Synthesis, characterization, fluorescence and biological studies of Mn(II), Fe(III) and Zn(II) complexes of Schiff bases derived from Isatin and 3-substituted-4-amino-5-mercapto-1,2,4-triazoles

Figures & data

Scheme 1. Synthesis of the Schiff bases I–IV.

Table 1.  Elemental analyses, molar conductance and magnetic moment data of metal complexes.

		M (%)		C (%)		H (%)		N (%)
Complex number	Empirical formula	Obsd	Calcd	Obsd.	Calcd	Obsd.	Calcd	Obsd.	Calcd	Molar conductance (Ohm^−1 cm^2 mol^−1)	μeff (BM)
1	[Mn(C10H6N5OS)2]	10.02	10.13	44.02	44.19	2.01	2.21	25.11	25.78	12.4	5.72
2	[Mn(C11H8N5OS)2]	9.42	9.63	46.99	46.23	2.20	2.80	23.98	24.52	8.9	5.81
3	[Mn(C12H10N5OS)2]	9.16	9.18	47.81	48.08	3.31	3.34	23.11	23.37	11.6	5.90
4	[Mn(C13H12N5OS)2]	8.93	8.77	49.05	49.76	3.02	3.82	22.31	22.33	10.9	5.75
5	[Fe(C10H6N5OS)2]Cl	9.39	9.67	41.42	41.45	1.87	2.07	23.98	24.18	74.2	5.10
6	[Fe(C11H8N5OS)2]Cl	9.71	9.22	42.91	43.49	2.24	2.63	23.82	23.06	76.2	4.98
7	[Fe(C12H10N5OS)2]Cl	8.78	8.81	45.68	45.35	2.91	3.15	21.89	22.05	74.9	5.14
8	[Fe(C13H12N5OS)2]Cl	8.11	8.45	46.88	47.06	3.58	3.62	21.68	21.12	74.8	5.21
9	[Zn(C10H6N5OS)2]	11.06	11.75	43.28	43.39	2.78	2.17	25.99	25.32	15.6	Diamagnetic
10	[Zn(C11H8N5OS)2]	11.16	11.18	45.91	45.44	2.11	2.75	23.81	24.09	14.8	Diamagnetic
11	[Zn(C12H10N5OS)2]	10.29	10.67	47.87	47.29	3.16	3.28	22.12	22.98	12.9	Diamagnetic
12	[Zn(C13H12N5OS)2]	10.69	10.20	48.21	48.97	3.02	3.77	21.48	21.98	11.7	Diamagnetic

Table 2.  The important infrared frequencies (in cm⁻¹) of metal complexes.

Complex number	Indole ring ν (NH)	Lactonyl ν (C˭O)	ν (C˭N)	ν (C‒S)	ν (M‒N)	ν (M‒S)
1	3198	1718	1601	754	460	358
2	3182	1716	1600	751	456	352
3	3112	1722	1598	757	472	362
4	3190	1714	1603	750	476	368
5	3196	1716	1600	756	462	356
6	3184	1717	1599	750	458	351
7	3110	1724	1601	759	474	366
8	3191	1715	1602	751	480	369
9	3199	1716	1598	752	458	355
10	3184	1715	1602	753	460	351
11	3110	1722	1596	758	474	363
12	3191	1714	1601	750	479	371

Table 3.  The important ¹H NMR and ¹³C NMR data of Schiff bases.

Schiff base	^1H NMR (d6-DMSO) (ppm)	^13C NMR (d6-DMSO) (ppm)
C10H7N5OS (SB I)	11.6 (s, 1H, NH), 10.1 (s, 1H, SH), 6.1–7.1 (m, 4H, Ar-H), 6.9 (s, 1H, CH of triazole)	113.1, 118.6, 125.5, 126.7, 144.6, 155.2, (isatin), 139.1 (C˭N), 160 (C=O), 185, 172 (triazole)
C11H9N5OS (SB II)	11.7 (s, 1H, NH), 10.4 (s, 1H, SH), 6.3–7.2 (m, 4H, Ar-H), 2.7 (s, 3H, CH3)	113.1, 118.6, 125.5, 126.7, 144.6, 155.2, (isatin), 139.5 (C˭N), 162 (C˭O), 185, 176 (triazole), 34.4(CH3)
C12H11N5OS (SB III)	11.9 (s, 1H, NH), 11.0 (s, 1H, SH), 6.9–7.5 (m, 4H, Ar-H), 2.2(q, 2H, CH2), 1.3(t, 3H, CH3)	113.1, 118.6, 125.5, 126.7, 144.6, 155.2, (isatin), 139.3 (C˭N), 165 (C˭O), 185, 178 (triazole), 11.1 (CH3), 31.5 (CH2)
C13H13N5OS (SB IV)	12.1 (s, 1H, NH), 11.03 (s, 1H, SH), 6.8–7.6 (m, 4H, Ar-H), 2.4 (t, 2H, CH2), 2.2 (m, 2H, CH2), 1.2 (t, 3H, CH3)	113.1, 118.6, 125.5, 126.7, 144.6, 155.2, (isatin), 139.3 (C˭N), 160 (C˭O), 185, 182 (triazole), 11.1 (CH3), 18.8 (CH2), 31.5(CH2)

