INTERCONVERSION BETWEEN POLYMERIC ORANGE AND MONOMERIC GREEN FORMS OFA SCHIFF BASE-OXOVANADIUM(IV) COMPLEX

The orange and green forms of the Schiff base-oxovanadium(IV) complex, [VO{sal-(RR)-stien}]. MeOH (1, green), [VO{sal-(RR)-stien}]. 2CHCl(3) (2, green), and [VO{sal-(RR)-stien}]. CH3CN (3, orange) (RR)-stien}=N ,N'-disalicylidene-(RR)-1,2-diphenyl- 1,2-ethanediamine), have been pr epared, and their crystal structures were determined by an X-ray metho d. The green forms, 1 and 2, contain mononuclear square pyramidal mole cules of the complex, while the orange form 3 consists of individual c omplexes stacked to give an infinite linear ... V=0 ... V=0 ... chain. 1, which crystallizes as monoclinic in space group P2(1) with Z=4, ha s the cell parameters a=16.684(2), b=16.923(4), c=9.249(3) Angstrom, b eta=105.76(2)degrees, and V=2513(1) Angstrom(3). 2, which crystallizes as triclinic in space group P1 with Z=2, has the cell parameters a=13 .187(3), b=13.469(3), c=10.450(3) Angstrom, alpha=103.72(2), beta=103. 20(3), gamma=63.03(2)degrees, and V=1591.2(7) Angstrom(3). 3 crystalli zes as triclinic in space group P1 with Z=2. The cell parameters are a =13.300(3), b=13.667(4), c=7.551(1) Angstrom, alpha=90.44(2), beta=94. 51(2), gamma=97.36(2)degrees, and V=1357(1)Angstrom(3). The final R in dices are R=0.059 and R(w)=0.062 for 1, R=0.098 and R(w)=0.090 for 2, and R=0.053 and R(w)=0.042 for 3. The structural characteristics of th ese complexes are compared and discussed. 3 shows piezochromism (mecha nochromism); its color changes from orange to green upon grinding. 1 a nd 2 turn orange when heated at 120 degrees C for a few minutes. The e xtent of conversion either by grinding or heating was studied by EXAFS (X-ray absorption fine structure) and IR spectroscopy. The orange cry stals turn green when exposed to chloroform vapor, and the green cryst als turn orange upon exposure to acetonitrile vapor.