duplicate by Laboratoire d’Analyse EÄ le´mentaire
[(dpdpm)NiBr(H2O)2(CH3CN)]Br (3). A solution of dpdpm
(2.00 g, 6.66 mmol) in acetonitrile (30 mL) was added to a stirred
suspension of NiBr2 (1.46 g, 6.70 mmol) in acetonitrile (30 mL).
The reaction mixture was stirred for 20 h at room temperature,
filtered, and the filtrate was evaporated to give a green solid (3.35
g, 85% crude yield). X-ray quality single crystals of 3 (green) were
obtained by slow diffusion of hexane into a concentrated solution
of acetonitrile kept at room temperature. mp ) 229 °C. µeff ) 3.33
µB. Anal. Calcd for C21H23N5O2NiBr2‚CH3CN: C, 43.37; H, 4.11;
1
de l’Universite´ de Montre´al. The H NMR spectra were recorded
on a Bruker Av400 (at 400 MHz). The IR spectra were recorded
between 4000 and 400 cm-1 using KBr pellets on a Perkin-Elmer
Spectrum One spectrophotometer using the Spectrum v.3.01.00
software. The UV-vis-NIR spectra were recorded between 1300
and 250 nm with a 1 cm quartz cell on a Varian Cary 500i; the
variable-temperature spectra were recorded on a Cary 500 spec-
trophotometer. The magnetic susceptibility measurements were
carried out at room temperature using the Gouy method with a
Johnson Matthey magnetic susceptibility balance, using HgCo-
(NCS)4 as standard.
Syntheses. [(dpdpm)Ni(µ-Br)Br]2 (1). A solution of dpdpm
(1.00 g, 3.33 mmol) in distilled acetone (25 mL) was added to a
stirred suspension of NiBr2 (0.75 g, 3.34 mmol) in distilled acetone
(25 mL). The reaction mixture was heated to reflux for 18 h, cooled
to room temperature, and filtered, and the remaining solid was
washed with Et2O (3 × 20 mL) to give an orange-brown powder
(1.30 g, 79% crude yield). X-ray quality single crystals (brown)
were obtained by slow diffusion of Et2O into a concentrated acetone
solution kept at room temperature. mp ) 260 °C. µeff ) 3.55 µB.
Anal. Calcd for [C19H16N4NiBr2]2: C, 43.98; H, 3.11; N, 10.80.
Found: C, 43.58; H, 2.99; N, 10.78%. 1H NMR (CD3OD): 59.55
(br), 40.47 (br), 7.58 (br), 7.47-7.44 (br), 7.34 (br), 7.37 (br), 7.18
(br), 6.72 (br), 2.144(s), -141.07(br), -160.34 ppm (br). IR (KBr,
cm-1): 3604 (s), 3392 (br), 3158 (m), 3118 (m), 3058 (m), 1631
(m), 1517 (m), 1491 (s), 1450 (s), 1437 (s), 1408 (s), 1385 (s),
1330 (m), 1313 (vs), 1253 (s), 1222 (s), 1199 (s), 1171 (m), 1098
(s), 1080 (s), 1074 (s),()w,999 (m), 940 (w),924 (w), 918 (m), 891
(m), 870 (m), 853 (m), 776 (s), 754 (vs), 704 (s), 692 (s), 656 (s),
637 (s), 614 (w), 605 (w), 497 (w).
1
N 13.19. Found: C, 42.99; H, 4.07; N, 12.91%. H NMR (CD3-
CN): 70.97 (br), 61.54 (br), 43.75 (br), 39.20 (br), 7.51-7.43, 6.53-
(br), 5.70 (br), 5.51(br), -129.97, -140.22 (br), -157.02 (br),
-161.82 ppm (br). IR: 3605 (s), 3392 (br), 2368-2241 (w), 1644
(br), 1515 (m), 1491(s), 1450 (s), 1438 (s), 1410 (s), 1384 (s), 1332
(w), 1309 (vs), 1252 (m), 1218 (s), 1193 (s), 1166 (m), 1109 (s),
1078 (m), 1067 (vs), 1031 (w), 1000 (m), 940 (w), 918 (m), 892
(m), 874 (m), 858 (w), 784 (s), 764 (vs), 754 (vs), 704 (s), 568
(w), 658 (w), 636 (m), 614 (w),724 (w), 604 (m), 504 (m).
