Probing Nuclear Spin Effects on Electronic Spin Coherence Via EPR Measurements of Vanadium (IV) Complexes

Supporting Information for: Probing Nuclear Spin Effects on Electronic Spin Coherence via EPR Measurements of Vanadium (IV) Complexes Michael J. Graham,† Matthew D. Krzyaniak,†,§ Michael R. Wasielewski,†,§ and Danna E. Freedman*,† †Department of Chemistry and §Argonne-Northwestern Solar Energy Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208- 3113, United States Inorg. Chem. S1 Table of Contents Experimental details S3 Table S1 Crystallographic information for 1 S12 Table S2 Crystallographic information for 2 S13 Table S3 Crystallographic information for 3 S14 Table S4 Cw-EPR fit parameters S15 Table S5 Proton grouping scheme used to calculate dipolar coupling in 1 S16 Table S6 Proton grouping scheme used to calculate dipolar coupling in 2 S17 Table S7 Proton grouping scheme used to calculate dipolar coupling in 3 S18 Table S8 ENDOR fit parameters S19 Table S9 T1 fit parameters S20 Table S10 Fit parameters for T1 temperature dependence S21 Table S11 T2 fit parameters in DMF-d7/toluene-d8 S22 Table S12 T2 fit parameters in MeCN-d3/toluene-d8 S23 Table S13 Variable-power nutation frequencies S24 Figure S1 Cw-EPR and echo-detected EPR spectra and fits S25 Figure S2 ENDOR spectra and fits S26 Figure S3 Saturation/inversion recovery data and fits S27 Figure S4 Selected Hahn echo decay data and fits S28 Figure S5 Nutation data S29 Figure S6 Fourier transforms of nutation data S30 Figure S7 Nutation frequency vs. pulsed field strength S31 References S32 S2 Experimental Details General Considerations. 2,6,8,10-Tetrathiobicyclo[5,3,0]dec-1(7)en-9-one (TTDEO) and the 1,2 ligands K2(C7H6S7) and K2(C9H6S8) were synthesized as previously reported. Potassium naphthalenide solution (50 mM) was synthesized by stirring 0.25 mmol naphthalene and 0.26 mmol potassium in 5.0 mL THF overnight under a nitrogen atmosphere. Vanadium tetrachloride bis(tetrahydrofuran) was synthesized as previously described.3 All other reagents and solvents were purchased from commercial vendors and dried and degassed before use. All manipulations detailed below were carried out under a nitrogen atmosphere in a Vacuum Atmospheres Nexus II glovebox equipped with a cold well. 2,4 K2(C5H6S4) was synthesized by a modified version of the previously-reported method. A solution of potassium methoxide was prepared by addition of potassium (86.8 mg, 2.22 mmol, 2.2 eq) to 0.5 mL methanol. This solution was then added to a solution of TTDEO (226.4 mg, 1.018 mmol, 1.0 eq) in 5 mL THF with stirring, resulting in immediate precipitation. The reaction was allowed to continue stirring for 6 hours to ensure complete deprotection, then filtered and rinsed with 2 2 mL THF. The off-white solid (269.8 mg, 97.2%) was collected, dried in vacuo, and used without further purification. K2[V(C5H6S4)3]∙2C6H6 (1∙2C6H6). A suspension of VCl4(THF)2 (85.4 mg, 0.253 mmol, 1.0 eq) in 6.0 mL THF was precooled to −78 °C, then added to a suspension of K2(C5H6S4) (208.2 mg, 0.7639 mmol, 3.0 eq) in 8.0 mL THF at −78 °C dropwise while stirring. The reaction was stirred at −78 °C for 5 minutes, then allowed to slowly warm to room temperature over approximately 30 minutes, and finally stirred at room temperature overnight. The reaction mixture was then filtered and rinsed with 2 2 mL THF, yielding dark blue-green solids and a deep blue filtrate, − which contains the monooxidized species [V(C5S4H6)3] . The blue-green solids were dissolved in acetonitrile and filtered to remove a brown, insoluble solid, then the filtrate was concentrated in vacuo and layered over benzene to afford dark blue-green bladed crystals (126.1 mg, 57.4%). IR (cm–1, diamond ATR) 2895(m), 1578(w), 1474(s), 1422(w), 1408(s), 1399(m), 1273(s), 1235(s), 1172(s), 1092(w), 1032(s), 998(s), 957(s), 900(s), 866(s), 814(s), 755(w), 697(vs), 658(w), S3 630(w), 606(w), 458(w), 434(s), 407(w). Anal. Calcd for C27H30K2S12V: C, 37.34; H, 3.48. Found: C, 36.97; H, 3.31. K[V(C7H6S6)3]. K2(C7H6S6) (210.3 mg, ~0.583 mmol, ~3.1 eq) was suspended in 10 mL THF, VCl4(THF)2 (64.3 mg, 0.191 mmol, 1.0 eq) was suspended in 10 mL THF, and both suspensions were cooled to −78 °C. The VCl4(THF)2 suspension was added dropwise to the K2(C7H6S6) suspension with stirring, and the reaction was allowed to stir cold for 45 minutes. The reaction was then allowed to warm