3.1.1. Synthesis of Ligands
H2Salen (salen-1). Under nitrogen atmosphere, o-phenylenediamine (7.03 g, 65 mmol) was added into a three-port flask containing 100 mL anhydrous ethanol. The flask was heated to reflux. After o-phenylenediamine was completely dissolved, salicylaldehyde (1.22 g, 10 mmol) was dropped into the flask. After 12 h, the mixture was cooled to room temperature and then transferred into a clean beaker for standing. A large number of orange crystals precipitated and were collected after being filtered, washed with anhydrous ethanol and dried in vacuo. Yield (based on o-phenylenediamine): 82%. EA (%) C20H16N2O2: calc. C 75.92, H 5.11, N 8.85, found C 75.98, H 5.04, N 8.81. UV-Vis (CH3Cl3) λmax/nm (ε/L.mol–1.cm–1): 240 (0.23 × 105), 267 (0.29 × 105), 334 (0.23 × 105). 1H NMR (400 MHz, CDCl3, TMS) δ (ppm): 6.90 (t, 2H, Ar-H), 7.04 (d, 2H, Ar-H), 7.21 (q, 2H, Ar-H), 7.24 (s, 2H, Ar-H), 7.32 (q, 2H, Ar-H), 7.35 (s, 2H, Ar-H), 8.61 (s, 2H, N=C-H), 13.04 (s, 2H, -OH). IR (KBr, v, cm–1): 3448(s), 2930(w), 2780(w), 1630(s), 1566(m), 1478(s), 1388(s), 1278(s), 1180(s), 762(s).
H2Salen-2tBu (salen-2). Salen-2 was obtained with the similar procedure for salen-1 except that salicylaldehyde was replaced by 3-tert-butylsalicylaldehyde (1.78 g, 10 mmol). Yield (based on o-phenylenediamine): 79%. EA (%) C28H32N2O2: calc. C 78.46, H 7.54, N 6.53, found C 78.51, H 7.52, N 6.48. UV-Vis (CH3Cl3) λmax/nm (ε/L.mol–1.cm–1): 241 (0.24 × 105), 275 (0.31 × 105), 366 (0.24 × 105). 1H NMR (400 MHz, CDCl3, TMS) δ (ppm): 1.43 (t, 18H, t-Bu), 6.85 (t, 2H, -OH), 7.23 (t, 2H, Ar-H), 7.25 (s, 2H, Ar-H), 7.31 (d, 2H, Ar-H), 7.34 (t, 2H, Ar-H), 7.39 (d, 2H, Ar-H), 8.66 (s, 2H, N=C-H). IR (KBr, v, cm–1): 3450(s), 3010(w), 2948(m), 2867(w), 1628(s), 1566(s), 1482(m), 1432(m), 1368(m), 1268(s), 1191(s), 753(s).
H2Salen-4tBu (salen-3). Salen-3 was obtained with the similar procedure for salen-1 except that salicylaldehyde was replaced by 3, 5-di-tert-butylsalicylaldehyde (2.34 g, 10 mmol). Yield (based on o-phenylenediamine): 75%. EA (%) C36H48N2O2: calc. C 79.94, H 8.96, N 5.18, found C 80.01, H 9.01, N 5.16. UV-Vis (CH3Cl3) λmax/nm (ε/L.mol–1.cm–1): 242 (0.23 × 105), 279 (0.22 × 105), 338 (0.16 × 105). 1H NMR (400 MHz, CDCl3, TMS) δ (ppm): 1.33 (t, 18H, t-Bu), 1.44 (t, 18H, t-Bu), 7.21 (d, 2H, -OH), 7.22 (t, 2H, Ar-H), 7.25 (d, 2H, Ar-H), 7.31 (t, 2H, Ar-H), 7.44 (d, 2H, Ar-H), 8.67 (s, 2H, N=C-H). IR (KBr, v, cm–1): 3452(s), 2961(m), 2866(w), 1634(s), 1566(w), 1477(w), 1438(w), 1382(s), 1272(m), 1172(s), 753(m).
