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complexes: synthesis, reactivity and magnetism rationalized by an
unexpected metal oxidation state
Andreas A. Danopoulos,*a,b Pierre Braunstein,*b Kirill Yu. Monakhov,*c Jan van Leusen,c Paul
Kögerler,*c,d Martin Clémancey,e Jean-‐Marc Latour,e Anass Benayad,f Moniek Tromp,g
Elixabete Rezabalh and Gilles Frisonh
a. Institute for Advanced Study (USIAS), Université de Strasbourg, 4 rue Blaise Pascal, 67081 Strasbourg Cedex, France, E-‐mail: [email protected]
b. Université de Strasbourg, CNRS, CHIMIE UMR 7177, Laboratoire de Chimie de Coordination, Institut de Chimie 4 rue Blaise Pascal, 67081 Strasbourg Cedex, France, E-‐mail: [email protected]
c. Institut für Anorganische Chemie, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany, E-‐ mail: [email protected]‐aachen.de, [email protected]‐aachen.de
d. Jülich-‐Aachen Research Alliance (JARA-‐FIT) and Peter Grünberg Institute 6, Forschungszentrum Jülich, 52425 Jülich, Germany
e. Laboratoire de Chimie et Biologie des Métaux, Equipe de Physicochimie des Métaux en Biologie, UMR 5249 CNRS/CEA-‐DRF-‐BIG/, Université Grenoble-‐Alpes,17 rue des Martyrs, Grenoble 38054, France
f. CEA / DRT / LITEN / DTNM / SEN / L2N, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France g. Van't Hoff Institute for Molecular Sciences, Sustainable Materials Characterisation, University of Amsterdam,
Amsterdam, The Netherlands h. LCM, CNRS, Ecole Polytechnique, Université Paris-‐Saclay, 91128 Palaiseau, France.
CH(CH3)2), in part masked by solvent), –1.15 (18H, N(SiMe3)2), –4.41 (4H), –10.17 (2H, CH=CH, imid‡),
–14.99 (4H, CH(CH3)2‡), –70.72 (12H, CH(CH3)2).
S6
With IAd: The experiment was carried out as above but using a 5-‐fold excess of IAd. The new
species detected in solution was formulated as [Fe(IAd){N(SiMe3)2}] based on the assignment of the 1H-‐NMR spectrum; under these conditions the ratio [4]/[Fe(IAd){N(SiMe3)2}] was ca. 1.1. 1H-‐NMR
Density functional theory (DFT) calculations were carried out with both the Gaussian09 18 and
the Orca19 packages. First, we have used the B3LYP density functional as implemented in Gaussian09,
combined with the 6-‐31G(d,p) basis set of all atoms but Co and Fe for which the LanL2DZ ECP and
related basis set has been used. Second, we have used the B3LYP density functional as implemented in
Orca, combined with the def2-‐SVP basis set of all atoms.
Single point energy calculations based on the X-‐ray structures have been achieved at both
levels for the full Co (3) and Fe (4) complexes at various electronic states. The open shell singlet state
(S=1/2-‐S=1/2) of the Co complex 3 has been initially obtained from an UDFT broken symmetry (BS)
calculation with Gaussian09, as well as with the Orca program. Other open shell states (S=3/2 -‐S=1/2
triplet for 3 and S=2-‐ S=1/2 quadruplet for 4) could be characterized using the BS formalism only with
the Orca program, starting respectively from the quintet state of 3 and the sextet state of 4.
Geometry optimizations of 3 in the triplet and closed-‐shell singlet states have been performed
with Gaussian09 without any constraint.
