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Tuning affinity and reversibility for O2 binding in dinuclear Co(ii) complexesElectronic supplementary information (ESI) available: Details on the computational chemistry calculations and resonance Raman spectra. CIF files. CCDC 913563, 913565, 913566, 913567 and 913568. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3dt50617g
The O 2 binding affinity of a series of dicobalt( ii ) complexes can be tuned between p (O 2 ) 50% = 2.3 10 3 and 700 10 3 atm at 40 C by varying the number of H and Cl atoms in the bridging acetato ligands of [Co 2 (bpbp)(CH (3 n ) Cl n CO 2 )(CH 3 CN) 2 ] 2+ , where bpbp = 2,6-bis( N , N -bis(2-py...
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| Main Authors: | , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Online Access: | Get full text |
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| Summary: | The O
2
binding affinity of a series of dicobalt(
ii
) complexes can be tuned between
p
(O
2
)
50%
= 2.3 10
3
and 700 10
3
atm at 40 C by varying the number of H and Cl atoms in the bridging acetato ligands of [Co
2
(bpbp)(CH
(3
n
)
Cl
n
CO
2
)(CH
3
CN)
2
]
2+
, where bpbp
= 2,6-bis(
N
,
N
-bis(2-pyridylmethyl)aminomethyl)-4-
tert
-butylphenolate and
n
= {0, 1, 2, 3}. O
2
binds most strongly to the deoxy complex containing the acetato bridge and the O
2
affinity decreases linearly as the number of Cl atoms is increased from 0 to 3 in [Co
2
(bpbp)(O
2
)(CH
3
CO
2
)]
2+
, [Co
2
(bpbp)(O
2
)(CH
2
ClCO
2
)]
2+
, [Co
2
(bpbp)(O
2
)(CHCl
2
CO
2
)]
2+
and [Co
2
(bpbp)(O
2
)(CCl
3
CO
2
)]
2+
. The O
2
affinities can be qualitatively correlated with both the p
K
a
value of the parent acetic or chloroacetic acid and the redox potential of the O
2
2
/O
2
&z.rad;
couple measured for the peroxide-bridged complexes. The redox potential varies between 510 mV (
vs.
Fc
0/+
) for the acetato-bridged complex to 696 mV for the trichloroacetato-bridged system. Despite the clear difference in reactivity in solution, there are no clear trends which can be correlated to O
2
affinity in the OO bond lengths in the X-ray crystal structures at 180 K (1.415(4)1.424(2) ) or in the frequencies of the peroxido OO stretch in the solid-state resonance Raman spectra at 298 K (830836 cm
1
). Using density functional theory calculations, we conclude that the Co(
ii
) atoms of the deoxy complexes coordinate solvent molecules as auxiliary ligands and that a conformation change of the ligand is involved in the reversible O
2
binding process. The alternative of five coordination in the deoxy Co(
ii
) complexes is therefore seen as less likely. The crystal structure and
p
(O
2
)
50%
are also reported for the 1-naphthoato-bridged oxy complex [Co
2
(bpbp)(O
2
)(C
10
H
7
O
2
)]
2+
, and the O
2
binding affinity in that case is also qualitatively consistent with the expectation from the p
K
a
of the parent 1-naphthoic acid.
The oxygen affinity for dinuclear Co(
ii
) complexes is tuned by systematically varying the number of chlorine groups in the ligand sphere. |
|---|---|
| ISSN: | 1477-9226 1477-9234 |
| DOI: | 10.1039/c3dt50617g |