High-spin enforcement in first-row metal complexes of a constrained polyaromatic ligand: synthesis, structure, and properties

Article abstract of DOI:10.1039/c8nj02072h

The coordination chemistry of a rigid tetradentate polypyridyl ligand has been developed with first-row transition metals Mn(ii), Fe(ii), Co(ii), Ni(ii), and Zn(ii). The polyaromatic ligand, 2,2′-di([2,2′-bipyridin]-6-yl)-1,1′-biphenyl (5, bpbb), is compr

Full text of DOI:10.1039/c8nj02072h

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High-spin enforcement in first-row metal
complexes of a constrained polyaromatic ligand:
synthesis, structure, and properties†
Cite this: New J. Chem., 2018,
42, 18667
a
Lizhu Chen,
Hunter A. Dulaney,a Branford O. Wilkins,b Sarah Farmer,a
a
a
Yanbing Zhang,
Frank R. Fronczekc and Jonah W. Jurss
*
The coordination chemistry of a rigid tetradentate polypyridyl ligand has been developed with first-row
transition metals Mn(II), Fe(II), Co(II), Ni(II), and Zn(II). The polyaromatic ligand, 2,20-di([2,20-bipyridin]-6-yl)-
1,10-biphenyl (5, bpbb), is comprised of 2,20-bipyridine donors positioned at the 2 and 20 carbons of a
biphenyl backbone. Notably, coordination of the typical strong field bipyridine fragments is constrained,
weakening the octahedral ligand fields around manganese, iron, and cobalt to give high-spin electronic
states. Solution magnetic susceptibility measurements were conducted across the series using the Evans
method and variable-temperature solid-state SQUID magnetometry was performed on two Fe(II) compounds,
including a bis(thiocyanato) species. Spin crossover behavior was not observed as the compounds remained
high-spin over the entire temperature range. The impact of the biphenyl bridge on M–N bond distances
and redox potentials has also been assessed by comparison to relevant first-row metal bis- and tris-
bipyridine compounds from the literature.
Received 27th April 2018,
Accepted 19th October 2018
DOI: 10.1039/c8nj02072h
rsc.li/njc
limited flexibility. Octahedral Fe(II) compounds of general form
[FeL6]2+ or FeL4(NCS)2 (where L is an N-heterocyclic donor such
Introduction
Tetradentate and pentadentate ligand frameworks are impor- as pyridine) comprise the vast majority of known spin crossover
tant classes of ligands for accessing stable first-row transition (SCO) compounds, which hold great promise for applications
metal complexes. The metal–ligand bonds of 3d metals are such as data storage and molecular electronics.7–9 SCO com-
often labile and prone to substitution. Thus, highly chelating pounds are typically studied in the solid state where abrupt
ligands are frequently employed to counter this characteristic transitions between spin states can be observed.7–9 One strategy
while affording well-defined coordination spheres with tunable used to engender SCO behavior is the design of sterically
properties. Given the high denticity of these ligand classes, the demanding ligands that allow tuning of the metal–ligand
number and relative orientation of labile coordination sites can bonding interactions to access complexes in which the ligand
be controlled, and specific geometries enforced, by clever ligand field strength and the spin-pairing energy are comparable.10,11
design in which preorganization, rigidity, and steric factors are This commonly manifests through added substituents at posi-
useful strategies.1,2
Biphenyl-based polydentate ligands have been employed in a 2,20-bipyridine or the 2 and 9 positions of 1,10-phenanthroline).12,13
number of areas, including bioinorganic model compounds,2–4
In this context, we sought to introduce strain remotely using
tions adjacent to the donor atoms (i.e. the 6 and 60 positions of
spin crossover complexes,5 and homogeneous catalysis.6 These a rigid polydentate scaffold as an underexplored approach to
systems exploit biphenyl as an unyielding structural unit whose SCO compounds. Our laboratory has been interested in pre-
substituted phenyl groups are not coplanar, allowing the organized frameworks,14 as in the present case which involves
appended donors to bind at a single metal center but with a tetradentate ligand that maximizes the chelate effect while
dictating the metal coordination geometry through limited
a Department of Chemistry and Biochemistry, University of Mississippi, University,
rotation about single bonds connecting rigid donor moieties.
Herein we report a straightforward and improved synthesis of
polyaromatic ligand 2,20-di([2,20-bipyridin]-6-yl)-1,10-biphenyl2
and its metalation with mid-to-late first-row transition metals.
Metal complexes of Mn(II), Fe(II), Co(II), Ni(II), and Zn(II) were
prepared to evaluate how the structural constraints of the ligand
are balanced with the geometric and electronic preferences of
MS 38677, USA. E-mail: jwjurss@olemiss.edu
b Department of Chemistry, Texas A&M University, College Station, TX 77843, USA
c Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, USA
† Electronic supplementary information (ESI) available. CCDC 1837621 (5-Mn),
1837622 (5-Fe), 1837623 (5-Co), 1837624 (5-Ni), and 1837625 (5-Zn). For ESI and
crystallographic data in CIF or other electronic format see DOI: 10.1039/
c8nj02072h
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the metal centers. Solid-state structures and optical, magnetic, and polarization effects.16 A semi-empirical absorption correc-
and electrochemical properties of this series are described.
tion (SADABS) was applied.17 Space groups were identified
based on systematic absences, E-statistics, and successive
refinement of the structures. The structures were solved using
direct methods and refined by least-squares refinement on F2
and standard difference Fourier techniques using SHELXL.18
Thermal parameters for all non-hydrogen atoms were refined
anisotropically, and hydrogen atoms were included at ideal
positions. For the structure of 5-Zn, a poorly resolved outer-
sphere diethyl ether molecule could not be successfully mod-
eled in the difference map. The data was treated with the
SQUEEZE procedure in PLATON.19 Full details of the structure
determination in CIF format have been deposited into The
Cambridge Crystallographic Data Centre (CCDC), and have the
following deposition numbers: CCDC 1837621 (5-Mn), 1837622
(5-Fe), 1837623 (5-Co), 1837624 (5-Ni), and 1837625 (5-Zn).†
Coordination polyhedra for the central metal atoms were
produced using the Diamond 4.0 Crystal and Molecular Struc-
ture Visualization program.20
Experimental section
Materials and methods
Unless otherwise noted, all synthetic manipulations were carried
out using standard Schlenk techniques or in an MBraun glovebox
under nitrogen atmosphere. Tetrahydrofuran, dichloromethane,
toluene, and diethyl ether were dried with a Pure Process
Technology solvent purification system. Compounds iodomethane,
phosphorus(V) oxybromide, 2-tri-n-butylstannylpyridine, chloro-
benzene, palladium(0) tetrakis(triphenylphosphine), and dichloro-
( p-cymene)ruthenium(II) dimer were purchased from Oakwood
Chemicals. Anhydrous metal salts, iron(II) trifluoromethane-
sulfonate and iron(III) chloride, were purchased from Strem
Chemicals and Fisher Scientific, respectively. Potassium
hexacyanoferrate(III) was purchased from Sigma Aldrich and
2-phenylpyridine was acquired from Chem-Impex International.
Water was purified with a Barnstead NANOpure Diamond system.
