Synthesis, Spectroscopic Investigation of Co(II),. Ni(II). and Cu(II) Complexes with 2-meracapto-5-(2,4-dinitrophenyl)-1,3,4-oxadiazole or 2-meracapto-5-((4-(dimethylamino)benzylidene)amino)-1,3,4-thiadiazole Ligands

Introduction

The reaction of ions with thiones compounds have been the subject of various  characterization as these chemical compounds contain active groups [NH-CS ↔ -N=C(SH)], and are helpful parent compounds for S including peer of heterocyclic bases.^1-5 The ( thiadiazole or oxadiazole )-thione ligands have many coordinate model with metal ions, such as S, N as monodentate, or Sand N as chelate bidentate, N, S-bridging.^3-6 The heavy metals such as Pt(II), Pd(II) and Ag(I) were interacted  with nitrogen and sulfur donor atoms have been known for its anticancer against  with possibility to improve metal-based drugs.^1-4 The coordination properties of N and S including heterocyclic ligands, such as triazoles, oxadiazoles, is an emerging and rapidly developing area of research.^5-14

Recently, many research works involving M(II) ions with thiones have been published.^5-20 In the present work, I report the preparation of Co(II), Ni(II) and Cu(II) complexes with new thione ligands.

Experimental

Methods and Materials

The MX₂ (Where M = Co, Cu, X= Cl and M= Ni , X= NO₃), and organic compounds were s provided from Sigma-Aldrich, Fluka, or BDH companies, and used without further purification, Melting points were measured on an on SMP40 / Stuart Company, The conductivity of 10^-3 M of DMSO or DMF solutions of prepared complexes were measured at 25^oC using Digital conductivity meter. The infrared spectra of prepared ligands and its complexes were recorded with KBr disc in the 4000 – 400 cm^-1 range on Shimadzu 8400S FTIR Spectrophotometer. The Ultra violet visible data of prepared compounds were measured on Shimadzu UV-1800 Spectrophotometer in 200-1100nm using DMSO as a solvent. Magnetic properties were carried out at 25^oC by Bucker BM6 instrument applying Faraday method. CHN  element contents were determined by Eurovectro EA 3000/ Italy. The ¹HNMR spectra were recorded on Bucker / 300MHz  spectrometer with DMSO-d⁶ as solvent and Me4Sias internal reference. Metal content was determined on Shimadzu SMP30.

Preparation of ligands

Preparation of 2-meracapto-5-(2,4-dinitrophenyl)-1,3,4-oxadiazole (IpotH)

A gradual addition of CS2 (0.076g; 0.001mol)  to a mixture of 2,4-dinitrobenzohyrazide (2.200g; 0.001mmol) and KOH (0.560g; 0.001mol) in EtOH (10ml) with stirring. The mixture was refluxed for 20h. The solvent was evaporated to half under vacuum , and  ice to the reduced mixture was added, and followed by add of conc. HCl with  cooling, and left at room temperature to complete the precipitate process. The yellow ppt. was  filtered off, rinsed with H₂O and dried in oven under vacuum (Yield: 74%, m.p. 170-173^oC) (Scheme 1).

Scheme 1: Preparation of IpotH ligand   Click here to View scheme

 

Preparation of 2-meracapto-5-((4-(dimethylamino)benzylidene)amino)-1,3,4-thiadiazole (daptH)

To an ethanoic solution of 2-mercapto-5-amino-1,3,4-thiadiazol (1.500g; 0.011mol) in EtOH (10ml), a solution of 4-(dimethylamino)benzaldehyde (1.640g; 0.011 mol) in EtOH(10ml) and some drops of CH₃COOH (glacial) was added with stirring. The orange solution was refluxed for 4h and cooled on ice bath, the orange ppt. was formed. The product was filtered and rinsed with EtOH (5ml) and Et₂O (5ml), and dried in oven under vacuum (Yield: 75%, m.p. 225-226^oC) (Scheme 2).

Scheme 2: Preparation of daptH ligand Click here to View scheme

 

General preparation of complexes (1-3)

A solution of IpotH ligand (0.29 g, 1.10mmol) in EtOH/Acetone (1:1) (15 ml) was added to (0.505mmol) of the MX₂ (Where M = Co, Cu, X= Cl and M= Ni , X= NO₃ ) dissolved in distal water (10 ml). The mixture was refluxed for 2 h. The ppt. afforded  was filtered off, rinsed with distal water, and dried in oven under vacuum.

