Synthesis and Characterization of Complex Compounds of Tetra-aza Macrocyclic Ligand

This paper deals with the synthesis and characterization of a macrocyclic ligand (L) and its new-fangled complex compounds of the general formula [M-L Cl2] for M= Ru(III), and [M-L] for Pt(II) and Pd(II) where L is a macrocyclic ligand resulted from the condensation reaction of ethylene diamine and ethyl acetoacetate. The ligand and its coordination compounds are formulated according to the chemical analysis, electronic, infrared, HNMR and mass spectra, as well as magnetic susceptibility values.


Introduction
The coordination chemistry of macrocyclic ligands is a fascinating area of research.The synthetic, kinetic and structural aspects [1][2] of poly-aza macrocyclic complexes have received considerable attention and a variety of such systems have been synthesized [3][4][5][6][7][8][9] .The poly-aza macrocyclic complexes, particularly those of tetra-aza macrocycle along with the penta-aza and higher poly-aza macrocycles, have been widely studied in view of their potential for binding more than one metal ion [10][11][12] .The relationship of electronic properties and reactivity of these synthetic macrocyclic complexes to those of naturally occurring macrocycles, such as porphyrins 13 and corrins, continues to promote great interest in their design and preparation.
The aim of this work is the production of novel macrocyclic ligand and its ruthenium(III) platinum(II) and palladium(II) complexes by using simple condensation method (Scheme 1).Thus, macrocyclic ligand and its complexes are synthesized and characterized by using different techniques.

Experimental
All chemicals and solvents were reagent grade and used as received.C, H, N and M analyses were determined at the analytical unit of RSIC Chandigarh University, Chandigarh.IR spectra (as KBr pellets) were recorded (4600-400 cm -1 ) on a Perkin-Elmer 681 spectrophotometer.Electronic spectra in the 200-900 nm regions were recorded on a Perkin-Elmer 550 spectrophotometer.Mass spectra were recorded on Jeol SX-102(FAB), 1 H-NMR spectra were obtained with a Perkin-Elmer R32-90 MHz spectrophotometer using TMS as internal standard and DMSO-d 6 as solvent from CDRI, Lucknow.Magnetic susceptibility values were measured at 25 o C by the Gouy's method using mercury tetrathiocyanatocobaltate(II) as the magnetic standard.

Preparation of {M(II)-(L)-Cl 2 }
To the hot ethanolic solution of ligand (L) (0.01 m.mol, 0.2 g), hot ethanolic solution of metal chlorides [M-Cl 2 .xH 2 O; 0.5g, where, M= Ru(III),Pt(II) and Pd(II)] with few drops of hydrochloric acid was added.The solution mixture was then refluxed for 2h.On cooling, colored precipitates were then filtered and washed with cold water and dried in vacuum (Scheme 1).The analytical data are given in Table 1.