All other chemicals were reagent or ACS grade, purchased from
commercial vendors, and used without further purification. 1H
and 13C NMR spectra were obtained using Bruker spectrometers
operating at 500 MHz (1H) or 126 MHz (13C) as noted. Spectra were
calibrated to residual protiated solvent peaks; chemical shifts are
reported in ppm. High-resolution electrospray ionization mass
spectra (HR-ESI-MS) were obtained with a Waters SYNAPT HDMS
Q-TOF mass spectrometer and elemental analyses of carbon,
hydrogen, and nitrogen were conducted by Atlantic Microlab,
Inc., Norcross, Georgia. UV-Vis spectra were recorded on an
Agilent/Hewlett-Packard 8453 UV-Visible Spectrophotometer
with diode-array detector. Solution magnetic susceptibilities
were determined by NMR using the Evans method.15
SQUID magnetometry
For both iron-containing compounds, crystals were crushed
into a polycrystalline powder and loaded into NORELL quartz
NMR tubes. A slight excess by mass of eicosane was deposited
on top of the powder and the quartz tubes were flame sealed
under vacuum. The eicosane was melted in a warm water bath
(42 1C) and allowed to re-solidify in order to immobilize the
powder samples. The sealed tubes were placed in straw sample
holders, and these sample holders were loaded into a Quantum
Design MPMS 3 SQUID magnetometer (TAMU Vice President of
Research). DC (direct current) magnetic susceptibility measure-
ments of the samples were recorded under a static magnetic field
of 0.1 T in the temperature range of 300 K to 2 K. The data was
corrected for diamagnetic contributions from the straw and the
quartz tube. The intrinsic diamagnetism of the iron complexes
and eicosane was also corrected for by using Pascal’s constants.15
Electrochemical measurements
Electrochemistry was performed with a Bioanalytical Systems,
Inc. (BASi) Epsilon potentiostat employing a three-electrode
cell equipped with glassy carbon disk (3 mm dia.) working
electrode, platinum wire counter electrode, and a silver wire
quasi-reference electrode. Cyclic voltammograms were collected
in anhydrous acetonitrile containing 0.1 M Bu4NPF6 electrolyte,
and referenced at the end of experiments using ferrocene as an
internal standard.
Synthesis
A literature procedure was used for the preparation of
2,20-di(pyridin-2-yl)-1,10-biphenyl, precursor 1.21 A different syn-
thetic route to ligand 5 (bpbb) has been reported previously.2
2,20-([1,10-Biphenyl]-2,20-diyl)bis(1-methylpyridin-1-ium) iodide,
2. To a solution of 1 (0.50 g, 1.6 mmol) in acetonitrile (10 mL),
iodomethane (1.5 mL, 24.1 mmol) was added dropwise under
nitrogen and the solution was refluxed for 2 days. A yellow
suspension forms over the course of the reaction. The reaction
X-ray crystallography
Single crystals were coated with Paratone-N hydrocarbon oil mixture is allowed to cool to room temperature before diethyl
and mounted on the tip of a MiTeGen micromount. Tempera- ether (25 mL) is added and the precipitate is collected by vacuum
ture was maintained at 100 K with an Oxford Cryostream filtration, washed with diethyl ether, and dried to yield a light
1
700 during data collection at the University of Mississippi, yellow solid (1.05 g, 60%). H NMR (MeOD, 500 MHz): d 9.13
Department of Chemistry and Biochemistry, X-ray Crystallo- (d, J = 6.3 Hz, 2H), 8.41 (t, J = 7.9 Hz, 2H), 8.07 (t, J = 1.6 Hz, 2H),
graphy Facility. Samples were irradiated with Mo-Ka radiation 7.8 (dd, J = 8.0, 7.6 Hz, 4H), 7.62 (t, J = 7.6, 2H), 7.56–7.49 (bt, 2H),
with l = 0.71073 Å using a Bruker Smart APEX II diffractometer 7.12 (s, 2H). 13C NMR (MeOD, 126 MHz): d 148.878 (s), 146.75 (s),
equipped with a Microfocus Sealed Source (Incoatec ImS) and 138.81 (s), 133.60 (s), 133.03 (s), 132.56 (s), 132.17 (s), 131.84 (s),
APEX-II detector. The Bruker APEX2 v. 2009.1 software package 130.86 (s), 130.35 (s), 128.82 (s), 128.37 (s). HR-ESI-MS (M+) m/z
was used to integrate raw data which were corrected for Lorentz calc. for [2]2+, 169.0891, found, 169.0901.
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6,60-([1,10-Biphenyl]-2,20-diyl)bis(1-methylpyridin-2(1H)-one), 3. (m, 2H), 7.25–7.20 (m, 1H), 6.84 (d, J = 7.8 Hz, 1H). 13C NMR
This reaction is performed under air. K3Fe(CN)6 (2.48 g, spectra matched previously reported data.2 HR-ESI-MS (M+)
7.54 mmol) was dissolved in water (10.3 mL) and cooled to m/z calc. for [5 + H+], 463.1923, found, 463.1917.
0 1C. Next, NaOH (2.51 g, 62.8 mmol) in water (9.4 mL) and 2
5-Mn, [Mn(bpbb)(OH2)(OTf)](OTf). In a round bottom flask,
(0.93 g, 1.57 mmol) in water (4.7 mL) were added dropwise to
[Mn(MeCN)2(OTf)2]n (47 mg, 0.11 mmol) and 5 (50 mg, 0.11 mmol)
the first solution, simultaneously, via two dropping funnels
were added and subsequently dissolved in acetonitrile. After
over a period of 1.5 h. The reaction mixture was then stirred for
stirring under nitrogen at room temperature overnight, the
3 h at 0 1C before it was heated at 40 1C overnight. Saturated
reaction mixture was taken to dryness by rotary evaporation.
aqueous NaCl (28 mL) was added before dichloromethane
The manganese complex was recrystallized from acetonitrile
(3 ꢀ 50 mL) was used to extract the product. The organic phase
with slow diethyl ether diffusion. Crystals were collected,
was dried over anhydrous Na2SO4 and taken to dryness by
dried under vacuum, and exposed to air to give the compound
rotary evaporation. The resulting solid was dissolved in 8 : 2
as indicated. Yield = 94 mg (90%). Elem. anal. calc. for
ethyl acetate : methanol, filtered through neutral alumina to
C34H24F6MnN4O7S2: C, 48.99; H, 2.90; N, 6.72. Found: C, 49.08;
remove impurities and taken to dryness. Finally, the solid was
dissolved in a minimum amount of dichloromethane to which
hexanes was added to produce a light yellow solid that was
H, 3.01; N, 6.67. HR-ESI-MS (M+) m/z calc. for [Mn(bpbb)(OTf)]+,
666.0745, found, 666.0731.
collected by vacuum filtration to yield product (0.33 g, 76%).
1H NMR (CDCl3, 500 MHz): d 7.51 (dt, J = 1.4 Hz, J = 7.5 Hz, 2H),
7.44 (dd, J = 1.4 Hz, J = 7.5 Hz, 2H), 7.39 (dd, J = 1.5 Hz,
J = 7.4 Hz, 2H), 7.20 (dd, J = 1.4 Hz, J = 7.6 Hz, 2H), 7.12
(t, J = 7.15 Hz, 2H), 6.48 (dd, J = 1.4 Hz, J = 9.2 Hz, 2H), 5.45
(d, J = 6.9 Hz, 2H), 3.0 (s, 6H). 13C NMR (CDCl3, 126 MHz): d
139.59 (s), 138.44 (s), 133.70 (s), 132.26 (s), 130.48 (s), 129.88 (s),
129.62 (s), 128.45 (s), 128.31 (s), 118.90 (s), 118.79 (s), 34.59 (s).
HR-ESI-MS (M+) m/z calc. for [3 + Cs+], 501.0579, found, 501.0574.
