Switching on oxygen activation by cobalt complexes of pentadentate ligands

Article abstract of DOI:10.1039/c1dt10594a

The monoanionic N₄O ligand N-methyl-N,N′-bis(2- pyridylmethyl)ethylenediamine-N′-acetate (mebpena^-) undergoes oxidative C-N bond cleavage in the presence of Co(ii) and O₂. The two resultant fragments are coordinated to the

Full text of DOI:10.1039/c1dt10594a

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PAPER
Switching on oxygen activation by cobalt complexes of pentadentate ligands†
Mads S. Vad,a Anne Nielsen,a Anders Lennartson,a Andrew D. Bond,a John E. McGradyb and
Christine J. McKenzie*a
Received 7th April 2011, Accepted 26th July 2011
DOI: 10.1039/c1dt10594a
The monoanionic N4O ligand N-methyl-N,N¢-bis(2-pyridylmethyl)ethylenediamine-N¢-acetate
(mebpena-) undergoes oxidative C–N bond cleavage in the presence of Co(II) and O2. The two resultant
fragments are coordinated to the metal ion in the product [CoIII(2-pyridylformate)(mepena)]ClO4
(mepena- = N-methyl-N¢-(2-pyridylmethyl)ethylenediamine-N¢-acetato). Bond cleavage does not occur
in the presence of chloride ions and [CoIII(mebpena)Cl]+, containing intact mebpena-, can be isolated.
The oxidative instability of the mebpena- in the presence of Co(II) and air stands in contrast to the
oxidative stability of the family of very closely related penta- and hexa-dentate ligands in their cobalt
complexes. Cyclic voltammetry on the matched pair [CoIIICl(mebpena)]+ and [CoIICl(bztpen)]+,
bztpen = N-benzyl-N,N¢,N¢-tris(2-pyridylmethyl)ethylenediamine, shows that substitution of a pyridine
donor for a carboxylato donor results in a relatively small cathodic shift of 150 mV in the
E◦(Co(II)/Co(III)) oxidation potential, presumably this is enough to determine the contrasting metal
oxidation state in the complexes isolated under ambient conditions. DFT calculations support a
proposal that [CoII(mebpena)]+ reacts with O2 to form a Co(III)-superoxide complex which can abstract
an H atom from a ligand methylene C atom as the initial step towards the observed oxidative C–N
bond cleavage.
Introduction
Cobalt–O2 complexes of
a range of ligands including
dien,1 salen,2 porphyrin,3 pentacyano,4 trispyrazoleborato5 and
tetraazamacrocyclic,6 ligands have served as important bench-
mark structural and spectroscopic models for elucidating dioxy-
gen binding in heme enzymes.7 Aware of this well-known
background in the utility of cobalt for trapping dioxygen-
derived adducts, we explored the cobalt chemistry of the
matched pair of pentadentate monoanionic N4O and neutral
N5 ligands, N-alkyl-N,N¢-bis(2-pyridylmethyl)ethylenediamine-
N¢-acetate (Rbpena-), Scheme 1(a), and N-alkyl-N,N¢,N¢-tris(2-
pyridylmethyl)ethylenediamine (Rtpen), Scheme 1(b). These lig-
ands were first prepared in our laboratory,8,9,10 and both the
iron and manganese complexes of Rtpen and Rbpena- ex-
hibit biomimetic reactivity pertinent to O2 catabolism and an-
abolism. This reactivity implies the formation of as yet un-
detected dioxygen adducts. The parent hexadentate monoan-
ionic N5O ligand N,N,N¢-tris(2-pyridylmethyl)ethylenediamine-
N¢-acetate (tpena-)11 and neutral N6 ligand, N,N,N¢,N¢-tetrakis(2-
Scheme
neutral N5 pentadentate ligands (a) N-R-N,N¢-bis(2-pyridylmethyl)-
ethylenediamine-N¢-acetate (Rbpena-),
methyl, benzyl and
(b) N-R¢-N,N¢,N¢-tris(2-pyridylmethyl)ethylenediamine (Rtpen),
methyl, ethyl, propyl, isopropyl, 2-hydroxyethyl, phenyl, benzyl.
The monoanionic N5O and neutral N6 hexadentate ligands (c)
N,N,N¢-tris(2-pyridylmethyl)ethylenediamine-N¢-acetate (tpena-) and (d)
N,N,N¢N¢-tetrakis(2-pyridylmethyl)ethylenediamine (tpen).
1
Ligands in this study. The monoanionic N4O and
R
=
R
=
aDepartment of Physics and Chemistry, University of Southern Denmark,
Campusvej 55, 5230, Odense M, Denmark. E-mail: chk@ifk.sdu.dk;
Fax: (+45) 6615 8760; Tel: (+45) 6550 2518
bInorganic Chemistry Laboratory, Department of Chemistry, University of
Oxford, South Parks Road, Oxford, OX1 3QR, United Kingdom
† Electronic supplementary information (ESI) available. CCDC reference
numbers 821028–821032. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c1dt10594a
pyridylmethyl)ethylenediamine (tpen)12 used for comparisons in
our work are depicted also in Scheme 1. Notably, all of the
10698 | Dalton Trans., 2011, 40, 10698–10707
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©

ethylendiamine-based ligands in Scheme 1 are close relatives of
one of the mainstays in coordination chemistry, edta4-.13
was observed in the gas phase and an ion assigned to the
ferryl species [FeIVO(Rtpen)]2+ is generated. This ion undergoes
subsequent loss of the mass equivalent to the aldehydic derivative
of the dangling alkyl group R, suggesting that a C–H activation
and O atom transfer can occur in the gas phase. Since this
report, related ferryl(IV) complexes based on neutral N5 donor
sets have been structurally characterised.20,21 By contrast, oxygen
inserted products are isolated from the reaction of the Fe(III)–
Rbpena- complexes with dihydrogen peroxide, alkyl peroxides
or O2 and ascorbic acid.17 When the R group in Rbpena- is a
benzyl group, its oxygenation results in the formation of an Fe(III)
complex of the previously unknown hexadentate dianionic ligand
N-(2-oxidobenzyl)-N,N¢-bis(2-pyridylmethyl)ethylenediamine-
N¢-acetate, (bzObpena)]+, Scheme 2(c). When the dangling benzyl
group is replaced by a methyl group, regiospecific insertion of
an O atom into an Namine–Fe bond to give a coordinated N-
oxide (Fe–O–NR3), Scheme 2(d) occurs. Both the products in
Scheme 2(c) and (d) provided strong circumstantial evidence
for the generation of an undetected Fe(V) perferryl O atom
transfer reagent. In summary, it seems that the Fe species and
ligand oxidation chemistry we have observed indicates that the
monoanionic N4O systems and their neutral N5 counterparts can
access the FeVO and FeIVO species, respectively, and that both
these species are capable of C–H activation. By contrast, air-
stable Mn(II) complexes of both Rtpen22 and Rbpena- 8 have been
isolated.
