Electronic Supplementary Information (ESI) Dual Homogeneous and Heterogeneous Pathways in Photo- and

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1 Electronic Supplementary Information (ESI) Dual Homogeneous and Heterogeneous Pathways in Photo- and Electrocatalytic Hydrogen Evolution with Nickel(II) Catalysts Bearing Tetradentate Macrocyclic Ligands Lingjing Chen, Gui Chen, Chi-Fai Leung, Shek-Man Yiu, Chi-Chiu Ko, Elodie Anxolabe he re-mallart, Marc Robert*, and Tai-Chu Lau*, Institute of Molecular Functional Materials, and Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong SAR, China. UniversitéParis Diderot, Sorbonne Paris Cité, Laboratoire d Electrochimie Moléculaire, Unité Mixte de Recherche Université CNRS no. 7591, Bâtiment Lavoisier, 15 rue Jean de Baïf, 7525 Paris Cedex 13, France. Corresponding Authors: bhtclau@cityu.edu.hk, robert@univ-paris-diderot.fr Page 1 of 18

2 Contents Figure S1 ESI/MS spectra of [Ni 2 (L5) 2 (µ-cl) 2 ](ClO 4 ) 2 in CH 3 CN Figure S2 (left) Cyclic voltammograms for 1 mm [Ni(L5)Cl] + in.1 M n Bu 4 NPF 6 in CH 3 CN at different scan rates (.25~.25 V/s). (right) Height comparison of Ni II /Ni I couple (Δi) of 1 mm [Ni(L3)] 2+, [Ni(L5)Cl] + and [Ni(L6)] Figure S3 Cyclic voltammograms of 1 mm nickel complexes in CH 3 CN solution containing.1 M n Bu 4 NPF 6. Scan rate =.1 V/s Figure S4 Emission quenching (left) and Stern-Volmer plot (right) of [Ir(dF(CF 3 )ppy) 2 (dmbpy)]pf 6 ([IrPS] +,.4 mm) solution by TEA in aqueous THF (1% H 2 O) Figure S5 (A) Transient absorption spectrum of [IrPS] + (.3 mm) in the presence of TEA (.6 M) after 355 nm laser excitation. (B) Spectroelectrochemical absorption spectrum of [IrPS] by reduction of [IrPS] + at V vs SCE... 6 Figure S6 CV of [Ir(dF(CF 3 )ppy) 2 (dmbpy)]pf 6 (1 mm) in.1 M n Bu 4 NPF 6 solution in CH 3 CN. Scan rate =.1 V/s Figure S7 (Left) Spectrophotometric changes during irradiation of a solution containing [Ni(L4)] 2+ (.4 mm), [IrPS] + (.1 mm) and TEA (.6 M) in 9:1 THF/H 2 O); (Right) Spectroelectrochemical characterization of [Ni(L4)] + (.8 mm in 1. ml THF solution with applied potential at -1.5 V vs SCE).. 7 Figure S8 Comparison of [IrPS] + (1 mm) and [Ru(bpy) 3 ] 2+ (1 mm) photosensitizer on H 2 generation in 2.5 ml THF/H 2 O (9:1, v/v) solution consisting [Ni(L4)] 2+ (.1 mm) and TEA (.6 M) under irradiation for 27 h Figure S9 Effect of ph on photocatalytic hydrogen production in 2.5 ml THF/H 2 O (9:1, v/v) solution containing [Ni(L4)] 2+ (.1 mm), [IrPS] + (1 mm) and TEA (.6 M) under irradiation for 2 h. (a) ph = 9.5 without addition of any acid; (b) ph = 4. after addition of.25 ml of 5.1 M of trifluoroacetic acid in THF; (c) ph = 2.5 when TEA was replaced by ascorbic acid (.1 M) Figure S1 Particle distribution determined by DLS measurements. Particles formed by irradiation (LED, whiter light) of 2.5 ml THF/H 2 O (9:1, v/v) solution containing [Ni(L1)] 2+ (.1 mm), [IrPS] + (1 mm) and TEA (.6 M)... 8 Figure S11 Particle distribution determined by DLS measurements. Particles formed by irradiation (LED, whiter light) of 2.5 ml THF/H 2 O (9:1, v/v) solution containing [Ni(L6)] 2+ (.1 mm), [IrPS] + (1 mm) and TEA (.6 M)... 9 Scheme S1 Schematic diagram of bulk electrolysis system Page 2 of 18