General preparation of complexes (4-6)

A solution of daptH ligand (0.20 g, 0.074mmol) in EtOH/Acetone (1:1) (15 ml) was added to (0.037mmol) of the MX₂ (Where M = Co, Cu, X= Cl and M= Ni , X= NO₃ ) dissolved in distal water (10 ml). The mixture was refluxed for 3 h. The ppt. produced  was filtered off, rinsed with distal water, and dried in oven under vacuum.

Results and Discussion

Synthesis and Characterization of IpotH and its Complexes

Reaction of  two moles of IpotH ligand  with one mole transition metal MX₂ (Where M = Co, Cu, X= Cl and M= Ni , X= NO₃)  in distal water gave the complexes of the type [MX₂(k²-IpotH)₂], where M= Co (1), X = Cl; Ni (2), X= NO₃; Cu (3), X = Cl, (See. scheme 3). The result complexes are stable in air at room temperature, and are soluble in DMSO and DMF. but insoluble in MeOH, EtOH, acetone, CHCl₃ …. etc. The IpotH ligand has been  investigated by CHN., ¹H NMR, .UV and IR techniques, Where as its complexes have been investigation by molar conductivity, CHNM, UV-visible, and IR techniques.

Scheme 3: Preparation of IpotH complexes  (1-3) Click here to View scheme

 

A 10^-3M of DMSO and DMF of complexes solutions was prepared and the conductivity of at 25°C were recorded and listed in Table 1.The values of conductivity of the prepared complexes refer that these complexes are non-electrolytes.²¹

The IpotH  ligand is bonded towards the metal ions as bidentate through the N and S atoms  to give octahedral arrangement around metal ions.

The ¹H nmr spectrum of IpotH in DMSO-d6 (Fig. 1) shows a singlet peak at dH= 4.401ppm due to the proton of thiol group, whereas the protons of phenyl ring appeared as unsolved multiplets within d (6.81-7.87) ppm range. The peak of H-phenyl ring represents three protons, while the SH peak  represents one proton, as indicated from the integration values under each signal.

Figure 1: 1H NMR spectrum of IpotH  measured in DMSO-d6 Click here to View figure

 

IR spectrum of 2-meracapto-5-(2,4-dinitrophenyl)-1,3,4-oxadiazole (IpotH) (Fig 2) shown a bands at ( 3093, 2538, 1627, 1552, 1380)cm^-1 assigned to n(=C-H), n(S-H) , n(C=N), n(C=C), and n(NO₂).

Infrared spectra of the of complexes [MX₂(k²– IpotH)₂] display a strong band at (1568-1594)cm^-1 due to the n(C=N) this bond are shifted to low frequency from that of the free ligand which appeared at (1627) cm^-1  This  indicating that IpotH ligand bounded through the nitrogen atom with metal ions.^8,17,22 And the n(S-H) was shifted to lower frequency compared with the free ligand.

The spectra also showed  new bands at (483-508) cm^-1  and (435-568) which due to  n(M-S) and n(M-N) cm^-1  respectively,^{8,17,19,23,24} other IR bands are listed in Table 2.

Figure 2: IR spectrum of IpotH ligand Click here to View figure

 

Synthesis and Characterization of [MX₂(k²– daptH)₂] Complexes

The refluxed two moles of  daptH ligands  in mixture of EtOH and acetone with one mole of transition metal MX₂ (Where M = Co, Cu, X= Cl and M= Ni , X= NO₃ )  in distal water gave the complexes of the type [MX₂(k²-daptH)₂], where M= Co (1), X = Cl; Ni (2), X= NO₃; Cu (3), X = Cl, (See. scheme 4).  All complexes are stable toward air and wetness, and obtained in high yields (over 70%), and dissolved in DMSO and DMF while partial solubility in warm CHCl₃ and warm CH₂Cl₂. The prepared complexes  have been investigated by CHNM analysis, IR spectra, conductivities measurements, and ¹H NMR for free ligand.