[(dpdpm)2NiBr2] (4) and [(dpdpm)2NiBr(H2O)]Br (5). A
solution of dpdpm (0.50 g, 1.66 mmol) in distilled hot methanol
(20 mL) was added to a stirred suspension of NiBr2 (0.18 g, 0.82
mmol) in distilled methanol (15 mL). The reaction mixture was
stirred for 20 h at room temperature under nitrogen, filtered, and
the filtrate evaporated to give a green solid (0.56 g, 81% crude
yield). X-ray quality single crystals of 4 (green) were obtained by
slow diffusion of Et2O into a concentrated (green) solution of CH2-
Cl2 kept at room temperature and under nitrogen. Alternatively,
repeating this same recrystallization procedure but with the solution
exposed to air gave blue crystals of 5. The latter were also obtained
by exposing the green crystals of 4 to ambient atmosphere
overnight. 4: mp ) 120 °C. µeff ) 3.26 µB. Anal. Calcd for
C38H34N8 Ni Br2. CH2Cl2: C, 51.81; H, 3.79; N, 12.39. Found: C,
[(dpdpm)NiBr2(H2O)] (2a). A solution of dpdpm (0.50 g, 1.66
mmol) in methanol (30 mL) was added to a stirred suspension of
NiBr2 (0.36 g, 1.66 mmol) in (30 mL) methanol. The reaction
mixture was stirred for 20 h at room temperature, filtered to remove
unreacted NiBr2, and evaporated to give a dark green powder (2.99
1
51.60; H, 3.26; N, 12.25%. H NMR (CDCl3): 60.33 (br), 38.75
(br), 7.18 (br), -141.05 (br), -162.17 ppm (br). IR: 3430 (br),
3146 (m), 3110 (m), 3098 (m), 3062 (m), 2962 (m), 2925 (m),
2855 (m), 2377 (w), 1629 (br), 1513 (m), 1491 (s), 1450 (s), 1433
Inorganic Chemistry, Vol. 46, No. 18, 2007 7631

Baho and Zargarian
(s), 1404 (m), 1382 (m), 1303 (s), 1272 (w), 1250 (w), 1222 (m),
1189 (s), 1161 (m), 1106 (s), 1085 (m), 1066 (vs), 1000 (w), 979
(w), 938 (m), 915 (m), 889 (m), 872 (w), 788 (w), 754 (vs), 725
(s), 699 (s), 669 (w) 658 (m), 634 (m), 605 cm-1 (w). 5: mp )
120 °C. µeff ) 3.01 µB. Anal. Calcd for C38H34N8 O1 Ni Br2: C,
54.51; H, 4.09; N, 13.38. Found: C, 54.51; H, 3.97; N, 13.52%.
1H NMR (CDCl3): 60.39 (br), 37.79 (br), 7.46 (br), 6.68 (br)
-162.99 ppm (br). IR (KBr, cm-1): 3512 (s), 3431 (br), 3104 (m),
3052 (s), 2918 (m), 2850 (m), 2375 (w), 2361 (w), 2347 (w), 2019
(w), 1820 (w), 1763 (w), 1603 (br), 1522 (m), 1516(m), 1491 (s),
1449 (s), 1435 (s), 1411 (m), 1384 (m), 1332 (m), 1305 (s), 1250
(m), 1220 (s), 1193 (s), 1187 (s), 1167 (m), 1108 (s), 1087 (m),
1064 (vs), 1000(w), 990 (w), 980 (w), 938 (w), 918 (m), 914 (m),
890 (m), 873 (m), 856 (w), 762 (vs), 752 (vs), 700 (s), 683 (w),
657 (m), 636 (m), 618 (w), 604 (w).
Crystallographic Studies. All diffraction data sets were collected
on a Bruker AXS SMART 2K diffractometer mounted with Cu
KR radiation at 100(2) K (SMART software).31 Cell refinement
and data reduction were carried out using SAINT.32 All structures
were solved by direct methods using SHELXS97,33 and the
refinements were done on F2 by full-matrix least-squares.34 All non-
hydrogen atoms were refined anisotropically. The positional
parameters for H atoms in water molecules were refined isotropi-
cally, but all other hydrogens were constrained to the parent atom
using a riding model.
