PHYSICO-CHEMICAL STUDIES ON SOME MONOXIME COMPLEXES AND THEIR MIXED LIGAND CYANIDE AND THIOCYANATE COMPLEXES

Abstract

Oximes are well defined crystalline solids which constitute an important class of organic compounds. Their metal complexes have a very broad spectrum of applications ranging from analytical and physiological to industrial- The dioximes which contain two oxime groups have been extensively studied while the monoximes derived from diketones have received scant attention. This is despite the fact that the monoximes have got similar potentials as compared to the dioximes. Some of the work done on monoximes bears ample testimony of this. It was, therefore, thought worthwhile to carry out some studies on the complexes of monoximes derived from diketones. The present work deals with the transition metal complexes of monoximes derived from benzilj 2,3-butanedioneJ 2,4-pentanedione and 1-phenyl-1,2-propane dione» General methods of synthesis of a-monoximes like, oc-benzilmonoxime*, l-phenyl-l,2-propanedione monoxime; 2,4-pentanedione monoxime and 2,3-butanedione monoxime consist in carrying out the reaction between the carbonyl compounds and hydroxylamine hydrochloride under appropriate conditions- The nature, rate of the reaction and yield are dependent on the conditions of the reaction and the method applied* 11 Complexes of a-monoximes(cc-benzilmonoximeJ 1-phenyl- 112~propanedionemonoxime ; 2,4-pentanedionemonoxime i 2»2- butanedionemonoxime) with chromium(lll), manganese(II), iron(HI), cobalt( II), nickel (H)and copper(ll) and their mixed ligand thiocyanate complexes (with manganese(ll), cobalt(ll). and copper(ll) metal ions) have been prepared in methanolic solutions* Tetradentate diamine dioximes of oc-benzilmonoximei 1-phenyl-1,2-propanedionemonoxime -, 2,4-pentanedione monoxime and 2»>butanedionemonoxirae have been prepared with ethylenediamine in methanol, refluxing the solution for about j£i« Methanolic solution of tetradentate diamine dioxime react with metals like manganese(ll),cobalt(ll), nickel(ll) and copper(ll) to give diamine dioxime metal complexes. The nickel(ll) and copper(H) diamine dioxime complexes were reacted with BF, (in ether) to give fluorobridged macrocyclic complexes* All complexes are soluble in organic solvents and insoluble in water. The composition of the complexes was established through chemical analysis and conductometric titrations. Molar conductance data in methanol or nitro benzene show that the complexes have a non-electrolytic nature, except nickel(ll) and copper(ll) fluoro-bridged macrocyclic complexes which show conductance values corresponding to HI electrolytes* Ill a-*monoxime complexes Conductometric titration curves show the formation of 112 complexes with bivalent metal ions like mangancse(ll), cobalt(H), nickel(U) and copper(H) and 1*3 complexes with trivalent metal ions like chromium(III) and iron(lll). The values of |*eff for chromium(lll) and iron(III) complexes correspond to those for high spin and low spin octahedral species respectively The Meff values in the case of nickel(H) and copper(ll) show the square planar geometry of crmonoxime complexes- While manganese(H) and cobalt(H) complexes show high spin tetrahedral geometry. The infrared spectra of a-monoximes and their complexes ^ show bands in the 1660-1510 cm"1, 1230-1205 cm"1, 930-915 «T and 1300 cm"1 regions which can be assigned to v(ON>, V(N-O) and v(C-O) stretching vibrations respectively- The lowering of v(C=N) and v(C-O) frequencies in the complexes observed in mainly due to coordinate bond formation. The infrared spectra of cc-monoximes show a band around 3100-3260 cm"1 which is due to intermolecularly hydrogen bonded -OH group. The complete absence of this band in the complexes suggests that the hydrogen atom of the oximino moiety is replaced by metal- The electronic spectra of all these complexes are typical of octahedral, tetrahedral and square planar complexes. The observed bands have been assigned on the iv basis of spectral transitions expected for bivalent or trivalent metal complexes. The values of the absorption bands have been used to calculate the ligand field parameters- Quantitative characterisation of complex compounds and their reactions in solution have been extensively carried out. Equilibria in solution of complex compounds are