Synthesis and Study of Mixed Ligand-Metal Complexes of 1, 3, 7-Trimethylxanthine and 1, 3-Dimethyl-7H-purine-2, 6-dione with Some Other Ligands

This work presents synthesis and study of a new mixed ligand metal complexes of 1,3,7-trimethylxanthine and 1,3-dimethyl-7H-purine-2,6-dione with some other ligands like SCN and OCN ions to give the general formula [M(Tx)2(Tp)2XY] where M=Co(II), Ni(II), Cu(II), Zn(II) and Cd(II), Tx=1,3,7trimethylxanthine, Tp= 1,3-dimethyl-7H-purine-2,6-dione, X= SCN and Y= OCN. The resulting products were found to be solid which have been characterized using UV-Visible and infrared spectroscopy. Elemental analyses were performed using C, H, N analysis and atomic absorption techniques. The magnetic susceptibility and the conductivity were also measured. The present results suggest that the 1,3,7-trimethylxanthine and 1,3-dimethyl-7H-purine2,6-dione were coordinated with metal ions through the nitrogen atom. Thiocyanate ion was coordinated with metal ions through the sulfur atom and the cyanate ion was coordinated with metal ions through the oxygen atom.


Introduction
The purine bases (constituents of the nucleic acids) are playing an important role of biological activity.In last few years the interaction of metal ions with nucleic acids has been very active area of inorganic and structural chemistry 1 .Thus, methylxanthine derivatives as possible inhibitor leads are also used therapeutically as anti-inflammatory agents, considered corrosion inhibition capability and they have significant efficiency as a non-toxic.Moreover, these derivatives are competitive inhibitors against a fungal family 18 chitinase.The enzyme assays has also revealed that these methylxanthines are active against human chitinases [2][3][4] .The early studies indicated that the 1,3,7-trimethylxanthine ingestion could result in both increase and decrease in different individuals but more recent studies have confirmed the average increased delta activity with 1,3,7-trimethylxanthine. Thus, some studies were evaluated the possibility of the synergistic effects of the selected antibiotics with 1,3,7trimethylxanthine against Staphylococcus aureus 5 .
The study of metals coordination with the purines reveals in vitro the mechanism of their coordination with DNA 6 .The most studies on complexes have shown that the unsubstituted purines normally coordinated to the metals via imidazole nitrogen atom 7 .In this work, the interaction of 1,3,7-trimethylxanthine and 1,3-dimethyl-7H-purine-2,6-dione with metal ions Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) is investigated.

Experimental
All chemicals were obtained from commercial sources and were used without further purifications (CoCl 2 .6H 2 O, NiCl 2 .6H 2 O, CuCl 2 .2H 2 O, ZnCl 2 , Cd(NO 3 ) 2 .4H 2 O, KOCN and KSCN) from Riedeal-Dehaenage.1,3,7-trimethylxanthine and 1,3-dimethyl-7H-purine-2,6dione were obtained from BDH, methanol, ethanol and dimethylsulfoxide from Fluka.The I.R spectra in the range of 4000-400 cm -1 were recorded as potassium bromide disc on a Shimadzu FTIR-8300 Fourier transform infrared spectrophotometer.UV-Visible spectra were measured in dimethylsulfoxide (DMSO) using Shimadzu UV-Visible recorder spectrophotometer UV-160.Elemental analysis (C, H, N) was performed by the micro analytical unit on a Berkin Elemer B-240 Elemental Analyzer.Determinations for metals were carried out using gravimetric methods.Conductivity measurements were carried out at 25 o C in DMSO using Philips Pw-9526 digital conductivity meter.Melting point was determined using a Stuart-Melting Point Apparatus.The magnetic susceptibility measurements were eventually obtained using a Balance Magnetic Susceptibility Balance Model MsB-MK1.

Results and Discussion
Elemental analysis and melting point data obtained were in good agreement with the values calculated from the proposed empirical formula.The lower value observed of molar conductivities in DMSO indicates the non electrolyte behavior of the complexes 8 .Table 1 gives in details of the physical properties of the complexes.