2,20-Bis(6-bromopyridin-2-yl)-1,10-biphenyl, 4. In an oven-dried
flask, 10 equivalents of phosphorus(V) oxybromide (1.95 g, 6.8 mmol)
was added to 3 (0.25 g, 0.68 mmol) and heated to 105 1C overnight
with stirring under nitrogen atmosphere. The reaction was allowed
to cool to room temperature and quenched with aqueous NH4OH
until strongly basic. The resulting precipitate was collected by
filtration and washed with water. Dichloromethane was used to
dissolve the solid before it was washed three times with water
in a separatory funnel. The organic phase was dried over
anhydrous sodium sulfate and evaporated to dryness to afford
a light yellow solid, which was purified by silica gel column
chromatography eluting with 15 : 1 hexanes : ethyl acetate to
yield a pure white solid (0.29 g, 92%). 1H NMR (CDCl3,
500 MHz): d 7.53 (m, 2H), 7.49–7.44 (m, 2H), 7.45–7.39 (m,
4H), 7.27 (dd, J = 0.9 Hz, J = 7.8 Hz, 2H), 7.20 (t, J = 7.7 Hz, 2H),
6.68 (dd, J = 0.85 Hz, J = 7.6, 0.9 Hz, 2H). 13C NMR (CDCl3,
126 MHz): d 158.70 (s), 141.59 (s), 139.54 (s), 138.47 (s), 137.83 (s),
131.29 (s), 130.41 (s), 129.39 (s), 128.28 (s), 125.87 (s), 123.34 (s).
HR-ESI-MS (M+) m/z calc. for [4 + Cs+], 596.8578, found, 596.8571.
2,20-Di([2,20-bipyridin]-6-yl)-1,10-biphenyl, 5 (bpbb). In an oven-
dried flask, 4 (0.25 g, 0.50 mmol) was dissolved in anhydrous
toluene to which a solution of 2-tributylstannylpyridine (0.49 g,
1.33 mmol) in anhydrous toluene was added dropwise. Then,
0.8 mol % of Pd(PPh3)4 (4.9 mg, 0.004 mmol) was added and
the reaction mixture was refluxed for 72 hours. After it was
cooled to room temperature, the solvent was removed, and
purification was achieved by silica gel column chromatography
5-Fe, [Fe(bpbb)(MeCN)(OTf)](OTf). In a round bottom flask,
Fe(OTf)2 (0.11 g, 3.1 mmol) and 5 (0.14 g, 3.1 mmol) were added
and subsequently dissolved in methanol. The mixture was stirred
under nitrogen at room temperature overnight. The solvent was
subsequently removed by rotary evaporation, and the solid was
re-dissolved in acetonitrile. Crystals were obtained by slow
diffusion of diethyl ether into the concentrated solution. Yield =
93 mg (89%). Elem. anal. calc. for C36H25F6FeN5O6S2ꢁ(H2O)1.5
ꢁ
(C4H10O)0.5: C, 49.52; H, 3.61; N, 7.60. Found: C, 49.27; H,
3.57; N, 7.20. HR-ESI-MS (M+) m/z calc. for [Fe(bpbb)(OTf)]+,
667.0715, found, 667.0717.
5-Co, [Co(bpbb)(MeCN)(OTf)](OTf). In a round bottom flask,
Co(MeCN)2(OTf)2 (48 mg, 0.11 mmol) and 5 (50 mg, 0.11 mmol)
were added and subsequently dissolved in acetonitrile. After
stirring under nitrogen at room temperature overnight, the pink
orange reaction mixture was concentrated. Crystals of the cobalt
complex were obtained by slow diethyl ether diffusion into the
solution, collected, dried under vacuum. Yield = 95 mg (90%). Elem.
anal. calc. for C36H25CoF6N5O6S2ꢁ(H2O)1.5ꢁ(C4H10O)0.5: C, 49.36;
H, 3.60; N, 7.57. Found: C, 49.14; H, 3.49; N, 7.23. HR-ESI-MS
(M+) m/z calc. for [Co(bpbb)(OTf)]+, 670.0696, found, 670.0615.
5-Ni, [Ni(bpbb)(MeCN)(ClO4)](ClO4). Caution! Perchlorate
salts are potentially explosive and should be handled in small
amounts with care! In a round bottom flask, Ni(ClO4)2ꢁ6H2O
(40 mg, 0.11 mmol) and 5 (50 mg, 0.11 mmol) were added and
subsequently dissolved in acetonitrile (10 mL). After stirring
under nitrogen at room temperature overnight, the light violet
reaction mixture was taken to dryness by rotary evaporation.
Crystals of the resulting nickel complex were grown from acetonitrile
with slow diethyl ether diffusion. Yield = 84 mg (91%). Elem. anal.
calc. for C34H25Cl2N5NiO8ꢁ(H2O)0.5ꢁ(MeCN)0.5: C, 53.16; H, 3.51;
N, 9.74. Found: C, 53.12; H, 3.50; N, 9.76. HR-ESI-MS (M+) m/z calc.
for [Ni(bpbb)(ClO4)]+, 619.0683, found, 619.0670.
5-Zn, [Zn(bpbb)(OTf)](OTf). In a round bottom flask, Zn(OTf)2
eluting with 1 : 1 : 0.1 ethyl acetate : hexanes : dichloromethane (39 mg, 0.11 mmol) and 5 (50 mg, 0.11 mmol) were added and
to yield a white solid (0.143 g, 82%). 1H NMR (500 MHz, CDCl3): subsequently dissolved in acetonitrile. After stirring under
d 8.58 (d, J = 4.8 Hz, 1H), 8.06 (d, J = 7.8 Hz, 1H), 7.65–7.57 nitrogen at room temperature overnight, the colorless reaction
(m, 2H), 7.53 (d, J = 7.4 Hz, 2H), 7.47 (t, J = 7.2 Hz, 1H), 7.43–7.24 mixture was taken to dryness by rotary evaporation. Crystals of
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the resulting zinc complex were grown from acetonitrile with Synthesis
slow diethyl ether diffusion. Yield = 91 mg (90%). 1H NMR
The seminal publication involving ligand 5 reported a synthesis
(Fig. 1A) with an overall yield of just 18%.2 We have established an
improved route to this compound as shown in Fig. 1B. Briefly, a
ruthenium-catalyzed homocoupling of 2-phenylpyridine affords
precursor 1.21 Next, procedures for 2,20-bipyridine functionaliza-
tion were adapted,22 beginning with the methylation of 1 to form
intermediate 2 as a light yellow precipitate that is simply collected
by filtration. Oxidation of 2 with potassium ferricyanide gives 3
in high yield, followed by bromination with phosphorus
oxytribromide to produce 4. Notably, compound 4 is a versatile
intermediate for future substitution of electronically disparate
donor moieties for ligand tunability. A palladium-catalyzed
Stille coupling with 2-(tributylstannyl)pyridine gives the desired
bipyridine-derivatized product 5 in 30% overall yield. We note
that methylation of 1 gives a mixture of mono- and dimethylated
(2) products. In practice, the product mixture is carried through
the next two steps and undesired compounds are removed during
purification of 4, which was found to be easiest.
(CD3CN, 500 MHz): d 8.47 (m, 3H), 8.29 (dt, J = 1.65, 7.9 Hz, 1H),
8.22 (dd, J = 1.3, 5 Hz, 1H), 8.10 (dd, J = 2.45, 6.5 Hz, 1H), 7.65
(dt, J = 1.01, 5.4 Hz, 1H), 7.50 (d, J = 7.6 Hz, 1H), 7.31 (t, J =
7.5 Hz, 1H), 7.24 (dt, J = 0.8, 8.4 Hz, 1H), 6.91 (d, J = 7.65 Hz,
1H). Elem. Anal. calc. for C34H22F6N4O6S2Zn: C, 49.44; H, 2.68;
N, 6.78. Found: C, 49.71; H, 2.81; N, 6.73. HR-ESI-MS (M+)
m/z calc. for [Zn(bpbb)]+, 675.0656, found 675.0629.