3 Scheme S2 Assumed mechanism for H 2 evolution during electrochemical reduction of [Ni(L4)] 2+ in the presence of HClO Figure S12 Voltammograms of [Ni(L4)] 2+ (.19,.37,.56,.73 and.91 mm) with 1 mm HClO 4 in.1 M n Bu 4 NPF 6 in CH 3 CN; 3 mm glassy carbon electrode showing catalytic H 2 production. Reference electrode: Ag/Ag + electrode; Counter electrode: platinum wire. Ferrocene was used as internal standard Figure S13 Charge (left) and current (right) versus time for bulk electrolysis experiments under Ar with an applied potential of -.95 V vs SCE. Conditions: 1 mm [Ni(L4)] 2+ and 1 mm HClO 4 in.1 M n Bu 4 NPF 6 in CH 3 CN. Working electrode: glassy carbon (.7 cm 2 ); Reference electrode: Ag/Ag + electrode separated from the electrolyte by a bridge containing.1 M n Bu 4 NPF 6 in CH 3 CN solution was employed; Counter electrode: platinum grid separated from the electrolyte by a bridge containing.4 M Et 4 N(CH 3 CO 2 ) and.1 M n Bu 4 NPF 6 in CH 3 CN solution was used. The volume of the electrolysis solution was 9 ml Figure S14 SEM of the electrode surface after electrolysis of [Ni(L4)] 2+ for 4 h in the conditions described in Figure S13. The species with random appearing on the carbon surface may be crystal salt from the electrolyte Figure S15. EDX of the electrode surface after electrolysis of [Ni(L4)] 2+ for 4 h, in the conditions described in Figure S Figure S16 UV-visible spectrum of [Ni(L4)] 2+ in CH 3 CN before and after electrolysis in the conditions described in Figure S Figure S17 EDX of the electrode surface after electrolysis of [Ni(L4)] 2+ for 17.6 h at -.95 V vs SCE, in the presence of 1 mm HClO 4 using glassy carbon electrode (3 mm diameter) as working electrode Table S1 X-ray crystallographic data of [Ni(L3)](ClO 4 ) 2.5CH 3 CN Table S2 Selected bond lengths (Ǻ) and angles ( o ) of [Ni(L3)](ClO 4 ) 2.5CH 3 CN Table S3 X-ray crystallographic data of [Ni(L4)](ClO 4 ) 2 (CH 3 COCH 3 ) Table S4 Selected bond lengths (Ǻ) and angles ( o ) of [Ni(L4)](ClO 4 ) 2 (CH 3 COCH 3 ) Table S5 X-ray crystallographic data of [Ni 2 (L5) 2 (µ-cl) 2 ](ClO 4 ) Table S6 Selected bond lengths (Ǻ) and angles ( o ) of [Ni 2 (L5) 2 (µ-cl) 2 ](ClO 4 ) Table S7 X-ray crystallographic data of [Ni(L6)](ClO 4 ) Table S8 Selected bond lengths (Ǻ) and angles ( o ) of [Ni(L6)](ClO 4 ) References Page 3 of 18

