Azido, cyanato, and thiocyanato coordination induced distortions in pentacoordinated [CoIIA(bip)]2 (A = NCS-, N3-, or NCO-) Complexes

Article abstract of DOI:10.1002/ejic.200900577

A new family of distorted pentacoordinate [Co₂] complexes was prepared and structurally characterized. In [Co^IIA-(bip)] ₂·S (1-3) [A = NCS^-, N₃^-, NCO^-; S = dmf, MeOH, dcm; Hbip =

Full text of DOI:10.1002/ejic.200900577

FULL PAPER
DOI: 10.1002/ejic.200900577
Azido, Cyanato, and Thiocyanato Coordination Induced Distortions in
Pentacoordinated [CoIIA(bip)]2 (A = NCS–, N3 , or NCO–) Complexes
–
Mrinal Sarkar,[a] Rodolphe Clérac,[b,c] Corine Mathonière,[d,e] Nigel G. R. Hearns,[b,c]
Valerio Bertolasi,[f] and Debashis Ray*[a]
Keywords: N,O ligands / Bridging ligands / Cobalt / Structure elucidation / Magnetic properties
A new family of distorted pentacoordinate [Co2] complexes
was prepared and structurally characterized. In [CoIIA-
(bip)]2·S (1–3) [A = NCS–, N3–, NCO–; S = dmf, MeOH, dcm;
Hbip = 2,6-bis(phenylmethyliminomethyl)-4-methylphenol],
the nonbonded Co···Co separations are in the 3.243 to
3.254 Å range, and the pseudohalide-coordinated CoII ions
are asymmetrically doubly bridged by the phenolate oxygen
atoms of the ligand. The complementary basal–apical (b–a)
and apical–basal (a–b) coordination modes of the phenolate
bridges of bip– offer one O and two N donors for metal-ion
coordination. In the three dinuclear complexes, the h.s. CoII
ions are coupled antiferromagnetically to yield a singlet
ground state. The solid-state variable-temperature magnetic
susceptibility measurement data on the complexes were fit-
ted to an isotropic Heisenberg dimer model that allowed esti-
mation of the antiferromagnetic interactions for 1–3.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
tain symmetry.[10] Several reports have been made on octa-
hedral (Oh) or tetrahedral (Td) symmetries,[11–16] and only
few cases are known in distorted trigonal-bipyramidal
(TBP) or square-pyramidal (SP) symmetries.[17–22] The mag-
netic properties of CoII in the low TBP or SP symmetries
can be treated in a simple manner, as the ground term does
not have first-order orbital angular momentum; thus, a
spin-only treatment is valid.[9,10,23] Recently, it was reported
Introduction
The synthesis and synthetic applications of high-spin
CoII complexes have been the subject of current research
2
in controlled preparation, molecular structure, and magnet-
ism.[1–5] These complexes have attracted attention because
of their fascinating magnetic properties as well as their bio-
logical relevance. In the first context, dinuclear CoII com-
plexes may act as mimics of the active biosites such as in
methionine aminopeptidase[6] and can show DNA cleavage
activity.[7] Methionine aminopeptidase is known to be a Co2
metallohydrolase responsible for removal of the N-terminal
methionine from protein chains and contains cobalt ions in
distorted octahedral and trigonal bipyramidal geometries.[8]
that low-spin square-planar CoII diporphyrin complexes
2
having a Pac-Man-like cleft can show interesting dioxygen
reduction chemistry.[24] Because of these different features
of the Co2+ ion, earlier we studied its coordination behavior
and reactivity toward imidazolidinyl trisphenol ligands.[25]
Recently, we also reported the successful use of one 2,6-
diformyl-4-methylphenol (Hdfp) or 2,6-bis(benzyliminome-
thyl)-4-methylphenol (Hbip) (Scheme 1) as coligands for the
High-spin CoII complexes show difficulties in magnetic
2
analysis because of orbital angular momentum,[9] which is
completely or partially quenched in a ligand field of a cer-
preassembly of CoII units as a template for binding of
2
imidazolidinyl trisphenol ligand.
[a] Department of Chemistry, Indian Institute of Technology,
Kharagpur 721302, India
Fax: +91-3222-82252
E-mail: dray@chem.iitkgp.ernet.in
[b] CNRS, UPR 8641, Centre de Recherche Paul Pascal (CRPP),
Equipe “Matériaux Moléculaires Magnétiques”,
115 avenue du Dr. Albert Schweitzer, Pessac 33600, France
[c] Université de Bordeaux, UPR 8641,
Pessac 33600, France
[d] CNRS, UPR 9048, Institut de Chimie de la Matière Condensée
de Bordeaux (ICMCB),
Scheme 1.
87 avenue du Dr. Albert Schweitzer, Pessac 33608, France
[e] Université de Bordeaux, UPR 9048,
The main objectives of the present investigation are (i) to
scrutinize the efficacy of the bridging phenolate-only li-
gands to assemble discrete [Co2L2]-type complexes, (ii) to
examine the role of different pseudohalides for geometric
distortions in such an assembly process, and (iii) to stabilize
Pessac 33608, France
[f] Dipartimento di Chimica e Centro di Strutturistica Diffratto-
metica, Università di Ferrara,
via Borsari 46, 44100 Ferrara, Italy
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.200900577.