Scheme 4: Preparation of daptH complexes  (4-6) Click here to View scheme

 

The molar conductance values refer to that these complexes are non-electrolytes. The daptH  ligand is coordinated with metal ions as bidentate through the N and S atoms to give octahedral arrangement around metal ions.

The ¹H nmr spectrum of daptH in DMSO-d6 (Fig. 3) shows a singlet peak at dH= 3.024ppm due to the proton of methyl group, and this peak represents six protons. and the proton of thiol group appeared as broad singlet at  dH= 3.792ppm. The protons of  phenyl ring appeared at d6.06ppm as doublet with coupling to the neighboring protons (³J_H-H= 8.40Hz) assigned to the H2,2′ proton, and a doublet at d7.59ppm with (³J_H-H= 8.40Hz) for the H1,1′ proton. Whereas the protons of HC=N group appeared singlet at 8.212ppm.

Figure 3: 1H NMR spectrum of daptH  measured in DMSO-d6 Click here to View figure

 

IR spectrum of 2-meracapto-5-((4-(dimethylamino.)benzylidene)amino)-1,3,4-thiadiazole (daptH) (Fig. 4)shown a bands at (3091, 2906, 2549, 1691, 1650, 1529, 1460) cm^-1 assigned to n(=C-H),   n(C-H)aliph.,  n(S-H)., n(C=N)., n(C=N) ring, n(C=C), and n(C-N).

IR spectra of the of complexes [MX₂(k²-daptH)₂] showed a strong band at (1587-1614)cm^-1 due to the n(C=N) in heterocyclic ring this bond are shifted to low frequency from that of the IpotH ligand which appeared at (1650) cm^-1  this  refer to  that IpotH ligand bounded through the nitrogen atom with metal ions.^8,17,22  And the n(S-H) was shifted to lower frequency , this mean the metals ions coordinated through S atom. Other IR bands of the prepared complexes are registered in Table 2.

Figure 4: IR spectrum of daptH ligand Click here to View figure

 

Electronic Spectra

The solution of the electronic measurements were prepared in using DMSO as a solvent in 10^-3 M are given in Table 3. The UV-Vis. spectra of the prepared ligands IpotH and daptH showed two bands for each ligand, at 28751 and 32258 for the IpotH and at 26385 and 32154 for the daptH which assigned to the n→π* and π→π* respectively. The spectra for all prepared complexes are showed a similar transition as showed in the free  ligands it also showed the transitions of the metal d orbitals.^21,26

In the [CoCl₂(k²-IpotH)₂] spectrum, the band appeared at 9814, 10384, and 18832 cm^-1 which due to ⁴A₂ → ⁴T₂(F), ⁴A₂ → ⁴T₁(F), ⁴A₂ → ⁴T₁(P),   transition respectively. The Co(II) complex showed the μ_eff value 5.1(B.M), indicating octahedral geometry around the center atom. Whereas in the [Ni(NO₃)₂(k²– IpotH)₂] spectrum, the band appeared at 9425, 11328, and 14728 cm^-1 which due to ³A₂ → ³T₂(F),. ³A₂ → ³T₁(F),. ³A₂ → ³T₁(P), transition respectively. Furthermore, octahedral geometry for Ni(II) is also supported by its magnetic moment μ_eff value 3.1(B.M). The other spectroscopic and physical data are in full agreements with the proposed formulations.^25,26

Table 1: Color., Yield, m.p., and CHNM of prepared ligands and its complexes.