4 Current ( A) Current ( A) Intensity, cps 1.4x x1 8 1.x1 8 8.x1 7 6.x , {[Ni(L5)]} , {[Ni(L5)](Cl)} + 432, {[Ni(L5)]ClO 4 } + 4.x1 7 2.x , {[Ni(L5)]-H} m/z, amu Figure S1 ESI/MS spectra of [Ni 2 (L5) 2 (µ-cl) 2 ](ClO 4 ) 2 in CH 3 CN. 5 scan rate:.25 V/s scan rate:.2 V/s 4 scan rate:.15 V/s scan rate:.1 V/s 3 scan rate:.5 V/s scan rate:.25 V/s mm [Ni(L3)] 2+.5 mm [Ni 2 (L5) 2 ( -Cl) 2 ] 2+ (1 mm [Ni(L5)Cl] + ) 1 mm [Ni(L6)] i = 34.5 A Potential vs SCE in MeCN (V) -1-2 i = 35.5 A i = 31.3 A Potential vs SCE in MeCN (V) Figure S2 (left) Cyclic voltammograms for 1 mm [Ni(L5)Cl] + in.1 M n Bu 4 NPF 6 in CH 3 CN at different scan rates (.25~.25 V/s). (right) Height comparison of Ni II /Ni I couple (Δi) of 1 mm [Ni(L3)] 2+, [Ni(L5)Cl] + and [Ni(L6)] 2+. Page 4 of 18

5 Intensity (1 5 CPS) I /I Offset Current values ( A) 5 4 [Ni(L6)] 2+ [Ni(L5)Cl] [Ni(L4)] 2+ [Ni(L3)] 2+ 1 [Ni(L2)] 2+ [Ni(L1)] Potential vs SCE (V) Figure S3 Cyclic voltammograms of 1 mm nickel complexes in CH 3 CN solution containing.1 M n Bu 4 NPF 6. Scan rate =.1 V/s. 3 mm.32 mm mm 1.25 mm mm 2.46 mm mm Wavelength (nm) y = 1+1.4x R 2 = [TEA] (1-9 M s) Figure S4 Emission quenching (left) and Stern-Volmer plot (right) of [Ir(dF(CF 3 )ppy) 2 (dmbpy)]pf 6 ([IrPS] +,.4 mm) solution by TEA in aqueous THF (1% H 2 O). Page 5 of 18

6 i ( A) Absorbance OD A 4nm 448nm 54nm 537nm B 399nm 441nm 535nm Wavelength (nm) Figure S5 (A) Transient absorption spectrum of [IrPS] + (.3 mm) in the presence of TEA (.6 M) after 355 nm laser excitation. (B) Spectroelectrochemical absorption spectrum of [IrPS] by reduction of [IrPS] + at V vs SCE. 6 df(cf 3 )ppy -/2- : -1.8 V 4 dmbpy /- : V 2 Ir IV/III : +1.7 V Potential vs SCE in MeCN (V) Figure S6 CV of [Ir(dF(CF 3 )ppy) 2 (dmbpy)]pf 6 (1 mm) in.1 M n Bu 4 NPF 6 solution in CH 3 CN. Scan rate =.1 V/s. Page 6 of 18

7 Intensity Intensity nm nm Wavelength (nm) Wavelength (nm) Figure S7 (Left) Spectrophotometric changes during irradiation of a solution containing [Ni(L4)] 2+ (.4 mm), [IrPS] + (.1 mm) and TEA (.6 M) in 9:1 THF/H 2 O); (Right) Spectroelectrochemical characterization of [Ni(L4)] + (.8 mm in 1. ml THF solution with applied potential at -1.5 V vs SCE). 12 [IrPS] + 1 TON cat Irradiation time (h) [Ru(bpy) 3 ] 2+ Figure S8 Comparison of [IrPS] + (1 mm) and [Ru(bpy) 3 ] 2+ (1 mm) photosensitizer on H 2 generation in 2.5 ml THF/H 2 O (9:1, v/v) solution consisting [Ni(L4)] 2+ (.1 mm) and TEA (.6 M) under irradiation for 27 h. Page 7 of 18

