Supporting Information (SI) for the manuscript:

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1 Supporting Information (SI) for the manuscript: Field-Induced Slow Magnetic Relaxation in a Six-Coordinated Mononuclear Cobalt(II) Complex with a Positive Anisotropy Julia Vallejo, Isabel Castro,* Rafael Ruiz-García, Joan Cano,* Miguel Julve, Francesc Lloret, Giovanni De Munno, Wolfgang Wernsdorfer, and Emilio Pardo S1

2 Experimental Section Materials. All chemicals were of reagent grade quality. They were purchased from commercial sources and used as received. Physical techniques. Elemental analyses (C, H, N) were performed at the Servicio Central de Soporte a la Investigación (SCSIE) from the Universitat de València (Spain). FT IR spectra were recorded on a Perkin-Elmer 882 spectrophotometer as KBr pellets. cis-[co II (dmphen) 2 (NCS) 2 ] EtOH (1). X-ray quality well-formed purple prisms of 1 were grown after several weeks by slow diffusion in an H-shaped tube of water/ethanol (1:1 v/v) mixtures containing stoichiometric amounts of Co(NCS) 2 (0.044 g, 0.25 mmol) in one arm and 2,9-dimethyl-1,10-phenantroline monohydrate (0.11 g, 0.50 mmol) in the other one at room temperature. The crystals were collected by filtration and air-dried (0.12 g, 79% yield). Anal. Calcd. for C 30.5 H 25.5 CoN 6 O 0.25 S 2 (603.1): C, 60.73; H, 4.26; N, 13.93%. Found: C, 61.08; H, 3.98; N, 13.92%; IR (KBr): 2080 (ν NCS ), 1497, 1590 cm 1 (ν C=C ). X-ray crystallographic data collection and structure refinement. X-ray diffraction data of 1 were collected with a Nonius Kappa CCD area detector using graphite-monochromated Mo-K α radiation (α = Å). Data were processed through the DENZO and SCALEPACK programs. 1,2 The structure was solved by direct methods and subsequently completed by Fourier recycling using the SHELXTL software package. 3 The ethanol molecule is disordered. This disorder has been treated assuming a population factor of 0.5 for the carbon and 0.25 for the oxygen. All non- 1 COLLECT, Nonius BV, Denzo-Scalepack Z. Otwinowski, W. Minor, Processing of X-ray Diffraction Data Collected in Oscillation Mode, in: C.W. CarterJr., R.M. Sweet (Eds.), Methods in Enzymology, Macromolecular Crystallography, Part A, vol. 276, Academic Press, 1997, p SHELXTL; Bruker Analytical X-ray Instruments, Madison, WI, S2

3 hydrogen atoms, except oxygen and carbon atoms of the ethanol molecule, were refined anisotropically. The hydrogen atoms of the dmphen ligands were set in calculated positions. The hydrogen atoms of the crystallization ethanol molecule were not located. The final full-matrix least-squares refinements on F 2, minimizing the function w( F o - F c ) 2, reached convergence with the values of the discrepancy indices given in Table S1. The final geometrical calculations were carried out with the PARST 4 program whereas the graphical manipulations were performed with the DIAMOND 5 and CRYSTAL MAKER 6 programs and the XP utility of the SHELXTL system. Crystallographic data (excluding structure factors) for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication number CCDC Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK [fax: (+44) ; deposit@ccdc.cam.ac.uk]. Magnetic measurements. Variable-temperature ( K) direct current (dc) magnetic susceptibility measurements under an applied field of 0.1 (T < 20 K) and 1.0 kg (T 20 K), and variable-field (0 7.0 T) magnetization measurements at low temperatures in the range of K were carried out with a Quantum Design SQUID magnetometer. Variable-temperature ( K) alternating current (ac) magnetic susceptibility measurements under different applied static fields in the range of kg were carried out with a Quantum Design Physical Property Measurement System (PPMS). The magnetic susceptibility data were corrected for the diamagnetism of the constituent atoms and the sample holder. Dc and ac magnetic measurements were carried out by powdering and restraining the sample in order to prevent any 4 Nardelli, M. J. Appl. Crystallogr. 1995, 28, D. Palmer, CRYSTAL MAKER, Cambridge University Technical Services, Cambridge, UK, DIAMOND 2.1d, Crystal Impact GbR, CRYSTAL IMPACT, Brandenburg, K.; Putz, H. GbR, Postfach S3

