Preparation and Study of Some Mn ( II ) , Co ( II ) , Ni ( II ) , Cu ( II ) , Cd ( II ) and Pb ( II ) Complexes Containing Heterocyclic Nitrogen Donor Ligands

This paper presents a new mixed-ligand complexes with the general formula [M(BT)(BI)2X2] where BT=benzotriazole, BI=benzimidazole, X=SCN and M=Mn(II), Co(II), Ni(II), Cu(II), Cd(II) and Pb(II). The reaction was carried out by using the appropriate molar ratios of metal:ligand (1:1:2:2) (M:BT:BI:X) as required. The resulting products were found to be solids, not soluble in water and in ordinary organic solvents but highly soluble in DMSO. These complexes have been studied by UV-Visible, IR and (H, C) NMR spectra, molar conductivity, elemental analysis of C, H, N, determination of metal and magnetic susceptibility. The result suggests that the benzimidazoleas as a monodentate was coordinated with the metal ions through the N atom. Nevertheless, the benzotriazole as bidentate was coordinated with the metal ions through the N2 and N3 atoms. SCN was coordinated with the metal ions through the nitogen atom.


Introduction
Heterocyclic nitrogen play an important role in coordination chemistry 1,2 .The triazole derivatives have discrete or super molecules in particular, benzotriazole displays remarkable efficiency as a corrosion inhibitor for copper and its alloys, very useful as fungicides and bactericides 3,4 .Benzotriazole was widely used in the construction of metal-organic frameworks due to the multifunctional linking role, an interesting case of linkage isomerization has been reported for benzotriazole complexes 5,6 .Furthermore, the reactivity and the properties of transition metal complexes with imidazole derivatives have been studied over the last decades, a few cases involving the interaction of the benzimidazole and benzotriazole ligands with the metal ions complexes are known 2 .Numerous related the heterocyclic ligands have been synthesized that contain other heteroaromatic ring systems 7 .The aim of this paper is to study the coordination chemistry of two ligands that contain benzotriazole and benzimidazole.Each of these ligands is capable of coordinating to the metal ions.Moreover, the benzotriazole have two nitrogen atoms capable of coordination 7 .The IR spectra in the region of 4000-400 cm -1 KBr disc were recorded by using shimadzu FTIR.8400S fourier transform infrared spectrophotometer. 1 H NMR and 13 C NMR spectra were recorded using the JEOL JNM-ECP 400 spectrometer in DMSO-d 6 , relative to the internal standard tetramethylsilane (TMS).The UV-Visible were carried out on Shimadzu UV-Visible recorder spectrophotometer UV-160 in DMSO solution 10 -3 M. Philips PW 9526 digital conductivity meter was used to measure molar conductivity.The magnetic susceptibilities were measured by using balance magnetic susceptibility model MSB.MK1 at 25 °C.Elemental analysis C H N was performed by using a Carlo Erba 1106 Elemental Alanyzer and the metal percentage in the complexes was determined following the gravimetric methods.Finally the melting points were recorded by using Stuart melting point apparatus.

Preparation of metal(II) complexes [M(BT)(BI) 2 X 2 ]
An ethanolic solution of benzotriazole 0.17-0.34g (1.42-2.85mmole) in 15 mL in ethanol and an ethanolic solution of benzimidazole 0.35-0.69g (2.96-5.84mmole) were added respectively to an aqueous solution of the metal salts.The aqueous solution of NH 4 SCN 0.22-0.44g (2.89-5.78mmole) was added to the mixture with constant stirring.The products were immediately precipitated which were filtered off, washed and recrystallised with 1:1 mixture of water: ethanol and dried in an oven 60 °C.

Results and Discussion
All the prepared complexes in this work were insoluble in water and methanol but soluble in dimethylsulfoxide.Thus, the complexes are non-elctrolytes as the molar conductance is found to be in the range of 5.6-8.4ohm -1 cm 2 mol -1 in 10 -3 M in DMSO 8,[9][10][11] .The physical properties and elemental analysis are listed in Table 1

Electronic spectral studies
The electronic spectra of the free ligands The electronic spectrum of the benzotriazole in DMSO shows strong bands at 273 nm and 312 nm due to the electronic transitions π→π * and n→ π * respectively.The benzimidazole spectrum exhibited absorption bands at 275 nm which is caused by π→π * and another bands at 348 nm due to electronic transition of n→ π *12-13 .Finally, the spectrum of Ammonium thiocyanate shows the electronic transition of π→ π * and n→π * at 216 and 351 nm respectively.