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M. Sarkar, R. Clérac, C. Mathonière, N. G. R. Hearns, V. Bertolasi, D. Ray
FULL PAPER
Scheme 2. Possible binding mode of bridging phenolate groups of two ligands.
analogous to that reported earlier in the literature[34] and
its reaction with cobalt(II) salts was investigated in the pres-
ence of three pseudohalides. Satisfactory routine characteri-
zations were made from melting-point determinations, ele-
mental analyses, FTIR, and 1H and 13C NMR spec-
troscopy. A general procedure, as depicted in Scheme 3, was
followed for the synthesis of complexes 1–3 in the presence
of stoichiometric amounts of NH4SCN, NaN3, and Na-
OCN, cobalt(II) salts, and Hbip in CH3OH at room tem-
perature in air.
the 2+ oxidation states of cobalt in highly distorted coordi-
nation environments using nonplanar (basal–apical) phe-
nolate bridges (Scheme 2). We have successfully achieved
our goal by using Hbip.
The choice of the ligands are important, as they can exhi-
bit nonplanar binding modes and nonregular coordination
geometries, which are often noticed in dinuclear CoII active
sites in proteins. Thus, the manipulation of the binding
ability of the donor atoms of the ligand system around the
cobalt ions is crucial to control the metal-ion coordination
geometries. CoII ions can adopt various geometries such as
tetrahedral, square-planar, square-pyramidal, and trigonal
bipyramidal, in addition to their distorted versions, de-
pending upon the steric and electronic nature of the donor
atoms.[26–32] Newer types of coordination behavior of Hbip
(Scheme 1) have been explored for various reasons, includ-
ing their importance in coordination chemistry, molecular
magnetism, and catalysis.[33] Herein three complexes [CoII-
This synthetic procedure allows the synthesis of neutral
[CoIIA(bip)]2 complexes with high purity and in very good
yield. Addition of an excess amount of NH4SCN, NaN3,
or NaOCN could not yield any isothiocyanato-, azido-, or
cyanato-bridged di or tetracobalt complex. (Scheme 3)
With a similar type of di-Schiff base H3bemp ligand
(Scheme 1) having two more terminal alcohol groups, we
earlier showed the µ3-OMe bridge driven aggregation of a
[CoIII4] species.[35] Exactly similar to this, we tried to obtain
µ3-OMe/A bridged compound 7 (Scheme 3). We were un-
able to characterize and crystallize any of such compounds.
The macrocyclic template effect was observed earlier in the
closely related dioxime-based ligand Hdox (Scheme 1) for
an octahedral high-spin dicobalt(II) complex.[36] Expected
compound 4 was not isolated from the reaction of Hbip
with Co(OAc)2·4H2O, Co(NO3)2·6H2O, or Co(ClO4)2·
6H2O in the absence of A– in MeOH. In different crystalliz-
ing solvents and solvent mixtures, X-ray quality single crys-
tals of 1–3 were obtained. Weakly coordinating or nonco-
–
A(bip)]2·S (1–3) (A = NCS–, N3 , or NCO–; S = dmf,
MeOH, dcm) derived from the nonplanar assembly of two
Hbip ligands following three different pseudohalide coordi-
nation driven routes are reported. Selective binding of a
single pseudohalide anion to each CoII ion is responsible
for the nonplanar orientation of the ligands, resulting in
distortions of the pentacoordinate coordination geometries
unknown in synthesis but well recognized in biology. Com-
plexes 1–3 were crystallographically characterized and their
magnetic properties in highly distorted environments were
scrutinized.
–
–
ordinating anions like ClO4 , NO3 , or AcO– bearing cobalt
salts do not yield any characterizable product. Only the ex-
ternal addition of NaN3, NaOCN, or NH4SCN to the reac-
tion mixture led to the high-yield formation of pentacoordi-
Results and Discussion
Syntheses and Spectroscopic Characterizations
The synthesis and initial purification of Hbip [2,6-bis- nate dicobalt assemblies of nonregular coordination geome-
(phenylmethyliminomethyl)-4-methylphenol] (Scheme 1) is tries. This verifies the superior coordination ability of
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Ligand-Induced Distortions in Pentacoordinated [CoIIA(bip)]2
Scheme 3. Schematic representation for preferred ligand and pseudohalide binding for [Co2] assembly in three cases compared to other
unknown species.
Scheme 4. Likely mechanism of formation of [CoA(bip)]2·S (1–3) (A = NCS–, N3 , or NCO–; S = dmf, MeOH, dcm) by dimerization of
–
two initially formed monocobalt species through diphenolate basal–apical (b–a) bridges.
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FULL PAPER
NCS–, N3 , or NCO– as coligands against AcO–, NO3 , or bands at ca. 250 and ca. 325 nm can be assigned to the
–
–
– [37]
ClO4 . Presumably coordination of one A– and two sol- πǞπ* transition associated with the azomethine
vent molecules to each cobalt center and dimerization of group.[42,43] The moderately intense band at ca. 400 nm can
the neutral [CoIIA(bip)S2] species lead to the formation of be assigned to charge-transfer (CT) bands centered at
1–3 through phenolate basal–apical connection of the the CoII center and coordinated to bip–. A solution of 1
strong–weak category (I to III in Scheme 4). The neutral registers the d–d transition band at 578 nm (ε
=
=
complexes are either insoluble or sparingly soluble in water 199 Lmol–1 cm–1) and CT bands at 398 (ε
and common organic solvents, but they are soluble in polar 7360 Lmol–1 cm–1), 326 (ε
=
8590 Lmol–1 cm–1), and
organic solvents such as CH2Cl2, dmf, and dmso.
250 nm (23870 Lmol–1 cm–1). The only d–d transition may
4
4
The compounds appear to be stable both in the solid be assigned to the AЈ2(F) Ǟ AЈ2(P) transition.[44] A dmf
state and in solution, and they all melt above 350 °C. The solution of 2 exhibits all the above-mentioned electronic
molar conductivity (ΛM) values of all three complexes are transitions at 578 (ε = 439 Lmol–1 cm–1), 398 (ε =
in the range 6–10 Ω–1 cm2 mol–1 (28 °C) and correspond to 3683 Lmol–1 cm–1), 326 (ε
=
4016 Lmol–1 cm–1), and
electroneutral character.