4 displacement due to its magnetic anisotropy. Variable-field sweep rate ( T s 1 ) magnetization measurements were performed on a single crystal of 1 using a micro- SQUID in the temperature range of K. Spectroscopic measurements. X-band EPR spectra (ν = 9.47 GHz) of a polycrystalline powdered sample of 1 were recorded in non-saturating conditions at 8.0 K on a Bruker ER 200 D spectrometer equipped with a helium cryostat. UV Vis NIR spectra of polycrystalline powdered samples of 1 were recorded on a JASCO V-670 spectrophotometer equipped with an integrating sphere. The solid electronic absorption spectrum of 1 shows two very strong intra-ligand (IL) bands in the UV region located at 257 and 369 nm, together with the typically weak slightly split d d transitions in the visible and NIR regions centered at 528, 640, and 1150 nm which have been assigned to the 4 T 2g (F) 4 T 1g (F) (ν 1 ), 4 A 2g (F) 4 T 1g (F) (ν 2 ), and 4 T 1g (P) 4 T 1g (F) (ν 3 ) transitions respectively, of the octahedral high-spin d 7 Co II ion (O h point group). 7 The octahedral crystal field splitting ( o = 10Dq) and the inter-electronic repulsion parameter (B) for 1 can be calculated from the energy data of the d d transitions through the corresponding expressions derived from a crystal field treatment (eqs S1 S3 with o = {[5ν 2 2 (ν 2 2ν 1 ) 2 ] 1/2 2(ν 2 2ν 1 )}/4 and B = (ν 2 2ν 1 + o )/15). 7 ν 1 [ 4 T 2g (F) 4 T 1g (F)] = 5Dq (15/2)B + (1/2)(225B Dq BDq) 1/2 (S1) ν 2 [ 4 A 2g (F) 4 T 1g (F)] = 15Dq (15/2)B + (1/2)(225B Dq BDq) 1/2 (S2) ν 3 [ 4 T 1g (P) 4 T 1g (F)] = (225B Dq BDq) 1/2 (S3) 7 Koenig, E. Struct. Bond. 1972, 9, 175; (b) Dou, Y. S. J. Chem. Ed. 1990, 67, 134. S4

5 The value of the A parameter can then be estimated from the calculated values of the crystal field parameters obtained from the analysis of the electronic spectrum of 1 (Dq = 834 cm -1 and B = 848 cm -1 ) through eqs S4 and S5 [A is a parameter that takes into account the admixture between the excited 4 T 1g (P) and the ground 4 T 1g (F) levels when using the T 1 and P term isomorphism]. A = (1.5 c 2 )/(1 + c 2 ) c = (B/Dq) [ (B/Dq) (B/Dq) 2 ] 1/2 (S4) (S5) Computational details. Complete active space (CAS) calculations were performed on the structurally characterized molecular geometry of 1 with version 2.8 of the ORCA program 8 using the TZVP basis set proposed by Ahlrichs 9 and the auxiliary TZV/C Coulomb fitting basis sets. 10 In the magnetic anisotropy calculations, the contributions from the 10 quartet and 20 doublet excited states generated from an active space with seven electrons in five d orbitals have been included. The ten quartet states show different energies due to the rhombic distortion of the octahedral geometry. From the relative energy values of the 4 T 2g (F), 4 A 2g (F), and 4 T 1g (P) excited states with respect to the 4 T 1g (F) ground state, it is possible to evaluate the Dq and B parameters. Due to the low symmetry of the real complex, these real energies are split in 0, 486, and 623 cm 1 for 4 T 1g (F); 6382, 6771, and 6875 cm 1 for 4 T 2g (F); cm 1 for 4 A 2g (F); and 22679, 23760, and cm 1 for 4 T 1g (P). Thus, two electronic transitions occur in the NIR region and the rest in the UV-vis region. These energies for the last transitions are in good agreement with those obtained from the experimental electronic spectrum in the solid state, supporting thus the observed band splitting associated to the low molecular 8 Neese, F. Wiley Interdiscip. Rev.: Comput. Mol. Sci. 2012, 2, 73 9 (a) Schafer, A.; Horn H.; Ahlrichs, R. J. Chem. Phys. 1992, 97, (b) Schafer, A.; Huber C.; Ahlrichs, R. J. Chem. Phys. 1994, 100, (a) Eichkorn, K.; Treutler, O.; Ohm, H.; Haser M.; Ahlrichs, R. Chem. Phys. Lett. 1995, 240, 283. (b) Eichkorn, K.; Treutler, O.; Ohm, H.; Haser M.; Ahlrichs, R. Chem. Phys. Lett. 1995, 242, 652; (c) Eichkorn, K.; Weigend, F.; Treutler, O.; Ahlrichs, R. Theor. Chem. Acc. 1997, 97, 19. S5