The calculations indicate triplet and quartet electronic ground states, for 3 and 4, respectively
(Table S3). The spin densities of the ground state are illustrated in Figure S5 and the α-‐spin and β-‐spin
molecular orbitals of 3 in its triplet ground state are represented in Figure S6. In 3 one single electron
is on Co and a second slightly delocalized throughout the metal and the π system of the molecule. The
delocalized π-‐interaction of a single electron induces stabilization of the linear geometry; this was
established by full geometry optimizations in the triplet and closed-‐shell singlet states at the same
level of calculation: the former led to a complex with a structure very similar to the experimental (C-‐
Co-‐N: 179.7°), whereas the latter to a bent complex (C-‐Co-‐N: 142.3°). Analogous results were obtained
for 4 (two single electrons on Fe and one π electron slightly delocalized over the molecule).
Table S3. Relative energies (kJ/mol) of 3 and 4 for various electronic states.a
3 4
Singlet +210.3 Doublet +105.5
BSb singlet +67.6 (+62.8) Quartet 0.0 (0.0)
Triplet 0.0 (0.0) BS quartet -‐ (+18.1)
BSb triplet -‐ (+17.3) Sextet +188.7 (+179.8)
Quintet +233.2 (+208.1)
[a] Values obtained at the B3LYP/6-‐31G(d,p) – LanL2DZ (Fe/Co) level with Gaussian 09. Values in parentheses obtained at the B3LYP/def2-‐SVP level with Orca. [b] Broken symmetry
S15
In order to evaluate the multi-‐reference nature of the open-‐shell singlet state of the Co complex
3, T1 diagnosis was performed on CCSD(T) calculations. To that end, a simplified model, including
unsubstituted carbene and NH2 ligands, was used. These calculations pointed out to a multi-‐reference
nature of the configuration, as indicated by the 0.035 and 0.041 T1 values obtained respectively with
the 6-‐31G(d,p) (LanL2DZ on Co) and def2-‐TZVP basis sets. The open shell configurations calculated
here should thus present a markedly multiconfigurational character, and therefore, the electronic
structure and relative energies may not be estimated accurately enough by the BS DFT formalism.
Consequently, the relative energies and spin densities calculated for the open shell systems should be
carefully considered.
Figure S5. Spin density of the ground states of 3 and 4, as well as their BS triplet and quartet states.
S16
Figure S6. α-‐spin (left) and β-‐spin (right) molecular orbitals of 3 in its triplet ground state.
S17
3.2 Cartesian coordinates of the optimized geometries Table S4. Geometry optimization of 3 in the triplet state. E = -‐2178.493189 u.a C 0.002907 -‐1.207171 0.001673 C 0.687621 -‐3.385954 -‐0.017696 H 1.402001 -‐4.192766 -‐0.052260 C -‐0.666471 -‐3.390038 0.061176 H -‐1.375065 -‐4.201167 0.109640 C 2.465258 -‐1.652786 -‐0.130261 C 3.191437 -‐1.499717 1.067996 C 4.543437 -‐1.151016 0.961312 H 5.131379 -‐1.021004 1.864781 C 5.143208 -‐0.963226 -‐0.280517 H 6.192200 -‐0.687791 -‐0.339533 C 4.401026 -‐1.124859 -‐1.446644 H 4.878476 -‐0.972179 -‐2.409635 C 3.047073 -‐1.478385 -‐1.401624 C 2.566882 -‐1.699842 2.445761 H 1.517368 -‐1.973354 2.306218 C 3.244071 -‐2.855345 3.208365 H 3.200526 -‐3.791155 2.641306 H 2.747901 -‐3.018744 4.170985 H 4.298224 -‐2.639293 3.411865 C 2.588052 -‐0.398618 3.271041 H 3.611798 -‐0.060613 3.464006 H 2.102138 -‐0.557047 4.239963 H 2.058640 0.405122 2.751245 C 2.265995 -‐1.653745 -‐2.700662 H 1.257389 -‐1.992157 -‐2.447153 C 2.894688 -‐2.734477 -‐3.601624 H 3.900844 -‐2.453184 -‐3.929766 H 2.284617 -‐2.880219 -‐4.499330 H 2.970731 -‐3.695941 -‐3.083015 C 2.119575 -‐0.315675 -‐3.450984 H 3.095421 0.089770 -‐3.739405 H 1.612652 0.428149 -‐2.829119 H 1.532804 -‐0.455659 -‐4.365564 C -‐2.456942 -‐1.668835 0.141294 C -‐3.181772 -‐1.534798 -‐1.059754 C -‐4.536419 -‐1.194583 -‐0.959712 H -‐5.123106 -‐1.077919 -‐1.865801 C -‐5.140526 -‐0.998430 0.278739 H -‐6.191655 -‐0.730176 0.332612 C -‐4.399705 -‐1.142696 1.448010 H -‐4.880276 -‐0.983466 2.408370 C -‐3.042864 -‐1.485789 1.409346 C -‐2.552016 -‐1.741879 -‐2.434104 H -‐1.504391 -‐2.019920 -‐2.289038 C -‐3.230073 -‐2.895969 -‐3.197876 H -‐3.194847 -‐3.830300 -‐2.627827 H -‐2.728308 -‐3.064506 -‐4.156710 H -‐4.281723 -‐2.675585 -‐3.409416 C -‐2.563663 -‐0.441983 -‐3.261873 H -‐3.585272 -‐0.099280 -‐3.457976
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H -‐2.075702 -‐0.604321 -‐4.229146 H -‐2.032032 0.360266 -‐2.741845 C -‐2.261152 -‐1.635443 2.711231 H -‐1.254613 -‐1.984964 2.464538 C -‐2.892911 -‐2.690539 3.639704 H -‐3.895127 -‐2.394712 3.966966 H -‐2.279159 -‐2.820112 4.537375 H -‐2.978546 -‐3.662993 3.143603 C -‐2.106667 -‐0.279876 3.428176 H -‐1.597128 0.446226 2.787598 H -‐1.519333 -‐0.399877 4.345257 H -‐3.080398 0.137179 3.707244 C 1.736369 5.057989 -‐0.820551 H 1.702620 4.798707 -‐1.885123 H 2.713406 5.516316 -‐0.623254 H 0.975731 5.825959 -‐0.644232 C 1.707019 4.056620 2.076507 H 0.914633 4.749799 2.378987 H 2.669112 4.557500 2.241482 H 1.659757 3.193209 2.750830 C 2.981240 2.391369 -‐0.138368 H 2.996144 1.477095 0.464019 H 3.921768 2.924455 0.051551 H 2.975656 2.093001 -‐1.192382 C -‐1.756553 5.059515 0.801894 H -‐1.720417 4.799992 1.866266 H -‐2.734472 5.516712 0.606419 H -‐0.996909 5.828019 0.623965 C -‐1.726597 4.055779 -‐2.096306 H -‐0.934567 4.749185 -‐2.398988 H -‐2.689135 4.555187 -‐2.262949 H -‐1.677887 3.191173 -‐2.768957 C -‐2.999911 2.390163 0.120303 H -‐3.007242 1.471114 -‐0.475243 H -‐3.942501 2.916848 -‐0.077001 H -‐2.997115 2.098634 1.176303 N 1.078630 -‐2.054292 -‐0.052018 N -‐1.066650 -‐2.060217 0.070543 N -‐0.010412 2.699714 -‐0.010278 Si 1.497784 3.508091 0.264700 Si -‐1.518749 3.510794 -‐0.283775 Co -‐0.007191 0.804126 -‐0.009157
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Table S5. Geometry optimization of 3 in the closed-‐shell singlet state. E = -‐2178.564149 C -‐0.596493 -‐0.790349 0.222773 C -‐2.087039 -‐2.380717 0.951145 H -‐3.055540 -‐2.826061 1.109062 C -‐0.845668 -‐2.813401 1.269821 H -‐0.515694 -‐3.708458 1.770977 C -‐3.018999 -‐0.337087 -‐0.161375 C -‐3.274598 -‐0.297269 -‐1.549443 C -‐4.322877 0.520763 -‐1.993794 H -‐4.537688 0.577947 -‐3.056559 C -‐5.101816 1.244775 -‐1.098469 H -‐5.911694 1.869467 -‐1.464422 C -‐4.853558 1.158975 0.269482 H -‐5.477841 1.717845 0.959204 C -‐3.810981 0.372699 0.771282 C -‐2.507462 -‐1.142174 -‐2.564287 H -‐1.721816 -‐1.684588 -‐2.032053 C -‐3.431727 -‐2.193118 -‐3.211953 H -‐3.898572 -‐2.834390 -‐2.457253 H -‐2.860522 -‐2.831827 -‐3.894305 H -‐4.233652 -‐1.722332 -‐3.790812 C -‐1.815325 -‐0.277788 -‐3.634402 H -‐2.538851 0.298029 -‐4.221556 H -‐1.252973 -‐0.912617 -‐4.327349 H -‐1.110897 0.426819 -‐3.177369 C -‐3.596678 0.268141 2.279919 H -‐2.606260 -‐0.164276 2.449020 C -‐4.641139 -‐0.677544 2.911267 H -‐5.654296 -‐0.281776 2.779698 H -‐4.459809 -‐0.786888 3.985918 H -‐4.617062 -‐1.675229 2.462335 C -‐3.623794 1.632122 2.992803 H -‐4.611620 2.102188 2.941974 H -‐2.893852 2.323683 2.566517 H -‐3.384198 1.499441 4.053195 C 1.484980 -‐2.047611 0.878883 C 2.224632 -‐1.382229 1.879314 C 3.599070 -‐1.639481 1.945748 H 4.199156 -‐1.142260 2.699713 C 4.211674 -‐2.526253 1.063434 H 5.279936 -‐2.710118 1.135049 C 3.457852 -‐3.178079 0.093756 H 3.945144 -‐3.871836 -‐0.584214 C 2.079370 -‐2.955852 -‐0.023887 C 1.551855 -‐0.465534 2.897432 H 0.680638 -‐0.019921 2.409540 C 1.054645 -‐1.278795 4.111663 H 0.351196 -‐2.062823 3.815121 H 0.545715 -‐0.624759 4.828397 H 1.893279 -‐1.757959 4.629596 C 2.448717 0.693988 3.359502 H 3.292836 0.348449 3.966570 H 1.869488 1.384251 3.981227 H 2.843042 1.254018 2.507566
S20
C 1.278517 -‐3.732642 -‐1.068505 H 0.283029 -‐3.284271 -‐1.133269 C 1.104827 -‐5.204685 -‐0.637856 H 2.075182 -‐5.708798 -‐0.572207 H 0.492642 -‐5.748612 -‐1.365477 H 0.621983 -‐5.290536 0.340256 C 1.896740 -‐3.665292 -‐2.477486 H 2.022314 -‐2.633660 -‐2.813978 H 1.246293 -‐4.180817 -‐3.192501 H 2.874939 -‐4.155734 -‐2.518393 C 2.514525 4.332003 1.016217 H 3.010923 3.669867 1.734271 H 2.237561 5.248256 1.552153 H 3.253934 4.610380 0.257474 C 0.155783 4.804128 -‐0.880090 H 0.803702 5.065358 -‐1.723074 H -‐0.077234 5.728882 -‐0.338028 H -‐0.780194 4.410142 -‐1.292601 C -‐0.243561 3.230228 1.694766 H -‐1.201768 2.869262 1.309439 H -‐0.421972 4.162791 2.245284 H 0.134142 2.485981 2.402454 C 3.011211 3.291999 -‐2.774039 H 2.137006 3.493723 -‐3.403014 H 3.861094 3.096932 -‐3.439476 H 3.236854 4.207117 -‐2.216099 C 4.291954 1.504290 -‐0.631501 H 4.527632 2.358620 0.011536 H 5.151824 1.339898 -‐1.292693 H 4.192093 0.620964 0.008438 C 2.498635 0.289103 -‐2.770913 H 2.352825 -‐0.613120 -‐2.170649 H 3.389148 0.144407 -‐3.396054 H 1.632416 0.399031 -‐3.431666 N -‐1.929572 -‐1.147533 0.324261 N 0.055622 -‐1.850706 0.815405 N 1.313192 2.042944 -‐0.611842 Si 0.964336 3.520036 0.263328 Si 2.707827 1.793799 -‐1.640270 Co -‐0.024391 0.802570 -‐0.622656
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4. Magnetochemical Analysis 4.1 General methods
Magnetic data of 3 and 4 were recorded using a Quantum Design MPMS-‐5XL SQUID
magnetometer. The polycrystalline samples were compacted and immobilized into cylindrical PTFE
capsules. DC data were acquired as a function of the magnetic field (0.1−5.0 T at 2 K) and temperature
(2.0–290 K at 0.1 T). AC data were measured in the absence of a static bias field in the frequency range
1−1000 Hz (T = 2.0−50 K, Bac = 3 G). Data were corrected for the diamagnetic contributions of sample
Figure S7. χmT at 280 and 290 K of 3 (left) and 4 (right) under various magnetic fields.
