Arylazoimidazole Coordinated and Naphthalene-Dicarboxylato Bridged Polymers of Co(II) and Photochromic Zn(II) Complexes

Abstract

Naphtheledicarboxylato ((NDC2–) bridged coordination polymers (CPs) along with (E)-1-methyl-2-(p-chlorophenylazo)imidazole (ClPai-Me) coordination to Co(II), [Co(∝-NDC)0.5(∝4-NDC)0.5(ClPai-Me)]·0.5H2O (1), and to Zn(II), [Zn(∝-NDC)0.5(∝4-NDC)0.5(ClPai-Me)]·0.5H2O (2), have been characterized. In the single crystal X-ray structure of 1, ClPai-Me chelates to the Co(II) ion by N(azo) and N(imidazolyl), whereas in compound 2, it acts as a monodentate N(imidazolyl) donor to the Zn(II) ion. The coordination atmosphere around Co(II) in the 1 ion is distorted octahedral CoN2O4, whereas in the case of 2, it is distorted square pyramidal ZnNO4. Compounds 1 and 2 exhibit the right-handed (P) and left-handed (M) one-dimensional helical chain. NDC–2 is serving as a bridge between two M(II) ions to constitute μ-NDC and four M(II) ions to construct μ4-NDC to assemble three-dimensional polymers. Upon UV light (369 nm) irradiation, compound 2 shows trans-to-cis isomerization of -N═N–C6H4–Cl-p both in the solid and solution state but 1 remains silent. Prolonged light irradiation in the solid state (film phase) does not change the coordinated ClPai-Me in complexes 1 and 2, whereas the free stage of ClPai-Me undergoes photoreduction of the −N═N– bond and forms azo radicals with a concomitant permanent color change. The persistence of the radical has been characterized by electron paramagnetic resonance spectroscopy in the solid state at g = 2.009. The effective magnetic moment of 1 is 4.17 μB at 300 K, Co(II) ion of S = 3/2.