Photosalient Behavior of Photoreactive Zn(II) Complexes

Abstract

Solids showing unusual and unexpected properties are the key toward the development of new advanced functional materials. Here, we describe two different types of Zn(II) complexes obtained from three different derivatives of 4-styrylpyridine under the same experimental conditions: [Zn3(cin)6(2F-4spy)2·Zn2(cin)4(2F-4spy)2] (1), [Zn2(cin)4(4spy)2] (2), and [Zn2(cin)4(3F-4spy)2] (3), where cin = cinnamate, 2F-4spy = 2-fluoro-4′-styrylpyridine and 3F-4spy = 3-fluoro-4′-styrylpyridine. Of these 1 is a photostable inorganic cocrystal comprising a trinuclear Zn(II) complex and a paddlewheel Zn(II) complex, whereas 2 and 3 are photoreactive Zn(II) complexes with paddlewheel structure. The neighboring olefin bonds in the styrylpyridine ligands in 2 and 3 are aligned in a head-to-tail manner, but not the olefin bonds in the cinnamate ligands. The distance between the pairs of olefin bonds are 4.348(2) Å in 2 and 4.045(2) Å in 3. However, they not only undergo solid state photochemical [2 + 2] cycloaddition reaction under UV light but also show the photosalient behavior during the photoreaction. An overall increase in the percentage cell volume of 11.93% and 10.13% for 2 and 3, respectively, during the photoreaction appears to indicate a significant anisotropic expansion is responsible for the photosalient effect.