Figure 1. Cyclic voltammogram of Mn(II) (2) complex at a scan rate of 0.05 V s⁻¹.

Figure 2. Cyclic voltammogram of Fe(III) (6) complex at a scan rate of 0.05 V s⁻¹.

Table 4.  Antimicrobial results of metal complexes.

		Growth inhibition against bacteria (mm)				Growth inhibition against fungi (mm)
Complex number	Conc. (μg mL^−1)	S. aureus	B. subtilis	P. auregenosa	E. coli	A. niger	P. crysogenum
1	100	12	10	10	08	10	08
	200	14	15	14	10	12	12
	500	22	22	19	10	12	12
2	100	13	08	10	07	10	08
	200	15	15	15	07	12	08
	500	24	22	19	07	16	15
3	100	11	11	11	08	08	08
	200	15	14	15	09	10	08
	500	21	18	20	09	10	09
4	100	14	10	10	08	08	08
	200	16	12	12	10	10	10
	500	20	18	21	10	12	10
5	100	10	10	12	08	10	08
	200	16	14	15	10	12	10
	500	19	22	18	10	15	12
6	100	14	08	10	08	12	09
	200	16	14	15	10	12	09
	500	24	21	22	14	14	12
7	100	13	10	12	08	07	09
	200	15	14	16	10	10	12
	500	22	19	20	13	12	14
8	100	14	10	12	08	08	08
	200	16	12	13	10	10	10
	500	20	19	18	10	10	10
9	100	12	10	10	10	10	10
	200	14	12	14	12	14	12
	500	22	19	18	12	14	12
10	100	14	08	10	10	12	11
	200	18	15	14	12	14	11
	500	24	20	18	20	18	13
11	100	12	12	12	08	13	10
	200	16	14	14	12	13	10
	500	22	20	19	20	17	13
12	100	12	12	13	08	10	10
	200	12	13	16	10	12	14
	500	20	18	19	14	12	14
Streptomycin	500	28	29	35	25	–	–
Nyastatin	500	–	–	–	–	26	25

Table 5.  Anthelmintic activity results of metal complexes.

		P. postuma
		Time of attacks of paralysis (s)
Sl. No.	Compounds	50%	25%	10%	Time required for death (s) (50%)
1	Piperazine citrate	1602	2317	2805	3203
2	C10H7N5OS	1713	1755	1802	4102
3	C11H9N5OS	1812	1895	1911	3915
4	C12H11N5OS	1912	1952	2012	4012
5	C13H13N5OS	2016	1956	1958	4125
6	[Mn(C10H6N5OS)2]	890	1213	1500	3121
7	[Mn(C11H8N5OS)2]	1935	3115	3912	3414
8	[Mn(C12H10N5OS)2]	1009	1619	2117	3792
9	[Mn(C13H12N5OS)2]	782	1273	1624	3012
10	[Fe(C10H6N5OS)2]Cl	1125	1321	1542	3510
11	[Fe(C11H8N5OS)2]Cl	2319	3225	4253	3752
12	[Fe(C12H10N5OS)2]Cl	1507	2015	2512	4162
13	[Fe(C13H12N5OS)2]Cl	959	1579	1968	3415
14	[Zn(C10H6N5OS)2]	1010	1176	1523	4615
15	[Zn(C11H8N5OS)2]	3218	5135	1633	4612
16	[Zn(C12H10N5OS)2]	2119	3275	3298	4913
17	[Zn(C13H12N5OS)2]	1287	2111	2629	4301

Figure 3. DNA cleavage of Mn(II) (2), Fe(III) (6) and Zn(II) (10) complexes. M, standard molecular weight marker; C1, control DNA of S. aureus; Lane 1, S. aureus DNA treated with Mn(II); Lane 2, S. aureus DNA treated with Zn(II); C2, control DNA of A. niger; Lane 3, A. niger DNA treated with Fe(III); Lane 4, A. niger DNA treated with Mn(II); Lane 5, A. niger DNA treated with Zn(II).

Figure 4. Structure of metal complexes.

Figure 5. Structure of Fe(III) metal complexes.