S
1
Supplemental Information for
Effects of Lewis Acidic Metal Ions (M) on Oxygen
-
Atom Transfer Reactivity of
Heterometallic Mn
3
MO
4
Cubane and Fe
3
MO(OH) and Mn
3
MO(OH) Clusters
Davide Lionetti,
†
Sandy Suseno,
†
Emily Y. Tsui,
†
Luo Lu,
‡
Troy A. Stich,
‡
Kurtis M
. Carsch,
†,§
Robert J. Nielsen,
†,§
William A. Goddard, III,
†,§
R. David Britt,
‡
and Theodor Agapie*
,†
†
Division of Chemistr
y and Chemical Engineering, California Institute of Technology, 1200 East California
Boulevard, MC 127
-
72, Pasadena, California 91125
, United States
‡
Department of Chemistry, University of California, Davis, California 95616, United States
§
Materials and Process Simulation Center, California Institute of Technology, Pasadena, California 91125,
United States
Contents
Structural Reassig
nment
of [Mn
3
MO
2
(H)] Clusters
S
3
Table
S
1
.
Bond p
arameters
from c
omputation
S
5
Calculation of Mulliken Spin Populations.
S
6
Table
S
2
.
Mulliken Spin Population
s
.
S
6
Table S3
.
Comparison of Selected Bond Distances
for Mn
3
and Fe
3
Clusters
S
6
EPR Spectroscopy
S
7
Figure S
1
.
EPR spectra of
[Mn
III
3
CaO(OH)]
and
[Mn
II
Mn
III
2
CaO(OH)]
.
S
7
Figure S2.
EPR spectra of
[Mn
III
3
Sr
O(OH)]
and
[Mn
II
Mn
III
2
Sr
O(OH)]
.
S
8
NMR Spectroscopy
S
9
Figure
S3
.
1
H NMR
comparison of
[Mn
II
Mn
III
2
YO(OH)]
react
ivity with PPh
3
and
[LCaMn
3
O(OTf)
2
(OAc)
3
]
2
.
S
9
Figure
S4
.
1
H NMR
spectrum of
[Mn
III
3
ScO
3
]
.
S
9
Figure
S
5
.
1
H NMR
spectrum of
[Mn
III
3
YO(OH)]
2
.
S
10
Figure
S
6
.
1
H NMR
of reaction of
[Mn
III
Mn
IV
2
ScO
4
]
with PMe
3
.
S
10
Figure
S
7
.
1
H NMR
of reaction
of
[Mn
III
Mn
IV
2
ScO
4
]
with PMe
3
at 50 °C.
S
11
Figure
S
8
.
1
H NMR of reaction of
[Mn
III
Mn
IV
2
GdO
4
]
with PMe
3
.
S
11
Figure
S
9
.
1
H NMR
of reaction of
[Mn
III
Mn
IV
2
GdO
4
]
with PMe
3
at 50 °C.
S
12
Figure S
1
0
.
1
H NMR
of reaction of
[Mn
III
3
YO(OH)]
2
with PEt
3
.
S
12
Figur
e
S1
1
.
1
H NMR of reaction of
[Mn
III
3
YO(OH)]
2
with PPh
3
.
S
13
Figure
S1
2
.
1
H NMR of reaction of
[Mn
III
3
CaO(OH)]
with PEt
3
.
S
13
Figure
S1
3
.
1
H NMR of reaction of
[Mn
III
3
CaO(OH)]
with PPh
3
.
S
14
Figure
S1
4
.
1
H NMR of reaction of
[Mn
II
Mn
III
2
YO(OH)]
with PEt
3
.
S1
4
Figure
S1
5
.
1
H NMR of reaction of
[Mn
II
Mn
III
2
YO(OH)]
with PPh
3
.
S1
5
Figure
S
16
.
1
H NMR of reaction of
[Mn
II
Mn
III
2
CaO(OH)]
with PEt
3
.
S1
5
Figure
S1
7
.
1
H NMR of reaction of
[Mn
II
Mn
III
2
CaO(OH)]
with PPh
3
.
S
16
Figure S
18
.