8 Number / % 1 8 a TON cat b c Irradiation time (h) Figure S9 Effect of ph on photocatalytic hydrogen production in 2.5 ml THF/H 2 O (9:1, v/v) solution containing [Ni(L4)] 2+ (.1 mm), [IrPS] + (1 mm) and TEA (.6 M) under irradiation for 2 h. (a) ph = 9.5 without addition of any acid; (b) ph = 4. after addition of.25 ml of 5.1 M of trifluoroacetic acid in THF; (c) ph = 2.5 when TEA was replaced by ascorbic acid (.1 M). 4 2h Particle size / nm Figure S1 Particle distribution determined by DLS measurements. Particles formed by irradiation (LED, whiter light) of 2.5 ml THF/H 2 O (9:1, v/v) solution containing [Ni(L1)] 2+ (.1 mm), [IrPS] + (1 mm) and TEA (.6 M). Page 8 of 18

Number / % 4 2h 3 2 1 1 1 1 1 1 Particle size / nm Figure S11 Particle distribution determined by DLS measurements.

9 Number / % 4 2h Particle size / nm Figure S11 Particle distribution determined by DLS measurements. Particles formed by irradiation (LED, whiter light) of 2.5 ml THF/H 2 O (9:1, v/v) solution containing [Ni(L6)] 2+ (.1 mm), [IrPS] + (1 mm) and TEA (.6 M). Scheme S1 Schematic diagram of bulk electrolysis system. Page 9 of 18

10 Scheme S2 Assumed mechanism for H 2 evolution during electrochemical reduction of [Ni(L4)] 2+ in the presence of HClO 4. The rate determining first order catalytic rate constant k cat for H 2 evolution was evaluated according to the equation S1, 1,2 leading to a value of 22 s -1. i FS 2kcat D Ccat F 1 exp E E RT cat S1 S is the active surface during electrolysis (.7 cm 2 ), D is the catalyst diffusion coefficient (1-5 cm 2 /s) and was obtained from simulation of the reversible catalyst wave, C is the catalyst concentration (1-6 cat mol/ cm 3 ), E is the electrolysis potential (-.95 V vs SCE), E is the catalyst standard potential (-.98 V cat vs SCE), T is the temperature (293 K) and i is the averaged electrolysis current (i = Q faradaic yield /t = /144 =.15 ma; current density = i/s = 1.5 ma/ cm 2 ). Experimental data were taken from figure S13. Note that equation S1 is applicable for a mechanism for which fast Ni II catalyst reduction to Ni I is followed by reaction with a proton, leading to a Ni III H hydride intermediate, that further reacts with a second proton, leading to H 2 and regenerating the Ni III complex. 2 This latter species is then quickly reduced to Ni II (diffusion controlled reduction), thus closing the catalytic cycle. Cyclic voltammetry studies indicate it is indeed the most likely mechanism. Page 1 of 18

11 Charge (C) Current ( A) i c ( A) i c ( A) mm.73 mm.56 mm.37 mm.19 mm B Linear Fit of Sheet1 B Concentration of [Ni(L4)](ClO 4 ) 2 (mm) Potential vs SCE (V) Figure S12 Voltammograms of [Ni(L4)] 2+ (.19,.37,.56,.73 and.91 mm) with 1 mm HClO 4 in.1 M n Bu 4 NPF 6 in CH 3 CN; 3 mm glassy carbon electrode showing catalytic H 2 production. Reference electrode: Ag/Ag + electrode; Counter electrode: platinum wire. Ferrocene was used as internal standard Time (h) Time (h) Figure S13 Charge (left) and current (right) versus time for bulk electrolysis experiments under Ar with an applied potential of -.95 V vs SCE. Conditions: 1 mm [Ni(L4)] 2+ and 1 mm HClO 4 in.1 M n Bu 4 NPF 6 in CH 3 CN. Working electrode: glassy carbon (.7 cm 2 ); Reference electrode: Ag/Ag + electrode separated from the electrolyte by a bridge containing.1 M n Bu 4 NPF 6 in CH 3 CN solution was employed; Counter electrode: platinum grid separated from the electrolyte by a bridge containing.4 M Et 4 N(CH 3 CO 2 ) and.1 M n Bu 4 NPF 6 in CH 3 CN solution was used. The volume of the electrolysis solution was 9 ml. Page 11 of 18

