SYNTHESIS AND CHARACTERIZATION OF NOVEL FOUR HETERODIMETALLIC MIXED METAL COMPLEXES OF 2,6-PYRIDINEDICARBOXYLIC ACID

Four novel hetero dimetallic mixed metal complexes of 2,6-pyridinedicarboxylic acid (H2dipic), [Ni(H2O)5Co(dipic)2] (1), [Co(H2O)5Co(dipic)2][Ni(H2O)5Ni(dipic)2][Co(dipic)(H2O)3] (2), [Cu(H2O)5Ni(dipic)2]2[Co(dipic)(H2O)] (3) and [Ni(H2O)5Cu(dipic)2]2[Co(dipic)(H2O)] (4) have been prepared and characterized by elemental, AAS, spectral (IR and UV-Vis), and thermal analyses, as well as by using magnetic measurement and molar conductivity techniques. The results indicate that metal ions coordinate with 2,6-pyridinedicarboxylate ions (dipic) nitrogen atoms and carboxylate oxygen atoms of ligands. The mole ratio of dipic and metal ions in the complexes have been determined to be 2:2 (Co, Ni) for 1, 5:5 (3Co, 2Ni) for 2, 5:5 (Co, 2Ni and 2Cu) for 3 and 5:5 (Co, 2Ni and 2Cu) for 4 according to the results of elemental analysis. The structures of 1-4 might be proposed as octahedral ([Cu(dipic)(H2O)] unit for 2 square plane) according to results of spectroscopic analysis. The TG and DTA properties of compounds have been studied.

In  (4) have been prepared and characterized by elemental analysis (CHNS), AAS, spectral (IR and UV-Vis.), and thermal analyses, as well as by using magnetic measurement and molar conductivity techniques.

General methods and materials
All chemicals used were analytical reagents and were commercially purchased from Aldrich. Elemental analyses for C, H and N were performed on Elementar Vario III EL and Co, Ni and Cu were detected with Perkin Elmer Optima 4300 DV ICP-OES. FT-IR spectra were recorded in the 4000-400 cm -1 region with Bruker Optics, Vertex 70 FT-IR spectrometer using ATR techniques. Thermal analyses were performed on Pelkin Elmer SII Exstar 6000 TG/DTA 6300 model using platinum crucible with 10 mg sample. Measurements were taken in the static air within a 30-900 ºC temperature range. The UV-Vis spectra were obtained for DMSO solution of the compounds (10 -3 M) with a SHIMADZU UV-2550 spectrometer in the range of 200-900 nm. Magnetic susceptibility measurements at room temperature were performed using a Sherwood Scientific Magway MSB MK1 model magnetic balance by the Gouy method using Hg[Co(SCN) 4 ] as calibrant. The molar conductance of the compounds were determined in water/ethanol (1:1) and in DMSO (10 -3 M) at room temperature using a WTW Cond 315i/SET Model conductivity meter.

Synthesis of 1-4
A solution of 1 mmol (0.249 g) Co(CH 3 COO) 2 .4H 2 O and 2 mmol H 2 dipic (0.334 g) in water (30 mL) with stirring at room temperature for two hours was added dropwise to the solution of 1 mmol (0.248 g) Ni(CH 3 COO) 2 .4H 2 O in water (20 mL) with stirring at room temperature for two hours to complete the reaction. On filtration the reaction mixture, the solution was kept at room temperature for two weeks to give brown amorphous solid for 1 (0.377 g, 70% yield).
A solution of 1 mmol (0.248 g) Ni(CH 3 COO) 2 .4H 2 O and 2 mmol H 2 dipic (0,334 g) in water (30 mL) with stirring at room temperature for two hours was added dropwise to the solution of 1 mmol (0.249 g) Co(CH 3 COO) 2 .4H 2 O in water (20 mL) with stirring at room temperature for two hours to complete the reaction. On filtration the reaction mixture, the solution was kept at room temperature for two weeks to give brown amorphous solid for 2 (0.266 g, 50% yield).
A solution of 1 mmol (0.248 g) Ni(CH 3 COO) 2 .4H 2 O and 2 mmol H 2 dipic (0.334 g) in water (30 mL) with stirring at room temperature for two hours was added dropwise to the solution of 1 mmol (0.200 g) Cu(CH 3 COO) 2 .2H 2 O in water (20 mL) with stirring at room temperature for two hours to complete the reaction. On filtration the reaction mixture, the solution was kept at room temperature for two weeks to give green amorphous solid for 3 (0.346 g, 65% yield).
A solution of 1 mmol (0.200 g) Cu(CH 3 COO) 2 .2H 2 O and 2 mmol H 2 dipic (0.334 g) in water (30 mL) with stirring at room temperature for two hours was added dropwise to the solution of 1 mmol (0.248 g) Ni(CH 3 COO) 2 .4H 2 O in water (20 mL) with stirring at room temperature for two hours to complete the reaction. On filtration the reaction mixture, the solution was kept at room temperature for two weeks to give turquoise amorphous solid for 4 (0.400 g, 75% yield).
Suggested structures of the compounds (1-4) are shown in Figure 1.

RESULTS AND DISCUSSION
The infrared spectral data of the starting compound (H 2 dipic) and compounds 1-4 are given in Table 1. In the high frequency region, weak bands 3067-3098 cm -1 are attributed to the stretching vibrations of aromatic C-H for all compounds. There are also broad absorption bands at 3493-3474 cm -1 , which are attributed to the ν(OH) vibrations of water molecules for compounds 1-4. The carboxylate groups for compounds H 2 dipic and 1-4 exhibit strong carbonyl bands in the region of 1701-1456 cm -1 .  (Table 1).   Table 2. For all compounds (1-4), the first stage, an endothermic peak corresponds to the loss of water molecules, namely five moles for 1, thirteen moles for 2, eleven moles for 3, and eleven moles for 4. The exothermic second stage is consistent to the loss of dipic molecules, namely two moles for 1, five moles for 2, five moles for 3, and five moles for 4. The final decomposition products are CoO and NiO for 1, CoO and NiO for 2, CuO and NiO for 3, and CuO and NiO for 4, and they are identified by IR spectroscopy ( Table 2).

CONCLUSION
In the present work, four newly compounds (1-4) were prepared for the first time. The structures of 1-4 might be proposed as octahedral ([Cu(dipic)(H 2 O)] unit for 2 square plane) according to results of elemental, spectral, thermal analyses, magnetic measurement and molar conductivity.