[Mn(BT)(BI) 2 X 2 ]
The spectrum of light brown exhibited absorption band at 264 nm which belongs to the 6 A 1 g→ 4 T 1 g (G) .Another band appeared in the visible region at 634 nm which is assigned to 6 A 1 g→ 4 T 1 g (G) .The magnetic moment µ eff of the Mn(II) d 5 was 4.920 B.M, this value was in agreement with the expected value for spin only 14, .These rules are accepted for Mn +2 octahedral complexes 15 .

[Co(BT)(BI) 2 X 2 ]
The spectrum of dark green complex exhibited band at 272 nm due to the electronic transition 4 T 1 g (F) → 4 A 2 g (F) which corresponds to charge transfer C.T. Another band in the visible region at 539 and 760 nm, this may be attributed to the 4 T 1 g (F) → 4 T 1 g (P) and 4 T 1 g (F) → 4 T 2 g (F) respectively 15,16 .The value of µ eff of Co(II) d 7 complex was 4.561 B. M higher than the calculated value, this may be attributed to the orbital contribution 17,18 .All these values confirm that the formed Co(II) complex has octahedral geometry.

[Ni(BT)(BI) 2 X 2 ]
The spectrum of the gray complex d 8 shows strong band at 271 nm which may be attributed to the transition 3 A 2 g (F) → 3 T 1 g (P) which corresponds to the charge transfer.Another band noticed at 560 nm which is caused by 3 A 2 g (F) → 3 T 1 g (F) transition.The third band was observed at 649 nm due to 3 A 2 g (F) → 3 T 2 g (F) transition 19,20 .The value µ eff of Ni(II) d 8 was 2.602 B.M, this value was in agreement with the expected value 14, .Accordingly to the ligand field splitting energy 10Dq was found to be 15408.32cm -1 and the reaction inter electronic repulsion parameter B -was found to be 568.836cm -1 . These parameter values support an octahedral geometry for the Ni(II) complex 15,19,20 .

[Cu(BT)(BI) 2 X 2 ]
The octahedral Cu(II) complex was dark green, this color is an effective and shows the absorption bands in the visible region at 507 nm which is assigned to the 2 Eg (D) → 2 T 2 g (D).This transition is the characteristic for octahedral complex of Cu(II).Furthermore, the spin µ eff of Cu(II) complex d 9 was found to be 1.670 B. M within the expected value for one electron.
The diamagnetic of Cd(II) and Pb(II) complexes have shown absorption bands at 274 and 284 nm respectively.These bands may be attributed to the charge transfer M→L because of the electronic configuration of Cd(II) and Pb(II) which is confirmed the absence of any d-d transition.However, their spectrum suffered red shift with Hyper or Hypo chromic effect.The electronic spectral bands and the magnetic moments of the complexes are listed in Table 2.

Infrared spectra of the free ligands
The spectrum of the benzotriazole shows a weak band at 3247 cm -1 which belongs to ν(NH), another weak band was observed at 3078 cm -1 which is attributed to ν(C-H) aromatic [21][22][23] .Finally, the strong band belongs to ν(N=N) was found at 1500 cm -1 .The spectrum of benzimidazole exhibited broad band at 3150 cm -1 which is caused by ν(NH).A weak band noticed at 3040 cm -1 which is attributed to ν(C-H) aromatic, another weak sharp band appeared at 1640 cm -1 due to ν(C= N) 24 .The medium band belongs to ν(C=C) was found at 1605 cm -1 .The spectrum of thiocyanate ion shows a strong band at 2053 cm -1 which is assigned to ν(CN) and another band at 740 cm -1 was attributed to ν(CS) 25 .