5-Fe(NCS)2, Fe(bpbb)(NCS)2. In a round bottom flask, FeSO4ꢁ
7H2O (50 mg, 0.18 mmol) and NaSCN (29 mg, 0.39 mmol) were
added in methanol. The mixture was stirred under nitrogen at
room temperature. The mixture immediately formed a white
precipitate. The mixture was filtered through Celite. Ligand 5
(83 mg, 0.18 mmol) was added to the colorless filtrate which turned
purple immediately and was stirred overnight under nitrogen. The
solvent was then removed by rotary evaporation. The resulting solid
was dissolved in acetonitrile, and crystals were obtained by slow
diffusion of diethyl ether into the concentrated solution. Yield =
108 mg (95%). Elem. anal. calc. for C34H22FeN6S2: C, 64.36; H, 3.49;
N, 13.24. Found: C, 64.62; H, 3.64; N, 13.05. HR-ESI-MS (M+)
m/z calc. for [Fe(bpbb)(NCS)]+, 576.0946, found, 576.0925.
Complexation of metal ions Mn(II), Fe(II), Co(II), Ni(II), and
Zn(II) was performed in acetonitrile or methanol solutions by
stirring 5 with the appropriate metal precursor in a 1 : 1 ratio at
Fig. 1 Synthesis of 2,20-di([2,20-bipyridin]-6-yl)-1,10-biphenyl, 5. (A) Published route. (B) New route to tetradentate polypyridine ligand.
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room temperature overnight. Crystals were readily obtained transition metal atoms were also derived from the crystal
from concentrated acetonitrile solutions by slow diethyl ether structure of each complex as shown in Fig. 2.
diffusion to give pure complexes in B90% yield. The complexes
are not sensitive to air and moisture.
The Cu(II) and Zn(II) compounds are five-coordinate species.
Using the geometric parameter t introduced by Addison, Reedijk,
and coworkers for five-coordinate structures, the degree of distortion
from ideal geometries of square pyramidal and trigonal bipyramidal
X-ray crystallography
Solid-state structures were obtained by X-ray crystallography as can be indexed.24 A value of 1 is obtained for a perfect trigonal
shown in Fig. 2. The complexes all crystallize in the same space bipyramidal geometry while t is zero for an ideal square
group (P1) with similar unit cell parameters as presented in pyramidal geometry.24 Both five-coordinate compounds
%
Table 1, along with details of data collection. The biphenyl possess strongly distorted trigonal bipyramidal geometries as
bis(bipyridine) ligand 5 (also abbreviated bpbb) is tetradentate indicated by t = 0.72 for 5-Cu0 and 0.60 for 5-Zn.
in each complex with its metal–nitrogen bond distances
Ligated acetonitrile and an oxyanion complete the primary
ranging from 1.981 to 2.275 Å (Table 2). From Mn(II) to Ni(II) coordination sphere of the 6-coordinate Mn, Fe, Co, and Ni
across the series, distorted octahedral complexes are observed. complexes. Analogous to observations reported of first-row
The metal–ligand bond distances found in 5-Mn, 5-Fe, and 5-Co metals supported by a pentadentate polypyridyl ligand,23 M–N
are consistent with high-spin electronic states.23 Crystal struc- bond distances involving 5 decrease from left to right across the
tures of Cu(I) and Cu(II) complexes with 5 were previously row in the octahedral complexes as expected from the periodic
reported;2 selected bond distances of the Cu(II) complex are trend for effective ionic radii.25 This trend is shown graphically in
also included in Table 2 for comparison with the M(II) com- Fig. 3. It is worth noting that the dihedral angle of the biphenyl
plexes reported here. To clarify the coordination configuration backbone also decreases as the size of the metal ion becomes
of each metal center, coordination polyhedra of the central smaller in the 6-coordinate complexes. Although composed
Fig. 2 ORTEP diagrams of cations in 5-Mn (A), 5-Fe (B), 5-Co (C), 5-Ni (D) and 5-Zn (E) with thermal ellipsoids rendered at the 50% probability level.
Hydrogen atoms have been omitted for clarity. (bottom) Coordination polyhedra constructed from the donor atoms that constitute the immediate
coordination sphere around each transition metal ion.
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Table 1 Crystallographic data for structures of first-row transition metal complexes supported by 5
5-Mn
5-Fe
5-Co
5-Ni
5-Zn
Formula
Formula weight
Irradiation l (Å)
Temperature (K)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
a (1)
b (1)
C38H30F6MnN5O6.5S2
893.73
0.71073
100(2)
Triclinic
%
P1
9.2068(3)
13.8551(5)
15.2249(5)
85.908(2)
84.775(2)
81.762(2)
1910.73(11)
2
C38H30F6FeN5O6.5S2
894.64
0.71073
100(2)
Triclinic
%
P1
9.1892(2)
13.9385(3)
15.1654(3)
86.1230(10)
84.0350(10)
81.0590(10)
1905.83(7)
2
C38H30CoF6N5O6.5S2
897.72
0.71073
100(2)
Triclinic
%
P1
9.1905(5)
13.9412(9)
15.1233(9)
86.292(2)
83.904(3)
80.749(3)
1899.4(2)
2
C36H28Cl2N6NiO8
802.25
0.71073
100(2)
Triclinic
%
P1
8.8345(3)
13.4052(4)
14.4981(5)
88.5640(10)
89.0040(10)
88.179(2)
1715.34(10)
2
C34H22F6N4O6S2Zn
826.04
0.71073
100(2)
Triclinic
%
P1
9.014(5)
13.854(5)
14.960(5)
86.650(5)
87.807(5)
80.338(5)
1837.8(14)
2
g (1)
V (Å3)
Z
rcalc (g cmꢂ3
)
1.553
0.540
912
1.559
0.591
914
1.570
0.647
916
1.553
0.785
824
1.493
0.861
886
m (mmꢂ1
F(000)
)
Crystal size (mm3)
Theta range for
collection (1)
0.15 ꢀ 0.20 ꢀ 0.30
0.18 ꢀ 0.20 ꢀ 0.22
0.10 ꢀ 0.10 ꢀ 0.30
0.18 ꢀ 0.23 ꢀ 0.24
0.14 ꢀ 0.21 ꢀ 0.23
1.345 to 24.406
1.35 to 25.36
1.356 to 25.458
1.52 to 25.50
1.36 to 25.38
Index ranges
ꢂ9 r h r 10
ꢂ16 r k r 16
ꢂ17 r l r 16
22 804
ꢂ11 r h r 11
ꢂ16 r k r 16
ꢂ18 r l r 18
49 150
ꢂ11 r h r 11
ꢂ16 r k r 16
ꢂ18 r l r 18
27 618
ꢂ10 r h r 10
ꢂ16 r k r 16
ꢂ17 r l r 17
38 473
ꢂ10 r h r 10
ꢂ16 r k r 16
ꢂ17 r l r 18
39 220
Reflctns collected
Ind. reflctns (Rint
Data/restr./params
Final R indices [I 4 2s(I)]
)
5955 (0.0177)
5955/33/554
R1 = 0.0371,
wR2 = 0.0861
R1 = 0.0417,
wR2 = 0.0897
1.090
6873 (0.0204)
6873/2/550
R1 = 0.0270,
wR2 = 0.0730
R1 = 0.0288,
wR2 = 0.0745
0.949
6681 (0.0272)
6681/108/584
R1 = 0.0577,
wR2 = 0.1431
R1 = 0.0641,
wR2 = 0.1464
1.159
6238 (0.0316)
6238/0/480
R1 = 0.0248,
wR2 = 0.0682
R1 = 0.0252,
wR2 = 0.0685
1.029
6323 (0.0171)
6323/796/622
R1 = 0.0414,
wR2 = 0.1075
R1 = 0.0445,
wR2 = 0.1100
1.131
R indices (all data)
GOF
Largest diff. peak and
0.728 and ꢂ0.348
0.559 and ꢂ0.352
1.012 and ꢂ0.395
0.327 and ꢂ0.440
1.169 and ꢂ0.783
hole (e Åꢂ3
)
Table 2 Selected bond distances of first-row metal complexes supported by 5
Coordination environmenta
b
Bond distance
5-Mn
5-Fe
5-Co
5-Ni
5-Cu0
5-Zn
M–N1
M–N2
M–N3
M–N4
M–Navg
M–L
2.238(2)
2.235(2)
2.275(2)
2.238(2)
2.247
2.227(2)
L = MeCN
2.2001(17)
121.41
2.1748(13)
2.2081(13)
2.1967(13)
2.1495(13)
2.182
2.1609(14)
L = MeCN
2.1491(11)
118.91
2.096(4)
2.157(4)
2.172(4)
2.131(4)
2.139
2.134(8)
L = MeCN
2.181(3)
117.01
2.0406(13)
2.1366(13)
2.1339(12)
2.0622(13)
2.093
2.0585(14)
L = MeCN
2.2208(11)
108.41
1.981
2.205
2.037
2.060
2.071
2.305
L = Cl
—
119.41
2.060(2)
2.112(2)
2.086(2)
2.091(2)
2.087
—
M–Oc
2.21(2)
109.41
Dihedral angled
a
b
c
All bond distances are reported in Angstroms (Å). From ref. 2 where 5-Cu0 is [Cu(bpbb)Cl](ClO4)ꢁMeCN. Bound oxygen donor of coordinated
d
oxyanion, triflate or perchlorate. Dihedral angle of biphenyl backbone.