252 nm (ε = 14787 Lmol–1 cm–1). Compound 3 showed the
Steric crowding around the imine nitrogen atoms plays corresponding transitions at 581 (ε = 291 Lmol–1 cm–1), 400
an important role towards the solid-state crystallization of (6721 Lmol–1 cm–1), 327 (4231 Lmol–1 cm–1), and 251 nm
the complexes. Substitution of benzylamine in the synthesis (21692 Lmol–1 cm–1), respectively.
of Hbip by aniline and cyclohexylamine give Hpip and
Hcip, in which the imine nitrogen atoms are more crowded
(Scheme 3). Reaction of these two ligands with cobalt(II)
Description of the Structures
salts in presence of three different pseudohalides gave no
solid isolable product. Thus, the presence of methylene spa-
cers in the bip– ligands contribute to the distortion of the
pentacoordinate geometries around the cobalt(II) ions (vide
supra). In MeOH, the reaction of either Co(OAc)2·4H2O or
Co(NO3)2·6H2O or Co(ClO4)2·6H2O and NH4SCN or
NaN3 or NaOCN followed by the addition of a methanolic
solution of Hbip in a 1:2:2 molar ratio does not yield mo-
nonuclear complex 8 bearing the zwitterionic ligand H2bip+
(Scheme 3).
Single crystals suitable for X-ray structure determi-
nations were obtained by slow evaporation of a dmf solu-
tion of 1, a dcm/MeOH (1:1) solution of 2, and a dmf/dcm
solution of 3 after a week. Selected interatomic distances
and angles are collected in Table 1, and the crystallographic
data are summarized in Table 2.
The atom labeling scheme and molecular views (ORTEP)
of the complexes are shown in Figures 1–3. The three dif-
ferent solvents, dmf, MeOH, and dcm, either in pure form
or in a mixture, play important roles in the crystallization
process. Quality single crystals suitable for X-ray diffraction
analysis are only obtained from the above-stated choices of
single solvent and solvent mixtures.
Infrared Spectroscopy
The sharp peaks in the FTIR spectra of 1·dmf,
2·CH3OH, and 3·CH2Cl2 at 1628, 1627, and 1629 cm–1,
respectively, are characteristic of the C=N functionalities of
the deprotonated ligand bip–. The ν(C=N) stretching fre-
quency of the free ligand is observed at 1636 cm–1. Complex
1·dmf records one strong band at 2070 cm–1 for the ν(CN)
stretching of the terminally coordinated NCS–[38] ion, but
the ν(CS) stretching frequency in the 700–825 cm–1 region
could not be identified with certainty in the presence of
strong absorptions by the organic ligand in this region.[39]
Terminal coordination of azide groups to cobalt(II) ions in
2·CH3OH shows a very strong sharp band at 2050 cm–1 and
[CoII(NCS)(bip)]2·dmf (1·dmf)
The molecular structure of [CoII(NCS)(bip)]2 is shown in
Figure 1 together with the atom labeling scheme used. The
structure consists of a [CoII(NCS)(bip)]2 dinuclear complex.
Each cobalt atom is coordinated by the two imine nitrogen
atoms of two ligands, two phenolate oxygen atoms of two
ligands, and one nitrogen end of the NCS– group. The four-
membered ring formed by the two cobalt atoms and two
phenolate oxygen atoms of the bridge is essentially planar,
and none of the atoms deviate from the least-squares plane
by more than 0.936 Å. This [Co2O2] core is formed from
asymmetric [Co1–O1 1.979(3), Co1–O2 2.142(3), Co2–O1
2.136(3), and Co2–O2 1.976(3) Å] basal–apical bridging by
two phenolate oxygen atoms, and the two cobalt(II) centers
are separated by 3.24 Å (Supporting Information, Fig-
ure S1), which is different from the situation found in other
phenolate-oxygen-bridged dinuclear cobalt(II) com-
plexes.[45,46] This asymmetric bridging also contributes to
the increase in the Co···Co separation.
–
–
a weak band at 1345 cm–1 for the νas(N3 ) and νs(N3 )
stretching vibrations, respectively.[40] NCO–-bonded
3·CH2Cl2 registers a strong band at 2207 cm–1 for the asym-
metric ν(CN) stretching vibration and a medium intensity
peak at 1345 cm–1, which can be attributed to the pseudo-
symmetric ν(CO) stretching. The bending mode δNCO of
the coordinated cyanate anion could not be located in the
600–825 cm–1 region under the absorptions of the bip–
ion.[41]
The dihedral angle between the two O–Co–O planes of
the [Co2O2] core is 157.6°. The sums of the angles around
the oxygen atoms of the two phenolate oxygen bridges are
Electronic Spectroscopy
The electronic spectra of 1–3 in dmf solutions show sim- 358.9 and 360.0° and demonstrate that a trigonal planar
ilar spectral features in the 250–600 nm region. The intense orientation is more pronounced. The O–Co–O angles
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Ligand-Induced Distortions in Pentacoordinated [CoIIA(bip)]2
Table 1. Selected interatomic distances [Å] and angles for com-
plexes 1·dmf, 2·CH3OH, and 3·CH2Cl2.[a]
1·dmf
Co1–O1
Co1–O2
Co1–N1
Co1–N3
Co1–N5
Co1···Co2
O1–Co1–O2 73.1(1)
O1–Co1–N1 89.6(1)
O1–Co1–N3 118.8(1)
O1–Co1–N5 130.0(2)
O2–Co1–N1 161.6(1)
O2–Co1–N3 83.4(1)
O2–Co1–N5 89.0(1)
N1–Co1–N3 111.1(2)
N1–Co1–N5 97.7(2)
N3–Co1–N5 104.4(2)
Co1–O1–Co2 104.0(1)
O1–Co2–O2 73.3(1)
1.979(3)
2.142(3)
2.050(4)
2.061(4)
2.008(4)
3.2439(8)
Co2–O1
Co2–O2
Co2–N2
Co2–N4
Co2–N6
2.136(3)
1.976(3)
2.060(4)
2.068(4)
1.996(4)
O1–Co2–N2
O1–Co2–N4
O1–Co2–N6
O2–Co2–N2
O2–Co2–N4
O2–Co2–N6
N2–Co2–N4
N2–Co2–N6
N4–Co2–N6
Co1–O2–Co2
Co1–N5–C47
Co2–N6–C48
84.9(1)
162.5(1)
91.0(2)
118.4(1)
89.8(2)
125.3(2)
107.6(2)
111.6(2)
95.4(2)
103.9(1)
163.2(4)
162.8(4)
2·CH3OH
Figure 1. Labeled ORTEP view of [Co2(NCS)2bip2]·dmf (1·dmf)
with atom numbering scheme. Thermal ellipsoids are drawn at the
30% probability level; H atoms are omitted for clarity.