1
H and
31
P NMR of reaction o
f
[Fe
III
3
LaO(OH)]
with PPh
3
.
S
16
Figure
S
19
.
1
H NMR of reaction of
[Fe
III
3
CaO(OH)]
with PPh
3
.
S
17
Figure
S2
0
.
1
H and
31
P NMR of reaction of
[Fe
II
Fe
III
2
ScO(OH)]
with PMe
3
.
S
17
Figure S
2
1
.
1
H and
31
P NMR of reaction of
[Fe
II
Fe
III
2
LaO(OH)]
with PMe
3
.
S
18
Fi
gure
S2
2
.
1
H
and
31
P NMR of reaction of
[Fe
II
Fe
III
2
CaO(OH)]
with PMe
3
.
S
18
S
2
Crystallographic Information
.
S
19
Refinement details
S
19
Table
S4
.
Crystal and refinement data for complex
[Mn
III
3
ScO
3
]
S
20
Special refinement details for
[Mn
III
3
S
cO
3
]
S
21
Figure
S2
3
.
Solid
-
state structure of
[Mn
III
3
ScO
3
]
S2
1
Optimized Geometries for Calculated Complexes
S2
2
Figure
S
2
4
.
Optimized Structure of
ox
Ca’
.
S2
2
Figure
S
2
5
.
Optimized Structure of
red
Ca’
.
S2
2
Figure
S
2
6
.
Optimized Structu
re of
ox
Ca
’
’
.
S2
3
Figure
S
27
.
Optimized Structure of
red
Ca
’
’
.
S2
3
Figure
S
28
.
Optimized Structure of
red
Ca
’
’
-
noH
.
S2
4
References
S
25
S
3
Structural Reassignment of [Mn
3
MO
2
(H)] Clusters (M = Na
+
, Sr
2+
, Ca
2+
, Zn
2+
, Y
3+
).
As previously re
ported
,
modification of the synthetic protocol (
including use of
iodosobenzene (PhIO) in place of potassium superoxide as oxygen atom transfer agent
)
enables access to
tetrametallic clusters incorporating two oxygen atoms (
[Mn
III
3
MO(OH)]
,
[Mn
II
Mn
III
2
MO(OH)
]
, Figure 1)
. These complexes
were obtained from the same
LMn
II
3
(OAc)
3
precursor used for preparing [Mn
3
MO
4
] cubane clusters.
1
S
tructural
characterization of these materials by XRD revealed tetrametallic clusters
c
ontaining
a μ
4
-
oxo
ligand. A second oxygen atom was incorporated as a μ
2
-
bridge between the apical
(redox
-
inactive)
metal and one of the basal Mn centers. The oxidation states of the three Mn centers
in
these
clusters
were
originally
assigned
,
based
a combination of magnetic susceptibility,
XRD, and XAS data, as
[Mn
III
2
Mn
I
V
MO
2
]
and
[Mn
III
3
MO
2
]
clusters
. This interpretation of
the available data led
to assignment of the μ
2
-
bridge
s
as oxo
(O
2
–
) moieties
based on c
harge
balance
in the overall structures
.
Although these measurements were consistent with the
one
-
electron change in
redox state
,
assignment of
the absolute oxidation states remained
inconc
lusive
.
1
Subsequently, the
isostructural Fe
3
clusters (
[Fe
III
3
MO(OH)]
,
[Fe
II
Fe
III
2
MO(OH)]
, Figure 1), were prepared
and the μ
2
bridging moiety was conclusively identified as a hydroxo (HO
–
) ligand.
2
The Fe
oxidation sta
tes in Fe
3
clusters were unambiguously determined via Mössbauer spectroscopy
as Fe
III
3
and Fe
III
2
Fe
II
in complexes
[Fe
III
3
MO(OH)]
and
[Fe
II
Fe
III
2
MO(OH)]
, respectively.
The hydroxide assignment was derived from charge
-
balance of the XRD structures.