entirely of interconnected aromatic rings, the global flexibility in each metal from Mn(II) to Zn(II) and contain the metal–ligand
torsion angles enables 5 to accommodate metals of different size. bond distances of selected compounds, their associated refer-
A comparison of bond distances of the pyridine donors ences, and CCDC deposition numbers.
adjacent to the biphenyl (M–N2, M–N3) versus the distal pyridine
As typically found for d5 manganese compounds, 5-Mn and
donors of each bipyridine unit (M–N1, M–N4) reveals that, in the Mn(II) complexes listed in Table S1 (ESI†) have bond
general, the former have longer bond distances than the latter, distances that are consistent with high-spin electronic states.
indicating that the interior donors are more constrained by the Interestingly, the average Mn–N (bpy) bond distance observed
demands of the ligand and bind less strongly to the metal center. in 5-Mn is shorter (by B0.01 to 0.02 Å) than that of the related
The impact of the biphenyl bridge on the bipyridine (bpy) Mn(II) ions comprised of two unsubstituted 2,20-bipyridine
coordination chemistry of these complexes was assessed further ligands and carrying an overall charge of +1.26–30 This result
by comparison to relevant metal bis(bipyridine) complexes is in contrast to the remaining complexes supported by ligand 5
from the literature. Tables S1–S6 of the ESI† are grouped by which tend to have longer M–N (bpy) bond distances relative to
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lengths ranged from 2.059 Å for [Ni(bpy)2(OH2)(ONO2)]+ to
2.091 Å for Ni(bpy)2Cl2, while the average nickel–pyridine bond
distance for 5-Ni is 2.094 Å.
Next, the five-coordinate copper(II) and zinc(II) complexes
were compared to related bis(bipyridine) compounds. Copper
compound (5-Cu0) bearing 5 and a chloro ligand has an average
Cu–N (bpy) bond distance of 2.071 Å.2 Consistent with the
bridled coordination of 5 noted above, this average bond
distance is longer by B0.02 to 0.03 Å relative to the average
Cu–N (bpy) bond distances found in crystal structures of several
[Cu(bpy)2Cl]+ salts (Table S5, ESI†).45–47 In the same vein, 5-Zn,
ligated by the biphenyl-based polypyridine and a triflato donor,
has an average zinc–pyridine bond distance of 2.088 Å which is
longer than that of both [Zn(bpy)2Cl]+ and [Zn(bpy)2(OH2)]2+
(Table S6, ESI†).48,49 Together these results indicate that the
biphenyl bridge restrains bipyridine coordination to mid-to-late
first-row metal centers.
Fig. 3 Plot of average metal–nitrogen bond length (Å) involving 5 and the
effective ionic radius (Å) as a function of d electron count for the six-
coordinate metals (5-Mn, 5-Fe, 5-Co, and 5-Ni).
Electrochemistry
the unsubstituted 2,20-bipyridine donors. Given the collective
preference for the high-spin electron configuration, the relatively Cyclic voltammetry was conducted in anhydrous acetonitrile
shorter M–N (bpy) bond distances observed in 5-Mn suggests with the title compounds (Fig. 4). Multiple redox processes were
that 5 is suitably matched to Mn(II), which has the largest observed in the cyclic voltammograms (CVs) over a wide potential
effective ionic radius of the M(II) ions investigated here, allowing range (43 V); E1/2 values and peak potentials for the irreversible
stronger metal–ligand bonding interactions.
redox features are summarized in Table 3. All potentials are reported
Only a limited comparison of 5-Fe was possible with iron(II) in volts versus the ferrocenium/ferrocene couple (V vs. Fc+/0).
bis(bipyridine) complexes.31,32 Indeed, [Fe(bpy)2L2]n+ complexes Irreversible to quasi-reversible metal-based oxidations occur at
(where L is a labile monodentate ligand) are very rare due to 0.67 V (5-Mn), 0.95 V (5-Fe), 0.74 V (5-Co), each of which is a
formation of the thermodynamically favored d6 spin-paired MIII/II process, and at 0.09 V (5-Cu) which we assign to a CuII/I
[Fe(bpy)3]2+ complex.31,32 However, crystal structures with mono- couple. Similar oxidations were not observed with 5-Ni and
nuclear Fe(bpy)2 cores were found with anionic donors Clꢂ, CNꢂ, 5-Zn. As expected, 5-Zn is electrochemically silent at potentials
and NCSꢂ completing the octahedral coordination spheres positive of ꢂ1.4 V. The zinc complex, featuring a redox-inactive
(Table S2, ESI†).33–35 Despite the overall +1 positive charge of metal center, is useful in identifying ligand-based redox events
5-Fe, its average Fe–N (bpy) bond distance is longer than that of and has redox couples at ꢂ1.47, ꢂ1.58, and ꢂ2.17, followed by
the neutral compounds Fe(bpy)2Cl2,33 Fe(bpy)2(CN)2,34 and an irreversible reduction at ꢂ2.45 V. Consistent with previous
Fe(bpy)2(NCS)2.35 The longer bond lengths observed with 5-Fe observations,2 5-Cu exhibits two ligand-based reductions at
are consistent with a high-spin electronic state and highlight ꢂ2.07 and ꢂ2.26 V. Upon scanning positive, a sharp return
the weaker ligand field afforded by the rigid biphenyl-based oxidation is observed at ꢂ0.71 V, which is likely due to adsorp-
ligand 5. In addition, a strong temperature dependence was tion on the electrode surface given the reversible behavior
reported for Fe(bpy)2(NCS)2 in solid-state structures determined
at 110 and 298 K, which have average Fe–N (bpy) bond lengths
of 1.967 and 2.174 Å, respectively, indicating a change from low-
spin (110 K) to high-spin (298 K).35 This behavior is not observed
with 5-Fe, which has an average Fe–N (bpy) bond length of
2.183 Å in the solid-state at 100 K.
