Synthesis and Characterization of new Binuclear Chromium , Cadmium Complexes based on Terpyridine and Phenanthroline

In this research, four binuclear complexes:[(phen)Cd(NO3)2(μ-phen-dion)Cr(NO3)2(phen)] (NO3)2, [Cr(4-Ptpy)(μ-phen-dion)](NO3)[Cd(4-Ptpy)(μ-phen-dion)](NO3),[Cr(4-Ptpy)(μ-phen-dion)] (NO3)Cr(4-Ptpy)(μ-phen-dion)](NO3), and [Cd(4-Ptpy)(μ-phen-dion)](NO3) [Cd(4-Ptpy)(μ-phen-dion)] (NO3) were synthesized using reaction of chromium(III) nitrate nonahydrate, cadmium (II) nitrate tetrahydrate, phendion, and 4-phenylterepyrydine. The complexes were characterized using FT-IR spectroscopy, UV-Vis spectroscopy, 1H NMR, elemental analysis, and cyclic voltammetery (CV). These complexes were found to be binuclear coordination complexes. The chromium and cadmium centers were achieved hexacoordination by coordinating with 4-phenylterepyrydine groups, as tridentate chelating ligands and phendion as bidentate chelating ligands. keywords: Binuclear complex, Phendion, chromium, Cadmium, and terpyrydine.


INTROdUCTION
Oligopyridines and their metal complexes have gained extensive attention in the last decades 1 .The materials including the metal-coordinated 2,2':6',2''-terpyridines (tpy) with spacers at C(4') have opened up new opportunities for various applications in electronics, catalysis, energy, and medicine due to their electron transfer properties 2 .The role of metal ions in the structure and function of binuclear complexes is essential, yet often unknown at the mechanistic and molecular level 3 .The hypotheses about principles governing selectivity and specificity of oligopyridines for a given bridged metal are often based on theoretical assumption.
An attractive metal-binding ligand is tpy which has an exceptionally well understood coordination chemistry.Many substitutions at C(4') directly linked to the pyridine ring, such as hydroxyl, 4 chloro, 5 bromo, 6 methylthiol, 7 methylsulfonyl, 8 dimethylamino, 9 and phenyl have been prepared.
Recently, many efforts have been performed in the synthesis and characterization of the binuclear complexes [10][11][12][13] .The bridged dinuclear complexes, in which the two metal centers are coupled each other in a conjugated system, are shown to be promising materials for new molecular electronic or magnetic materials [14][15][16][17][18][19] .Therefore, it is very important to investigate the synthesis and properties of these binuclear complexes.Hence, we decided to synthesize new binuclear complexes that can use as semiconductors.

Materials and physical techniques
All synthetic work was performed at 60°C.The water was distilled and deionized.Cr(NO 3 )3.9H 2 O, Cd(NO 3 )2.4H 2 O, phendion, 4-phenylterpyridine were purchesed from Merck Chemical Co.FTIR spectra were recorded as KBr pellets on a FT-IR JASCO 460 spectrophotometer and the UV-Vis spectra were taken at room temperature on a JASCO 7850 spectrometer.Cyclic voltammetry was performed at 20°C in an DMF solution with 0.1M TBAH as a supporting electrolyte at scan rate 100 mV s -1 .1H NMR spectra were recorded on a Bruker AM 300 MHz spectrophotometer.

Synthesis of [(4-Ptpy)Cr(NO 3 ) (µ-phen-dion) Cr(NO 3 )(4-Ptpy)](NO 3 ) 4
To an aqueous solution containing chromium nitrate (1 mmol), phendion in ethanol (1 mmol) was added slowly and then the mixture was stirred at 60°C about 48 hours.After that, additional chromium nitrate (1 mmol) was then added to the solution and was stirred at the same temperature.Following After 24 h, 2 mmol of 4-Ptpy was added dropwise to the aqueous solution with continuous stirring for 3 days.Finally, solution filtered off and left to evaporate in beaker in air at room temperature, and green color crystals were formed.FT

RESULTS ANd dISCUSSION
The reaction of 4-Ptpy and phendion as ligand with chromium(III) nitrate nonahydrate, and cadmium(II) nitrate tetrahydrate result in the formation of four binuclear complexes.The FT-IR spectra of the [(4-Ptpy)Cr(NO 3 )(μ-phen-dion) Cr(NO 3 )(4-Ptpy)](NO 3 ) 4 shows absorption bonds at 1300 -1 400 cm -1 that it is related to the coordination of carbonyl groups of the phendione ligand to the metal.The peaks at 419 and 451 cm -1 are assigned to the vibration of Cr-N and Cr-O bonds [20][21] .The characteristic band of [(phen)Cd(NO 3 )2(μ-phen-dion) Cr(NO 3 )2(phen)](NO 3 ) 2 is the peak at 1400-1650 cm -1 that is attributed to the phenanthroline ligand.The peaks at about 434 and 590 cm -1 are related to the Cd-N and Cd-O bonds, confirming the formation of the binuclear complex.The peaks of C=C and C=N stretching modes at about 1585 and 1505 cm -1 , respectively, are moved to 1571 and 1500 cm -1 .
The UV-Vis absorption spectra of complexes in mixed solution (ethanol and water) is shown in Fig. 1a-b.The spectra exhibit characteristic π→π* and n→π* (phenanthrolin and terpyridine) in the 263 and 309 nm.As observed in the fig, the peak at 570 nm is attributed to the charge transfer of Cr [22][23][24] .
Cyclic voltammetry was done in an DMF with 0.1M TBAH as a supporting electrolyte at scan rate 100 mV s -1 (Fig. 2a-c).In this voltammogram, two reversible oxidation-reduction and two irreversible reduction couples peaks at -1.2 to -1.6 V are assigned to the 4-Ptpy ligand [25][26] .The peaks of -1.6 to -0.9 could be assigned to phendion ligand and Cr metal [27][28] .The region between 0 and -1 might be related to phendion and 4-Ptpy ligands.In this voltammogram, two quasi-reversible reduction couples at 0 and -1 V are assigned to the reduction of to phendion and 4-Ptpy ligands.In comparison with free ligands, the reduction couples shift to more positive potentials due to the coordination of ligands to the Cd center (Fig. 2c).Also, the figure showed no d-d electron transition for the Cd metal.The 1 H NMR spectra of complexes were obtained in DMSO-d 6 as shown in Fig. 3.The peaks at 7-9 ppm were assigned to the aromatic compounds [29][30] .The hydrogens of the ligands were observed as doublet and triplet peaks.The peaks of spectra were broad, due to the paramagnetic characteristic of chromium metal [31][32] (Figure 3).
Elemental analyses of the complexes were obtained,The values confirmed the successful syntheses of the bi-nuclear complexes.

CONCLUSION
Binuclear Cr(III) and Cd(II) complexes containing 4-phenylterpy and phenathroline ligands were synthesized conveniently and characterized by the various techniques.The complexes can further study and apply as semiconductors.