6 symmetry. Moreover, the two lowest transitions agree well with those values obtained from the fit of the magnetic susceptibility (415 and 920 cm -1 ). The calculated values of 10Dq and B of 7038 and 1064 cm 1 respectively, are in concordance with a weak ligand field. These values allow for an estimation of A as 1.46 which fully agrees with the value obtained from the analysis of the experimental electronic spectrum. On the other hand, from the composition of the natural orbitals, a value of κ equal to 0.95 is inferred, which is similar to that roughly procured from the spin density on cobalt atom (0.97). The g-tensor was calculated for the ground Kramer pair using Multi-reference Configuration Interaction (MRCI) wave functions with a first-order perturbation theory on the SOC matrix. 11 The calculated values of 2.4, 4.3, and 6.3 are close to those obtained from the experimental EPR spectrum. From these values we can deduce a value of χ M T = 2.00 cm 3 mol -1 K at low temperature, which is close to that obtained from the magnetic susceptibility measurements (χ M T = 1.80 cm 3 mol -1 K) or that extracted from the g components of the EPR spectrum (χ M T = 1.83 cm 3 mol -1 K). More importantly, the simulated magnetization curves obtained from the calculated g x, g y, and g z values applied on an effective doublet spin agree with the experimental curves. CAS calculations evidence a strong and positive value of the axial magnetic anisotropy (D = cm 1 ) with a rather high rhombicity value (E/D = 0.185). The calculated axial magnetic anisotropy is mainly ligated to the spin-orbit coupling (D SOC = cm 1 ) because of the almost negligible spin-spin contribution (D SS = +1.4 cm 1 ). Even for larger values of the contribution from the mixture with doublet excited states (D D = +4.5 cm 1 ), the spin-orbit coupling component is mainly associated to the contribution from other quartet excited states (D Q = cm 1 ). The large D Q value must be related to the fact that the first quartet excited states obtained by the promotion 11 Vancoillie, S.; Chalupský, J.; Ryde, U.; Solomon, E. I.; Pierloot, K.; Neese, F.; Rulísěk, Lu. J. Phys. Chem. B 2010, 114, S6

7 of one β electron from the d xz or the d yz orbital to the d x2 y2 orbital are very close in energy to the ground state (at 483 and 623 cm 1, respectively). Table S1. Summary of crystallographic data for 1 Formula C H CoN 6 O 0.25 S 2 M / g mol Crystal system Space group P-1 Triclinic a / Å (5) b / Å (4) c / Å (7) α / (3) β / (2) γ / (2) V / Å (11) Z 2 ρ calc / g cm µ / mm T / K 293(2) F(000) 623 Crystal size / nm 0.35 x 0.13 x 0.10 θ range for data collection / 1.42 to Index ranges -12 h 12, -14 k 12, -19 l 16 Reflect. collcd Independent reflections 6469 [R(int) = ] Completeness to theta = % Max. and min. transmission and Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 6469 / 0 / 360 Final R indices a,b [I > 2σ(I)] R1 = , wr2 = R indices (all data) R1 = , wr2 = Goodness-of-fit c on F Largest diff. peak and hole and e Å -3 a R 1 = ( F o F c )/ F o. b wr 2 = [ w(f o 2 F c 2 ) 2 / w(f o 2 ) 2 ] 1/2. c S = [ w( F o F c ) 2 /(N o N p )] 1/2. S7