quantitatively characterised by stability constants. The protonation and stability constants of cr* monoximes and their complexes have been determined in 75/. methanolwater mixture at 30°, 40° and 50°C by the potensometric method. A comparison of the stability constants of a-monoximes Jjr-benzilmonoxime (a-BMOH) ,1-phenyl-1,2-propanedionemonoxime (PMOH) 2,4-pentanedionemonoxime(PDMOH) and 2^-Butanedionemonoxime(BDM0H) ] shows the following stability order: a-BMO ^> PMO ^> BDMO > PDMO, Their metal complexes afford the following stability order* Cu(ll)>Ni(H) > Co(ll) >Mn(ll) and Fe(lIl)>Cr(lII). This stability order is similar to the Irving-Williams series. The thermodynamic parameters &G°, AH° and AS° corresponding to all protonation processes have been evaluated. Mixed Ligand Complexes Conductometric titration curves show 1*2! 2 (Metal* monoxime ' potassium thiocyanate) interaction ratio for complexation. The mixed ligand complexes having the general formula [,M lJncs).] where M(ll)=manganese(ll), cobalt(H) or copper(ll) and L = a-BMOH, PMOH, PDMOH and BDMOH. An interesting aspect of this reaction is the coordination of oximes in their protonated forms. pH investigation of the formation of the mixed complexes indicate that there is no liberation of proton during the complex formation. Magnetic measurements of all complexes show high spin octahedral geometry. The infrared spectra of all complexes show v(p-H) stretching vibration around 3200 cm which indicates the presence of protonated oxime in the complexes. The lowering of v(c=N) and v(C-O) stretching vibrations indicate the bonding of nitrogen of oximino moeity and carbonyl oxygen to the metal ions. These complexes also show the appearance of one sharp band around 2090 cm" , which can be assigned as v(c=N) group of N-bonded terminal thiocyanato group. The electronic spectra of all complexes are typical of octahedral complexes- Ligand field parameters have also been calculated with the help of the observed absorption -1 VI bands. Copper(H) mixed complexes show two absorption bands in the U.V. region due to the presence of nonequivalent nitrogen atoms. diamine dioxime complexes ~ a-monoximes and ethylenediamine react in the ratio of 2U to give rise to a tetradentate diamine dioxime* These oximes interact with metals in 1-1 mole ratio* Thio This ratio was confirmed by conductometric titrations* These tetradentate diamine dioxime exhibit geometrical isomerism and can form both cis and trans isomers* The ligand isomerisation from t**e anti to syn form is quite rapid in the presence of base, acids or metal ions* These ligands ionise to split off a proton at high PH (pK in the range of 11*00). The values of protonation constant shows that these ligands are weak acids (due to the presence of hydroxyl group) and also show very weak basicity due to the inherent Sp2 nitrogen. Thus the oxime group exhibits amphiprotic nature yielding salts with both acids and bases- The diamine dioxime complexes have a five fold coordinate geometry with general formula QKlHlx] where M=Manganese(II) cobalt(H), nic^Kn) and copperCH). LH = amine dioxide ligands and X=cr. Magnetic measurements of all complexes show that the flexes of manganese(H), VI1 cobaltCH) and copper(H) are high spin while the nickeldl) complexes are low spin with a trigonal bipyramid geometry* The infrared spectra shows the bands in the 1650 cm"1 and 175° of1 ^gions which can be assigned to the v(C=N) and a deformation of the 0-H-—0 group respectively- Electronic spectra data show the trigonal bipyramidalgeometry of all diamine dioxime complexes. Copper(H) complexes in methanolic solutions undergo oxidation to the copper(Hl) complexes on addition of H0 * All the copper(Hl) complexes are characterised by the spectral changes- These copper(lH) species show the complete absence of the copper(H) band above 20,000 cm - CT„„m-bridq^ macrocyclic complexes The tetradentate diamine dioxime nickolUl! and copperd!) complexes react with boron trifluorido rapidly to give the complexes QKlXbFjJJcI. These complexes are resistant to moderately concentrated acids, dilute alkali and a variety of organic solvents. Ml the nickelClD complexes are diamagnetic and copper(H) complexes have one unpaired spin value* The infrared spectra of these fluoro-bridged macrocyclic complexes show the absence of v(O-H) stretching