A PHYSICO-CHEMICAL STUDY OF NORMAL AND MIXED-LIGAND CHELATES OF OXOVANADIUM (IV) WITH OXYGEN AND NITROGEN DONOR LIGANDS

Abstract

The main aim of the Investigations presented in this thesis was to make a detailed study of mixed ligand chelates of oxovanadium (IV) with some oxygen and nitro gen donor complexlng agents. For the determination of formation constants of these mixed ligand derivatives, an information was required about the simple chelates of ft* VCT with the ligands involved in the present study. Alt hough most of these simple chelates had been reported earlier, a survey of literature revealed that in some cases, e.g., catechol, chromotropic acid, mandelic and lactic acids, a more comprehensive study was desirable before an understanding of their nature could be claimed. In such cases, therefore, a systematic physico-chemical study was carried out for obtaining the data for the mixed ligand systems. Although tartrate and malate complexes of VO(IV) have not been studied from the above point of view, inter esting results obtained In the study of vanadyl-mandelate and -lactate systems led to extend this work to the corres ponding tartrate and malete chelates. These have received a considerable importnnce in recent years, since in ammonia solution and in the solid state the complex (NH4)2[V0(tart)] (HgO) is the only example of vansdyl complex known to exhibit, at room temperature, four distinct absorption bands in the ligand field region (1000-380 mu ). In the study of the mixed ligand systems involv ing o-phenonthroline and ?,?,-dipyridyl as primary ligands, it was found that the successive reactions in the formation of mixed ligand chelates overlap. Deter mination of the formation constants of these complexes required a knowledge of equilibrium constants of the reactions associated with the formation of the simple VO-Phen and V0~Dipy chelates. Before investigating the formation of mixed ligand chelates, therefore, it was considered expedient to study the potentiometrie data arising from the interaction of vanadyl ion with the above nitrogen donor ligands. Due to the special charac teristics of systems described in this thesis and also dependent on the facilities available in our laboratories, the study has been based mainly on potentiometry. Although the major interest of the investigations lay in the mixed ligand complexes, the subject matter of the thesis has been divided for convenience in two separ ate parts dealing with the simple chelates followed by mixed ligand derivatives. SIMPLE CHELATES OF OXOVANADIUM (IV) At least one ligand atom Is Oxygen? 1-10 Oxalate ion readily forms complexes with oxo vanadium (IV). These complexes are mainly of the types: VO(ox). xHj>0, Mg[V0(ox)g](xH20) and ^[(VO^OX^J (xH20). Formation of the anhydrous compound (NH4)2[(VO)g(ox)3J has recently been claimed11. Acompound with the empirical formula VO(ox)(RgOx) (3H20) has been reported by Selbia 1? and Holmes • By using Job's method of continuous variations, the reaction of VOT* with malonic acid has been reported to produce a 1:1 complex. In alkaline solutions, malonato complexes of the general formula M2[V0(mal)2] .xH20 have been isolated by Schramm14. These derivatives have been reported to give different coloured species when dehydrated in stages. Tartrate complexes of VO(IV) have been a subject of research18"5*4 since the earliest days of vanadium chemistry. Jprgensen25 has suggested that in the complex ion (Vo(tart)] all the four oxygen atoms of the tartrate ion are coordina- 26 ted to the oxometal ion. Recently an interesting report , proclaiming the use of (KN4)2[vO(tart)] (H20) for the inhib ition of cholesterol synthesis In brain tumors, has appeared. Complexes of oxovanadium (IV) with other polybasic pn ©Q JJQ 30 acids, viz., salicylic f phthalic , succinic , sebacic30, citric30"32, ascorbic33 and picolinic34 acids have been pi-epared by treating a suspension of the organic acid in carbon tetrachloride with VOCl3 under anhydrous conditions. Mont and Martell35 have ntudied the Interaction of vanadyl Ion with salicylic acid,5-sulphosalicylic acid °. 4 titron, 5-sulpho-8-hydraxyquinollne and salicyl phosphate in aqueous medium. By using the potentiometric data of the systems, formation constants of the chelates have been determined. Stability constants of the vanadyl Chelates of EDTA36""33, I9ftA | H.IMDA39, chroraotropic40 41 and glycolic acids have also been determined. Salicyldehyde forms st ble chelates of the type M2[V0(Sal)2l (xH20). Acomplex with p-amino-salicyldehyde has also been syntheslsed . Reactions of VCr with other hydroxyaldehydes(4-phenyl-, 5-chloro-, 5-bromo-, 3,5-dlchloro-, and 3,5-dibromosalicyldehyde and p-hydroxynaphthaldehyde) and their imines have been recently 45 reported . 46 Dutta and Lahiry obtained a rose-coloured para magnetic complex ("vOBol with benzehydroxamic acid (BH). They also reported ' a cream-coloured hydrate fvOQjTl (H20) with quinaldinic acid (QH) and an isomeric olivegreen aquo complex [V0Q2(H20)]. Complexes of the type [rVOG2tJ have be?.i syntheslsed49 with guanylalkyl-and guanylalkoxyalkylureas(GH). Oxovanadium (IV) has been reported to form several complexes with 8-diketones. Amongst these, the blue-green bis (acetylacetonate) oxovanadium (IV) oomplex has received an expensive attention. This compound was 50 first prepared in 1876 by Guyard . In 1900 the same et e© compound was syntheslsed by Gach . Morgan and Moss formulated the complex as jVO(acac)2J. Rosenheim and Mong17 claimed it to be in a monohydrate form, [V0(acac)2 (H20)]. Again, in 1964 Jones53 studied this complex and concluded that the original formulation without water molecule was correct. By using Bjerrum»s method, Trujillo and Brito54 ob ained evidence for the formation of VO(acac)* and j"vo(acac)^] complexes in aqueous solutions. Recently, the vanadyl complexes of acetylacetone ere in aqueous and alcoholic solutions have been reported to undergo slow oxidation by atmospheric oxygen. The oxidation reaction has been claimed to proceed rapidly with hydrogen peroxide. Other 8-diketones which form complexes VO(IV) include: 3-cyanoacetylacetone | ?- 57 58 chloro-and ?-bromo-acetylaeetone ; acetyl methylacetone ; fiO benzoylacetone and its 1:1 adducts with bases. 8-hydroxyquinoline has been reported to form complexes having 1:1 and 1:1? ratios of vanadyl to ligand. Formation constants of these chelates hwe been determined by Bjerrum's method. Magnetic moment of VO(oxlne)2 has been measured • and the complex has been reported to form a stable pyridine adduot. Complexes of VC(IV) with Schiff bases formed from 8-dlketonea, ethylenedlamine and salicyldehyde have received a considerable attention in recent years. Amongst the complexes obtained from the Schiff bases derived from 6 8-diketones, reference may be made of the complex bis (acetyl acetonepropylenediiraino) oxovanadium (IV) which has been reported to be the first compound of VO(IV) to have been successfully resolved Into optical isomers. 70 More recently, Sacconl and Camplgli have studied the interaction of Schiff bases formed from ring substituted salicyldehydes and N-substituted ethylenediarainea. Complexes with the general formula [jUSALen-NCRjR'^VO have been syntheslsed. These complexes have been shown to have a five-coordinate structure.