PREPARATION AND CHARACTERIZATION OF SOME MIXED LIGAND COMPLEXES OF AMINO ACIDS AND ACID IMIDES

Abstract

The work embodied in this thesis is on the inter action of transition metal ions with organic ligands containing one or more salt forming groups e.g. (I) -C00H (II) -NH (III) -OH (IV) -SH etc The metal chelates of such ligands have been widely used in the medicinal, biolo gical, analytical and industrial fields. The studies aim at the preparation of such complexes and their characterization on the basis of various physico-chemical techniques. The ligands used are imides, amino acids, thiocarbamides and heterocyclic bases. A major portion of the thesis is devoted to the preparation of mixed ligand complexes and their characterization on the basis of chemical analysis, conductance, molecular mass determination, I.R., electronic spectra in solution, reflectance spectra and magnetic measurements. Detailed magneto-chemical analysis at varied temperatures, thermal analysis and powder X-ray diffraction studies of some of the complexes also constitute a part of the thesis. The thesis has been divided into three sections viz., A, B and C SECTION - A This section comprises of only one chapter dealing •with the characterization of the complexes formed by the interaction of potassium hexathiocyanatochromate(III) with ii some amino acids. Complexes of the type K[Cr(HCS)2A2] and K2[Cr(NCS)4X] where AH = leucine and isoleucine and XH = histidine, glutamic acid, tyrosine, nicotinic acid, methionine or asparigine; could be prepared in pure crystalline form and characterized on the basis of various physico-chemical studies. The values of 10 Dq were found between 16500 - 18500 cm"1. The magnetic moments of the complexes were in the range 3.65 - 4.20 B.M. which indicated an octahedral structure of the complexes. The values of B, Po^ and L.F.S.E. have also been calculated from the bands obtained in the electronic spectra of the complexes. Infrared spectra of the complexes indicated the coordina tion of thiocyanate through nitrogen while the amino acids were coordinated through the NH and carboxylic groups. The values of p35 (about 0.7) confirmed the presence of e good degree of covalency in the metal-ligand bonds. The ligand field strength of amino acids was found in the order : nicotinic acid < glutamic acid < tyrosine < histidine < isoleucine «=> leucine < methionine s*£ asparagine. SECTION - B This section comprises of two chapters : Chapter - I : In this chapter are incorporated the studies on the preparation and characterization of mixed ligand complexes of cobalt(Il), nickel(Il), copper(Il), palladium(Il) and platinum(Il) with phthalimide as primary and some iii N-aryl-^I1 -benzoylthiocarbamides [N-phenyl-^' -benzoylthiocarbamide; N-(m-tolyl)-N' -benzoylthiocarbamide; N-(m-chlorophenyl)-N! -benzoyl thio carbamide; N-(2,5-dichlorophenyl) -N1 -benzoylthio carbamide and N-( o-chlorophenyl) - N' -benzoylthio carbamide] as secoKd.?ry ligands. Complexes of the type [M(Phth.)2(L-L) j and [Mf (Phth.) 2(L-L) (H20) 2] , where N- Cu(Il), Pd(Il), Pt(II), Co(Il); M'=Ni(Il); Phth. = deprotonated phthalimide and L-L = different N-N'-disubstituted thiocarbamides, were isolated in solid form and characterized. The non-electrolytic nature of the complexes was confirmed from the conductance measurements. I.R. studies indicated the coordination of the phthalimide through nitrogen end those of the thiocarbamides through sulphur and oxygen of the carbonyl group forming a chelate ring. The magnetic moments around 4.50 B.M. in the case of cobalt(Il) complexes indicated their tetrahedral structure. Their electronic spectra gave two bands at 7600(0 and 17900( O corresponding to the transitions 2 -j 4A —) 4T (F) end 4. —9 4TX(P) respectively. The values of 10 Dq, B and p -were also calculated which also revealed their tetrahedral geometry. The magnetic moment of 2-10 B.M. and the presence of three bands at 14000, 15000 and 34800 cm"1 in the electronic spectra of copper(Il) complexes were indicative of tetragonelly distorted sequare planar geometry of the complexes. The bands were assigned as: 2-a - 2 2„ » 2_ and charge transfer respectively. In case of nickel(II) complexes, the magnetic moments of about 2.80 B.M. were lower than predicted for octahedral IV or tetrahedral geometries. The observed band energies were not found in agreement with the calculated ones considering the octahedral geometry. Hence it was concluded that the complexes were a mixture of paramagnetic octahedral and diamagnetic square planar molecules. Their electronic spectral bands were assigned as : B1-^ Ea(l2000 cm"1), ^-^B^ A2(13000 cm"1), Bj_—^E (21500 cm*"1) and B1—^A1(31000 cm"1). The diamagnetic behaviour of the Pd(ll) and Pt(II) complexes indicated their square planar structure. The electronic spectral bands of Pd(II) complexes were assigned as lAir^Eu(38000 cm"1)» 1hr—* ""E (30000 cm"1), • 1 -i ° 6 Alg • Bj_ (22500 cm" ) whereas the bands of Pt(ll) complexes were corresponding to the transitions lAlg—* 1A2u(40000 cm"1), 1Alg—> ^(39000 cm"1) and A1|—» Blu( 35000 cm"1). The values of A]_, *2 and a3 have also been calculated for these Pd(II) and Pt(ll) complexes. Chapter - II : This chapter has described the preparation and characterization of mixed ligand complexes of cobalt(Il) and nickel(Il) with phthalimide or succinimide as primary and some heterocyclic bases (quinoline, isoquinoline, morpholine, 2-aminopyridine, 8-hydroxyquinoline, acridine, 2-picoline and piperidine) as secondary ligands. The infrared spectra revealed the coordination of the deprotonated imide molecule through nitrogen and that of the heterocyclic bases through their respective hetero nitrogen atom. 8-hydroxyquinoline acted as bidentate and coordinated with the metal ion