Infrared spectra of free ligands
The spectrum of (Tp) shows strong bands at 3350, 1720 and 1668 cm -1 that may be attributed to the ν(NH), ν(C=O) and ν(N=C) respectively.In addition, on complex formation the band of C=N is shifted to the lower frequencies by 68-28 cm -1 .The spectrum of (Tx) exhibited a strong band at 1658 cm -1 which is attributed to the ν(N=C) is also shifted to lower wave number by 58-18 cm -1 , all these shifted indicate that the (C=N) group is involved in complex formation.Furthermore, the spectra of the complexes exhibited weak bands between 500-545 cm -1 due to ν(M-N).This indicates the coordination of Tx and Tp with metal ions through the nitrogen atom [9][10][11][12] .The asymmetrical and symmetrical vibrations in OCN -were noticed at 2165 cm -1 and 1207 cm -1 respectively in the spectra of free ligand.These bands have already shifted to the higher frequencies by 35-75 cm -1 and 7-18 cm -1 respectively.Thus, the spectra of the complexes show bands in the range of 560-580 cm -1 which indicated that the cyanate ion was coordinated with the metal ions through the oxygen atom [13][14][15] .
The potassium thiocyanate spectrum showed a very strong band at 2048 cm -1 which belongs to the ν(CN).This band appeared in the complexes between 2050-2140 cm -1 which is shifted to the higher frequencies by 2-92 cm -1 .Thus, the complexes exhibited weak bands between 415-440 cm -1 which are due to δ(M-SCN).Therefore, the SCN -was coordinated with metal ions through the sulfur atom 14,16 .Table 2 gives the diagnostic absorptions and their assignments.

Table 2. The characteristic infrared absorptions of the prepared complexes
found to be closer to that of spinning only 17 .The complexes of Zn 2+ , Cd 2+ were diamagnetic as expected from their electron configuration.The magnetic susceptibility data are presented in Table 3.

The electronic spectra of the complexes
The Co(II) complex shows electronic transitions of 4 T 1 g (F) → 4 A 2 g (F) at 280 nm, 4 T 1 g (F) → 4 T 1 g (P) at 429 nm and 4 T 1 g (F) → 4 T 2 g (F) at 904 and 990 nm respectively.The electronic spectrum of Ni(II) complex exhibited absorption bands at 284 nm and 389 nm which are attributed to the electronic transitions 3 A 2 g (F) → 3 T 1 g (P) and 3 A 2 g (F) → 3 T 1 g (F) respectively.It is also appeared in the visible region bands at 807 and 986 nm respectively which are attributed to the electronic transition as 3 A 2 g (F) → 3 T 2 g (F).The Cu(II) complex exhibited band in the visible region which is attributed to the electronic transition 2 Eg→ 2 T 2 g which splitted into two bands as 2 b 2 g (D) → 2 b 1 g (D) and 2 eg (D) → 2 b 1 g (D) at 567 and 777 nm respectively 19 .Finally, Zn(II) and Cd(II) complexes with an electronic configuration of (d 10 ) did not show any (d-d) transitions.Instead the absorption bands in the spectra were due to charge transfer transitions which suffered from red and blue shift with hyper chromic effect [19][20][21] .These absorptions were fully assigned in Table 4. Table 4. UV Visible spectra of free ligands and their complexes 10
The molar conductivity of complexes in DMSO solution was non-electrolyte.However, the configuration of the complexes was confirmed that the Tx and Tp were coordinated with metal ions through the nitrogen atom, while, the metal ions were coordinated with SCN - through the sulfur atom.However, the OCN was coordinated with metal ions through the oxygen atom.Therefore, it can be concluded from the presented results that the complexes have octahedral configuration, as shown in Figure 1.

Table 1 .
The physical properties of the prepared complexes

Table 3 .
The magnetic properties of the complexes at 25 ºC