Synthesis, physical characterization and biological evaluation of Schiff base M(II) complexes

Peer review under responsibility of University of Bahrain.

Figures & data

Figure 2 Shows the effect of ligand and its metal complexes toward Pseudomonas aeruginosa and Staphylococcus aureus at concentration 5 mM.

Figure 3 Shows the effect of ligands and their metal complexes toward Pseudomonas aeruginosa and Staphylococcus aureus at concentration 10 mM.

Scheme 1 General steps for preparation of the new ligand (L).

Table 1 Physical data of new ligand (L) and its metal complexes.

Comp.	Color	M.P.°C	Yield %	M. Wtg. mol^−1	Elemental analysis found(Calc.)				Metal percentage
					C	H	N	S	found	Calc.
L	Darkorange	150	70.0	378.09	38.25(38.08)	2.98(2.91)	14.55(14.81)	33.53(33.85)	---	---
Cu2L2	Brown	240d	54.1	958.09	32.25(32.56)	3.25(3.34)	11.81 (11.69)	26.47(26.72)	13.50	13.26
NiL2	Lightbrown	290d	55.5	808.69	35.27(35.61)	3.68(3.70)	13.35(13.84)	31.96(31.65)	7.15	7.25
CoL	Darkbrown	250d	52.3	538.43	33.92(33.43)	4.77(4.45)	10.12(10.40)	23.95(23.77)	11.00	10.94

d = decomposition degree

Table 2 Characteristic FTIR bands in (cm⁻¹) of the new ligand and its metal complexes.

Comp.	υCN ring	υCN	νNCS	νAr-N	υCS	υC-S	υC…S	υM-N	υM-S	υM-O	υM-Cl
L	1527	1591	1440	1371	1031	777	943	----	----	----	----
Cu2L2	1527	1581	1445	1371	1041	788	935	516	408	455	392
NiL2	1527	1561	1445	1371	1056	794	937	516	432	---	---
CoL	1527	1581	1445	1371	1058	790	932	550	430	509	390

Table 3 Electronic spectra, conductance in DMSO solvent and magnetic moment (B.M.) for the prepared ligand and its metal complexes.

Comp.	Absorption Bands(cm^−1)	Assignment	B°	B^/	β	Dq/B^/	10Dq	15B^/	μeff B.M.	μscm^−1	Suggested geometry
Cu2L2	14.814	^2Eg → ^2T2g	---	---	---	---	---	---	---	28	O.h
	23.955	LMCT
	37.037	LMCT
NiL2	13.947	^3A2g → ^1Eg	1035	559.3	0.54	1.9	10.626	5.598	3.2	22	O.h
	11.135	^3A2g → ^3T2g
	15.748	^3A2g → ^3T1g(F)
	23.255	^3A2g → ^3T1g(P)
CoL	11.695	^4T1g → ^4T2g	971	661	0.68	1.8	11.898	9.748	4.90	29	O.h
	18.518	^4T1g → ^4A2g
	18.685(cal.) 26.315	^4T1g → ^4T1g(P)

Figure 1 Shows the suggested structures of prepared new complexes.

Table 4 Thermal analysis data for metal complexes.

Comp.	Dissociation stages	Temp range in TG °C	Weight loss Found (Calcd.)%	Decomposition assignment
Cu2L2 (958.09)	Stage I	70–130	4.69 (4.80)	Outer sphere EtOH
	Stage II	130–250	3.35 (3.75)	Coordinated water molecules
	Stage III	250–340	6.57 (6.26)	2CH3
	Stage IV	340–810	51.61 (51.87)	2C10H5N4S, Cl2 of ligand
	Stage V	810–900	33.20 (33.30)	2CuS3
NiL2 (808.69)	Stage I	35–180	8.95 (8.90)	Outer sphere water molecules
	Stage II	180–390	7.68 (7.41)	4CH3
	Stage III	390–820	52.71 (52.67)	2C10H5N4S of ligand
	Stage IV	820–900	31.29 (30.99	NiS6
CoL (538.43)	Stage I	55–145	12.88 (12.81)	Outer sphere EtOH
	Stage II	145–200	6.42 (6.68)	Coordinated water molecules
	Stage III	200–295	5.39 (5.57)	2CH3
	Stage IV	295–780	46.35 (46.15)	C10H5N4S, Cl of ligand
	Stage V	780–865	29.67 (29.63)	CoS3

Table 5 Antibacterial screening data for the ligands and their complexes.

Comp.	Diameter of inhibition zone (mm); Concentration in mM
	Pseudomonas aeruginosa		Staphylococcus aureus
	5 mM	10 mM	5 mM	10 mM
L	−	−	−	−
Cu2L2	−	−	−	−
NiL2	+++	++	+	+
CoL	−	−	+	++
DMSO	−	−	−	−
Ampicillin	++	+++	++	+++

(−) no inhibition; (+) inhibition in diameter (0.25–0.82)mm; (++) inhibition in diameter (0.83–1.37)mm; (+++) inhibition in diameter (1.38–1.93)mm.