Crystal structures of selected cobalt(II) complexes were
also compared with 5-Co (Table S3, ESI†). Again, the average
cobalt–pyridine bond distance of 5-Co (2.139 Å) was found to be
longer relative to Co(bpy)2 ions bearing an anionic donor,36,37
reflecting the structural constraints of the tetradentate ligand.
Nearly equivalent average Co–N (bpy) bond distances were
observed between 5-Co and neutral Co(bpy)2Cl2 (2.142 Å),38
which are B0.08 Å longer than that of [Co(bpy)2(OH2)2]2+ as
expected on the basis of overall charge.39 Similar observations
were made for 5-Ni with respect to relevant octahedral nickel(II)
Fig. 4 CVs of 5-Mn, 5-Fe, 5-Co, 5-Ni, 5-Cu, and 5-Zn (at
concentrations) in anhydrous acetonitrile/0.1 M Bu4NPF6 solutions using
a glassy carbon disk electrode, n = 100 mV sꢂ1
1 mM
compounds featuring two unsubstituted 2,20-bipyridine donors.40–44
.
As summarized in Table S4 (ESI†), average Ni–N (bpy) bond
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Table 3 Redox properties of each complex in acetonitrile with 0.1 M
Bu4NPF6, n = 100 mV sꢂ1
Stronger Lewis acid–base bonding interactions are observed in
5-Mn compared to related Mn(II) compounds, which results
in greater electron density at the metal and a cathodic shift
of the MnIII/II couple. However, weaker bonds to each metal
center are present for the remaining compounds relative to
their [M(bpy)3]2+ counterparts, which give rise to anodic shifts
in the metal-based redox couples.
Redox potentials (V vs. Fc+/0
)
Complex
5-Mn
5-Fe
0.67b
0.95b
0.74
—
0.09
—
ꢂ1.71
ꢂ1.53c
ꢂ1.03c
ꢂ1.03
ꢂ0.71b
ꢂ1.47
ꢂ2.30
ꢂ2.30
ꢂ1.69
ꢂ1.57
ꢂ2.07c
ꢂ1.58
—
—
ꢂ1.96
ꢂ2.38
ꢂ2.26c
ꢂ2.17
—
—
—
—
5-Co
5-Ni
5-Cua
5-Zn
—
ꢂ2.45c
UV-visible spectroscopy
a
b
5-Cu is [Cu(bpbb)](ClO4)2ꢁMeCNꢁH2O as reported in ref. 2. Irreversible
UV-visible spectra of the compounds in acetonitrile are shown
in Fig. 5; associated absorption maxima and molar extinction
coefficients are presented in Table 4. An intense p-to-p* transi-
c
(Ep,a). Irreversible (Ep,c).
previously reported with this compound in acetonitrile using tion at around 310 nm (B22 000 Mꢂ1 cmꢂ1) is observed for all
Bu4NClO4 as the supporting electrolyte.2 Compound 5-Ni has five metal complexes. Given the high-spin electronic states
three reversible redox processes at ꢂ1.03, ꢂ1.57, and ꢂ2.38 V afforded by the constrained biphenyl bis(bipyridine) ligand,
that are tentatively assigned to NiII/I and NiI/0 metal-based the complexes have little-to-no absorbance in the visible region.
couples followed by a ligand-localized reduction, respectively. The iron complex 5-Fe has a weak absorption band at 410 nm
For 5-Co, an irreversible feature at ꢂ1.03 V is assigned to a CoII/I (660 Mꢂ1 cmꢂ1) that is ascribed to a metal-to-ligand charge
reduction with two reversible couples at ꢂ1.69 and ꢂ1.96 V transfer (MLCT) transition. Broad, low-intensity bands assigned
occurring that are likely ligand centered. Similarities in the CVs to Laporte-forbidden d–d transitions are observed at 815 nm
of 5-Fe and 5-Mn are apparent. Each complex has a two-electron (5-Fe), 482 nm (5-Co), and 550 and 923 nm (5-Ni) consistent
reduction at ꢂ1.53 V (5-Fe) and ꢂ1.71 V (5-Mn), which are at with the solid-state structures and distorted octahedral com-
similar potentials to the initial overlapping one-electron reduc- pounds in solution. Likewise, two broad bands at 677 and
tions of 5-Zn. On this basis, we assign these events as ligand- 960 nm are characteristic of 5-Cu.
based reductions and the most negative waves to MII/I couples.
Magnetism
To assess the influence of the biphenyl backbone on redox
potentials, the electrochemical data summarized in Table 3 was The Evans method was used to determine solution magnetic
compared to related first-row metal bis- and tris-bipyridine susceptibilities across the series as summarized in Table 4. The
complexes (Table S7, ESI†).36,50–58 Here, bipyridine-based reductions experimental magnetic moments are close to the theoretical
were generally found from approximately ꢂ1.3 to ꢂ2.3 V vs. Fc+/0
.
values expected for high-spin electronic states and/or the dn
Interestingly, metal-based redox couples of the complexes electron configuration of each M(II) ion, for example, as in d9
supported by 5 are typically more positive than those of the Cu(II) which will have one unpaired electron regardless of
corresponding [M(bpy)3]2+ complexes, with the exception of geometry or spin state. The deviation in the measured value
5-Mn. The processes assigned to the FeIII/II couples of 5-Fe (4.5 mB) for 5-Co from the anticipated theoretical spin-only
and [Fe(bpy)3]2+ occur at 0.95 and 0.69 V, respectively,51 magnetic moment (3.87 mB) is common of cobalt complexes,
whereas the MnIII/II couples of 5-Mn and [Mn(bpy)3]2+ appear including a previously reported high-spin Co(II) polypyridyl
at 0.67 and 0.93 V, respectively.50 Likewise, the CuII/I couple complex,23 and indicative of an overall magnetic moment with
of 5-Cu is observed at 0.09 V, or nearly 600 mV more positive significant orbital contribution.59
than for [Cu(bpy)3]2+.57 These metal-based redox potentials are
Intrigued by the work of Petzold and coworkers who have
consistent with the observed metal–pyridine bond distances. developed iron(II) compounds supported by hexadentate and
Fig. 5 UV-visible spectra of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) complexes with ligand 5 in acetonitrile.
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Table 4 UV-vis spectral properties and solution magnetic susceptibility of metal complexes bearing 5
5-Mn
5-Fe
5-Co
5-Ni
5-Cu
5-Zn
UV-Vis
308 (22 827)
307 (22 100)
410 (660)
815 (50)
308 (25 100)
482 (110)
307 (23 800)
550 (10)
923 (10)
315 (19 000)
677 (100)
960 (100)
317 (23 500)
meff at 298 K (mB)
5.9
5.2
4.5
2.7
1.5
—
Fig. 6 Temperature dependence of wmT for 5-Fe (A) and 5-Fe(NCS)2 (B).
dinucleating biphenyl-based N-donor ligands that exhibit spin Mn(II), Fe(II), and Co(II) complexes. Distorted trigonal bipyramidal
crossover behavior,5 we prepared a bis(thiocyanato) derivative geometries are found in solid-state structures of the Cu(II) and Zn(II)
5-Fe(NCS)2, in addition to 5-Fe. Their temperature-dependent derivatives. Indeed, the optical spectra, solution magnetic suscepti-
magnetic behavior was investigated by solid-state SQUID bility measurements, and temperature-dependent SQUID magne-
magnetometry. For compounds 5-Fe and 5-Fe(NCS)2, the plots tometry data are consistent in both the solid-state and solution
of DC susceptibility vs. temperature exhibited room tempera- analyses, confirming the structural integrity of the dissolved com-
ture wmT values of 3.98 emu K molꢂ1 and 3.76 emu K molꢂ1 plexes remains intact.