Comparis
on of the structural metrics of Fe
3
and Mn
3
clusters show elongation of a single M
–
(μ
4
-
O) bond in reduced complexes
[Fe
II
Fe
III
2
MO(OH)]
and
the Mn
analog,
initially assigned
as
Mn
III
3
M
(Table
S1
), suggesting the presence of a single
reduced Mn center
as
Mn
II
Mn
III
2
M
clusters, and therefore supporting assignment of Mn oxidation states in
the oxidized and
reduced Mn clu
sters
as Mn
III
3
and Mn
III
2
Mn
II
, respectively. Thus, by charge
-
balance of the
solid
-
state structure, the μ
2
bridging moiety
is assigned as OH
–
as in the Fe
3
clusters
resulting
in
reassigned
complexes
as
[Mn
III
3
MO(OH)]
and
[Mn
II
Mn
III
2
MO(OH)]
.
Density functional theor
y (DFT) calculations were carried out to further corroborate the
structural reassignment of complexes
[Mn
III
3
MO(OH)]
and
[Mn
II
Mn
III
2
MO(OH)]
.
Clusters
[Mn
III
3
Ca
O(OH)]
and
[Mn
II
Mn
III
2
Ca
O(OH)]
were modeled using Jaguar 8.4
3
(see
page S6
for
the
full computational protocol) both as originally assigned
–
[Mn
III
2
Mn
IV
CaO
2
]
(
ox
Ca’
) and [Mn
III
3
CaO
2
] (
red
Ca’
), respectively
–
and also according to the new structural
assignment proposed herein
–
[Mn
III
3
CaO(OH)] (
ox
Ca’’
) and [Mn
II
Mn
II
I
2
CaO(OH)] (
red
Ca’’
).
Selected bond metrics for the optimized structures as well as the values observed
experimentally (XRD) are shown in Table
S3
. For both oxidized and reduced complexes,
modeling of the clusters as the more reduced oxo
-
hydroxo species pr
ovides structural
p
arameters in closer agreement with the experimental values than those calculated for the
more oxidized dioxo clusters. In particular, the Mn(1)
–
O(2) distance, which is expected to be
sensitive to the nature of the μ
2
-
ligand, is calculated to be considerabl
y shorter for clusters
containing a μ
2
-
O
2
–
ligand (1.683 Å
and 1.697 Å for
ox
Ca’
and
red
Ca’
, respectively) than for
hydroxide
-
bridged clusters (1.830 Å and 1.907 Å for
ox
Ca’’
and
red
Ca’’
, respectively). The
experimental values (1.842(3) Å and 1.887(3) Å) a
gree more closely with the bond distances
from the computational studies, supporting the assignment of
[Mn
III
3
Ca
O(OH)]
and
[Mn
II
Mn
III
2
Ca
O(OH)]
as oxo
-
hydroxo clusters.
The new structural assignment for clusters
[Mn
III
3
M
O(OH)]
and
[Mn
II
Mn
III
2
M
O(OH)]
, is
fur
ther supported by electron paramagnetic resonance (EPR) spectroscopy. Normal
-
mode X
-
band EPR characterization obtained in CH
2
Cl
2
glass at cryogenic temperatures revealed weak
S
4
signals for
[Mn
III
3
Ca
O(OH)]
and
[Mn
III
3
Sr
O(OH)]
(Figure
S
1
a
and S
2
a), consistent
with
integer
-
spin systems, and more intense signals for
[Mn
II
Mn
III
2
Ca
O(OH)]
and
[Mn
II
Mn
III
2
Sr
O(OH)]
(Figure
S
1
b and S
2
b), consistent with half
-
integer systems. These
observations are inconsistent with the original oxidation state assignment for these clust
ers: a
Mn
III
2
Mn
IV
M
complex would be a half
-
integer spin system (d
4
, d
4
, d
3
), whereas a
Mn
III
3
M
species would be an integer
-
spin system (d
4
, d
4
, d
4
). The EPR data is consistent with the newly
proposed assignments of
[Mn
III
3
M
O(OH)]
as [Mn
III
3
] (d
4
, d
4
, d
4
, an integer
-
spin system) and
of
[Mn
II
Mn
III
2
M
O(OH)]
as [Mn
III
2
Mn
II
] (d
4
, d
4
, d
5
, a half
-
integer spin system). It should be
noted that the changes in assignment of the oxidation states and identity of bridging ligands
in clusters
[Mn
III
3
M
O(OH)]
and
[Mn
II
Mn
III
2
M
O(OH)]
bear no effect on the conclusions
of earlier studies on these complexes regarding the effect of the redox inactive metal on
reduction potentials.