12 Figure S14 SEM of the electrode surface after electrolysis of [Ni(L4)] 2+ for 4 h in the conditions described in Figure S13. The species with random appearing on the carbon surface may be crystal salt from the electrolyte. 8 cps/ev C N O F kev Figure S15. EDX of the electrode surface after electrolysis of [Ni(L4)] 2+ for 4 h, in the conditions described in Figure S13. Page 12 of 18

13 Absorbance.4 Before electrolysis After electrolysis for 4h wavelength / nm Figure S16 UV-visible spectrum of [Ni(L4)] 2+ in CH 3 CN before and after electrolysis in the conditions described in Figure S13. 8 cps/ev C N O F Ni P kev Figure S17 EDX of the electrode surface after electrolysis of [Ni(L4)] 2+ for 17.6 h at -.95 V vs SCE, in the presence of 1 mm HClO 4 using glassy carbon electrode (3 mm diameter) as working electrode. Page 13 of 18

14 Table S1 X-ray crystallographic data of [Ni(L3)](ClO 4 ) 2.5CH 3 CN. Chemical formula C 22 H 27.5 Cl 2 N 3.5 NiO 8 P Formula weight g/mol Crystal system monoclinic a (2) Å b (7) Å c (16) Å α 9. β 17.39(9) γ 9. Unit cell volume (7) Å 3 Temperature 133(2) K Space group C 1 2/c 1 No. of formula units per unit cell, Z 8 Radiation type Cu Kα Absorption coefficient, µ mm -1 No. of reflections measured No. of independent reflections 4652 R int.33 Final R 1 values (I > 2σ(I)).574 Final wr(f 2 ) values (I > 2σ(I)).1643 Final R 1 values (all data).632 Final wr(f 2 ) values (all data).1696 Goodness of fit on F CCDC number Table S2 Selected bond lengths (Ǻ) and angles ( o ) of [Ni(L3)](ClO 4 ) 2.5CH 3 CN. Selected bond lengths (Ǻ) Selected angles ( o ) Ni1-P (11) N1-Ni1-P (1) Ni1-N (3) N1-Ni1-N (14) Ni1-N (3) N2-Ni1-P (11) Ni1-N (3) N2-Ni1-N (14) N2-Ni1-N3 82.6(14) N3-Ni1-P (1) Page 14 of 18

15 Table S3 X-ray crystallographic data of [Ni(L4)](ClO 4 ) 2 (CH 3 COCH 3 ). Chemical formula C 24 H 36 Cl 2 N 3 NiO 9 P Formula weight g/mol Crystal system triclinic a (4) Å b 13.38(6) Å c 13.93(6) Å α (4) β (4) γ (4) Unit cell volume (12) Å 3 Temperature Space group P -1 No. of formula units per unit cell, Z 2 Radiation type 173(2) K Cu Kα Absorption coefficient, µ 3.57 mm -1 No. of reflections measured 1621 No. of independent reflections 5379 R int.344 Final R 1 values (I > 2σ(I)).116 Final wr(f 2 ) values (I > 2σ(I)).2796 Final R 1 values (all data).1195 Final wr(f 2 ) values (all data).2828 Goodness of fit on F CCDC number Table S4 Selected bond lengths (Ǻ) and angles ( o ) of [Ni(L4)](ClO 4 ) 2 (CH 3 COCH 3 ). Selected bond lengths (Ǻ) Selected angles ( o ) Ni1-P (2) N1-Ni1-P1 94.8(2) Ni1-N (6) N1-Ni1-N3 168.(3) Ni1-N (7) N2-Ni1-P (2) Ni1-N (6) N2-Ni1-N1 85.(3) N2-Ni1-N3 84.4(3) N3-Ni1-P1 95.5(2) Page 15 of 18

