Heptanuclear Mixed-Valence Co4IIICo3II Molecular Wheel—A Molecular Analogue of Layered Double Hydroxides with Single-Molecule Magnet Behavior and Electrocatalytic Activity for Hydrogen Evolution Reactions

We present a bifunctional heptanuclear cobalt(II)/cobalt(III) molecular complex formulated as [Co7(μ3–OH)4(H2L1)2(HL2)2](NO3)6·6H2O (1) (where H5L1 is 2,2′-(((1E,1′E)-((2-hydroxy-5-methyl-1,3-phenylene)bis(methanylylidene))bis(azanylylidene))bis(propane-1,3-diol)) and H2L2 is 2-amino-1,3-propanediol). Compound 1 has been characterized by single-crystal X-ray diffraction analysis along with other spectral and magnetic measurements. Structural analysis indicates that 1 contains a mixed-valence Co7 cluster where a central Co(II) ion is connected to six different Co centers (four CoIII and two CoII ions) by four μ3–OH groups, giving rise to a planar heptanuclear cluster that resembles a molecular fragment of a layered double hydroxide (LDH). Two triply deprotonated (H2L1)3– ligands form the outer side of the cluster while two singly deprotonated (HL2)− ligands are located at the top and bottom of the central heptanuclear core. Variable temperature magnetic measurements indicate the presence of weak ferromagnetic CoII···CoII interactions (J = 3.53(6) cm–1) within the linear trinuclear CoII cluster. AC susceptibility measurements show that 1 is a field-induced single-molecule magnet (SMM) with τ0 = 8.2(7) × 10–7 s and Ueff = 11.3(4) K. The electrocatalytic hydrogen evolution reaction (HER) activity of 1 in homogeneous phase shows an overpotential of 455 mV, with a Faradaic efficiency of 81% and a TOF of 8.97 × 104 μmol H2 h–1 mol–1.


Figure S11 .Figure S17 .Figure S19 .
Figure S11.Coordination environment of the four different cobalt centers in complex 1 S9 Figure S12.Different binding modes of the ligands (H2L 1 ) 3-(a) and (HL 2 ) -(b) in 1. S10 Figure S13.Structural comparison of complex 1 with NiFe-LDH.S10 Figure S14.Thermal variation of the molar magnetic susceptibility for compound 1 S11 Figure S15.Isothermal magnetizations at 1.9 K and 5.0 K for compound 1 S11 Figure S16.Zero field cooled (ZFC) and field cooled (FC) molar magnetic susceptibility for compound 1 measured with 1 and 10 mT after cooling in zero field S12 Figure S17.Field dependence of the relaxation time for compound 1 at 2.0 K S12 Figure S18.Linear sweep voltammograms for HER without catalyst using blank glassy carbon electrode (black trace) and with 0.5 mM catalyst (red trace) at different pH in the range 2-11.S13

Figure S9 .
Figure S9.XPS of compound 1 showing the presence of both Co 2+ and Co 3+ ions.

Figure S11 .S10Figure S12 .
Figure S11.Coordination environment of the four different cobalt centers in complex 1.

Figure S13 .Figure S14 .
Figure S13.Structural comparison of complex 1 with NiFe-LDH (JCPDS Card 40-0215).(a) Sphere model of the cations present in a layer of NiFe-LDH.(b) Side view of a layer of Ni-Fe-LDH.(c) Top view of a layer of Ni-Fe-LDH.(d) Sphere model of the cations present in a layer of compound 1.(e) Side view of a layer of compound 1. (f) Top view of the Co7 cluster in compound 1.Color code: Coordinated hydroxides/oxides = red.Ni/Fe/Co = blue.

Figure S17 .Figure S18 .
Figure S17.Field dependence of the relaxation time for compound 1 at 2.0 K. Solid line is the best fit to equation (1).

Figure S19 .Figure S20 .
Figure S19.(a)-(f) Tafel plots at the kinetic region corresponding to Figure 5 for all pH values.

Figure S23 .
Figure S23.Image of a glassy carbon electrode before (a) and after (b) the rinse test at pH = 2.

Figure S24 .
Figure S24.Rinse test with 0.2 mM of catalyst.In this test, the same working electrode after the catalysis is used to perform CV experiments in a catalyst-free solution at the same pH without mechanical polishing of the electrode.

Figure S25 .
Figure S25.UV-VIS spectra of the catalyst in pure water and at pH = 2.