N2–Co1
Co1–O1*
Co1–N3
2.067(2)
1.976(1)
2.030(2)
Co1–N1
Co1–O1
Co1···Co1*
O1*–Co1–O1
N3–Co1–O1
N1–Co1–O1
N2–Co1–O1
2.058(2)
2.128(1)
3.2541(8)
72.30(6)
91.32(7)
83.46(6)
158.39(6)
O1*–Co1–N3 136.94(8)
O1*–Co1–N1 118.39(6)
N3–Co1–N1 98.05(8)
O1*–Co1–N2 89.11(6)
N3–Co1–N2 95.17(8)
N1–Co1–N2 115.85(7)
the phenolate oxygen atoms vary significantly [Co1–O1
1.979(3) and Co1–O2 2.142(3) Å], with the shorter value
corresponding to the basal binding. However, the apical dis-
tances do not fall in the usual range of average CoII–Oph
distances observed in other pentacoordinate cobalt(II) com-
plexes.[19,42,45,46] The magnetically important Co–O–Co
angles are 104.0(1) and 103.9(1)°. The CoII–Nim distances
are similar [Co1–N1 2.050(4), Co1–N3 2.061(4), Co2–N2
2.060(4), and Co2–N4 2.068(4)] and are close to the bond
lengths observed in other pentacoordinate cobalt(II) com-
plexes.[42,43,45] The terminal Co–NNCS distances are similar
[Co1–N5 2.008(4) Å; Co2–N6 1.996(4) Å] and slightly
shorter than the average Co–Nim distance.[48] The thiocya-
nate terminal groups are almost linear, with N–C–S angles
of 178.6(5) and 179.1(5)°. The nonlinear monodentate coor-
dination of NCS– is reflected in the Co–N–C angles of
163.2(4) and 162.8(4)°.
Co1*–O1–Co1 104.89(6)
N4–N3–Co1
126.4(2)
3·CH2Cl2
N2–Co1
Co1–O1*
Co1–N3
2.070(4)
2.146(3)
1.984(5)
Co1–N1
Co1–O1
2.087(4)
1.967(3)
3.242(1)
72.3(2)
133.4(2)
88.3(1)
114.5(1)
104.0(1)
171.6(5)
Co1···Co1*
O1*–Co1–O1
N3–Co1–O1
N1–Co1–O1
N2–Co1–O1
Co*–O1–Co1
C24–N3–Co1
O1*–Co1–N3 90.3(2)
O1*–Co1–N1 159.1(1)
N3–Co1–N1 98.0(2)
O1*–Co1–N2 83.4(1)
N3–Co1–N2 105.6(2)
N1–Co1–N2 112.4(1)
[a] *: 1 – x, y, 1/2 – z.
[73.1(2) and 73.3(1)°] within the [Co2O2] diamond core indi-
cate considerable distortions at the metal ions. Two CoII
ions in distorted tbp polyhedra share the basal–apical:api-
cal–basal (b–a:a–b) mode of binding (Scheme 2b). Two
other alternative modes 1a and 1c are not observed. The
values of the trigonality index, τ, of the two cobalt(II) cen-
ters are 0.52 and 0.61, respectively [where β represents the
angles N1–Co1–O2 161.6(1)° and N4–Co2–O1 162.5(1)°; α
represents O1–Co1–N5 130.0(2) and O2–Co2–N6
125.3(2)°].[47] For an ideal value of β equal to 180° the cor-
responding τ values would have been 0.83 and 0.91. The
equatorial plane consists of the one phenolate oxygen atom,
one imine nitrogen atom of the other ligand, and the nitro-
The compound crystallizes with one disordered dimeth-
ylformamide solvent molecule, which is captured within the
crystal lattice through C–H···O hydrogen bonds [C8···O1A
(x – 1, y, z – 1) 3.15(1) Å and C8···O1B (x – 1, y, z – 1)
3.22(1) Å, for the two disordered moieties of dmf]. The
crystal-packing diagram along the a axis show regular ar-
rangement of isolated couples of 1 and dmf molecules with-
out any other intermolecular short contacts (Supporting In-
formation, Figure S2).