slowly to room temperature and subsequently stirred at room temperature overnight. The reaction mixture was filtered and the dark green solids were rinsed with 2 1 mL THF. The solids were then dissolved in THF (solubility is ~2 mg/mL) and crystallized by diffusion of Et2O vapor into the solution. The obtained crystals were crushed and dried in vacuo to afford a dark green powder (83.7 mg, 46.7%). K2[V(C7H6S6)3]∙3(MeCN) (2∙3MeCN). K[V(C7H6S6)3] (81.1 mg, 0.0865 mmol, 1.0 eq) was dissolved in 90 mL THF and cooled to −78 °C. A 50 mM THF solution of potassium naphthalenide (1.70 mL, 0.0867 mmol, 1.0 eq) was diluted to 5.0 mL by addition of THF, cooled to −78 °C, and added dropwise to the K[V(C7H6S6)3] solution over eight minutes. The reaction was stirred cold for 1.5 hours, then allowed to slowly warm to room temperature, and subsequently to stir at room temperature overnight. Solvent was removed from the resulting olive-brown reaction mixture in vacuo, and the residue was taken up in 4 mL MeCN. Olive- brown needles (51.7 mg, 54.3%) were obtained by slow diffusion of Et2O vapor into this solution. IR (cm–1, diamond ATR) 2954(w), 2903(m), 2849(m), 1619(s), 1603(m,sh), 1565(w), 1509(m,sh), 1469(w), 1458(w), 1441(m,sh), 1407(s), 1366(w), 1359(w), 1336(w), 1318(w), 1261(s), 1225(s), 1168(m), 1113(m), 1077(s), 1044(w), 1027(m), 1013(w), 1000(m), 962(w), 949(m), 901(m), 890(w), 869(s), 848(w,sh), 814(w), 786(m), 733(s), 660(w), 637(s), 612(m), 572(w), 551(w), 532(w), 515(m), 468(s), 447(w), 439(w), 427(w), 408(w). Anal. Calcd for C27H27K2N3S18V: C, 29.48; H, 2.47; N, 3.82. Found: C, 29.53; H, 2.48; N, 3.62. K2[V(C9H6S8)3]∙3.28MeCN (3∙3.28MeCN). Suspensions of K2(C9H6S8) (212.4 mg, 0.3908 mmol, 3.0 eq) in 8.0 mL THF and VCl4(THF)2 (44.6 mg, 0.132 mmol, 1.0 eq) in 8.0 mL THF were cooled to −78°C. (Note: An effective molecular weight of 543.56 g/mol was employed for 2 K2(C9H6S8) due to the as-synthesized salt being partially solvated. ) The VCl4(THF)2 suspension S4 was added dropwise with stirring over 5 minutes to the suspension of the ligand salt, and stirred cold for a further 5 minutes. The reaction was then allowed to slowly warm to room temperature and stir at room temperature overnight. Solvent was removed from the reaction in vacuo and the brown residue was then washed by stirring with 10 mL dimethoxyethane for 30 minutes followed by filtration. The washed solids were then extracted into MeCN, filtered to remove insolubles, and crystallized by slow diffusion of Et2O vapor into the MeCN solution, affording dark brown needles (69.4 mg, 38.2%). Monitoring by UV-vis spectroscopy shows that the complex begins to decompose in (dry, airfree) acetonitrile solution after ~24 hours. The pure solid remains stable in the solid state at room temperature under nitrogen for at least two weeks. IR (cm–1, diamond ATR) 2998(w), 2981(m), 2963(w), 2951(w), 2905(m), 2878(w), 2868(w), 2854(w), 2286(m), 2249(w), 1543(m), 1489(m), 1448(m), 1424(w), 1407(w,sh), 1393(vs), 1361(w), 1295(w), 1269(s), 1229(m), 1186(m), 1156(w), 1121(w), 1093(m), 1085(m), 1026(m), 997(m), 979(w), 920(m), 896(w,sh), 882(vs), 862(s), 842(w,sh), 815(m), 765(vs), 719(w), 701(w), 683(w), 659(m), 641(w), 621(w), 608(w), 596(w), 538(w), 525(w), 497(s), 486(w,sh), 465(w), 443(m), 424(w), 402(w). Anal. Calcd for C33.56H27.84K2N3.28S24V: C, 29.30; H, 2.03; N, 3.34. Found: C, 29.40; H, 2.15; N, 3.22. EPR Measurements. Solution samples for EPR measurements were prepared by dissolving 1–3 in 45 vol% MeCN-d3/toluene-d8 or 45 vol% DMF-d7/toluene-d8, loading into a 4mm OD quartz EPR tube (Wilmad 707-SQ-250M), freezing the sample in liquid nitrogen, and flame-sealing the tube under high vacuum. All measurements were taken on 0.32 mM solutions, except for the ENDOR spectrum of 3 and the cw spectra of 3 in DMF-d7/toluene-d8 and 2 in MeCN-d3/toluene- d8, which were acquired on 1.0 mM solutions. Due to its instability in solution, samples of 3 were frozen immediately after preparation and stored in liquid nitrogen until measurement. EPR data for 1–3 in MeCN-d3/toluene-d8, ENDOR data for 1–3 in DMF-d7/toluene-d8, and all cw data were obtained at X-band frequency (9.4–9.7 GHz) on a Bruker E680 X/W-band spectrometer equipped with a with a split ring resonator (ER4118X-MS5) and a 1 kW TWT amplifier (Applied Systems Engineering) at Northwestern University.

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