By analogy to the use of Co–dioxygen adducts in the elucidation
of heme-Fe chemistry, it is clear that structural characterisation
of a Co–O2 adduct of Rbpena- and Rtpen would shed light on
the possible mechanisms involved in the formation of the Fe(III)
species in Scheme 2, and the above mentioned O2 evolution
reaction with Mn complexes of Rbpena- and this was our
motivation for the work here; an investigation of the Co chemistry
of the series of related penta- and hexa-dentate N4O, N5, N5O and
N6 ligands depicted in Scheme 1. Although we did not succeed
in isolating Co–O2 adducts, we have unearthed yet another type
of C–H activation: the N4O ligands mebpena- and bzbpena-,
Scheme 1(a) R = Me, Bz, are susceptible to oxidation in their Co(II)
complexes in the presence of O2. By contrast, ligand oxidations are
not observed under equivalent conditions for the Co complexes of
the analogous neutral N5 ligand or their hexadentate N5O and N6
counterparts (Scheme 1(b), (c) and (d)).
Predominantly air-stable mononuclear Fe(II) complexes
[Fe(X)(Rtpen]n+, n = 1 or 2, X = Cl-,9 Br-,14 I-,14b CN-,14b
NCS-,14b NCO-,14b CF3SO3 ,15 CH3CO2 ,16 or NO,16 form in the
reactions of Rtpen (Scheme 1(b)) with Fe(II) salts. By contrast,
analogous reactions with Fe(II) salts and Rbpena- (Scheme 1(a))
give spontaneously Fe(III) complexes, for example the oxo-bridged
dinuclear complex [Fe2(O)(bzbpena)2]2+.17 The contrasting aerobic
chemistry of the Fe complexes of Rtpen and Rbpena- is a clear
indication of the expected redox, and consequent reactivity, tuning
imposed by alternating a pyridyl donor arm for a carboxylato
donor arm, in otherwise geometrically analogous ligands. The
reactivity is reminiscent of biological O2 reactivity seen for non-
heme enzymes: introduction of terminally coordinating aspartate
or glutamate, which ostensibly replaces histidine donors in the
coordination spheres of Fe, can effect a switching between oxygen
activation vs. reversible O2 binding, viz. the activity of hemerythrin
vs. methane monoxygenase.
-
-
In parallel with the aerobic Fe(II) and Fe(III) chemistry of the
monoanionic N4O and neutral N5 ligand systems respectively,
a difference of one oxidation state is emerging for the high-
valent iron-oxide chemistry of these ligands: Reactions with
peroxides of starting Fe(II) and Fe(III) complexes of Rtpen and
Rbpena- respectively, give contrasting results. [FeII(Cl)(Rtpen]+
reacts with dihydrogenperoxide to form unstable but spectroscop-
ically identifiable peroxo adducts, namely the purple low-spin
[FeIIIOOH(Rtpen)]2+ and blue high-spin [FeIIIOO(Rtpen)]+,9,14a,18
Scheme 2(a) and (b).19 Over the course of a few minutes at
room temperature these peroxide complexes decompose and the
starting Fe(II) complexes can be identified in condensed phases.
Homolytic cleavage of the O–O bond in [FeIIIOOH(Rtpen)]2+
Results and discussion
Synthesis and characterisation
The reaction between CoCl2 and mebpenaH, Scheme 1(a) R =
CH3 in methanol gives the red Co(III) complex [CoCl(mebpena)]+
(1) in Scheme 3. Elemental analysis of the solid compound
isolated after the addition of sodium perchlorate to solutions
of [CoCl(mebpena)]+ fits best with a mixture containing both
[CoCl(mebpena)]ClO4 (1·ClO4) and the sodium perchlorate dou-
ble salt 12[Na(ClO4)2(OH2)2]ClO4. The crystal selected for X-ray
analysis was found to be the double salt and no attempt was
made to obtain the simple 1 : 1 salt or the double salt of 1 in
pure bulk samples. Analogously, reaction between CoCl2 and the
neutral pentadentate analogue bztpen, Scheme 1(b) R = CH2C6H5,
in methanol, followed by addition of perchlorate gave the purple
Scheme 2 (a) Fe(III) hydroperoxides and (b) Fe(III) peroxides derived
from [FeII(Rtpen)]2+ R = methyl, ethyl, propyl, isopropyl, 2-hydroxyethyl,
phenyl, benzyl. (c) [FeIII(bzObpena)]+: oxygen atom inserted product
derived from [FeII(bzbpena)]+. (d) [FeIII(Cl)2(HmebpenaO)]+: oxygen atom
inserted product derived from [FeII(mebpena)]+.
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Dalton Trans., 2011, 40, 10698–10707 | 10699
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Fig. 1 The cyclic voltammograms of 1 (red line) and 2 (blue line)
were recorded in 0.1 M tetrabutylammoniumperchlorate in a solution of
acetonitrile against a Ag/AgCl reference electrode and calibrated against
the ferrocene/ferrocenium redox couple.
and hydroxido are both monodentate, monoanionic auxillary lig-
ands. The hydroxide/Co(III) combination rather than alternative
water/Co(II) combination is consistent with the M–L bond lengths
and metal ion geometry seen in the single-crystal X-ray structure
described below. A comparison of the optimised structure for 3
and its reduced and protonated counterpart [CoII(OH2)(bztpen)]2+
calculated using DFT supports the assignment of Co(III)–OH in
Scheme 3 Chemical structures of cations derived from single crystal
X-ray studies.
˚
the crystal structure (Co–O = 1.8709(12) A): the Co–O distance
˚
˚
air-stable [CoCl(bztpen)]ClO4 (2·ClO4) depicted in Scheme 3. The
chlorido complexes 1 and 2 are a matched pair of monocationic
complexes [CoCl(L)]+, L = mebpena- and bztpen, with the Co ions
in the +2 and +3 oxidation states, respectively. The formulations
reflect the expected tendency towards stabilisation of the harder
Co(III) by a negatively charged hard carboxylato ligand. The
presence of the methyl and benzyl R groups in mebpena- and
bztpen, respectively, is not expected to contribute significantly to
the redox chemistry of the metal ions. The cyclic voltammograms
measured for [CoCl(L)]ClO4, L = mebpena- or bztpen, 1 and 2,
show quasi-reversible redox waves for the Co(II)/Co(III) processes
centered around -307 mV for 1 and -159 mV for 2 vs. ferrocene,
Fig. 1. The separation of 211 mV for the Epa and Epc process for 1 is
significantly larger than the 143 mV for 2. It is somewhat surprising
that the difference in redox potentials for the Co(II)/Co(III)
complexes with the monoanionic N5Cl and dianionic N4OCl
coordination spheres was not greater, given that aerobic oxidation
of the solution mebpena- and bztpen Co(II) systems, vide infra,
gives very different outcomes in the absence of chloride: the former
shows metal and ligand oxidation, while the latter shows metal
oxidation only.