[CoII(N3)(bip)]2·CH3OH (2·CH3OH)
The molecular structure of [CoII(N3)(bip)]2 is shown in
gen end of the thiocyanate anion. The other imine nitrogen Figure 2 together with the atom labeling scheme used. A
atom and the second bridging phenolate oxygen atom are mononuclear CoII fragment and 1/2 molecule of solvent
in the apical positions. The angles around the CoII center methanol build up the crystallographic asymmetric unit.
in the equatorial plane differ considerably from the ideal Complex 2·CH3OH is a CoII dinuclear complex in the form
value of 120° [N3–Co1–O1 118.8(1), N3–Co1–N5 104.4(2), of two fused distorted TBPs of the [Co2N6O2] core. The
and N5–Co1–O1 130.0(2)°]. Bond lengths between CoII and dinuclear aggregate is bridged and chelated by two ligands
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FULL PAPER
–
in the same manner as in 1, with the exception that N3
cant H-bonding network is observed. A crystal-packing
ions are more angularly bound to the cobalt(II) ions and diagram along the c axis is shown in the Supporting Infor-
the presence of one methanol molecule of crystallization. mation (Figure S4).
The structure consists of a [CoII(N3)(bip)]2 moiety that pos-
[CoII(NCO)(bip)]2·CH2Cl2 (3·CH2Cl2)
sesses a crystallographic twofold rotational axis of sym-
The ORTEP view of [CoII(NCO)(bip)]2 is shown in Fig-
ure 3 together with the atom labeling scheme used. The last
member (i.e., 3) of this series of compounds is obtained by
binding of one NCO– to each of the CoII ions in a similar
manner with one dichloromethane molecule of crystalli-
zation. The asymmetric basal–apical bridging by two phe-
nolate oxygen atoms leads to a Co···Co separation of 3.24 Å
(Supporting Information, Figure S5). The value of the tri-
gonality index, τ, of the cobalt(II) center is 0.42 [where β
represents the angles N1–Co1–O1* 159.1(1)°; α represents
O1–Co1–N3 133.4(2)°], which is smaller than complex 1
but bigger than complex 2.[47]
metry passing through the center of the Co1–O1–Co1*–
O1* ring (*: 1 –x, y, 1/2 – z). Interestingly the value of the
trigonality index, τ, of the cobalt(II) center is 0.35 [where β
represents the angles N2–Co1–O1 158.39(6)°; α represents
O1*–Co1–N3 136.94(8)°], which is smaller than complex
1.[47] The [Co2O2] unit [Co1–O1 2.128(1) and Co1*–O1
1.976(1) Å] is formed from nonsymmetric basal–apical
binding of two phenolate oxygen atoms with a separation
of 3.25 Å (Supporting Information, Figure S3). The acute
O*–Co–O angle of 72.30(6)° within the [Co2O2] core indi-
cates a nonregular coordination site.
Figure 3. Labeled ORTEP view of [Co2(NCO)2bip2]·CH2Cl2
(3·CH2Cl2) with atom numbering scheme. Thermal ellipsoids are
drawn at the 30% probability level; H atoms are omitted for clarity.
Figure 2. Labeled ORTEP view of [Co2(N3)2bip2]·CH3OH
(2·CH3OH) with atom numbering scheme. Thermal ellipsoids are
drawn at the 30% probability level; H atoms are omitted for clarity.
The angles around CoII in the equatorial plane differ
considerably from the ideal value of 120° [N3–Co1–O1
133.4(2), N2–Co1–O1 114.5(1), and N2–Co1–N3
105.6(2)°]. The Co–O–Co angle is 104.0(1). The cyanato
terminal groups are almost linear with an N–C–O angle of
178.1(8)°. The NCO– groups like NCS– and N3– show typi-
The Co–O–Co angle that contributes to the magnetic in-
teractions is 104.89(6)°. The angles around the CoII in the
equatorial plane differ considerably from the ideal value of
120° [N3–Co1–N1 98.05(8), N3–Co1–O1* 136.94(8), and
N1–Co1–O1* 118.39(6)°]. The bond lengths between CoII
and the phenolate oxygen atoms vary significantly [Co1–
O1* 1.976(1) and Co1–O1 2.128(1) Å], with the shorter
value corresponding to the basal binding. However, the api-
cal distances do not fall in the usual range of pentacoordi-
nate CoII–Oph distances. The CoII–Nim [Co1–N1 2.058(2),
Co1–N2 2.067(2) Å] distances are similar and slightly
longer than the Co–NN3 distances [Co1–N3 2.030(2) Å].[48]
The azido terminal groups are almost linear with an N–
cal terminal binding and
a greater Co–N–C angle
–
[171.6(5)°] compared to NCS– and N3 in the previous two
structures. As in the two other complexes, no H-bonding
network is seen in the crystal packing (shown along the b
axis in Figure S6 in the Supporting Information).
The Role of the N-Benzyl Groups of Ligands in Molecular
Distortions
–
N–N angle of 177.7(3)°. The N3 groups show nonlinear
monodentate terminal binding and a smaller Co–N–N an-
The pendant benzyl groups of the ligands are responsible
gle [126.4(2)°] than that of NCS– in previous molecules. In for the noncoplanar placement of the two bip– ligands
the crystal packing, it is worth mentioning that no signifi- around two hs CoII ions. The two CoII ions lie in a distorted
4680
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 4675–4685

Ligand-Induced Distortions in Pentacoordinated [CoIIA(bip)]2
pentacoordination environment defined by three N- and
two O-donor atoms from the two ligands and two pseu-
dohalides. The best mean planes of two coordinated ligands
excluding the N-benzyl groups in three structures are in-
clined at an angle ranging from 54.36 to 63.06° (Figure 4;
Supporting Information, Figure S7). In the presence of one
bound pseudohalide to each CoII this arrangement of the
ligands favor highly distorted coordination geometry and
control the CoII···CoII separations and CoII–O–CoII bridge
angles.