Infrared spectra of complexes
The infrared spectra of the prepared complexes exhibited the following bands: ν(C=N) in the region of 1620-1630 cm -1 which was shifted to lower frequencies by 20-10 cm -1 compared with benzimidazole spectrum, which indicates that the coordination with metal ions was through nitrogen atom.Thus, the band appeared in the region of 1488-1496 cm -1 belongs to ν(N=N) in benzotriazole moved to lower frequencies by 12-4 cm -1 .Moreover, the spectra of the prepared complexes exhibited weak bands in the region of 550-570 cm -1 which is assigned to ν(M-N) which indicates that the coordination with metal ions was through the two nitrogen atoms 26 .
The coordination of SCN -ion through the nitrogen atom was confirmed by the bands in the region of 2067-2098 cm -1 which is shifted to higher frequencies 25 by 14-45 cm -1 .Furthermore, the spectra of the complexes shows weak bands between 424-460 cm -1 which is attributed to the δ (M-NCS).Table 3 gives the diagnostic absorption and their assignments.

H NMR spectra studies
The 1 H NMR spectrum of the benzotriazole shows singlet signal in 15.3 ppm which is attributed to the NH, this signal was appeared in the Cd(II) and Pb(II) complexes in 10.9 and 11.3 respectively.In addition, the spectrum of the ligand BT shows signals for 4H aromatic proton at: δ 8(H4), 7.59(H7), 7.29(H5) and 7.35(H6).However, these signals were shifted upfield in the complexes by 0.87-0.68ppm due to the H4 and H7 and by 0.17-0.05which are attributed to the H5 and H6 respectively [27][28][29] .The 1 H NMR spectrum of the benzimidazole shows single proton at 12 ppm which is attributed to the NH.This signal was shifted to the up field in both of Cd(II) and Pb(II) complexes by 1.1 and 0.7 ppm respectively.The appearance of NH group in both of the complexes which suggested that the coordination is impossible through the N1.Furthermore, the ligand BI shows signal protons at 7.50, 7.10, 7.24, 7.56 and 7.40 ppm which are attributed to the H4, H5, H6, H7 and H2 respectively.Hence, the distinct signals of H5 and H6 were appeared at high field and the signals of H4 and H7 can be obviously differentiated from H5 and H6.This is caused by the next neighbor of each proton from 1 H-1 H COSY experiment.Moreover, the signal proton of H2 was desheilded by 0.08-0.18ppm to the downfield δ in coordination complexes.This fact could be indicated that the benzimidazole was coordinated with the metal ions through the N3 atom [30][31][32] .The 1 H NMR spectra of the free ligands and their complexes were recorded in DMSO-d 6 and assignments of the peaks are listed in Table 4. ) and C2 respectively.On the complexes, only the signal due to the C2 was desheild to the downfield by 11.66-11.55ppm which is adjacent to the coordination site.Thus, the spectrum of the benzotriazole shows three signal protons at 139.80(C8,9), 128.30(C5,6) and 116.25(C4,7), because there are very strong overlap between (C8 and C9); (C5 and C6) and (C4 and C7) peaks.However, there is significant shift to the up field was observed on Cd(II) and Pb(II) complexes in C8,9 by 7.48-5.1 ppm.These signals support the involvement of N2 and N3 in complexation 28,29,32 .All the 13 C NMR chemical shifts (δ, ppm) are listed in Table 5.Table 5. 13

Conclusions
The new mixed ligand complexes of benzotriazole, benzimidazole and thiocyanate with some metal ions like Mn(II), Co(II), Ni(II), Cu(II), Cd(II) and Pb(II) were successfully prepared in this paper.
The molar conductance of these complexes was recorded in DMSO 10 -3 M solution and the result suggested that the products were non-electrolyte.The IR and ( 1 H, 13 C) NMR spectra suggested that the benzimidazole as a monodentate which was coordinated with the metal ions through the N3 atom.While the benzotriazole as a bidentate was coordinated with the metal ions through the N2 and N3 atoms.Moreovere, the definite geometries of the complexes were improved by the magnetic moment values and their electronic spectra.Thus, from the results presented the metal complexes have octahedral geometry for the Mn(II), Co(II), Ni(II), Cu(II) and Cd(II) complexes as can be seen in Figure . 1 and distorted octahedral for the Pb(II) complex as can be seen in Figure 2.

Table 2 .
Magnetic susceptibility and electronic spectra of the ligands and its complexes

Table 4 .
1H NMR chemical shifts (δ, ppm) of the free ligands and its complexes C NMR signals of the free ligands and its complexes in DMSO-d 6