1
All comparisons within this series of complexes remain
valid, as changes
affect compounds across the entire series. The reactivity studies described next were focused
on the available oxo
-
hydroxo complexes.
S
5
Table
S
1
.
Bond Parameters
(
Measured in Å) from Computation
Bond
ox
Ca
(XRD)
1
ox
Ca
’
ox
Ca
’’
redCa
(XRD)
1
red
Ca
’
red
Ca
’’
red
Ca
’’
-
noH
Mn2
–
N4
2.095
2.122
2.140
2.089
2.176
2.278
2.277
Mn2
–
N3
2.241
2.292
2.251
2.341
2.264
2.254
2.341
Mn2
–
O3
1.884
1.908
1.893
1.936
1.876
2.101
2.106
Mn2
–
O4
2.265
2.224
2.248
2.111
2.281
2.282
2.262
Mn2
–
O7
1.913
1.922
1.906
1.971
1.922
2.096
2.094
Mn2
–
O1
1.913
1.889
1.918
2.159
1.906
2.203
2.195
Mn3
–
N5
2.161
2.107
2.255
2.290
2.287
2.256
2.194
Mn3
–
N6
2.124
2.166
2.125
2.205
2.142
2.219
2.170
Mn3
–
O5
2.232
2.226
2.379
2.322
2.149
2.308
2.397
Mn3
–
O4
1.872
1.857
1.911
2.092
1.935
1.939
1.910
Mn3
–
O9
1.910
1.896
1.867
2.129
1.938
1.928
1.884
Mn3
–
O1
2.017
2.054
1.944
1.939
1.848
1.827
1.907
Mn1
–
N1
2.170
2.208
2.161
2.211
2.151
2.278
2.303
Mn1
–
N2
2.129
2.145
2.143
2.156
2.187
2.131
2.159
Mn1
–
O3
2.215
2.279
2.261
2.250
2.281
2.142
2.178
Mn1
–
O5
1.878
1.908
1.896
1.900
2.029
1.941
1.912
Mn1
–
O1
1.958
1.972
2.006
1.860
2.141
1.958
1.894
Mn1
–
O2
1.842
1.683
1.830
1.887
1.697
1.837
1.907
Ca1
–
O1
2.452
2.445
2.479
2.397
2.474
2.424
2.410
Ca1
–
O2
2.349
2.556
2.422
2.368
2.394
2.389
2.504
O2
–
OTf
(
2.847
)
a
--
2.692
2.742
--
2.664
--
a
distance between O2 and H
-
bonded 1,2
-
dimethoxyethane (DME) solvent molecule
S
6
Calcula
tion of
Mulliken Spin Population
s
Mulliken population analysis was employed to assign oxidation states of all atoms based
on the number of unpaired spins. The bridging alkoxides exhibited
α
spins on the order
of ~ 0.10 due to the highly covalent Mn
-
O bonds
. Spin on the remaining scaffold was
found to be negligible ( < 0.02
α
spins per remaining atoms). For
red
Ca
’’
, Mulliken spin
population revealed an alternative oxidation state assignment in which Mn2 is assigned as
Mn(II) as Mn3 is assigned as Mn(III).
Table
S
2
.
Mulliken Spin Population
s
.
Atom
ox
Ca
’
ox
Ca
’’
red
Ca
’
red
Ca
’’
red
Ca
’’
-
noH
Mn1
3.49
3.83
3.72
3.82
3.85
Mn2
3.87
3.87
3.88
3.86
3.87
Mn3
3.86
3.88
3.84
4.82
4.81
Ca1
0.01
0.00
0.00
0.00
0.00
O1
0.00
0.00
0.00
0.00
0.00
O2
-
0.61
0.00
0.18
0.00
0.00
Table
S
3
. Comparison of Selected Bond Distances (in Å) for Complexes
[Fe
III
3
CaO(OH)]
(oxFe)
,
[Fe
II
Fe
III
2
CaO(OH)]
(redFe)
,
[Mn
III
3
CaO(OH)]
(oxCa)
,
[Mn
II
Mn
III
2
CaO(OH)]
(redCa)
(XRD),
ox
Ca’,
ox
Ca’’,
red
Ca’, and
red
Ca’’ (DFT).