In contrast to the reactions producing the matched pair 1 and
2 (apart from the respective Co(III) and Co(II) oxidation states),
the reactions of Co(II) with mebpena- and bztpen do not result
in analogous outcomes (apart from a common Co(III) oxidation
states when chloride is absent from the reaction mixtures). Reac-
tion of bztpen and Co(II) perchlorate in methanol–water (1 : 1) in
air gave the Co(III) hydroxo compound [Co(OH)(bztpen)](ClO4)2
(3·(ClO4)2·H2O), Scheme 3. This contrasts to the Co(II) oxidation
state seen for the chlorido complex, 2, despite the fact that chlorido
in the optimised structure of 3 is 1.89 A, compared to 2.28 A
˚
and 3.01 A in the high-spin and low-spin optimised structures
of [CoII(OH2)(bztpen)]2+, respectively. The trend is repeated in
the remaining five metal–ligand bond lengths where the average
absolute deviation compared to the crystal structure is larger for
the two spin states of [CoII(OH2)(bztpen)]2+: 9 pm and 25 pm for
the doublet and the quartet respectively compared to 7 pm for
[CoIII(OH)(bztpen)]2+. Overlays of the DFT-optimized structures
with the crystal structure of 3 are included as ESI.†
Analogous complexation reactions using mebpenaH and
cobalt(II) perchlorate were less straightforward. The ESI mass
spectrum (ESI, Fig. S1†) of a red solid isolated from the reaction
shows two dominant ions, one assignable to 1 (m/z 407.3) and one
+
at m/z 403.3 (mass equivalent to {Co(mebpena) + 2O–H} ). A
possible source of chloride ions in the reaction needed for the for-
mation of 1 is from the ligand synthesis. Despite considerable effort
(e.g. attempted syntheses using the ester protection/deprotection
of the carboxylate group coupled with chromatography or treat-
ment with silver nitrate), we were not able to rectify this without an
unacceptable loss of ligand. Thus as an alternative synthetic route
we performed a metathesis reaction using the Mn(II) complex
[Mn2(mebpena)2(H2O)2](ClO4)2.8 Reaction of cobalt perchlorate
with [Mn2(mebpena)2(H2O)2](ClO4)2 in MeOH–H2O solution in
air, or under a stream of O2, at room temperature results, after
several days, in the formation of red crystals of the heteroleptic
Co(III) complex of the derivatives of mebpena- resulting from
oxidative C–N cleavage adjacent to the N–CH3 group. The red
Co(III) complex [Co(2-pyridylformate)(mepena)]+ (4), Scheme 3,
where mepena- is the unknown tetradentate ligand N-methyl-
N¢-(2-pyridylmethyl)ethylenediamine-N¢-acetate (Scheme 4), was
10700 | Dalton Trans., 2011, 40, 10698–10707
This journal is
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©

was reported 20 years ago from an aerobic synthesis starting
with a Co(II) source.31 We have not repeated this synthesis,
however a conventional outer-sphere oxidation of [CoII(tpen)]2+
in solution seems likely. The N5O ligand N,N,N¢-tris(2-
pyridylmethyl)ethylenediamine-N¢-acetate (tpena-), Scheme 1(c),
has only very recently been reported.11 As an aside, until this
report, tpena- was the missing link in the series of hexadenate
ethylenediamine based ligands containing four glycinato and/or 2-
pyridylmethyl arms spanning from edta4- to tpen. For the purpose
of this study we had independently prepared this new ligand using
a different synthesis (described in the experimental section) and
can report here the first complex to be isolated in the solid state
and its X-ray crystal structure. Reaction of tpenaH with Co(ClO4)2
produces the simple Co(III) complex, [Co(tpena)](ClO4)2·1/2H2O
(5·ClO4·1/2H2O), Scheme 3. The yield of [Co(tpena)]2+ was not
affected by variation of O2 pressure. This suggests that a free
coordination site/labile exchangeable auxiliary solvent ligand is
necessary for the mebpena- oxidation to occur and this corrob-
orates the observations made with the coordinatively saturated
N4OCl coordination sphere.
Scheme 4 C–N cleavage of mebpena- to give 2-pyridylformate (pfa-) and
N-methyl-N¢-(2-pyridylmethyl)ethylenediamine-N¢-acetate (mepena-).
crystallographically characterised in 4·ClO4. This result indicated
that m/z 403.3 ion with a mass equivalent to {Co(mebpena) +
+
2O–H} seen in initial attempts was in fact complex 4 and this
was confirmed by the ESI mass spectra of the crystals (ESI,
Fig. S2†).
Since the formation of 4 is an oxidative process, it is pertinent
to consider the metal-based oxidants which might be gener-
ated from reaction of a [CoII(mebpena)]+ species and O2. The
ESI mass spectra of a reaction mixture containing equimolar
(in terms of mebpenaH : Co2+) [Mn2(mebpena)2(H2O)2](ClO4)2
and cobalt(II) perchlorate, recorded after purging for 10 min
with O2 (ESI, Fig. S3†) shows no sign of 4: however there
is a major ion at m/z 372.2 corresponding to the proposed
intermediate [CoII(mebpena)]+ and some less abundant ions
for solvated derivates, [CoII(mebpena)(H2O)]+ m/z 390.2 and
[CoII(mebpena)(CH3OH)]+ m/z 404.2. Over the course of days,
while the peak for 4 grows in, no ions assignable to viable
intermediates other than [CoII(mebpena)]+ and its solvates are
detected. The fact that e.g., a Co-dioxygen adduct is not observed
cannot be used to conclude its absence in solution phases. For
example, gas phase dioxygen adducts are expected to be very
unstable due to facile reductive dissociation of neutral O2.23,24
This is the first documentation of the occurrence of oxidative C–
N cleavage with the series of ligands in Scheme 1. The formation
of 4 is noteworthy in the sense that the product derived from the
alkyl group being cleaved also remains bound to the metal ion,
albeit in a modified form. In other words, all of the daughter
products of the precursor ligand remain bound to cobalt. Colbran
and co-workers,25 have most likely observed a similar reaction: C–
N cleavage of 2,6-bis(bis(2-pyridylmethyl)amino)methypyridine
(bpa–tpa) to give the Co(III) complex of carboxylated tpa,
[Co(tpaCO2)Cl]+. Likewise, Comba and co-workers26 observed
demethylation of one of the two tertiary amine donors of a
tetradentate bispidine N4 ligand. In both of these reactions, the fate
of the leaving alkyl group is assumed, e.g., this would be undetected
formaldehyde in the demethylation reaction. These examples show
close resemblance to the system reported here, however the litera-
ture also contains examples of ligand degradation via oxidative
C–N cleavage by metal-based oxidants generated through O2
activation by vanadium, cobalt, copper and iron.27,28,29,30 We have
also carried out parallel studies using the benzylated N4O ligand,
bzbpena-, Scheme 1(a) R = CH2C6H5. The results are more
complicated; aside from C–N cleavage, oxygenation of the benzene
ring, analogously to the reaction seen for the corresponding iron
complex17 occurs (see ESI†).