8 Table S2. Selected ac magnetic data a for 1 at different dc applied fields. E a b H a (kg) τ b (s) (cm 1 ) α c χ c S (cm 3 mol 1 ) χ c T (cm 3 mol 1 ) a Applied dc magnetic field. b The values of the preexponential factor (τ 0 ) and activation energy (E a ) are calculated through the Arrhenius law [τ = τ 0 exp(e a /k B T)]. c The values of the α parameter, adiabatic (χ S ) and isothermal (χ T ) susceptibilities are calculated from the experimental data at 6.0 K through the generalized Debye law (see text). S8

9 Figure S1. Perspective view of the mononuclear cobalt(ii) unit of 1 with the atom-numbering scheme for the metal coordination environment. The dotted lines illustrate the intramolecular C H π type interactions, between the terminal methyl-substituted aromatic rings from each of the two dmphen ligands. S9

10 Figure S2. Projection views of the dmphen ligands of 1 from two neighboring mononuclear units along the [01 1] direction showing the intermolecular π-π stacking interactions. The ligands from each mononuclear unit are shown in different colors. S10

11 Figure S3. Projection view of adjacent heterochiral chains of mononuclear units of 1 with alternating (Λ, )-chiralities along the crystallographic a axis. The metal coordination polyhedron from each mononuclear unit of opposed chirality is shown in different colors [symmetry codes: (a) = 1 x, 1 y, z; (b) = x, y, 1 + z; (c) = 1 x, 1 y, 1 z; (d) = x, y, 1 + z; (e) = 1 x, y, 1 z]. Hydrogen atoms are omitted for clarity. S11

12 Figure S4. Temperature dependence of χ M T for 1 ( ) under an applied dc field of 0.1 (T < 20 K) and 1.0 kg (T 20 K). The solid line is the best-fit curve (see text). S12

13 Figure S5. H/T dependence of M of 1 in the temperature range of K. The solid lines are the best-fit curves (see text). S13

14 Figure S6. Perspective views of the calculated 3d metal orbitals for the quartet (S = 3/2) spin ground state of 1. The molecular x and y axes are taken along the bisector of the equatorial bonds while the z axis is taken along the axial bonds. S14

15 Figure S7. Solid electronic absorption spectrum of 1 at 25 C. S15

16 Figure S8. X-band EPR spectrum of a polycrystalline sample of 1 at 9.0 K. S16

17 Figure S9. Temperature dependence of χ M (a) and χ M (b) of 1 in a 2.5 kg applied static field and under 4.0 G oscillating field in the frequency range of 0.1 (grey) 10 (red) khz. The insets show the Cole-Cole plot at 6.0 K (a) and the Arrhenius plot (b) in the high temperature region for an applied static field of 2.5 kg. The solid lines are the best fit curves (see Table S2). S17

18 Figure S10. Temperature dependence of χ M (a) and χ M (b) of 1 in a 5.0 kg applied static field and under 4.0 G oscillating field in the frequency range of 0.1 (grey) 10 (red) khz. The insets show the Cole-Cole plot at 6.0 K (a) and the Arrhenius plot (b) in the high temperature region for an applied static field of 5.0 kg. The solid lines are the best fit curves (see Table S2). S18

19 Figure S11. Field dependence of the normalized magnetization of 1 at 0.5 (a), 0.3 (b), 0.15 (c), and 0.03 K (d) with varying field sweep rates in the range of T s 1. S19