SYNTHESIS AND CHARACTERIZATION OF 16, 17MEMBERED TETRA AZA MACROCYCLIC COMPLEXES

Received: 06 January 2017 Final Accepted: 02 February 2017 Published: March 2017 Oxo tetra aza macrocylic transition metal complexes [M(C15H25N5O)Cl2] or [M(C16H27N5O)Cl2]; M= Co(II), Ni(II), Cu(II) and Zn(II) have been synthesized by the template condensation reaction of Oamino benzoic acid, triethylene tetramine, and 1,3dibromo propane or dibromo methane in methanol medium. All the complexes have been characterized on the basis of elemental analysis, IR, NMR, EPR, UVvis, conductivity and magnetic moment data. All the complexes are non ionic in nature and exhibit an octahedral geometry. Copy Right, IJAR, 2017,. All rights reserved.


Results and Discussion:-
The template condensation reaction of triethylene tetraamine, oaminobenzoic acid and dibromo alkane resulted in the formation of macrocyclic complexes as shown in Scheme I. All these compounds were obtained as polycrystalline solids. They are freely soluble in dimethyl sulphoxide, dimethylformamide and acetonitrile. The results of elemental analysis are consistent with their proposed 1:1 (metal to ligand) stoichiometry . All the complexes exhibited low molar conductivity values in DMSO (1320 ohm 1 cm 2 mol 1 ) which support (17) the nonionic nature of these compounds.

IRStudies:-
The IR spectra of all the complexes exhibited a single sharp band in the region 32503270 cm 1 which may be assigned to coordinated NH stretching vibration. This information together with the appearance of four bands in the ranges 16801710, 15301570, 12501260 and 650670. cm 1 assignable (18) to amide I (C=O); amide II (CN +  NH), amide III ( NH) and amide IV ( C=O) bands respectively, suggests the formation of the proposed macrocyclic framework. The absorption bands appearing in the region 28802930 and 14101460 cm 1 in all the ligands may reasonably be assigned to the CH stretching and CH bending vibrational modes, respectively. The appearance of a low medium intensity band in the region 410450 cm 1 assignable to (MN) further confirms the involvement of nitrogen in coordination. However, no complex gave bands assignable to primary amines or carboxylic acid groups.

NMRStudies:-
The 1 H NMR spectra of zinc macrocyclic complexes showed a multiplet, in the region 8.418.56 ppm which can be assigned (19) to amide (NHCO) protons. This clearly shows that the condensation of oaminobenzoic acid and triethylene tetraamine, has indeed taken place. A multiplet appearing in the region 3.353.61 ppm may be ascribed to the methylene protons (CONCH 2 ). The complexes showed a multiplet in the region 6.987.26 ppm corresponding to the phenyl ring protons. Another multiplet observed for all the complexes in the region 2.582.60 ppm may be assigned to the methylene proton between the nitrogen atoms (CH 2 N). The spectra of all the complexes showed multiplet in the region 6.216.40 ppm which corresponds (20) to the secondary amino protons (CNH). No compound exhibited signal corresponding to the carboxylic or secondary amino protons, which supports the proposed structure shown in Scheme 1.

EPRStudies:-
The EPR spectra of polycrystalline copper(II) macrocyclic complexes at room temperature show a single band with g || and g  values 2.24, 2.30 and 2.13, 2.09 respectively. None of the complexes exhibited hyperfine splitting which may be due to the fact that the paramagnetic centres are not diluted. The existence of g || > g  values 2.24, 2.30 and 2.13, 2.09 respectively. None of the complex exhibited hyperfine splitting which may be due to the fact that the paramagnetic centres are not diluted. The existence of g || > g  suggests (21) that dx 2 y 2 is the ground state. The g values are related to the axial symmetry parameters, G by the following expression, G=(g || 2)/(g  2). The G values measure the extent of exchange interaction between copper centres in the polycrystalline solid. If G >4, exchange interaction is negligible, and if G <4, considerable exchange interaction exists in the solid complexes (22) . In the present case, G values were found to be 1.85 and 3.33. 1026

Electronic Spectral Studies:-
The electronic spectra of cobalt complexes exhibited two ligand field bands in the ranges 1380014000 and 2220022300 cm 1 which are assignable (23,24) to 4 T 1g (F)  4 A 2g (F) and 4 T 1g (F)  4 T 1g (P) transitions respectively in an octahedral geometry (25) . The appearance of two bands in the electronic spectra of nickel complexes in the ranges 1155011600 and 1750017650 cm 1 may be assigned (25) to 3 A 2g (F)  3 T 1g (F) and 3 A 2g (F)  3 T 1g (P) transitions, respectively suggesting an octahedral geometry for Ni 2+ complexes. The electronic spectra of copper complexes exhibited two welldiscernible bands in the ranges 1640016700 and 1880019100 cm 1 assignable (2628) to 2 B 1g  2 B 2g and 2 B 1g  2 E 2g transitions, respectively which are characteristic of an octahedral geometry. The high intensity bands observed around 37000 cm 1 for all the complexes in the ultraviolet region of the spectra may be assigned as metal to ligand charge transfer transitions. The magnetic moment data (Table 1) for all the complexes are consistent with the high spin octahedral geometry around these metal ions which further supports the electronic spectral results. (2931)