All details concerning the refinement of the crystal structures
are listed in Tables 1 and 2. The relevant bond distance and angles
are tabulated in Tables 3 and 4. Crystallographic data for the
structural analysis have been deposited with the Cambridge
Crystallographic Data Centre, CCDC No. 633340 (1), 633341 (2a),
633342 (2b), 633343 (3), 633344 (5), and 633345 (4). Copies of
this information may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: +44-
1223-336-033; email: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
Testing the Reversible Solvato-, Vapo-, and Thermochromic
Behaviors of Complexes 1, 2a, 4, and 5. Dissolving solutions of
2a (8.2-9.8 mM) gave different colors depending on the solvent
and the temperature of the solution. At room temperature, 2a is
dark olive in acetone, forest green in CH3CN, and light blue in
MeOH; the color of the CH2Cl2 solutions was concentration-
dependent, giving light pink in dilute solutions and brown in
concentrated solutions. Evaporation of all these solutions regener-
ated the green solid 2a. Moreover, evaporation of concentrated
acetone solutions with heating led to the precipitation of a brownish
solid identified as 1. The UV-vis-NIR spectra of these solutions
were recorded and are presented in Figures 8-11. The thermo-
chromism of the complexes was studied by recording the variable-
temperature UV-vis-NIR spectra (-10 to 60 °C). The spectral
features are discussed in the Results and Discussion section.
The UV-vis-NIR spectra for solutions of complexes 4 and 5
were recorded to monitor any spectral changes as a function of
solvent and temperature. Figures 13-15 show the variable-
temperature spectra of 4 in CH2Cl2 (4.7 mM), MeOH (3.9 mM),
and CH3CN (8.7 mM). The sensitivity of complex 4 to humidity
required that its spectra be recorded using crystals of 4 that had
been kept in a drybox or in a desiccator containing CaCl2 in order
to minimize any direct contact with humidity. The variable-
temperature spectra recorded for a 6.6 mM CH2Cl2 solution of 5
are shown in Figure 16. The thermochromism of 4 and 5 is
discussed in the Results and Discussion section.
The crystal structures of 2a, 2b, 3, and 5 are stabilized by
intermolecular hydrogen bonds. The details on O-H‚‚‚O distances
are available from the detailed structure reports. The structure of
complex 4 contained two disordered solvent molecules of CH2Cl2,
which were refined isotropically using a constrained model.
Disordered solvent molecules were then introduced over two
positions and refined using the ISOR restrained technique. For the
sake of clarity, molecules of solvents (in 2b, 3, and 4) and the
counterions (in 2b, 3, and 5) have been removed from the ORTEP
III35 diagrams.
The vapochromic behavior of 1 and 2b was studied briefly, as
follows. A crystal of 2b was fixed onto a glass fiber attached to
the inside of the cap for a 5 mL drum vial. The cap was then placed
on top of the vial containing 0.2 mL of a given solvent (benzene,
Et2O, or toluene). Exposure of the crystal to the solvent vapor
caused a color change from green to brown in less than 2 min.
Visual inspection of the transformed crystal showed that it was no
longer crystalline. Exposing this solid to ambient humidity brought
back the initial green color over a few days.
(31) SMART, Release 5.625, Bruker Molecular Analysis Research Tool;
Bruker AXS Inc.: Madison, WI, 2001.
(32) SAINT, Release 7.06, Integration Software for Single Crystal Data;
Bruker AXS Inc.: Madison, WI, 2003.
(33) Sheldrick, G. M. SHELXS, Program for the Solution of Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(34) (a) SHELXTL, Release 5.10, The Complete Software Package for Single
Crystal Structure Determination; Bruker AXS Inc.: Madison, WI,
1997. (b) SAINT, Release 7.06. Integration Software for Single Crystal
Data; Bruker AXS Inc.: Madison, WI, 2003. (c) SMART, Release
5.625, Bruker Molecular Analysis Research Tool; Bruker AXS Inc.:
Madison, WI, 2001. (d) Sheldrick, G. M. SADABS, Bruker Area
Detector Absorption Corrections; Bruker AXS Inc.: Madison, WI,
1996. (e) Sheldrick, G. M. SHELXS97, Program for Crystal Structure
Solution; University of Go¨ttingen: Go¨ttingen, Germany, 1997. (f)
Sheldrick, G. M. SHELXL97, Program for Crystal Structure Refine-
ment; University of Go¨ttingen: Go¨ttingen, Germany, 1997. (g) Spek,
A. L. PLATON, Molecular Geometry Program; University of Utre-
cht: Utrecht, Holland, 2000.
Acknowledgment. The Natural Sciences and Engineering
Research Council of Canada and Fonds Que´be´cois de la
Recherche sur la Nature et les Technologies are gratefully
acknowledged for their financial support. The authors are
grateful to Profs. C. Reber and G. Hanan for access to their
Carry spectrometers and for valuable discussions.
(35) Burnett, M. N.; Johnson, C. K. ORTEPIII-Oak Ridge Thermal Ellipsoid
Plot Program for Crystal Structure Illustrations, Technical Report
ORNL-6895; Oak Ridge National Laboratory: Oak Ridge, TN, 1996.
IC070093M
7632 Inorganic Chemistry, Vol. 46, No. 18, 2007