H4Salen-8tBu (salen-4). Under nitrogen atmosphere, 3, 3′-diaminobenzidine (2.5 g, 11.67 mmol), 3, 5-di-tert-butylsalicylaldehyde (15 g, 64.01 mmol) and p-toluenesulfonic acid (0.1 g, 0.58 mmol) were added into a 1000 mL flask. Freshly distilled toluene was added to set up an azeotropic dewatering device. After 72 h, the solvent was removed in vacuo and solids were washed with ethanol. The mixture was recrystallized by dissolving it in methylene chloride and tetrahydrofuran, respectively. A high-purity ligand was obtained. Yield (based on 3, 3′-diaminobenzidine): 60%. EA (%) C72H94N4O4: calc. C 80.09, H 8.79, N 5.19, found C 80.14, H 8.86, N 5.12. UV-Vis (CH3Cl3) λmax/nm (ε/L.mol–1.cm–1): 230 (0.95 × 105), 281 (0.58 × 105), 365 (0.54 × 105). 1H NMR (400 MHz, CDCl3, TMS) δ (ppm): 1.32 (s, 36H, t-Bu), 7.15~7.62 (m, 50H, Ar-H), 8.44 (s, 4H, N=C-H), 11.51 (s, 4H, -OH). IR (KBr, v, cm–1): 3448(s), 2953(s), 2864(w), 1635(s), 1580(w), 1471(m), 1432(m), 1384(m), 1269(w), 1168(s), 768(w).
3.1.2. Synthesis of Complexes
(Salen-
1)Co(III)Cl. The ligand salen-
1 (0.07 g, 0.22 mmol) and decrystallized water Co(OAc)
2 (0.05 g, 0.27 mmol) were dissolved in 10 mL anhydrous methanol. The mixture was stirred at room temperature for 12 h, and then anhydrous LiCl (0.05 g, 1.10 mmol) was added and passed in oxygen to continue the reaction for 12 h. Solvent was removed under reduced pressure and the residue was dissolved in CH
2Cl
2. The organic layer was rinsed with saturated aqueous Na
2SO
4 (50 mL × 3) and NaCl (50 mL × 3), respectively. The organic layer was dried over Na
2SO
4, filtered and dried in vacuo. The crude product was recrystallized from CH
2Cl
2 and anhydrous CH
3CH
2OH to obtain a brown-red solid [
54]. Yield: 82%. EA (%) C
20H
14CoN
2O
2Cl: calc. C 58.77, H 3.45, N 6.85, found C 58.83, H 3.48, N 6.81. UV-Vis (CH
3Cl
3) λ
max/nm (ε/L
.mol
–1.cm
–1): 254 (0.41 × 105), 369 (0.11 × 105), 387 (0.11 × 105), 473 (0.08 × 105). IR (KBr,
v, cm
–1): 3440(s), 2920(w), 2850(w), 1614(s), 1560(m), 1477(s), 1386(s), 1269(s), 1145(s), 762(s).
(Salen-2)Co(III)Cl. (Salen-2)Co(III)Cl was obtained with the similar procedure for (salen-1)Co(III)Cl except that ligand salen-1 was replaced by ligand salen-2 (0.09 g, 0.22 mmol). Yield: 75%. EA (%) C28H30CoN2O2Cl: calc. C 64.56, H 5.80, N 5.38, found C 64.49, H 5.73, N 5.43. UV-Vis (CH3Cl3) λmax/nm (ε/L.mol–1.cm–1): 260 (0.40 × 105), 369 (0.14 × 105), 391 (0.16 × 105), 508 (0.07 × 105). IR (KBr, v, cm–1): 3440(s), 2949(m), 2863(w), 1613(s), 1527(s), 1489(m), 1387(s), 1261(w), 1145(s), 741(s).
