General Procedure for the Synthesis of the Complexes

To a solution of H₂L (0.0500 g, 0.103 mmol, 1 equiv.) in MeOH (4 mL) was added a solution of Mn(OAc)₂·4H₂O, Co(OAc)₂·4H₂O or Zn(OAc)₂·2H₂O (0.103 mmol, 1 equiv.) in MeOH (2 mL), and the solution was left to stir for 17 h at ambient temperature. A solution of NaBPh₄ (0.0352 g, 0.103 mmol, 1 equiv.) in MeOH (3 mL) was added and the resulting suspension was stirred for an additional 4 h at ambient temperature. The product was collected on a glass frit and washed with Et₂O. ([MnHL](BPh₄): 0.0498 g, 0.0579 mmol, 56%), ([CoHL](BPh₄): 0.0271 g, 0.0314 mmol, 30%), ([ZnHL](BPh₄): 0.0565 g, 0.0649 mmol, 63%). The solids were each dissolved in acetone (1 mL) and Et₂O was vapour diffused to form crystals suitable for single-crystal X-ray diffraction. RP-HPLC [MnHL][BPh₄]: R_T = 6.06 min; [CoHL][BPh₄]: R_T = 6.05 min; [ZnHL][BPh₄]: R_T = 6.01 min; ¹H NMR [ZnHL](BPh₄) (600 MHz, DMSO-d₆): δ = 1.96 (s, 3H, CH₃), 2.03 (s, 3H, CH₃), 2.31 (s, 6H, CH₃), 2.40, 2.59, 2.72, 2.88, 3.04 (m, 16H, NCH₂CH₂N), 2.74 (d, 3H, CH₃, ³J_H-H = 4.3 Hz), 2.98 (d, 3H, CH₃, ³J_H-H = 4.5 Hz), 3.40 (s, 2H, NCH₂CN), 3.60 (s, 2H, NCH₂CN), 6.78 (t, 4H, ArH, ³J_H-H = 7.0 Hz), 6.92 (t, 8H, ArH, ³J_H-H = 7.5 Hz), 7.17 (m, 8H, ArH), 6.56 (q, 1H, NHCH₃), 8.22 (q 1H, NHCH₃), 10.01 (s, 2H, NH); ¹³C{¹H NMR (150 MHz, DMSO-d₆): δ = 17.2 (CH₂CCH₃), 18.1 (CH₂CCH₃), 28.9 (CSNCH₃), 30.7 (CSNCH₃), 45.2 (CH₂NCH₃), 51.8, 54.1, 54.9 (NCH₂CH₂N), 58.7 (NCH₂CN), 61.3 (NCH₂CN), 121.5 (ArC), 125.3 (ArC), 135.5 (ArC), 148.6 (C=N), 157.3 (C=N), 163.2 (ArCB), 179.8 (C=S); HRMS (ESI) [ZnHL + H]⁺: m/z = 549.2249 (experimental), 549.2249 (calculated); [MnHL + H]⁺: m/z = 540.2335 (experimental), 540.2338 (calculated); [CoHL + H]⁺: m/z = 544.2298 (experimental), 544.2289 (calculated).