Figure 5. Angle between the chelate rings of bip– and dfp–.
bridging interactions from the phenolate groups in the
basal–apical mode result in intermediate III, which finally
separates 1–3 from the reaction mixture. A similar type of
aggregation reaction of two trinuclear fragments into a
hexanuclear unit was described by us for a NiII6 complex.[51]
Magnetic Properties
The solid-state magnetic properties of 1·dmf, 2·CH3OH,
and 3·CH2Cl2 were investigated by using dc susceptibility
measurements in the temperature range 1.8–300 K in a 1 T
magnetic field (Supporting Information, Figure S8). The
data reported in Figure 6 were plotted as χT vs. T. At room
temperature, the χT products are 4.1, 4.9, and
4.5 cm3 Kmol–1 for 1·dmf, 2·CH3OH, and 3·CH2Cl2,
respectively.
Figure 4. Nonplanar orientations of ligands showing the incli-
nation of the mean planes of two coordinated ligands excluding the
N-benzyl groups in 1·dmf.
A nonsymmetric basal–apical bridge from the phenolate
oxygen atoms further stabilizes the distorted geometries.
This bridge is responsible for the change in metal–metal
separations and metal–oxygen–metal angles, as apical bind-
ing always leads to out-of-plane longer bonds, which is
most common in azido-bridged CuII systems (Scheme 2).[49]
Interestingly with a similar dioxime-based ligand Hdox
(Scheme 1) the dinuclear complex of CoII exhibits a nearly
planar structure in which each metal center adopts an octa-
hedral coordination geometry and basal–basal binding.[36]
The two CoII ions lie in a plane defined by four N- and two
O-donor atoms from the two ligands.
Figure 6. Plot of χT vs. T per mol of 1·dmf, 2·CH3OH, and
3·CH2Cl2 (where χ is defined as M/H per dinuclear CoII complex).
The solid lines are the best fit obtained by using the isotropic dinu-
clear S = 3/2 Heisenberg model described in the text. The inset is
a scheme of the core of 1–3.
Spontaneous Dimerization for Unsymmetrical Phenolate
basal–apical (b–a) and apical–basal (a–b) Bridges
Recently, we reported the coordination behavior of Hdfp
The values of χT are in reasonably good agreement with
as a bridging coligand in the symmetrical basal–basal mode the theoretical value of 3.75 cm3 Kmol–1, which is expected
of binding to octahedral hs CoII ions.[14] The Co–O dis- for two isolated paramagnetic hs Co2+ ions (d7, S = 3/2)
tances were 2.085 and 2.057 Å within the CoII2(dfp) frag- with g = 2. The fact that the observed χT products is
ment. Herein the dihedral angles between the two chelate slightly higher than the theoretical value, indicating a g fac-
rings of bip– in the three complexes are 156.8, 155.8, and tor higher than 2, is likely due to the effects of the magnetic
154.8° as compared to 163.0° observed in the case of dfp– anisotropy associated with each hs Co2+ ion. Upon cooling,
binding (Figure 5).[14,50]
both χT products continuously decrease for all compounds,
The bidentate N,O chelation from one half of the first indicating that dominant antiferromagnetic exchange inter-
–
bip– ligand to CoII and binding of one A– (NCS–, N3 , or actions exist between the two Co2+ ions of the dinuclear
NCO–) and two solvent molecules yield the electroneutral complexes. At 1.8 K and under 1 T, the χT product reaches
intermediate I (Scheme 4). Interaction toward dimerization 0.10, 0.10, and 0.07 cm3 Kmol–1, as expected when intramo-
of two such species takes place through the interactions lecular antiferromagnetic interactions dominates to lead
from dangling imine nitrogen atoms from a second bip– here to a singlet ground state (ST = 0). Below ca. 50 K,
ligand and produces intermediate II. In the next step, there may also be the additional contributions of intermo-
Eur. J. Inorg. Chem. 2009, 4675–4685
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4681

M. Sarkar, R. Clérac, C. Mathonière, N. G. R. Hearns, V. Bertolasi, D. Ray
FULL PAPER
lecular antiferromagnetic interactions and/or second-order magnetic effects like the intermolecular antiferromagnetic
spin–orbit coupling associated with the distorted pentaco- interactions or magnetic anisotropy. Indeed, these effects
ordinate site symmetry at each Co2+ metal ion center.[52] might explain the lower quality of the fit for 2·CH3OH that
The susceptibility of such CoII complexes are usually not possesses the higher g value of the series and thus probably
theoretically reproducible, as no analytical expression that the larger spin–orbit coupling. Therefore, it is difficult to
includes intramolecular magnetic interaction and second- further analyze the magnetic data and make an accurate
order spin–orbit couplings can be easily used. Nevertheless, correlation between the geometry of the Co–O2–Co bridge
the general shape and trend of the χT vs. T plots for 1·dmf, and the obtained magnetic interactions. This point is rein-
2·CH3OH, and 3·CH2Cl2 (Figure 6) are similar to that re- forced by the fact that, as far as we know, no other complex
ported for another structurally related dinuclear, pentacoor- displays similar geometry with Co–O bond lengths of about
dinate hs CoII complex, with distorted SP site symmetry at 1.97–1.98 Å and 2.13–2.15 Å in order to directly correlate
each of the Co2+ metal ion centers.[22] Lastly, there is an the Co–O–Co angles with the interaction parameter. Never-
additional slight deviation of the χT value for 1·dmf and theless, a relatively good linearity is found plotting J as a
3·CH2Cl2 below ca. 30 K at low fields (typically 1000 Oe), function of the average Co–O–Co giving: J(K) = 824–8 θ(°)
indicating the presence of a trace amount of byproducts (Supporting Information, Figure S9). It is worth emphasiz-
that display a magnetic order in the measured samples (this ing that this linear relation must be considered with caution
byproduct is also seen in the χ vs. T data, Figure S8 in the and will have to be confirmed by the magnetic properties
Supporting Information, and the M vs. H data that display of future dinuclear CoII complexes of the same geometry.