16 Table S5 X-ray crystallographic data of [Ni 2 (L5) 2 (µ-cl) 2 ](ClO 4 ) 2. Chemical formula C 3 H 42 Cl 4 N 6 Ni 2 O 8 S 2 Formula weight g/mol Crystal system triclinic a 8.156(5) Å b (8) Å c (12) Å α (5) β (5) γ (5) Unit cell volume 191.6(2) Å 3 Temperature 133(2) K Space group P -1 No. of formula units per unit cell, Z 2 Radiation type Cu Kα Absorption coefficient, µ mm -1 No. of reflections measured 1621 No. of independent reflections 6732 R int.272 Final R 1 values (I > 2σ(I)).637 Final wr(f 2 ) values (I > 2σ(I)).1661 Final R 1 values (all data).71 Final wr(f 2 ) values (all data).179 Goodness of fit on F CCDC number Table S6 Selected bond lengths (Ǻ) and angles ( o ) of [Ni 2 (L5) 2 (µ-cl) 2 ](ClO 4 ) 2. Selected bond lengths (Ǻ) Selected angles ( o ) Ni1-S (14) S1-Ni1-Cl (5) Ni1-N1 2.66(4) S1-Ni1-Cl (5) Ni1-N2 1.98(4) Cl1-Ni1-Cl (5) Ni1-N3 2.7(4) N1-Ni1-S (13) Ni2-S (15) N1-Ni1-Cl (13) Ni2-N4 2.71(5) N1-Ni1-Cl (13) Ni2-N (4) N2-Ni1-S (11) Ni2-N6 2.83(5) N3-Ni1-S (13) Ni1-Cl (13) Ni1-Cl1-Ni2 95.9(5) Ni1-Cl (14) Ni2-Cl2-Ni (5) Ni2-Cl (14) Ni2-Cl (14) Page 16 of 18

17 Table S7 X-ray crystallographic data of [Ni(L6)](ClO 4 ) 2. Chemical formula C 15 H 25 Cl 2 N 3 NiO 8 S Formula weight g/mol Crystal system triclinic a (7) Å b (7) Å c (11) Å α 93.47(7) β 16.68(7) γ (7) Unit cell volume 122.8(1) Å 3 Temperature 133(2) K Space group P -1 No. of formula units per unit cell, Z 2 Radiation type Cu Kα Absorption coefficient, µ mm -1 No. of reflections measured 6453 No. of independent reflections 361 R int.169 Final R 1 values (I > 2σ(I)).473 Final wr(f 2 ) values (I > 2σ(I)).1251 Final R 1 values (all data).489 Final wr(f 2 ) values (all data).1263 Goodness of fit on F CCDC number Table S8 Selected bond lengths (Ǻ) and angles ( o ) of [Ni(L6)](ClO 4 ) 2. Selected bond lengths (Ǻ) Selected angles ( o ) Ni1-S (9) N1-Ni1-S (9) Ni1-N (3) N1-Ni1-N (11) Ni1-N (3) N2-Ni1-S (8) Ni1-N (3) N2-Ni1-N (11) N2-Ni1-N3 85.(11) N3-Ni1-S (8) Page 17 of 18

18 References (1) Costentin, C.; Dridi, H.; Savéant, J.-M. J. Am. Chem. Soc. 214, 136, (2) Costentin, C.; Savéant, J.-M. ChemElectroChem 214, 1, Page 18 of 18

Highly Efficient and Selective Photocatalytic CO 2 Reduction by Iron and Cobalt Quaterpyridine Complexes

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