X-Ray crystal structures
Single-crystal X-ray structures have been obtained for compounds
containing all of the key cations 1–5 shown in Scheme 3. The
cations are shown in Fig. 2(a)–(e) and selected bond distances and
angles are listed in Table 1. Except for 2, all of the complexes
contain Co(III), and the bond distances and angles are consistent
with the Co(III) and Co(II) oxidation states. The tetrafluoroborate
salt of 2 was reported recently16 and the conformation of the
ligand in the new perchlorate salt is identical. For the matched
pair of chloride complexes 1 and 2, the average Co–N/O bond
˚
˚
distance is 1.930 A for 1 and 2.185 A for 2, and the mean of the
deviations from 90◦ for cis donor angles is 4.1◦ for 1 and 9.9◦ for
2. The carboxylate group of 1 is trans to a pyridine donor. As
mentioned above, 1·[Na(ClO4)2(OH2)2]·ClO4 is a double salt. The
Na+ cations are octahedrally coordinated by the O atoms of two
water molecules, two perchlorate anions and two carbonyl groups
of adjacent molecules of 1. The chloride ligands in complexes 1
and 2 are both located trans to the aliphatic amine donors, that
bearing the methyl group in 1 and that bearing the two pyridyl
groups in 2. The carboxylato and pyridine arms attached to the
same tertiary N atom in 1 are bound meridionally. The carboxylate
groups of 2-pyridylformate and mepena- in 4 are located trans to
each other and the remaining N donors of mepena- are arranged
meridionally. The conformation of the bztpen in complex 3 is the
same as in complex 2, i.e., the hydroxido and chlorido ligand
occupy equivalent sites in these Co(III) and Co(II) complexes
respectively. In 5·ClO4·1/2H2O, the Co-donor bond distances and
the slightly distorted octahedral coordination geometries around
Co1 are comparable in two crystallographically distinct cations. In
contrast to the structure of 1, the carboxylato and pyridine arms
attached to the same tertiary N atom are bound facially.
Given the differences in the reactivity of the Co complexes
of mebpena-, bzbpena- compared with bztpen, it was perti-
nent also to compare the aerobic Co chemistry of the com-
plexes of their parent hexadentate ligands. A Co(III) com-
plex, [Co(tpen)](ClO4)3 of the neutral N6 ligand N,N,N¢,N¢-
tetrakis(2-pyridylmethyl)ethylenediamine (tpen),12 Scheme 1(d),
Mechanistic considerations for aerobic ligand oxidations in the
Co(II) complexes of mebpena-
The experimental work summarised in the previous paragraphs
clearly indicates that mebpena-, in its solution-state Co(II)
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 10698–10707 | 10701
©

◦
˚
Table 1 Details of the Co coordination environment in 1–5 (A,
)
1
2
3
4
5a
Co1–Cl1
Co1–O1
Co1–N1
Co1–N2
Co1–N3
Co1–N4
O1–Co1–N1 87.39(9)
O1–Co1–N2 86.17(9)
O1–Co1–N3 88.80(9)
O1–Co1–N4 170.21(9) N1–Co1–N5 77.50(7)
O1–Co1–Cl1 89.10(6)
N1–Co1–Cl1 175.24(7) N2–Co1–N3 145.34(7) N1–Co1–N2 86.94(6)
N1–Co1–N2 88.76(10) N2–Co1–N4 74.85(7)
N1–Co1–N3 83.15(10) N2–Co1–N5 96.18(7)
N1–Co1–N4 96.37(10) N2–Co1–Cl1 102.39(5) N1–Co1–N5 85.41(6)
N2–Co1–Cl1 94.22(8) N3–Co1–N4 84.24(7)
N2–Co1–N3 170.66(10) N3–Co1–N5 103.26(7) N2–Co1–N4 84.33(6)
N2–Co1–N4 84.88(10) N3–Co1–Cl1 104.30(6) N2–Co1–N5 98.46(6)
N3–Co1–Cl1 93.56(8)
N3–Co1–N4 100.60(9) N4–Co1–Cl1 88.24(5)
N4–Co1–Cl1 87.61(7) N5–Co1–Cl1 94.61(5)
2.2346(8) Co1–Cl1
1.8939(18) Co1–N1
2.3500(7) Co1–O1
2.1933(19) Co1–N1
2.2083(19) Co1–N2
1.8709(12) Co1–O1
1.9630(15) Co1–O3
1.9975(15) Co1–N1
1.9306(16) Co1–N2
1.9376(15) Co1–N3
1.9338(15) Co1–N4
1.8803(14) Co1–O1
1.9041(14) Co1–N1
1.9391(17) Co1–N2
1.9693(18) Co1–N3
1.9466(17) Co1–N4
1.9198(17) Co1–N5
1.885(3)
1.935(4)
1.940(4)
1.950(4)
1.941(4)
1.890(3)
1.942(4)
1.949(4)
1.953(4)
1.929(4)
1.944(4)
92.79(14)
86.60(14)
1.975(2)
1.928(2)
1.935(2)
1.918(2)
Co1–N2
Co1–N3
Co1–N4
Co1–N5
N1–Co1–N2 80.41(7)
N1–Co1–N3 76.24(7)
N1–Co1–N4 99.82(7)
2.116(2)
2.254(2)
2.151(2)
Co1–N3
Co1–N4
Co1–N5
1.931(4)
O1–Co1–N1 176.27(6) O1–Co1–O3 177.94(6)
O1–Co1–N1 91.53(15)
O1–Co1–N2 86.52(14)
O1–Co1–N3 175.67(15) 176.48(14)
O1–Co1–N4 88.91(14)
O1–Co1–N5 87.19(15)
N1–Co1–N2 89.48(16)
N1–Co1–N3 85.07(16)
O1–Co1–N2 93.05(6)
O1–Co1–N3 95.55(6)
O1–Co1–N4 88.54(6)
O1–Co1–N1 87.49(7)
O1–Co1–N2 91.61(7)
O1–Co1–N3 92.75(7)
O1–Co1–N4 93.46(7)
O3–Co1–N1 94.53(7)
O3–Co1–N2 88.08(7)
O3–Co1–N3 87.89(7)
O3–Co1–N4 84.53(7)
88.79(14)
86.71(14)
89.12(15)
85.51(16)
N1–Co1–Cl1 171.92(5) O1–Co1–N5 90.90(6)
N1–Co1–N3 84.63(6)
N1–Co1–N4 95.16(6)
N1–Co1–N4 171.36(16) 170.91(16)
N1–Co1–N5 82.69(17)
N2–Co1–N3 96.12(15)
N2–Co1–N4 81.94(16)
N2–Co1–N5 169.81(16) 168.95(15)
N3–Co1–N4 94.86(16)
N3–Co1–N5 89.72(15)
82.43(15)
96.44(15)
82.04(15)
N2–Co1–N3 171.11(6) N1–Co1–N2 87.58(7)
N1–Co1–N3 83.47(7)
N1–Co1–N4 178.27(7)
N2–Co1–N3 169.87(7)
N2–Co1–N4 93.83(7)
N4–Co1–N5 170.99(7) N3–Co1–N4 93.62(6)
93.37(15)
90.01(15)
N3–Co1–N5 83.68(6)
N4–Co1–N5 177.18(6) N3–Co1–N4 95.04(7)
N4–Co1–N5 105.95(16) 106.60(16)
a Two complexes in the asymmetric unit, labelled with suffixes A and B in the crystal structure.