a tiny but typical S-shape curve around zero field). Such
magnetic impurities cannot be easily corrected for, but their
Concluding Remarks
effect on the magnetic data of the major compound is mini-
mized at 1 T (it was checked for all compounds that the M
vs. H plot at 1 T is still linear; i.e., in the low field or Curie
limit). Thus, for the purposes of modeling the χT data only,
the data collected at 1 T were used for the fit. On the basis
of the structure, the complex can be topologically viewed
as a spin dimer composed of two S = 3/2 CoII ions. The
single-crystal X-ray structures of these compounds reveal a
distorted SP ligand field at each CoII ion that should not
exhibit any first-order spin–orbit coupling in idealized C4v
site symmetry, as the degeneracy of the occupied dxy,xz,zy
orbitals is lifted. Thus, this effect should be small and the
magnetic data were approximately modeled by using an iso-
tropic Heisenberg spin Hamiltonian to estimate the value
of the exchange interaction:
In summary, the [CoII2] nuclearity in the form of two
shared and distorted square-pyramids, in a new family con-
taining three different pseudohalide anions, was achieved
by the combined action of coordinations of three different
pseudohalide anions and a pendant benzyl group bearing
the Schiff base ligand anion bip–. These coordinations in-
troduce a pair of complementary basal–apical phenolate
bridges that cause, within these [CoII2] assemblies, weak in-
tramolecular antiferromagnetic interactions. Binding of a
single pseudohalide anion to each hs CoII ion is responsible
for the nonplanar orientation of the two ligands, ensuing
in distortions of the coordination geometries remarkable in
synthesis but familiar in biology. We are currently working
to exploit other bridging groups in this reaction system in
order to induce the formation of heterometallic binuclear
and high nuclearity complexes.
H = –4J{SCo,1·SCo,2
}
where J is the exchange interactions within the [CoII2] com-
plex; Si the spin operators for each spin carriers. The appli-
cation of the van Vleck equation[53] to the Kambe’s vector
coupling scheme[54] allows a determination of the low-field
analytical expression of the magnetic susceptibility:[55]
Experimental Section
Materials and Physical Measurements: Ammonium thiocyanate, so-
dium azide, triethylamine, and cobalt acetate tetrahydrate were ob-
tained from SRL Chem. (India). Sodium cyanate was obtained
from Lancaster (England). 2,6-Bis(benzyliminomethyl)-4-methyl-
phenolate (Hbip) was prepared by a literature procedure.[34] All
other chemicals and solvents were reagent grade materials and were
used as received without further purification. Microanalyses were
As seen in Figure 6, this model was able to reproduce performed by using a Perkin–Elmer model 2400 microanalyzer.
FTIR spectra were recorded with a Perkin–Elmer RX1 spectrome-
ter. The solution electrical conductivity and electronic spectra were
obtained by using a Unitech type U131C digital conductivity meter
with a solute concentration of about 10–3  and a Shimadzu 1601
UV/Vis/NIR spectrophotometer, respectively. 1H and 13C NMR
spectra were recorded in CDCl3 with a Bruker AC 200 NMR spec-
trometer by using TMS as the internal standard. The magnetic
susceptibility measurements were obtained with the use of a Quan-
tum Design SQUID magnetometer MPMS-XL housed at the Cen-
tre de Recherche Paul Pascal. This magnetometer works between
well the experimental χT vs. T data from 300 to 1.8 K. The
best set of parameters obtained by using the above model
are J/kB = –10.6(4) K and g = 2.21(4) for 1·dmf, J/kB
–18.1(7) K and g = 2.49(2) for 2·CH3OH, and J/kB
=
=
–11.6(3) K and g = 2.30(3) for 3·CH2Cl2. It is worth men-
tioning that the obtained parameters must be taken with
caution due to the likely presence of second-order spin–
orbit effects that have not been taken into account in this
model. The J parameters might thus be slightly overesti-
mated as they could contain phenomenologically other 1.8 and 400 K for dc applied fields ranging from –7 to 7 T. Mea-
4682 Eur. J. Inorg. Chem. 2009, 4675–4685
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Ligand-Induced Distortions in Pentacoordinated [CoIIA(bip)]2
surements were performed on polycrystalline samples of 14.86,
11.00, and 10.67 mg, for 1·dmf, 2·CH3OH, and 3·CH2Cl2, respec-
tively The magnetic data were corrected for the sample holder and
diamagnetic contributions. All experimental procedures were car-
ried out in air at room temperature.
[CoII2(NCO)2(bip)2]·CH2Cl2 (3·CH2Cl2): Prepared by the same
method a that used for 1 by using NaNCO instead of NH4SCN.
Single crystals suitable for X-ray analysis were obtained from a
dcm/MeOH mixture after 5 d. Yield: 0.318 g (72%).
C49H44Cl2Co2N6O4 (969.6966): calcd. C 60.69, H 4.57, N 8.66;
found C 60.61, H 4.46, N 8.41. FTIR (KBr): ν = 3448 (vs), 2207
˜
CAUTION!! Metal azide complexes are potential explosives. Only
a small amount of material should be prepared and handled with
caution.
(vs), 1629 (vs), 1552 (vs), 1345 (m), 705 (m) cm–1. Molar conduc-
tance (dcm): ΛM = 5 Ω–1 cm2 mol–1. UV/Vis (CH2Cl2): λ (ε,

–1 cm–1) = 581 (291),400 (6721), 327 (4213), 251 (21692) nm.