through nitrogen and the deprotonated phenolic oxygen atom. The magnetic moments of the nickel(ll) complexes were in the range 2.98 - 3.64 B.M. which indicated an octahedral structure of the complexes. The three observed bands in the electronic spectra were assigned due to the transitions A^(F)—> T2 (F) (8200-9000 cm"1) C"^)} 3A2 (F)—fr3"^ (F) (14000-16000 cm"1) {v2) and 3A2g(F)—i\ (P) (26000-28300 cm"1) (v3). The calculated band energies of v2 and y3 transitions were found in close agreement with the observed values. The magnetic moments at cryogenic temperatures also confirmed 'A' ground term of the metal ion in these complexes of nickel(Il). The magnetic moment values in the range 4.81 - 5.08 B.M. in the case of quinoline, isoquinoline, 2-aminopyridine, acridine and 2-picoline complexes of Co(II) indicated their octahedral structure. The observed bands in their electronic spectra were assigned as : 4T1 (F) fr^gJ 14600 - 16100 cm"1) (*2) and 4T (F) »4lig(p) (17200-18400 cm"1) (v3) • In case of morpholine, 8-hydroxyquinoline and piperidine complexes of Go(Il), the room temperature magnetic moments were in the range 4.33 - 4.63 B.M. which indicated their tetrahedral structure. Two bands corresponding to the 4k ,„s ^4r transitions A2 (F)—> Tig(p) (^3) 8nd charge transfer respectively, were obtained at^as: 24000 cm" andc=:3000( The higher c values of the main band of these complexes vi and independence of magnetic moments with temperature also confirmed their tetrahedral structure. SECTION - C This section also comprises of two chapters. Chapter - I : This chapter is devoted to the studies on the antiferromagnetically coupled dimeric complexes of 8-quinolinol with copper(ll) imides. Complexes of the type [Cu(Im)(Q)]2 where Im = deprotonated phthalimide or succinimide and HQ = 8-hydroxyquinoline,could be prepared in well crystalline form and characterized on the basis of different physico-chemical^studies. The observed molecular masses of the complexes indicated their dimeric nature. From I.R. spectra it was concluded that the deprotonated imides were coordinated to the metal ion through nitrogen whereas 8-hydroxyquinoline acted as bidentate ligand. The deprotonated phenolic oxygen of 8-hydroxyquinoline formed a bridge between two metal centres. Detailed analysis of magnetic susceptibilities at different temperatures indicated the presence of antiferromagnetism in these complexes. The susceptibility data at different temperatures were fitted to the Bleaney- Bowers equation which gave best fit parameters as : 2J = -136 cm"1 and -128 cm"1 ; g = 2.18 and 2*16 for the phthalimide and succinimide complex respectively. The complexes did not obey Curie~Wiess law at lower temperatures. vii Curie-Weiss constants calculated for higher temperature range were found to be C = 0.525 and 0.515 and 0 = 134 and 126° respectively for these two complexes. Powder X-ray diffraction patterns of the complexes could be indexed for tetragonal crystal system, which can accommo date square planar or tetrahedrel molecules very well. Observed densities of 2«10 and 1.05 indicated the presence of four molecules per unit cell. Electronic spectra of the complexes gave a band atr-:- 14000 cm" which is at lower energy than those of the square planar monomeric complexes of copper(Il) with the present ligands, in which this band appears at =a* 15000 cm"1. This red shift in the dimeric species and the presence of only one band has confirmed the tetrahedral distortion in the square planar geometry and the trans-structure of the complexes. One more band of high intensity at 25000 cm"1( e s=s 8800) may be due to the combined effect of L—*•* M charge transfer and intraligand transitions, a characteristic feature of oxo-bridged copper(II) complexes. Chapter - II : This chapter has accommodated the studies on the linear magnetic chains with anisotropic coupling in the complexes of some heterocyclic bases with copper(II) imides. Complexes of the type [Cu(Im)2(Hb)2(H20)].xH20 where Im = deprotonated phthalimide or succinimide; Hb = quinoline, isoquinoline, 2-aminopyridine, acridine or 2-picoline and x = 1.5 or 2, were synthesized and viii characterized. Thermal analysis revealed the presence of lattice as well as coordinated water. It has been found from their I.R. studies that coordination of the deprotonated imide occurred through nitrogen whereas that of heterocylic bases through the hetero nitrogen atom. It also gave an evidence of the formation of water bridges in the complexes. The magnetic data in the temperature range 50 - 300°K reflected the presence of linear chains of antiferromagnetically coupled copper(Il) ions bridged by water molecules. The values of exchange integral and 'g' were evaluated and discussed in terms of anisotropic Ising-Heisenberg Hamiltonian. .fi N 9t= -2J I [S±z Si+1z + y(S±x Si+1x + Siy S±+1y)3 for infinite chains. Analysis of the results revealed that the isotropic Heisenberg as well as anisotropic Ising model were equally applicable in these systems and the inter-chain interactions were practically negligible in comparison to the inter-dimer interactions. From the X-ray powder diffraction data the presence of tetragonal unit coll and 2 or 4 stoichiometric species per unit cell were confirmed. The electronic spectra gave a broad band in the region 17500 - 18000 cm with a shoulder on lower energy side. These were resolved into three gaussian components. On the basis of position and intensity of the band of highest energy the geometry of the complexes was confirmed to be D4, and the resolved bands were assigned (in the order of ix increasing energy) as : \g~> \g ;\^ \g and g^- > Eg. Another band at about 27000 cm"1 might be either due to the dimeric nature of the complexes or charge transfer transitions.