Bond
oxFe
(XRD)
redFe
(XR
D)
oxCa
(XRD)
red
Ca
(XRD)
ox
Ca
’
(DFT)
ox
Ca’’
(DFT)
red
Ca’
(DFT)
red
Ca’’
(DFT)
M
1
–
O
1
2.023(2)
1.928(5)
1.958(3)
1.860(3)
1.972
2.006
2.141
1.894
M
2
–
O
1
1.927(2)
1.904(5)
1.913(3)
2.159(3)
1.889
1.918
1.906
2.195
M
3
–
O
1
1.945(2)
2.140(5)
2.017(3)
1.939(3)
2
.054
1.944
1.848
1.907
M
1
–
O
2
1.881(2)
1.923(5)
1.842(3)
1.887(3)
1.683
1.830
1.697
1.907
S
7
EPR Spectroscopy
Figure
S
1
.
Temperature
-
dependent CW X
-
Band EPR perpendicular
-
mode spectra of the
frozen solutions of (a)
[Mn
III
3
CaO(OH)]
and (b)
[Mn
II
Mn
III
2
Ca
O(OH)]
dissolved in
dichloromethane
. Experimental parameters: microwave frequency = 9.36
–
9.38 GHz; power
= 0.07962 mW for (a) and 0.1589 mW for (b); modulation amplitude = 10.0 G; modulation
fre
quency = 100
kHz.
[Mn
III
3
CaO(OH)]
[Mn
II
Mn
III
2
CaO(OH)]
S
8
Figure S2.
Temperature
-
dependent CW X
-
Band EPR perpendicular
-
mode spectra of the
frozen solutions of (a)
[Mn
III
3
Sr
O(OH)]
and (b)
[Mn
II
Mn
III
2
Sr
O(OH)]
dissolved in
dichloromethane
. Experimental parameters: microwave frequency = 9.3
6
–
9.38 GHz;
power = 0.07962 mW for (a) and 0.1589 mW for (b); modulation amplitude = 10.0 G;
modulation frequency = 100 kHz.
[Mn
II
Mn
III
2
Sr
O(OH)]
[Mn
III
3
Sr
O(OH)]
S
9
NMR Spectroscopy
Figure
S3
.
(
Top
)
1
H NMR (300 MHz, CD
2
Cl
2
) spectrum of
the intermediate species
formed from the reaction of
[M
n
II
Mn
III
2
YO(OH)]
with 10 equiv. PPh
3
within 30 mins.
(
Bottom
)
1
H NMR (300 MHz, CD
3
CN
) spectrum
[LCaMn
3
O(OTf)
2
(OAc)
3
]
2
dimer.
4
Figure
S4
.
1
H NMR (300 MHz, C
6
D
6
) spectrum of
[Mn
III
3
ScO
3
]
.
S
10
Figure
S
5
.
1
H NMR (300 MHz, CD
2
Cl
2
) spectrum of
[Mn
III
3
YO(OH)]
2
.
F
igure
S
6
.
1
H NMR (300 MHz, C
6
D
6
) of reaction of
[Mn
III
Mn
IV
2
ScO
4
]
with PMe
3
(10
equiv).
[Mn
III
Mn
IV
2
ScO
4
]
S
11
Figure
S
7
.
1
H NMR (300 MHz, C
6
D
6
) of reaction of
[Mn
III
Mn
IV
2
ScO
4
]
with PMe
3
(10
equiv) at 50 °C.
Figure
S
8
.
1
H NMR (300 MHz, C
6
D
6
) of reaction of
[Mn
III
Mn
IV
2
Gd
O
4
]
with PMe
3
(10
equiv) at room temperature.
[Mn
III
Mn
IV
2
ScO
4
]
[Mn
III
Mn
IV
2
Gd
O
4
]
[Mn
III
Mn
IV
2
Gd
O
4
]