Multifunctional Properties of a Zn(II) Coordination Complex

Metal complexes exhibiting multifunctional properties are very rare. Here, we report a Zn(II) complex, [Zn(benzoate)(25F-spy)2], where 25F-spy = 2′,5′-difluoro-4-styrylpyridine, displays unpredicted photosalient behavior while it undergoes a [2 + 2] cycloaddition reaction and exhibits unusual thermal expansion with occasional jumping, second-harmonic generation (SHG), and two-photon photoluminescence (2PPL). In the solid state, the 25F-spy ligands are packed in a head-to-tail manner. The distance between the pairs of olefin bonds, 4.279(2) Å, is not suitable for undergoing a [2 + 2] photocycloaddition reaction. However, these crystals not only undergo photodimerization quantitatively but also exhibit a photosalient effect under UV light. An interesting anisotropic thermal expansion facilitates the crystals to jump occasionally when they are heated to 140 °C, similarly to the thermosalient effect. Thermal expansion values along X1, X2, and X3 are -54.46, 106.42, and 151.69 × 10-6 K-1, respectively, with V = 204.26 × 10-6 K-1 (30-140 °C). Furthermore, these crystals exhibit light-frequency upconversion via both SHG and 2PPL. Altogether, a single crystal shows all of these diverse solid-state properties.