(Salen-3)Co(III)Cl. (Salen-3)Co(III)Cl was obtained with the similar procedure for (salen-1)Co(III)Cl except that ligand salen-1 was replaced by ligand salen-3 (0.12 g, 0.22 mmol). Yield: 72%. EA (%) C36H46CoN2O2Cl: calc. C 68.29, H 7.32, N 4.42, found C 68.23, H 7.40, N 4.39. UV-Vis (CH3Cl3) λmax/nm (ε/L.mol–1.cm–1): 264 (0.27 × 105), 369 (0.11 × 105), 411 (0.08 × 105), 513 (0.05 × 105). IR (KBr, v, cm–1): 3450(s), 2955(s), 2860(w), 1610(s), 1527(s), 1489(w), 1387(s), 1261(w), 1145(w), 743(s).
(Salen-
3)Co(III)DNP. The ligand salen-
3 (1.00 g, 1.85 mmol) and Co(OAc)
2.4H
2O (0.33 g, 1.3 mmol) were dissolved in 100 mL absolute ethanol. The mixture was heated to 80 °C for 30 min and then cooled to room temperature. The solvent was removed in vacuo and washed with cold methanol (15 mL × 3). The solid was dissolved in 10 mL CH
2Cl
2 and recrystallized by 200 mL
n-hexane. After 24 h, a dark red crystal (salen-
4)Co(II) was obtained. The (salen-
4)Co(II) (0.07 g, 0.12 mmol) was dissolved in 50 mL CH
2Cl
2 and 2, 4-dinitrophenol sodium (0.02 g, 0.12 mmol) was added. The resulting solution was stirred for 2 h at room temperature in an oxygen atmosphere. Solvent was removed in vacuo to obtain the black crude product. The crude product was recrystallized from CH
2Cl
2 and
n-hexane, respectively, and then dried in vacuo at 60 °C for 24 h [
40]. Yield: 71%. EA (%) C
42H
49CoN
4O
7: calc. C 64.61, H 6.33, N 7.18, found C 64.53, H 6.29, N 7.14. UV-Vis (CH
3Cl
3) λ
max/nm (ε/L
.mol
–1.cm
–1): 263 (0.48 × 105), 321 (0.33 × 105), 430 (0.30 × 105), 533 (0.17 × 105). IR (KBr,
v, cm
–1): 3450(s), 2955(m), 2866(w), 1615(s), 1572(w), 1521(s), 1457(m), 1387(s), 1257(s), 1170(s), 753(w).
(Salen-
3)Co(III)TFA. (Salen-
3)Co(III)Cl (0.08 g, 0.12 mmol) and CF
3COOAg (0.03 g, 0.12 mmol) were dissolved in 15 mL CH
2Cl
2. Under oxygen atmosphere, the mixture was stirred for 24 h in the dark. Solvent was removed by vacuum filtration. A red-black solid was obtained and recrystallized from CH
2Cl
2 and
n-hexane, respectively [
55]. Yield: 73%. EA (%) C
38H
46CoN
2O
4F
3: calc. C 64.22, H 6.52, N 3.94, found C 64.29, H 6.61, N 4.01. UV-Vis (CH
3Cl
3) λ
max/nm (ε/L
.mol
–1.cm
–1): 263 (0.40 × 105), 308 (0.14 × 105), 401 (0.16 × 105), 506 (0.07 × 105). IR (KBr,
v, cm
–1): 3450(s), 2955(s), 2866(m), 1687(m), 1628(s), 1526(s), 1459(s), 1387(s), 1252(s), 1182(s), 753(m).