(indicative of electron g-factors greater than 2.00), which
Notably, 5-Fe represents a rare example of an iron bis(bipyridine)
steadily decreased to final wmT values of 2.70 emu K molꢂ1 and complex possessing two labile monodentate ligands. Synthetic
1.64 emu K molꢂ1 respectively (Fig. 6). Room temperature wmT routes to [Fe(bpy)2L2]n+ complexes are elusive due to the favored
values for high-spin Fe(II) complexes are generally in the range of formation of the tris(bpy) complex, which is a consequence of a
3–3.5,60 but higher values have been reported as well.61 This steady change from high spin to low spin between [Fe(bpy)2L2]n+ to the
decrease in wmT can be attributed to zero-field splitting in the more stable spin-paired [Fe(bpy)3]2+ ion.31,32 In addition
complexes and/or thermal depopulation of excited electronic to steric considerations, we hypothesize that the biphenyl-
states. Spin crossover behavior was not observed as the com- linked bis(bipyridine) ligand may prevent this spin change
pounds maintained high-spin electron configurations over the and negate the thermodynamic driving force that would other-
entire temperature range, as indicated by the absence of a wise favor the tris(bpy) derivative. Spin crossover behavior was
precipitous drop of the wmT values at lower temperatures.
not observed in the iron(II) compounds 5-Fe and 5-Fe(NCS)2.
These results indicate that 5 weakens the ligand field strength
around iron and, due to its limited flexibility, may be less
accommodating to the changes in metal–ligand bond distances
that accompany a spin transition from high-to-low.
Conclusions
In closing, we report an improved synthesis of a rigid poly-
aromatic N4-donor ligand and have greatly expanded its known
coordination chemistry. Structural, electrochemical, spectroscopic,
and magnetic properties of a series of mid-to-late first-row transi-
tion metal complexes supported by the tetradentate polypyridine
scaffold have been investigated. From X-ray crystallography, the
ligand field around each metal ion is noticeably constrained by the
limited flexibility (confined to rotation about the single bonds
connecting each aromatic unit) afforded by the biphenyl backbone.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
High spin electronic states, based in part on the metal–ligand bond Acknowledgment is made to the donors of The American
lengths, and distorted octahedral geometries are observed for the Chemical Society Petroleum Research Fund for support of this
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15 (a) D. F. Evans, J. Chem. Soc., 1959, 2003–2005; (b) G. A. Bain
and J. F. Berry, J. Chem. Educ., 2008, 85, 532–536.
16 APEX2, v. 2009, Bruker Analytical X-Ray Systems, Inc,
Madison, WI, 2009.
research (58707-DNI3). We also acknowledge seed grant fund-
ing from the National Science Foundation (OIA-1539035) and
start-up support from the University of Mississippi.
17 G. M. Sheldrick, SADABS, Version 2.03, Bruker Analytical
X-ray Systems, Inc, Madison, WI, 2000.
18 (a) G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr.,
1990, 46, 467–473; (b) G. M. Sheldrick, Acta Crystallogr., Sect. A:
Found. Crystallogr., 2008, 64, 112–122; (c) G. M. Sheldrick,
SHELXL-2014/7: Program for crystal structure determination,
References
1 (a) T. J. Collins, Acc. Chem. Res., 1994, 27, 279–285; (b) P. Comba,
Coord. Chem. Rev., 1999, 182, 343–371; (c) R. D. Hancock, Chem.
Soc. Rev., 2013, 42, 1500–1524.
¨
¨
University of Gottingen, Gottingen, Germany, 2014.
19 (a) A. L. Spek, PLATON – A Multipurpose Crystallographic
Tool, Utrecht University, Utrecht, The Netherlands, 2007;
(b) A. L. Spek, PLATON SQUEEZE: A tool for the calculation
of the disordered solvent contribution to the calculated
structure factors, Acta Crystallogr., Sect. C: Struct. Chem.,
2015, 71, 9–18.
2 E. Mu¨ller, C. Piguet, G. Bernardinelli and A. F. Williams,
Inorg. Chem., 1988, 27, 849–855.
3 (a) O. P. Anderson, J. Becher, H. Frydendahl, L. F. Taylor and
H. Toftlund, J. Chem. Soc., Chem. Commun., 1986, 699–701;
(b) S. Knapp, T. P. Keenan, X. Zhang, R. Fikar, J. A. Potenza
and H. J. Schugar, J. Am. Chem. Soc., 1990, 112, 3452–3464;
(c) E. Mu¨ller, G. Bernardinelli and J. Reedijk, Inorg. Chem.,
1996, 35, 1952–1957; (d) M. R. Malachowski, M. Adams,
N. Elia, A. L. Rheingold and R. S. Kelly, J. Chem. Soc., Dalton
Trans., 1999, 2177–2182.
20 H. Putz and K. Bradenburg, Diamond – Crystal and Molecular
Structure Visualization, Crystal Impact: GbR, Kreuzherrenstr., 102,
53227 Bonn, Germany, http://www.crystalimpact.com/diamond.
21 X. Guo, G. Deng and C.-J. Li, Adv. Synth. Catal., 2009, 351,
2071–2074.
´
4 (a) M. Reglier, C. Jorand and B. Waegell, J. Chem. Soc., Chem.
Commun., 1990, 1752–1755; (b) M. R. Malachowski, A. S. Kasto,
M. E. Adams, A. L. Rheingold, L. N. Zakharov, L. D. Margerum
and M. Greaney, Polyhedron, 2009, 28, 393–397.
5 (a) H. Petzold and S. Heider, Eur. J. Inorg. Chem., 2011,
1249–1254; (b) S. Heider, H. Petzold and G. Teucher,
Eur. J. Inorg. Chem., 2013, 2382–2388.
¨
22 M. Bottger, B. Wiegmann, S. Schaumburg, P. G. Jones,
W. Kowalsky and H.-H. Johannes, Beilstein J. Org. Chem.,
2012, 8, 1037–1047.
23 R. J. M. Klein Gebbink, R. T. Jonas, C. R. Goldsmith and
T. D. P. Stack, Inorg. Chem., 2002, 41, 4633–4641.
24 A. W. Addison, T. N. Rao, J. Reedijk, J. van Rijn and G. C.
Verschoor, J. Chem. Soc., Dalton Trans., 1984, 1349–1356.
25 R. D. Shannon, Acta Crystallogr., Sect. A: Cryst. Phys., Diffr.,
Theor. Gen. Crystallogr., 1976, 32, 751–767.
26 N. Palanisami and R. Murugavel, Inorg. Chim. Acta, 2011,
365, 430–438.
27 K. B. Dillon, C. Bilton, J. A. K. Howard, V. J. Hoy, R. M. K.
Deng and D. T. Sethatho, Acta Crystallogr., Sect. C: Cryst.
Struct. Commun., 1999, 55, 330–332.
¨
6 (a) M. Kettunen, C. Vedder, F. Schaper, M. Leskela,
I. Mutikainen and H.-H. Brintzinger, Organometallics,
2004, 23, 3800–3807; (b) C. Vedder, F. Schaper, H.-
H. Brintzinger, M. Kettunen, S. Babik and G. Fink, Eur.
J. Inorg. Chem., 2005, 1071–1080; (c) G. J. P. Britovsek,
J. England and A. J. P. White, Dalton Trans., 2006, 1399–1408;
(d) T. Chen, X.-G. Liu and M. Shi, Tetrahedron, 2007, 63,
4874–4880.
