SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF R(3)ASX(2) COMPOUNDS (R=ME,PH,P-FC6H4 OR P-MEOC(6)H(4') - X(2)=BR-2, I-2 OR IBR) - DEPENDENCY OF STRUCTURE ON R,X AND THE SOLVENT OF PREPARATION

Compounds of stoichiometry R(3)AsX(2) (R = p-MeOC(6)H(4), Ph or Me; X = Br or I; R = p-FC6H4, X = I). R(3)Asl(4) (R = p-FC6H4 or Ph) and Ph( 3)AslBr have been synthesised in anhydrous diethyl ether and character ised by elemental analysis and Raman spectroscopy. Single-crystal X-ra y diffraction studies of Ph(3)AsBr(2) showed it to possess a molecular trigonal-bipyramidal structure, in contrast to Ph(3)AsI(2) which adop ts the molecular four-co-ordinate structure Ph(3)As-I-l. Both Me(3)AsI (2) and Me(3)AsBr(2) have the molecular four-co-ordinate structure, Me (3)As-X-X, thus illustrating that the structure of R(3)AsX(2) compound s isolated from diethyl ether is dependent on R and X. The structure o f Ph(3)AslBr also revealed four-co-ordinate molecular geometry in cont rast to Ph(3)AsBr(2). The compound Ph(3)AslBr showed no dual occupancy of the halogen sites, and the heavier halogen is bound directly to th e arsenic. The X-ray powder diffraction patterns of Ph(3)AsX(2) (X(2) = Br-2, I-2 or IBr) have been recorded and are compared. Solution stud ies an R(3)AsI(2) (R = p-FC6H4, Ph or p-MeOC(6)H(4)) again showed the sensitivity of these molecules to the nature of R. For example. (p-FC6 H4)(3)Asl(2) was not formed in any solvent employed; instead, equimola r quantities of (p-FC6H4)(3)Asl(4) and (p-FC6H4)(3)As were isolated; P h(3)Asl(2) was only formed in non-polar solvents upon dropwise additio n of a light petroleum solution of I-2 to a saturated solution of Ph(3 )As in the same solvent. The compound (p-MeOC(6)H(4))(3)Asl(2) was the quantitative product from the direct reaction of the tertiary arsine with I-2 in diethyl ether. Its stability constant in CCl4 is approxima tely 2.5 times greater than that calculated for Ph(3)Asl(2).