Fig. 2 The structures of (a) 1 in the crystal structure of 12[Na(ClO4)2(OH2)2]ClO4 (b) 2 in the crystal structure 2·ClO4, (c) 3 in the structure of
3(ClO4)2·1.15H2O, (d) 4 in the structure of 4(ClO4) and (e) 5 in the structure of 5(ClO4)2·0.5H2O.
10702 | Dalton Trans., 2011, 40, 10698–10707
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The Royal Society of Chemistry 2011
©

Scheme 5 Proposed mechanism for C–N cleavage in mebpena- in the presence of Co(II), dioxygen and water.
complex, is unstable towards aerobic oxidation, resulting
an aldehyde and a secondary amine. Hydrogen peroxide and
peroxyacids32,33 are known to oxidise aldehydes to carboxylic
acids, thus the aldehyde could be further oxidized to a car-
boxylate by the hydroperoxide ligand in a Bayer–Villiger34 type
reaction, leaving a final rapid outer-sphere oxidation of the
metal center to give the isolated product complex 4. Carbon-
based radicals have been suggested previously as intermediates
in oxidative N-dealkylations.25a,35,36 Comba and co-workers26 pro-
posed that a carbon-based radical can be generated by H atom
transfer from a methyl group to a weakly Co(II)-coordinated
dihydrogenperoxide, to form ultimately a Co(III)–hydroxide and
water.
A comparison with the complexes of the corresponding neutral
metpen ligand, where we have found no evidence for ligand
oxidation, are also informative here. The O2 binding reaction,
[CoII(metpen)(OH2)]2+ + O2 → [CoIII(metpen)(O2)]2+ + H2O is
slightly less exergonic (DrG = -1.8 kcal mol-1), as might be expected
for a neutral ligand, and the barrier to the subsequent C–H
activation event is marginally higher (DG‡ = 25.8 kcal mol-1). The
small differences are consistent with the fact that the Co(III)/Co(II)
redox potentials for 1 and 2 were only 150 mV apart. Thus both
trends are consistent with lower reactivity for the complexes of
metpen, although the differences in the calculated DrG are small
and within the confidence limits of DFT.
in C–N cleavage. The reaction apparently depends on the
presence of a free coordination site/labile sixth ligand. As
mentioned in the Introduction, there is ample precedence for
the formation of mononuclear Co(III) superoxide complexes
by direct reaction of an appropriate Co(II) precursor and O2.
This seemed an obvious starting point when considering the
mechanism. A minimum corresponding to a superoxido complex
[CoIII(mebpena)OO∑]+ (Scheme 5, 6), the putative product of the
reaction of [CoII(mebpena)(OH2)]+ with O2, was located using
DFT. This H2O/O2 exchange reaction is marginally exergonic
(DrG = -3.7 kcal mol-1). From this intermediate, the C–N bond
cleavage seen in mebpena- could be initialised by an intramolecular
hydrogen atom abstraction from the methylene group adjacent to
the methyl-bearing amine nitrogen by the superoxido ligand in 6.
It is important to emphasise that pseudo-octahedral complexes
of mebpena- such as [CoIII(mebpena)OO∑]+ have a number of
coordination isomers, and indeed we have located seven distinct
isomers of 6 that lie within 5 kcal mol-1 of each other. The free
energy surface for C–H activation starting from the most stable
of these is shown in Fig. S19,† and leads to a radical intermediate
[CoIII(mebpena-H∑)OOH]+ with a barrier of DG‡ = 23.7 kcal
mol-1. The free energy surfaces for C–H activation starting from
alternative coordination isomers of 6 lie approximately parallel
to that shown in Fig. S19,† and lead to a variety of coordination
isomers of [CoIII(mebpena-H∑)OOH]+, including the one that
would lead directly to the crystallised product. Barriers (measured
relative to the most stable coordination isomer of 6) lie between
23.7 and 33.7 kcal mol-1.
An alternative explanation may relate to the potential de-
protonation of the aquo precursors [CoII(mebpena)(OH2)]+ and
[CoII(metpen)(OH2)]2+, which would be expected to be more
favourable in the latter, dicationic, case. Formation of a hydroxido
ligand would certainly reduce the rate of exchange with O2,
allowing an irreversible outer-sphere oxidation to dominate,
producing the structurally characterised complex 3. This implies
that it may be possible to access a similar metal-based oxidant
derived from [CoII(metpen)]2+ and O2 in the strict absence of a
sixth auxiliary ligand (solvent or anion), and form a complex
After H atom abstraction to give [CoIII(mebpena–H∑)OOH]+
a subsequent rapid cascade of reactions could start with Co(III)
oxidation of the radical arm to generate an iminium ion, which
is readily hydrolysed to a secondary amine and an aldehyde. This
oxidation step could either be intramolecular (i.e. the Co(III) is
from the same complex) or intermolecular, involving a second
Co(III) centre. The products of the iminium ion hydrolysis are
∑
-
analogous to that in the structurally characterised 2 and 3 (O2
replaces Cl-/OH-).
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The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 10698–10707 | 10703
©

Biosystems/MDS SCIEX), both equipped with a nanospray ion
source. The isotope patterns of all m/z assignments were checked
by comparison to the calculated theoretical patterns. Cyclic
Voltammetry (CV) was recorded in acetonitrile solution under
dry anaerobic conditions using an Autolab system (Eco Chemie,
The Netherlands), controlled by GPES software. The working
electrode was a Pt disk, the auxiliary electrode was a platinum wire
and the reference electrode was Ag/AgCl. 0.1 M TBAClO4 (TBA =
tetrabutylammonium) was used as electrolyte. All measurements
were calibrated versus the ferrocene/ferrocenium (Fc0/+) redox
couple E 1 = 0.44 V. CV spectra were recorded at a scan rate
of 50 mV 2s-1.