Seq.	Compounds	Color	Yield (%)	m.p.(°C)	Molar conductivity (DMSO/DMF) 10-3M: Ω-1 mol-1 cm-1)	μeff (B.M)	Elemental Analysis Found (Calc.)%
							C	H	N	M
1	IpotH	Light yellow	74	170-173	–	–	35.67 (35.83)	1.36 (1.50)	20.69 (20.89)
2	[CoCl2(k2– IpotH)2]	Light violet	79	181-185	10 / 19	5.1	28.67 (28.84)	1.34 (1.21)	16.57 (16.82)	8.72 (8.85)
3	[Ni(NO3)2(k2– IpotH)2]	Green	86	215-218	12 / 18	3.1	26.89 (26.72)	1.28 (1.12)	19.65 (19.48)	8.27 (8.16)
4	[CuCl2 (k2– IpotH)2]	Brown	76	161-165	14 / 23	1.7	28.79 (28.65)	1.43 (1.20)	16.87 (16.70)	9.27 (9.47)
5	daptH	Orange	75	225-226	–	–	49.43 (49.98)	4.31 (4.58)	20.86 (21.19)	–
6	[CoCl2(k2– daptH)2]	Dark brawn	81	265-267	6 / 15	4.8	39.86 (40.12)	3.28 (3.67)	16.71 (17.02)	8.83 (8.95)
7	[Ni(NO3)2(k2– daptH)2]	Light green	72	292-294	10 / 17	2.8	37.23 (37.14)	3.59 (3.40)	19.58 (19.69)	8.11 (8.25)
8	[CuCl2 (k2– daptH)2]	Green	88	253-256	15 / 22	1.5	39.52 (39.84)	3.24 (3.65)	16.66 (16.90)	9.45 (9.58)

 

Table 2: IR data (cm^-1) of the prepared ligands and their complexes.

Complexes	v(C-H)ar	v(C-H)aliph	v(S-H)	v(C=N)	v(NO2)	v(M-N)	v(M-S)
IpotH	3093	–	2538	1627	1350	–	–
[CoCl2(k2– IpotH)2]	3058	–	2521	1568	1371	512	443
[Ni(NO3)2(k2– IpotH)2]	3052	–	2498	1591	1360	483	423
[CuCl2 (k2– IpotH)2]	3089	–	2518	1594	1360	568	508
daptH	3091	2906	2552	1650	–	–	–
[CoCl2(k2– daptH)2]	3058	2889	2528	1587	–	521	438
[Ni(NO3)2(k2– daptH)2]	3098	2923 2858	2531	1614	–	498	421
[CuCl2 (k2– daptH)2]	3052	2968 2887	2518	1607	–	508	427

 

Table 3: Electronic spectral data of prepared ligands and its complexes in DMSO.

Seq.	Compounds	Absorption bands cm-1	Assigned transition
1	IpotH	32258, 28751,	n→π* , π→π*
2	[CoCl2(k2– IpotH)2]	30675, 27932,9814, 10384, 18832	n→π* , π→π*,4A2g → 4T2g(F) ., 4A2g→ 4T1g(F) ., 4A2g→4T1g(P)
3	[Ni(NO3)2(k2– IpotH)2]	30796, 24938,9425, 11328, 14728	n→π* , π→π*,3A2g→ 3T2g(F), .3A2g→ 3T1g(F), .3A2g→ 3T1g(P),
4	[CuCl2 (k2– IpotH)2]	31546, 23578,11699	n→π* , π→π*,2Eg → 3T2g
5	daptH	26385, 32154	n→π* , π→π*
6	[CoCl2(k2– daptH)2]	33,180, 25,4528,265, 9,346, 15,455	n→π* , π→π*,4A2g → 4T2g(F), . 4A2g→ 4T1g(F), .4A2g→ 4T1g(P)
7	[Ni(NO3)2(k2– daptH)2]	30581, 24631,9434, 10358, 13661	n→π* , π→π*,3A2g → 3T2g(F), . 3A2g → 3T1g(F), .3A2g → 3T1g(P),
8	[CuCl2 (k2– daptH)2]	29326, 22897,11628	n→π* , π→π*,2Eg → 3T2g

 

Conclusions

In summary, we have synthesized IpotH ligand by refluxing CS2 and 2,4-dinitrobenzohyrazide and KOH or daptH ligand by condensation of 2-mercapto-5-amino-1,3,4-thiadiazol with 4-(dimethylamino)benzaldehyde and their complexes with Co(II), Ni(II) and Cu(II)  to afford  mononuclear complexes of the type [MX₂(k²-thione)₂],(M(II) = Co, Ni and Cu). The thione ligand bonded as bidentate chelating through the nitrogen and sulfur atoms to give octahedral  geometry around the metal ions with 1:2 (metal: ligand) stoichiometry. The prepared ligands and its complexes were characterization by CHNM analysis, IR spectroscopy , molar conductivity, magnetic susceptibility, UV-Visible and ¹H NMR data.

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