Synthesis, spectroscopic and biological aspects of iron(II) complexes

Figures & data

Scheme 1 Synthesis of ligands.

Scheme 2 Proposed reactions for the dimeric complex formation.

Table I.  ¹H NMR and ¹³C NMR spectral data of Schiff bases^a.

Compounds	^1H NMR δ-ppm	^13C NMR δ-ppm
A^2	7.5–7.8 (5H, m, Ar-H), 7.1–8.5 (4H, m, Py-H), 9.1 (1H, s, CH = N)	128.8–132.1(Ar), 113.5–144.5(Py), 157.9(Py, C = N), 149.1(Py, C = N), 161.1(CH = N).
A^3	7.0–7.4 (4H, m, Ar-H), 7.1–7.7 (3H, m, Thiophene-H), 7.5 (1H, s, CH = N)	122.1–130.4 (Ar), 128.5–143.0(Thiophene), 150.2 (C–N), 155.3 (CH = N)
A^4	7.4–8.0 (16H, m, Ar-H), 8.7 (2H, s, CH = N)	114.5–135.7v(Ar), 150.8 (C–N), 160.0(CH = N)
A^5	7.5–7.8 (10H, m, Ar-H), 5.2 (4H, t, CH2-aliphatic), 8.7 (1H, s, CH = N)	128.8–136.4 (Ar), 161.2 (CH = N), 54.1(C–N, aliphatic)
A^6	7.0–7.8 (12H, m, Ar-H), 3.8(6H, s, CH3-aliphatic), 8.6 (2H, s, CH = N)	115.0–132.8 (Ar), 163.5 (C–O, Ar), 123.5 (C–N), 160.5 (C = N), 56.0(OCH3)
A^7	7.4–7.9 (18H, m Ar-H)	120.5–133.7 (Ar), 165.8 (C = N), 155.3 (C–N)
A^8	7.3–7.4 (4H, m, Ar-H), 1.6(4H, m), 1.7 (4H, m), 2.35(2H,t)	124.2–130.7(Ar), 180.5(C = N), 140.0(C–N, Ar), 22.3, 25.8, 37.0

^a A² (bap): Benzylidene-2-aminopyridine; A³ (tca): Thiophene-2-carboxaldeneaniline; A⁴ (bendan): Bis(benzylidene)-1,8-diaminonaphthalene; A⁵ (benen): Bis(benzylidene)ethylenediamine; A⁶ (bmbbd): N,N′-Bis-(4-methoxybenzylidene)benzene-1,2-diamine; A⁷ (bcpded): N,N′-Bis-(3-Chlorophenyl)-1,2-Diphenyl-ethane-1,2-diimine; A⁸ (dcbd): N,N′-Dicyclohexylidene-benzene-1,2-diamine.

Table II.  Infrared spectral data of complexes^a.

Compounds	ν (O–H) cm^− 1	ν (C = O) cm^− 1 Pyridone	ν (C–S) cm^− 1	ν (COO)asy cm^− 1	ν (COO)sym cm^− 1	Δν cm^− 1	ν (C–Cl) cm^− 1	ν (C = N) cm^− 1 Azo methine	ν (C = N) cm^− 1 Ring	ν (M–N) cm^− 1	ν (M–O) cm^− 1	ν (M–S) cm^− 1
L	3520	1708	–	1624	1384	240	–	–	–	–	–	–
A^1	–	–	–	–	–	–	–	–	1585	–	–	–
A^2	–	–	–	–	–	–	–	1615	1593	–	–	–
A^3	–	–	765	–	–	–	–	1622	–	–	–	–
A^4	–	–	–	–	–	–	–	1629	–	–	–	–
A^5	–	–	–	–	–	–	–	1629	–	–	–	–
A^6	–	–	–	–	–	–	–	1608	–	–	–	–
A^7	–	–	–	–	–	–		1601	–	–	–	–
A^8	–	–	–	–	–	–	–	1602	–	–	–	–
I	–	1630	–	1582	1380	202	1130	–	1618	530	511	–
II	–	1629	–	1590	1383	208	1138	1565	1620	540	505	–
III	–	1629	752	1585	1382	203	1137	1580	–	540	506	420
IV	–	1633	–	1577	1365	215	1135	1593	–	535	510	–
V	–	1626	–	1584	1378	206	1145	1607	–	538	512	–
VI	–	1628	–	1591	1389	202	1149	1575	–	534	508	–
VII	–	1629	–	1590	1382	208	1117	1579	–	540	507	–
VIII	–	1632	–	1575	1364	211	1129	1570	–	536	509	–

^a See Table I and A¹ (bipym): 2,2′-bipyridylamine; L(Cip): 7-chloro-1-cyclopropyl-6-fluoro-4-oxo-1,4-dihydro-quinoline-3-carboxylic acid; Pip: piperazine.