Conclusions
The replacement of a pyridine donor by a carboxylate donor
in the pentadentate Rtpen and Rbpena- ligands respectively
enables O2 activation in both their Fe and Co complexes, but
with different outcomes. In the case of Fe, the oxygenations
depicted in Scheme 2(c) and (d) were observed. For Co oxidative
C–N cleavage reaction occurs. N-dealkylation in complexes of
multidentate ligands containing aminomethylpyridine moieties
has been sporadically observed, our example is the first where
all products of the C–N cleavage remain coordinated in the
product. The difference in reactivity for Fe and Co complexes
of Rbpena- might be traced back to the different dioxygen-
derived metal-based oxidants that the two metals are capable of
stabilising: FeVO and Co(III)–OO(superoxide). It is noteworthy
that with its one carboxylate group, the N4O ligand system,
Rbpena-, mimics the endogenous monoanionic 3His-1carboxylate
or 2His-1carboxylate donor sets found in many non-heme O2
activating enzymes. The one or two extra neutral N donors
in the Rbpena- ligands relative to their biological counterparts
serve to prevent hydrolysis and oligomerisation, in analogy to the
protective function of proteins. A C–N cleavage reaction, namely
the demethylation of nucleobases, is catalyzed by non-heme
2His-1Asp Fe(II) a-ketoglutarate dependent enzymes ABH2,
ABH337,38,39 and AlkB.40,41,42,43,44 Our results point to dioxygen
activation to give a metal-based oxidant capable of C–H activation
by the Co(II) complexes of Rbpena- but not of Rtpen, when the
sixth coordination site is not blocked by a ligand that O2 cannot
substitute, e.g. Cl- in 1 or pyridine in 5. In terms of O2 activation via
CAUTION! Although we encountered no problems during prepa-
ration of the perchlorate salts, Perchlorate salts of metal complexes
are potentially explosive and should be handled with caution in small
quantities.
Synthesis
N-Methyl-N,N¢-bis(2-pyridylmethyl)ethylenediamine-N¢-acetic
acid
(mebpenaH),
[Mn2(mebpena)2(H2O)2](ClO4)2
and
[Mn2(bzbpena)2(H2O)2](ClO4)2 were prepared as described
previously.8 N,N¢-Bis-2-picolylethylenediamine (bispicene) was
prepared as described previously.48
1,2,3-Tris-2-picolylimidazolidine. Bispicene
(3.5317
g,
14.6 mmol) and 2-pyridinal (1.393 ml, 14.6 mmol) in dry
diethylether (5 ml) were stirred overnight under CaCl2 protection.
The volume of the solvent was reduced in vacuo to precipitate the
product as pale green microcrystals. Recrystallisation from hot
diethylether afforded colorless crystals of X-ray quality (2.1513 g,
44%). dH (CDCl3): 2.7, 3.3 (4 H, m, NCH2CH2N, AA¢BB¢), 3.95,
3.91, 3.67, 3.62 (4 H, dd, 2 ¥ NCH2C5H4N, AB), 4.26 (1 H, s,
NCH(C5H4N)N), 7.06 (2 H, t, 2 ¥ C5H py), 7.17 (1 H, td, C5¢H
py), 7.32 (2 H, d, 2 ¥ C3H py), 7.55 (2 H, td, 2 ¥ C4H py), 7.68
(1 H, td, C4¢H py), 7.87 (1 H, dd, C3¢H py), 8.44 (2 H, dd, 2
¥ C6H py), 8.49 (1 H, dd, C6¢H py). dC (CDCl3): 51.504 (2 ¥
NCH2C5H4N), 59.024 (NCH2CH2N), 89.322 (NC(C5H4N)N),
121.985 (2 ¥ C5 py), 122.957 (2 ¥ C3 py), 123.306 (C5¢ py), 123.347
(C3¢ py), 136.395 (2 ¥ C4 py), 136.839 (C4¢ py), 148.509 (C6¢ py),
148.988 (2 ¥ C6 py), 159.282 (2 ¥ C2 py), 161.076 (C2¢ py).
metal coordination, the comparison of the E 1 Co(III)/(II) values
2
for the best matched pair that we have, [CoCl(L)]+, L = mebpena-
or bztpen, 1 and 2, is interesting in the sense that the difference in
these potentials was (at least to us) surprisingly small (150 mV).
Our combined results with the Mn, Fe and Co complexes
of the related penta and hexadentate ethylenediamine-based
ligands Rtpen, Rbpena-, tpen and tpena-, define some of the
oxidative degradation pathways by which transition metal cata-
lysts based on multidentate ligands containing carboxylato and
aminomethylpyridine groups45 are potentially unstable under
oxidising conditions. Such instability may limit the lifetimes of
such catalysts. In this respect, it is interesting that we have not
yet seen evidence for oxidative ligand degradation reactions in the
Mn complexes of mebpena-, which apart from being used as the
starting material for the synthesis of the Co complex reported
here, have been shown to catalyse the tert-butylhydrogenperoxide
(TBHP) oxidation of water where turnovers in excess of 104
(mol[O2] per mole of Mn) have been measured.46,47
N,N,N¢-Tris-2-picolylethylenediamine. 1,2,3-Tris-2-picolyli-
midazolidine (1.2307 g, 3.71 mmol) was dissolved in dry methanol
(40 ml). Solid NaBH3CN (0.2339 g, 3.72 mmol) and trifluoroacetic
acid (569 mL, 7.43 mmol) were added carefully (Caution! For-
mation of HCN possible) and the reaction mixture was stirred
overnight under CaCl2 protection. NaOH (38 ml of a 4 M aqueous
solution) was added. The reaction mixture was stirred for 5–6 h and
extracted with CHCl3 (3 ¥ 20 ml). The organic phase was dried on
Na2SO4 and filtered. The filtrate was evaporated in vacuo leaving
the product as a thin yellow oil (1.2268 g, 99%). dH (CDCl3):
2.755 (4 H, s, NCH2CH2N), 3.799 (6 H, s, NCH2C5H4N), 7.11 (3
H, td, 2 ¥ C5H py, C5¢H py), 7.260 (1 H, d, C3¢H py), 7.515
(2 H, d, 2 ¥ C3H py), 7.60 (3 H, m, 2 ¥ C4H py, C4¢H py),
8.482 (3 H, m, 2 ¥ C6 py, C6H py). dC (CDCl3): 46.780, 54.208
(NCH2CH2N), 55.054 (NCH2C5H4N), 60.741 ((NCH2C5H4N)2),
121.966, 122.089, 122.290, 122.373, 123.161, 123.404 (2 ¥ C3 py,
2 ¥ C5 py, C3¢ py, C5¢ py), 136.478, 136.546, 136.647 (2 ¥ C4 py,
Experimental
Physical measurements
Elemental analyses were performed at the Chemistry Depart-
ment at Copenhagen University, Denmark. IR spectra of the
complexes in KBr discs were measured using a Hitachi 270-
30 IR spectrometer. Electrospray ionisation mass spectra (ESI
MS) were obtained using a Finnigan Mat TSQ700-Triple Stage
Quadrupole mass spectrometer (MDS Proteomics A S-1) and a Q-
Star Pulsar quadrupole time-of-flight mass spectrometer (Applied
10704 | Dalton Trans., 2011, 40, 10698–10707
This journal is
The Royal Society of Chemistry 2011
©

C4¢ py), 149.104, 149.322 (2 ¥ C6 py, C6¢ py), 159.687, 159.937
(2 ¥ C2 py, C2¢ py).