IR spectra
The preliminary identification of the macrocyclic ligand has been obtained from its IR spectrum, which shows the absence of uncondensed functional groups of ethylene diamine (i.e., stretching modes of starting materials) and suggests the formation of the proposed macrocycle.The appearance of strong absorption band in the region 1600-1650 cm -1 corresponds to υ>C=N stretching frequency (where, υ = frequency).A single sharp band observed for the ligand at 3300 cm -1 corresponds to υN-H of secondary >CO-NH group.The absorption bands in the region 2900, 2950 & 3000 cm -1 and 1380, 1460 & 1470 cm -1 in the ligand may reasonably, attributed to υC-H stretching and C-H bending vibration modes, respectively (Table 2).The red shift of the complex compounds for υ>C=N and υN-H modes are found in the regions 1590-1600 cm -1 and 3250-3280 cm -1 , respectively.However, the positions of these bands are consistent with those reported for the analogous complexes 14 .The negative shifts in υN-H mode along with the appearance of new bands in the region 450-470 cm -1 assignable to υM-N vibrations, suggest that the imide nitrogen is coordinating to the metal ions.The position of imide band, which does not undergo any change and the absence of a band attributable to υM-O [500-550 cm -1 ] vibrations indicate that the imide oxygen is noncoordinating.(Representative IR spectra of macrocyclic ligand and its representative coordination compound Pd(II) are given in the Figure 1).The 1 H NMR spectra of the macrocyclic complexes show multiplets in the region δ1.03 -1.36 and δ 2.15-2.64attributed to CH 3 (6H) protons and the methylene protons (4H) of acetoacetate moiety, respectively.The transition metal complex shows broad singlet at 8.23 for Pt (II) macrocyclic complex whereas, small singlet is observed for Pd (II) δ8.2 which is attributable to imide protons (2H).Singlets and multiplets observed in the region δ 3.03-δ 3.57 for macrocyclic complexes may possibly assigned to methylene protons (>CH 2 ) adjacent to nitrogen.The shift of the signals towards lower field is an identification of the coordination of macrocycle ( 1 H NMR spectrum of the macrocylic ligand [L] is given in Figure 2 and representative 1 HNMR spectrum of Pt(II) macrocyclic complex is given in Figure 3).

Mass spectra
The determination of molecular weight of macrocyclic ligand (L) and its transition metal complexes by mass spectra has been very useful in completing their characterization.The fragmentation patterns of the ligand and its representative complex are given in the schemes 2 and 3 and shown in the Figures 4 and 5

Electronic spectra
The electronic spectral band in case of ruthenium complex is not observed due to charge transfer.The magnetic moment value of Ru(III) macrocyclic complex is found to be in the range of 1.7-1.85B.M.which is paramagnetic and lower than the spin only value (1.9 B.M.).
The Pt(II) macrocyclic complex is found to be diamagnetic and have d 8 configuration implying a square planar geometry.Pd(II) macrocyclic complex 18 is also found to be diamagnetic in nature.

Conclusion
The present investigation deals with the synthesis and characterization of tetraaza macrocyclic ligand and its transition metal complexes.On the basis of various physicochemical studies, the nature as well as to some extent, structure and stereochemistry of macrocyclic ligand and its complexes have been suggested.

Figure 1 .
Figure 1.IR spectra of macrocyclic ligand and its complex [Pd-L] 1 H NMR spectra The 1 HNMR spectrum of the macrocyclic ligand shows triplet in the region δ1.10 -δ1.15 (where,δ= chemical shift) and singlet at δ 1.88 corresponding to CH 3 (6H) protons and CH 2 (4H) protons of acetoacetate moiety 15 , respectively.The 1 HNMR spectrum of [L] shows a broad signal observed at δ 8.53 that may be attributed to imide protons 16 (2H).A quartet that observed in the region δ 3.91-δ 3.98 and singlet at δ 4.35 possibly ascribed to methylene CH 2 (8H) protons 17 of diaminoethane moiety.The 1 H NMR spectra of the macrocyclic complexes show multiplets in the region δ1.03 -1.36 and δ 2.15-2.64attributed to CH 3 (6H) protons and the methylene protons (4H) of acetoacetate moiety, respectively.The transition metal complex shows broad singlet at 8.23 for Pt (II) macrocyclic complex whereas, small singlet is observed for Pd (II) δ8.2 which is attributable to imide protons (2H).Singlets and multiplets observed in the region δ 3.03-δ 3.57 for macrocyclic complexes may possibly assigned to methylene protons (>CH 2 ) adjacent to nitrogen.The shift of the signals towards lower field is an identification of the coordination of macrocycle ( 1 H NMR spectrum of the macrocylic ligand [L] is given in Figure2and representative 1 HNMR spectrum of Pt(II) macrocyclic complex is given in Figure3).

Table 1 .
Analytical data of tetra-aza macrocyclic ligand (L) and its complexes.

Table 2 .
IR spectral data of given tetraaza macrocyclic ligand (L) and its complexes.