Table III.  Electronic spectral data of the ligands and complexes^a.

	λmax in DMSO
Compounds	π–π* transition	d–d transition	MLCT	μeff BM
I	262	520	721	4.99
II	263	580	750	5.08
III	264	539	758	4.84
IV	264	590	763	5.04
V	263	560	775	4.89
VI	262	540	777	4.73
VII	275	635	805	4.69
VIII	263	564	807	5.17

^a see Table I.

Figure 1 Suggested structures of the complexes.

Table IV.  Antimicrobial activity of compounds.

	Zone of Inhibition in mm
Compounds	E. Coli	B. Subtilis	S. aureus	S. typhi	B. cereus	S. marcescens
Control	11	11	10	11	11	11
FeSO4·3H2O	13	16	19	14	18	19
LH(Cpf. HCl)	28	34	40	32	31	37
Std. 1 (Ofl. HCl)	30	34	39	33	30	32
Std. 2 (Lef. HCl)	33	36	38	29	28	34
Std. 3 (fluconozole)	15	19	11	12	11	12
A^1	12	15	25	18	19	22
A^2	17	17	12	12	11	16
A^3	13	14	16	14	15	19
A^4	19	12	11	16	12	14
A^5	11	11	11	11	12	19
A^6	13	14	13	14	15	14
A^7	17	11	12	16	15	17
A^8	14	14	15	11	11	19
I	45	40	45	25	25	38
II	42	40	44	26	28	38
III	45	40	41	27	25	34
IV	44	38	39	28	29	22
V	46	43	41	29	31	35
VI	41	40	40	33	24	36
VII	45	40	43	26	26	35
VIII	42	39	40	26	28	40

Table V.  DNA interaction data for the complexes.

Compound	DNA μgm	Compound λmax nm	A^n λmax nm	L λmax nm	Fe(II) λmax nm
I [Fe2(L)2(A^1)2(pip)]·5H2O	0	275.0	260.4	260.0	268.4
	3	261.2	259.6	259.2	259.6
	5	260.4	258.6	258.8	258.0
	7	244.6	245.0	247.4	245.2
II [Fe2(L)2(A^2)2(pip)]·5H2O	0	270.6	260.6	260.0	268.4
	3	261.4	258.4	259.2	259.6
	5	258.4	258.0	258.8	258.0
	7	247.4	249.4	247.4	245.2
III [Fe2(L)2(A^3)2(pip)]·5H2O	0	271.5	260.0	260.0	268.4
	3	262.4	258.2	259.2	259.6
	5	260.4	257.8	258.8	258.0
	7	249.8	246.6	247.4	245.2
IV [Fe2(L)2(A^4)2(pip)]·5H2O	0	274.3	263.0	260.0	268.4
	3	260.0	259.2	259.2	259.6
	5	258.8	258.2	258.8	258.0
	7	246.6	244.2	247.4	245.2
V [Fe2(L)2(A^5)2(pip)]·5H2O	0	276.7	265.2	260.0	268.4
	3	261.4	259.2	259.2	259.6
	5	259.0	258.2	258.8	258.0
	7	248.0	246.6	247.4	245.2
VI [Fe2(L)2(A^6)2(pip)]·5H2O	0	273.0	261.7	260.0	268.4
	3	261.8	258.8	259.2	259.6
	5	258.6	258.0	258.8	258.0
	7	247.6	244.6	247.4	245.2
VII [Fe2(L)2(A^7)2(pip)]·5H2O	0	267.9	259.0	260.0	268.4
	3	260.8	258.4	259.2	259.6
	5	258.6	258.0	258.8	258.0
	7	247.0	245.4	247.4	245.2
VIII [Fe2(L)2(A^8)2(pip)]·5H2O	0	272.8	260.3	260.0	268.4
	3	261.2	259.4	259.2	259.6
	5	258.8	258.4	258.8	258.0
	7	247.4	247.4	247.4	245.2

Figure 2 Absorption spectra of complex [Fe₂(L)₂(A¹)₂(pip)]·5H₂O in absence and presence of DNA.