[Co(2-pyridylformate)(mepena)]ClO4
(4·ClO4). [Mn2(meb-
pena)2(H2O)2](ClO4)2 (203 mg, 0.21 mmol) and Co(ClO4)2·6H2O
(154 mg, 0.42 mmol) were mixed in methanol (2 ml) and water
(2 ml). Dioxygen was bubbled through the reaction mixture until
the colour changed from pink to red–brown (5–10 min). Dark
red crystals of [Co(2-pyridylformate)(mepena)]ClO4 (84 mg,
40%) were deposited after one week at low temperature (4 ◦C).
N,N,N¢-Tris-2-picolylethylenediamine-N¢-acetic acid (tpenaH).
A mixture of N,N,N¢-tris-2-picolylethylenediamine (0.1212 g,
0.36 mmol), bromoacetic acid (0.0513 g, 0.37 mmol) and Cs2CO3
(0.2208 g, 1.14 mmol) in absolute ethanol (4 ml) was heated
overnight under reflux and N2. The solvent was removed under
reduced pressure and the residue was redissolved in chloroform
to precipitate CsBr which was filtered off. The filtrate was
evaporated in vacuo leaving a brown oil (0.15 g). dC (CDCl3):
51.744, 51.795 (NCH2CH2N), 60.056, 60.401, 60.723, 60.820
(2 ¥ NCH2C5H4N, NC¢H2C5H4N, NCH2COOH), 121.940,
121.999, 122.077, 122.240, 123.130, 123.666, 124.137 (2 ¥ C3 py, 2
¥ C5 py, C3¢ py, C5¢ py), 136.379, 136.409, 136.532 (2 ¥ C4 py, C4¢
py), 149.134, 149.187, 149.420 (2 ¥ C6 py, C6¢ py), 158.899, 159.380
(2 ¥ C2 py, C2¢ py), 176.042 (C O).
ESI MS (MeOH) m/z: 403.2 ([Co(2-pyridylformate)(mepena)]+,
+
100%), 419.3 ({[Co(2-pyridylformate)(mepena)]
+
[O]} ,
29%). IR (KBr) n (cm-1): 1666 (C O, vs), 1098 (ClO4 ,
vs). Anal. calcd (%) for C17H22.6N4O9.3ClCo ([Co(2-
pyridylformate)(mepena)]ClO4·1.3H2O) C: 38.81, H: 4.33,
N:10.65. Found C: 38.85, H: 3.89, N: 10.46.
-
[Co(tpena)](ClO4)2·1/2H2O.
(5·ClO4). Co(ClO4)2·6H2O
(73.7 mg, 0.20 mmol) in water (1 ml) was added to tpenaH
(79.1 mg, 0.20 mmol) in methanol (2 ml). After three days,
orange crystals of [Co(tpena)](ClO4)2·1/2H2O (80 mg, 60%) were
deposited. ESI MS (MeOH) m/z: 356.1 ([Co(tpena - C6H6N)]+,
32%), 388.1 ([Co(tpena - CO2 - 2H)]+, 18%), 389.1 ([Co(tpena -
CH3COOH)]+, 22%), 405.1 ([Co(tpena - CO2)]+, 8%), 427.4
([Co(tpena - CO2 + Na+)]+, 18%), 448.1 ([Co(tpena - H)]+, 100%),
[Co(mebpena)Cl]ClO4 (1·ClO4). CoCl2·6H2O (640 mg,
2.7 mmol) in a mixture of methanol (2 ml) and water (2 ml)
and NaClO4·H2O (4.5 g, 32 mmol) in water (2 ml) were
added to mebpenaH (843 mg, 2.7 mmol) in methanol (3 ml).
The product deposited as red crystals and powder (410 mg,
30%). It appears to be a mixture of [Co(mebpena)Cl]ClO4
and the double salt [CoCl(mebpena)]2[Na(ClO4)2(OH2)2]ClO4
for which the crystal structure was solved. ESI MS (MeCN)
m/z: 407.3 ([Co(mebpena)Cl]+, 100%). IR (KBr) n (cm-1):
1667 (C O, vs), 1094 (ClO4, vs). Anal. calcd (%) for
([Co(mebpena)Cl]ClO4 )x ([CoCl(mebpena)]2 [Na(ClO4 )2(OH2 )2 ]-
ClO4)1-x, x = 0.8813, C: 39.61, H: 4.15, N: 10.87. Found C: 39.62,
H: 4.13, N: 10.87.
+
548.1 ({[Co(tpena)]ClO4} , 27%). IR (KBr) n (cm-1): 1685 (C O,
-
s), 1094 (ClO4 , vs). Anal. calcd (%) for C22H25N5O10.5Cl2Co
([Co(tpena)](ClO4)2·1/2H2O) C: 42.57 H: 5.59 N: 10.79. Found
C: 42.49 H: 4.49 N: 10.85.
Computational details
The quantum chemical calculations were performed with the
Gaussian03 software package. The functional BLYP49,50,51 with
the basis set TZVP52 were applied on all element except Co. For
Co the SDD53 Stuttgart/Dresden effective core potential basis set
were utilised. Frequency calculations were performed to confirm
the nature of all stationary points and to calculate the free energies
of the molecules in the gas phase.
[Co(bztpen)Cl]ClO4
(2·ClO4). CoCl2·6H2O
(49
mg,
0.21 mmol) in water (2.5 ml) and NaClO4·H2O (250 mg,
1.78 mmol) in water (5 ml) were added to bztpen (88 mg,
0.21 mmol) in methanol (10 ml). After 2 h, purple crystals
deposited (94 mg, 73%). ESI MS (CH3CN), m/z: 241.61
([Co(bztpen)]2+, 55%), 256.61 ([Co(bztpen)Cl]2+, 40%), 518.17
([Co(bztpen)Cl]+, 100%). Anal. calcd (%) for C27H29N5O4Cl2Co
([Co(bztpen)Cl]ClO4) C: 52.53, H: 4.73 N: 11.34, found C: 51.74,
H: 4.70, N: 11.03.