7 M. A. Halcrow, Polyhedron, 2007, 26, 3523–3576.
8 S. O. Schmidt, S. Kisslinger, C. Wu¨rtele, S. Bonnet, S. Schindler
and F. Tuczek, Z. Anorg. Allg. Chem., 2013, 639, 2774–2778.
9 P. Gu¨tlich, A. B. Gaspar and Y. Garcia, Beilstein J. Org. Chem.,
2013, 9, 342–391.
28 M. Shao, Z.-X. Miao and M.-X. Li, Acta Crystallogr., Sect. E:
Struct. Rep. Online, 2006, 62, m2575–m2577.
29 G. Fernandez, M. Corbella, M. Alfonso, H. Stoeckli-Evans
´
and I. Castro, Inorg. Chem., 2004, 43, 6684–6698.
30 X.-M. Chen, K.-L. Shi, T. C. W. Mak and B.-S. Luo, Acta
Crystallogr., Sect. C: Cryst. Struct. Commun., 1995, 51, 358–361.
31 H. Irving and D. H. Mellor, J. Chem. Soc., 1962, 5222–5237.
´
10 (a) A. Bousseksou, G. Molnar, L. Salmon and W. Nicolazzi,
Chem. Soc. Rev., 2011, 40, 3313–3335; (b) S. Brooker, Chem.
Soc. Rev., 2015, 44, 2880–2892; (c) M. A. Halcrow, Crystals,
2016, 6, 58.
ˆ
32 M.-N. Collomb, A. Deronzier, K. Gorgy and J.-C. Lepretre,
New J. Chem., 2000, 24, 455–461.
11 E. C. Constable, G. Baum, E. Bill, R. Dyson, R. van Eldik,
D. Fenske, S. Kaderli, D. Morris, A. Neubrand, M. Neuburger,
D. R. Smith, K. Wieghardt, M. Zehnder and A. D. Zuberbu¨hler,
Chem. – Eur. J., 1999, 5, 498–508.
33 S. Parsons, R. Winpenny and P. A. Wood, CCDC 248214:
Experimental Crystal Structure Determination, 2014, DOI:
10.5517/cc8b8xr.
34 Y. Wang, X. Ma, S. Hu, Y. Wen, Z. Xue, X. Zhu, X. Zhang,
T. Sheng and X. Wu, Dalton Trans., 2014, 43, 17453–17462.
35 M. Konno and M. Mikami-Kido, Bull. Chem. Soc. Jpn., 1991,
64, 339–345.
36 S.-P. Luo, L.-Z. Tang and S.-Z. Zhan, Inorg. Chem. Commun.,
2017, 86, 276–280.
12 E. D. McKenzie, Coord. Chem. Rev., 1971, 6, 187–216.
13 D. Onggo and H. A. Goodwin, Aust. J. Chem., 1991, 44, 1539–1551.
14 (a) L. Chen, A. Khadivi, M. Singh and J. W. Jurss, Inorg.
Chem. Front., 2017, 4, 1649–1653; (b) X. Su, K. M. McCardle,
J. A. Panetier and J. W. Jurss, Chem. Commun., 2018, 54,
3351–3354; (c) W. Yang, S. Sinha Roy, W. C. Pitts, R. Nelson,
F. R. Fronczek and J. W. Jurss, Inorg. Chem., 2018, 57,
9564–9575.
37 S. Gao, J.-W. Liu, L.-H. Huo and H. Zhao, Acta Crystallogr.,
Sect. E: Struct. Rep. Online, 2004, 60, m1202–m1204.
18676 | New J. Chem., 2018, 42, 18667--18677 This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018

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NJC
Paper
38 K. A. Kumar, M. Amuthaselvi and A. Dayalan, Acta Crystal- 49 G. Singh, I. P. S. Kapoor, D. Kumar, U. P. Singh and N. Goel,
logr., Sect. E: Struct. Rep. Online, 2011, 67, m468. Inorg. Chim. Acta, 2009, 362, 4091–4098.
39 V. Ciornea, L. Mingalieva, J.-P. Costes, G. Novitchi, 50 S. A. Richert, P. K. S. Tsang and D. T. Sawyer, Inorg. Chem.,
I. Filippova, R. T. Galeev, S. Shova, V. K. Voronkova and
A. Gulea, Inorg. Chim. Acta, 2008, 361, 1947–1957.
40 B.-S. Zhang, Z.-X. Liu, L.-H. Liu, T. Pan and S.-F. Ye,
Acta Crystallogr., Sect. E: Struct. Rep. Online, 2009, 65,
m48.
1989, 28, 2471–2475.
´
´
51 J. P. F. Rebolledo-Chavez, M. Cruz-Ramırez, R. Patakfalvi,
F. J. Tenorio Rangel and L. Ortiz-Frade, Electrochim. Acta,
2017, 247, 241–251.
ˆ
52 M.-N. Collomb, A. Deronzier, K. Gorgy and J.-C. Lepretre,
41 M. Garai, D. Dey, H. R. Yadav, A. R. Choudhury, N. Kole and
B. Biswas, Polyhedron, 2017, 129, 114–122.
New J. Chem., 2000, 24, 455.
53 M. A. W. Lawrence and A. A. Holder, Inorg. Chim. Acta, 2016,
42 D. J. Chesnut, R. C. Haushalter and J. Zubieta, Inorg. Chim.
Acta, 1999, 292, 41–51.
441, 157.
54 R. Prasad and D. B. Scaife, J. Electroanal. Chem., 1977, 84,
´
´
´
´
43 Y. Rodrıguez-Martın, J. Gonzalez-Platas and C. Ruiz-Perez,
373–386.
Acta Crystallogr., Sect. C: Cryst. Struct. Commun., 1999, 55, 55 P. N. Bartlett and V. Eastwick-Field, Electrochim. Acta, 1993,
1087–1090. 38, 2515–2523.
44 B. Hipler, M. Doring, C. Dubs, H. Gorls, T. Hu¨bler and 56 O. S. Fomina, Y. A. Kislitsyn, V. M. Babaev, I. K. Rizvanov,
¨
¨
E. Uhlig, Z. Anorg. Allg. Chem., 1998, 624, 1329–1335.
45 M. A. Sharif, M. Tabatabaee, V. Beik and H. R. Khavasi,
O. G. Sinyashin, J. W. Heinicke and D. G. Yakhvarov, Russ.
J. Electrochem., 2015, 51, 1069–1078.
CCDC 749881: Experimental Crystal Structure Determination, 57 R. R. Ruminski, Inorg. Chim. Acta, 1985, 103, 159–161.
2014, DOI: 10.5517/cct59qz.
46 A. Jayamani, N. Sengottuvelan, S. K. Kang and Y.-I. Kim,
Polyhedron, 2015, 98, 203–216.
47 P. Nagle, E. O0Sullivan, B. J. Hathaway and E. Mu¨ller,
J. Chem. Soc., Dalton Trans., 1990, 0, 3399–3406.
48 J.-C. Yao, F.-J. Yao, J.-B. Guo, W. Huang and S.-H. Gou,
CCDC 271110: Experimental Crystal Structure Determina-
tion, 2014, DOI: 10.5517/cc933hz.
58 R. J. Crutchley, R. Hynes and E. J. Gabe, Inorg. Chem., 1990,
29, 4921–4928.
59 F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry,
Wiley-Interscience: New York, 5th edn, 1988.
60 S. Kisslinger, H. Kelm, S. Zheng, A. Beitat, C. Wu¨rtele,
R. Wortmann, S. Bonnet, S. Herres-Pawlis, H.-J. Kru¨ger and
S. Schindler, Z. Anorg. Allg. Chem., 2012, 638, 2069–2077.
61 A. Kimura and T. Ishida, Inorganics, 2017, 5, 52–63.
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