[CoII2(NCS)2(bip)2]·dmf (1·dmf): To a solution of the ligand
(0.342 g, 1.00 mmol) in methanol (15 mL) was added a solution of
Co(OAc)2·4H2O (0.498 g, 2.00 mmol) in methanol (20 mL), fol-
lowed by the dropwise addition of a solution of NH4SCN (0.304 g,
4.00 mmol) in methanol (15 mL), and the mixture was stirred at
ambient temperature in air. After 15 min, NEt3 (0.14 mL,
1.00 mmol) was added, and the reaction mixture was stirred for
1 h. After evaporation of the reaction mixture, a pale-green solid
was obtained. The solid was isolated, washed with cold methanol,
and dried under vacuum over P4O10. Single crystals suitable for X-
ray analysis were obtained from dmf after 10 d. Yield: 0.344 g
(75%). C51H49Co2N7O3S2 (989.9921): calcd. C 61.87, H 4.98, N
X-ray Crystallographic Procedures for 1·dmf, 2·CH3OH, and
3·CH2Cl2: The intensity data of complexes 2 and 3 were collected
on single crystals by using a Bruker-APEX-2 X-ray diffractometer
equipped with graphite-monochromated Mo-Kα radiation (λ =
0.71073 Å) by the hemisphere method. Data were collected at
293 K. The intensity data of complex 1 was collected with a Nonius
Kappa CCD diffractometer by using graphite monochromated
Mo-Kα radiation (λ = 0.7107 Å) at low temperature (120 K). Infor-
mation concerning X-ray data collection and structure refinement
of the compound is summarized in Table 2. In the final cycles of
full-matrix least-squares on F2 all non-hydrogen atoms were as-
signed anisotropic thermal parameters. The positions of the H
atoms bonded to C atoms were added (C–H distance 0.97 Å) in a
riding model. In compound 1·dmf, the dmf molecule was found to
be disordered and its HC=O moiety was refined over two positions
with an occupancy of 0.5 each. In compound 2·CH3OH, the
CH3OH solvent molecule is disordered across a center of symmetry
9.90; found C 61.79, H 4.87, N 9.64. FTIR (KBr): ν = 3447 (vs),
˜
2071 (vs), 1628 (vs), 1558 (vs), 1341 (m), 707 (m) cm–1. Molar con-
ductance (dmf): ΛM = 4 Ω–1 cm2 mol–1. UV/Vis (dmf): λ (ε,

–1 cm–1) = 578 (199), 398 (7360), 326 (8590), 250 (23870) nm.
[CoII2(N3)2(bip)2]·CH3OH (2·CH3OH): Prepared by the same
method as that used for 1 by replacing NH4SCN with NaN3. Single and was refined with an occupancy of 0.5. The corresponding hy-
crystals suitable for X-ray analysis were obtained from a dcm/ drogen atoms could not be determined. In compound 3·CH2Cl2,
MeOH mixture after 4 d. Yield: 0.345 g (78%). C47H46Co2N10O3 the CH2Cl2 solvent molecule is situated on a twofold axis, displays
(916.8134): calcd. C 61.57, H 5.05, N 15.27; found C 61.49, H 4.94,
N 15.01. FTIR (KBr): ν = 3447 (vs), 2050 (vs), 1627 (vs), 1551
some disorder, and was refined anisotropically. The corresponding
hydrogen atoms could not be determined. The structures were
solved by direct methods (SIR97)[56] All other calculations were
˜
(vs), 1345 (m), 705 (m) cm–1. Molar conductance (dcm): ΛM
=
6 Ω–1 cm2 mol–1. UV/Vis (CH2Cl2): λ (ε, –1 cm–1) = 578 (439), 398 performed by using SHELXL-97[57] and PARST[58] implemented in
(3683), 326 (4016), 252 (14787) nm.
WINGX system of programs.[59] CCDC-707903 (for 1·dmf),
Table 2. Crystallographic data for 1·dmf, 2·CH3OH, and 3·CH2Cl2.
1·dmf
2·CH3OH
3·CH2Cl2
Formula
M
Space group
Crystal system
a [Å]
b [Å]
c [Å]
C51H49Co2N7O3S2
989.9921
P21/n
monoclinic
10.7411(2)
28.5248(5)
15.1638(3)
94.3202(8)
4632.80(15)
120
C47H46Co2N10O3
916.8134
C2/c
monoclinic
22.131(5)
11.689(3)
17.061(4)
93.688(6)
4404.4(17)
293
C49H44Co2N6O4Cl2
969.6966
C2/c
monoclinic
19.215(5)
22.901(6)
12.682(3)
124.737(6)
4586(2)
293
β [°]
V [Å3]
T [K]
Z
4
4
4
Dc [gcm–3]
F(000)
1.419
2056
8.58
34170
8973
0.0779
1.383
1904
8.07
29677
5207
0.0354
1.404
2000
8.91
24506
4021
0.0424
µ(Mo-Kα) [cm–1]
Measured reflns.
Unique reflns.
Rint
Obsd. reflns. [IՆ2σ(I)]
θmin–θmax [°]
hkl ranges
R(F2) (obsd. reflns.)
wR(F2) (all reflns.)
No. variables
Goodness of fit
∆ρmax; ∆ρmin [eÅ–3]
6061
3841
2699
2.25–26.00
–13, 13; –35, 34; –18, 18
0.0662
0.1707
588
1.031
1.61; –0.53
1.84–28.00
–29, 29; –15, 14; –20, 20
0.0373
0.1101
280
1.025
0.50; –0.309
1.78–25.00
–22, 22; –27, 23; –14, 15
0.0511
0.1699
286
1.056
0.733; –0.467
Eur. J. Inorg. Chem. 2009, 4675–4685
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4683

M. Sarkar, R. Clérac, C. Mathonière, N. G. R. Hearns, V. Bertolasi, D. Ray
FULL PAPER
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Received: June 23, 2009
Published Online: September 21, 2009
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