Single-crystal X-ray diffraction
Selected crystallographic data are presented in Table 2. Diffraction
data were collected using a Bruker-Nonius X8 APEX-II instru-
ment (Mo-Ka radiation). Structure solution and refinement was
carried out using SHELXTL.54 H atoms on C atoms were placed
at calculated positions and allowed to ride during subsequent
refinement. For 1, the Na+ cation lies on a crystallographic
inversion centre, and the perchlorate anion bound to it was
modelled as disordered in two orientations, each with 50% site
occupancy. The unbound perchlorate anion was also modelled as
disordered with the Cl atom lying on a crystallographic 2-fold
axis. The H atoms of the water molecule were visible in difference
Fourier maps and their positions were refined with restrained O–H
and H ◊ ◊ ◊ H distances. Refinement of 2 was routine. In 3, one of the
perchlorate anions was modelled as disordered in two orientations
with 85 : 15% site occupancy. The H atom associated with the OH
group was clearly visible in the difference Fourier map, and it was
included in the as-found position then allowed to ride on atom
O1 during subsequent refinement. The structure contains regions
occupied by H2O molecules: one of them (O1W) was refined with
site occupancy 85%, and its associated H atoms were clearly visible
and included in the model in the as-found positions. These H
[Co(OH)(bztpen)](ClO4)2 (3·(ClO4)2·H2O). Co(ClO4)2·6H2O
(147 mg, 0.40 mmol) in water (6 ml) was added to bztpen
(171 mg, 0.40 mmol) in methanol (10 ml). The reaction mixture
was purged with oxygen for 5 min. After six days, a reddish–
brown powder was isolated and recrystallized from methanol–
water to give the product as small aggregated crystals (80 mg).
+
ESI MS (MeOH) m/z: 598.1 ([Co(OH2)(bztpen)]ClO4} , 89%),
+
580.8 ([Co(bztpen)]ClO4} , 25%), 389.1 ([Co(bztpen - C6H6N)]+,
40%), 249.6 ([Co(OH)(bztpen)]2+, 100%), 240.6 ([Co(bztpen -
H)]2+, 98%). dH (D2O): 2.618, 3.714, 3.960, 4.382, 4.963 and
5.190 (6 ¥ 1 H, d, NCH2C5H4N/NCH2C5H5), 3.003 (1 H, td,
NCH2CH2N), 3.258 (2 H, m, NCH2CH2N), 3.810 (1 H, td,
NCH2CH2N), 4.264 (d, NCH2C5H4N/NCH2C5H5), 4.802 (d,
NCH2C5H4N/NCH2C5H5), 7.022 (1 H, d, C6H py), 7.299–8.046
(14 H, aromatic), 8.662 (1 H, d, C6H py), 9.076 (1 H, d, C6
py). IR (KBr) n (cm-1): 1610 (C O, m), 1088 (ClO4, vs). Anal.
calcd C27H32N5O10Cl2Co ([Co(bztpen)OH](ClO4)2·H2O) (%) for C:
45.27 H:4.50 N: 9.78. Found C: 45.23, H: 4.15 N: 9.58.
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 10698–10707 | 10705
©

Table 2 Crystallographic data for 1–5
1
2
3
4
5
+
-
-
2+
Formula
[C17H21ClCoN4O2
]
[C27H29ClCoN5+] [ClO4
]
[C27H30CoN5O2+
]
[C17H20CoN4O4+] [ClO4
]
[C22H24CoN5O2 ]
2
Na+[ClO4-]3·2H2O
1172.89
Monoclinic
C2/c
[ClO4-]2·1.15H2O
[ClO4-]2· 0.5H2O
M/g mol-1
Crystal system
617.38
Orthorhombic
Pbca
16.3600(12)
17.8210(10)
18.0306(13)
90
90
90
5256.8(6)
8
1.560
0.901
120(2)
0.20 ¥ 0.12 ¥ 0.04
purple
3.55–25.88
77571
4971
0.079
3534
718.50
502.75
Monoclinic
P21/n
657.30
Monoclinic
P21/c
17.5150(15)
22.3432(18)
13.4944(8)
90
101.220(3)
90
5180.0(7)
8
1.686
0.938
180(2)
Triclinic
¯
Space group
P1
˚
a/A
37.978(5)
8.0037(10)
14.7034(18)
90
101.149(2)
90
4385.0(10)
4
1.777
1.157
120(2)
0.18 ¥ 0.14 ¥ 0.13
purple
8.6824(5)
11.6313(7)
15.8043(9)
76.450(3)
87.333(3)
69.100(2)
1448.32(15)
2
10.1794(3)
17.2327(6)
11.5761(4)
90
105.851(1)
90
1953.45(11)
4
1.709
1.072
180(2)
0.23 ¥ 0.10 ¥ 0.08
red
3.66–27.98
19471
4699
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V/A
Z
Dc/g cm-3
1.648
0.846
120(2)
0.28 ¥ 0.20 ¥ 0.20
purple
3.58–26.00
72725
5661
m(Mo-Ka)/mm-1
T/K
Crystal size/mm
Crystal colour
q Range/◦
Reflections collected
Unique reflections
Rint
Observed reflections
[I > 2s(I)]
No. of parameters
No. of restraints
R1 [I > 2s(I)]
wR2 (all data)
GOF on F2
0.12 ¥ 0.12 ¥ 0.03
orange
3.56–25.03
40797
9036
0.096
3.74–25.02
20404
3855
0.051
3058
0.036
5087
0.026
4310
5363
373
15
0.033
0.079
1.02
352
0
0.033
0.077
1.02
431
20
0.028
0.070
1.04
281
0
0.039
0.098
1.09
730
0
0.054
0.141
1.03
atoms form hydrogen bonds to the OH group bound to Co(III)
and also to one perchlorate anion. Two further atom sites were
also clearly identifiable, which were included in the model as O2W
and O3W, both refined with 15% site occupancy. Atom O2W lies in
a suitable position to accept a hydrogen bond from the OH group
bound to Co(III), but it was difficult to place H atoms on O2W
and O3W in such a way as to form a coherent hydrogen-bond
network. Thus, the H atoms associated with O2W and O3W are
not included in the model, so that the atom sites sum to 1.2 H atoms
per unit cell less than the stated empirical formula. Although this
disordered arrangement of H2O molecules around the OH group is
clearly an approximation, the assignment of the OH group can be
made confidently on the basis of the Co(III)–OH bond length (as
described in the Discussion). Refinement of 4 and 5 was routine.
For 4, the H atom on N2 was visible in the Fourier map, but
ultimately included in a geometrical position and allowed to ride
on N2 for the final stages of refinement. For 5, which contains two
crystallographically distinct complexes, the H atoms of the water
molecule were not apparent from the X-ray data, and these were
included so as to make reasonable intermolecular contacts (one
to a perchlorate anion, and one directed towards a neighbouring
pyridyl ring).
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