A new class of thermo- and solvatochromic metal-organic frameworks based on 4-(pyridin-4-yl)benzoic acid

Using 4-(pyridin-4-yl) benzoic acid, 44pba (1) as a ligand, two new metal-coordination networks [Co-4(44pba)(8)](n)center dot[(DMF)(3)center dot(EtOH)(0.25)center dot(H2O)(4)](n) (2) and [Ni-4(44pba)(8)](n)center dot[(DMF)(3.5)center dot(EtOH)center dot(H2O)(1.5)](n) (3) were synthesized by solvothermal methods and structurally characterized. Compounds 2 and 3 are isostructural but differ in their solvent content. Each is a 2D-network which forms a spiral parallel to [001], giving rise to three distinct large channels, accounting for some 47% of the unit cell volume. Both 2 and 3 display water-induced phase transformations with chromotropism, which has been confirmed by TGA and XRPD analysis. Solvatochromism in 2 is also evident with crystals exhibiting a range of colours depending on the solvent included. This phenomenon has been characterized using TGA, XRPD and UV-vis spectrophotometry.