S22
Figure S8. Illustration of the best possible least–squares fits (solid lines) for the alternative electron
configuration scenarios (i), top, and (ii), bottom, for 3 (left) and 4 (right). All χmT vs. T data at 0.1 Tesla, all
magnetization curves (insets) at 2.0 K. a) SQ = 20%, b) SQ = 11%, c) (fit only to magnetization data, SQMm = 2.7%)
overall SQ = 8.4%, and d) SQ = 12%. Besides the poor SQs and curves badly reproducing the data, the estimated
ligand field parameters are physically unlikely or impossible being either very small (for a), even quasi–free ion)
values or very large values (> 60000 cm–1) with partly incorrect signs.
S23
Table S6. Least–squares fit parameters calculated by CONDON 2.020 according to the “MII+e–” model described in
the text for [M(IPr){N(SiMe3)2}].
Parameter M = Co (3) M = Fe (4)
B a) / cm–1 1115 1058
C a) / cm–1 4366 3901
ζ3d a) / cm–1 533 410
!!! b) / cm–1 27201±62 31912±20
!!! b) / cm–1 40150±223 43505±68
J c) / cm–1 –0.1±0.2 –0.5±0.1
SQ d) 7.7% 2.8%
a) Racah parameters and one-‐electron spin-‐orbit coupling constants;21 b) ligand field parameters in Wybourne notation; c) Heisenberg parameter, “–2J” convention; d) goodness of fit.
4.3 Magnetic ac data
Figure S9. In-‐phase (χm’) and out-‐of-‐phase (χm’’) magnetic molar susceptibility of 3 as a function of temperature
T at zero static bias field.
S24
Figure S10. In-‐phase (χm’) and out-‐of-‐phase (χm’’) magnetic molar susceptibility of 4 as a function of
temperature T at zero static bias field.
Figure S11. Relaxation time τ vs. T–1 of 4, black (8.5–14 K) and green lines (3.0–5.5 K): fit to Arrhenius
expression; blue dashed line: fit considering quantum tunnelling, Raman and Orbach relaxation; red line: fit
considering quantum tunnelling, Orbach and another Arrhenius-‐type relaxation.
S25
5. XPS Studies
All samples were prepared in a glove box and transferred to the spectrometer using a transfer
vessel under argon. The X-‐ray Photoemission Spectra were recorded using focused monochromatized
Al-‐Kα radiation (1486.6 eV) (Figures S12 and S13). The spectrometer (VersaProbe-‐II, ULVAC-‐Phi) was
calibrated using photoemission lines of gold (Au 4f7/2 = 83.9 eV, with reference to the Fermi level). The
core level peaks and survey spectra were recorded with constant pass energy of 23.3 and 117.9 eV,
respectively. All spectra were recorded using electron and argon charge neutralizer guns to minimize
surface charging effects that may occur at insulating powder surface during the photoemission
process. All spectra were calibrated using the contamination carbon C 1s peak at 285 eV. The XPS
spectra were fitted using Multipak V9.1 software in which a Shirly background was assumed and the
peak fittings of the experimental spectra were defined by a combination of Gaussian (80%) and
Lorentzian (20%) distributions.
