Interconversion between polymeric orange and monomeric green forms of a 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) (H-2{sal-(RR)-stien}=N,N'-disalicylidene-(RR)-1,2-diphenyl- 1,2-ethanediamine), have been prepared, and their crystal structures were determined by an X-ray method. The green forms, 1 and 2, contain mononuclear square pyramidal molecules of the complex, while the orange form 3 consists of individual complexes stacked to give an infinite linear ... V=0 ... V=0 ... chain. 1, which crystallizes as monoclinic in space group P2(1) with Z=4, has the cell parameters a=16.684(2), b=16.923(4), c=9.249(3) Angstrom, beta=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 crystallizes 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 indices 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 these complexes are compared and discussed. 3 shows piezochromism (mechanochromism); its color changes from orange to green upon grinding. 1 and 2 turn orange when heated at 120 degrees C for a few minutes. The extent of conversion either by grinding or heating was studied by EXAFS (X-ray absorption fine structure) and IR spectroscopy. The orange crystals turn green when exposed to chloroform vapor, and the green crystals turn orange upon exposure to acetonitrile vapor.