(Salen-
4)[Co(III)Cl]
2. The ligand salen-
4 (0.24 g, 0.22 mmol) was dissolved in 100 mL anhydrous methanol. The mixture was heated to reflux at 65 °C. After the ligand was completely dissolved, decrystallized water Co(OAc)
2 (0.09 g, 0.50 mmol) was dissolved in. Under oxygen atmosphere, anhydrous LiCl (0.02 g, 0.50 mmol) was added. After 12 h, the solvent was removed in vacuo. The residue was dissolved in CH
2Cl
2 and recrystallized by anhydrous CH
3CH
2OH. The resulting solution was filtered and washed to obtain a brown-red solid [
40]. Yield: 82%. EA (%) C
72H
90Co
2N
4O
4Cl
2: calc. C 68.40, H 7.18, N 4.43, found C 68.46, H 7.23, N 4.49. UV-Vis (CH
3Cl
3) λ
max/nm (ε/L
.mol
–1.cm
–1): 232 (1.02 × 105), 268 (0.72 × 105), 421 (0.17 × 105), 513 (0.12 × 105). IR (KBr,
v, cm
–1): 3440(s), 2955(s), 2859(w), 1610(s), 1515(s), 1489(m), 1381(s), 1259(s), 1171(s), 761(m).
(Salen-
4)[Co(III)DNP]
2. Under nitrogen atmosphere, the ligand salen-
4 (2.16 g, 2.0 mmol) was dissolved in 20 mL CH
2Cl
2, and Co(OAc)
2 (0.72 g, 4.04 mmol) was dissolved in 80 mL anhydrous methanol. The mixture was stirred for 3 h at room temperature to obtain the (salen-
4)Co(II) complex. Under oxygen atmosphere, (salen-
4)Co(II) (1.20 g, 1.0 mmol) was dissolved in 50 mL CH
2Cl
2, and 2, 4-dinitrophenol sodium (0.41 g, 2.0 mmol) was added. The mixture was stirred for 3 h. Solvent was removed in vacuo to obtain the crude product. The crude product was recrystallized from CH
2Cl
2 and
n-hexane, respectively to obtain a dark green solid [
40]. Yield: 76%. EA (%) C
42H
49Co
2N
4O
7: calc. C 68.69, H 6.20, N 7.18, found C 68.60, H 6.13, N 7.09. UV-Vis (CH
3Cl
3) λ
max/nm (ε/L
.mol
–1.cm
–1): 235 (1.07 × 105), 270 (1.00 × 105), 418 (0.47 × 105), 533 (0.26 × 105). IR (KBr,
v, cm
–1): 3443(s), 2955(s), 2868(w), 1614(s), 1573(m), 1522(s), 1483(m), 1386(s), 1253(s), 1197(s), 783(m).
(Salen-4)[Co(III)TFA]2. (Salen-3)Co(III)TFA (0.09 g, 0.12 mmol) and CF3COOAg (0.06 g, 0.25 mmol) were dissolved in 15 mL CH2Cl2. Under oxygen atmosphere, the mixture was stirred for 24 h in dark and filtered to remove the insoluble substances. Solvent was removed in vacuo to obtain a red-black solid. The solid was recrystallized from CH2Cl2 and n-hexane, respectively. Yield: 68%. EA (%) C76H90Co2N4O8F6: calc. C 64.31, H 6.39, N 3.95, found C 64.41, H 6.32, N 3.88. UV-Vis (CH3Cl3) λmax/nm (ε/L.mol–1.cm–1): 231 (1.01 × 105), 269 (0.68 × 105), 425 (0.22 × 105), 519 (0.17 × 105). 1H NMR (400 MHz, CDCl3, TMS) δ (ppm): 1.33 (s, 36H, t-Bu), 1.43 (s, 36H, t-Bu), 6.99 (s, 6H, Ar-H), 7.26 (s, 4H, Ar-H), 7.34 (s, 4H, Ar-H), 7.79 ((s, 4H, C = N-H). IR (KBr, v, cm–1): 3453(s), 2957(s), 2870(w), 1682(w), 1613(s), 1522(s), 1484(m), 1387(s), 1253(s), 1175(s), 783(m).