Figure S12. XPS spectrum of 3.
S26
Figure S13. XPS spectrum of 4. Table S7. Binding energies (eV) and FWHM (eV) of 2p3/2 and 2p1/2 peaks and their satellites
3 4
2p3/2 780.7 710.0
FWHM 4.0 4.1
satellite 785.7 714 .5
FWHM 5.5 3.1
2p1/2 796.4 723.1
FWHM 3.6 3.8
satellite 802.1 727.2
FWHM 6.0 3.6
S27
6. EXAFS and XANES Studies of 3
The Co K edge (7709 eV) XAS data was obtained at the Diamond Light Source, United Kingdom
on beam line B18. The sample of 3 was prepared in the glove box in a small capillary, sealed and
measured. The Co K-‐edge XANES data processing and EXAFS analysis were performed using IFEFFIT
version 1.2.11d with the Horae package (Athena and Artemis).22 Fitting was done in k-‐ and R-‐space
and in multiple weightings of k1, k2 and k3, simultaneously. The EXAFS could be fitted with one Co-‐N/C
contribution at 1.89(2) and one Co-‐N/C at 1.96(1) Å with low Debye Waller factors (EXAFS cannot
distinguish between N and C as they are neighbouring atoms in the periodic table and have very
similar back scatterings amplitudes), nicely corresponding to the single crystal data.
The 1st derivative of the Co K-‐edge XANES of sample 3, in comparison to some representative
Co(II) and Co(III), is given in Figure S14 (the normalised Co K edge XANES spectra are in Figure 3, in
the main paper). The first derivative can be used to accurately determine the number of pre-‐edge
features as well as the position of the pre-‐edges and main edge (the main sàp transition). For the
reference samples, one pre-‐edge is present, with the main edge being the second maximum in the 1st
derivative. For sample 3, the third maximum in the 1st derivative is the edge position, since this sample
displays two clear pre-‐edge features. It is clear that sample 3 represents an overall Co2+. The feature is
broad towards higher energy, which suggests some electron density is distributed away from the Co
centre. The XANES is known to be dependent on the ligand and geometry as well as the oxidation state
of the central metal,23 but the EXAFS in combination with XANES pre edge features supporting the
linear coordination only further support the Co2+ assignment. More support and insights in the XANES
are obtained from simulation the XANES and corresponding empty density of states (DOS) (XANES
probes the empty DOS).
Figure S14. Normalised Co K-‐edge XANES (left) and 1st derivative (right) of normalized XANES for Co references compounds as well as sample 3.
The FEFF9 code was used to perform ab initio self-‐consistent field, real-‐space, full multiple
scattering calculations.24 The calculations were performed using the Hedin-‐Lundquist exchange
correlation potential. A (final state rule) core hole is included on the absorber atom to mimic the final
S28
state of the photon absorption process. The XANES simulation including the corresponding l-‐projected
empty (DOS) as calculated simultaneously is presented in Figure S15. Whereas the 1st pre-‐edge is due
to pd hybridization, making the dipole forbidden s → d transition slightly visible, the 2nd pre-‐edge
originates from hybridization of the Co-‐p and Co-‐d with C-‐p mostly, and little mixing from Np. The high
intensity of this pre-‐edge is due to the empty character of the orbital, which is indicative of the linear
nature around the Co centre and also suggest the channel of charge redistribution being the aromatic
part of the molecule.
Figure S15. Calculated DOS (primary y-‐axis) and XANES (secondary y-‐axis) as a function of relative energy
(calculated). The vertical line at ca. –9 eV indicates the highest occupied molecular orbital. Since XANES probes
the empty density of state, the orbitals above –9 eV might be visible depending on symmetry and orbital overlap.
The main transition is Co-‐s to Co-‐p and thus the Co-‐p DOS will reflect best the features observed.
S29
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