A series of metal–organic polymers assembled from MCl2 (M = Zn, Cd, Co, Cu): structures, third-order nonlinear optical and fluorescent properties

Abstract

In this paper four metal–organic polymers {[Zn(fcz)Cl₂]·CH₃OH}_n1, {[Cd(fcz)₂Cl₂]·CH₃OH·2H₂O}_n2, {[Co(fcz)₂Cl₂]·2CH₃OH}_n3 and {[Cu(fcz)₂Cl₂]·2CH₃OH}_n4 (fcz = fluconazole: α-(2,4-difluorophenyl)-α-(1H-1,2,4-triazol-l-ylmethyl)-1H-1,2,4-triazole-l-ethanol) were synthesized and characterized by X-ray single crystal diffraction. Polymer 1 consists of 1-D infinite chains arranged along the b-axis. All of polymers 2–4 exhibit a 2-D rhombohedral grid structure. We study the third-order nonlinear optical properties of fcz and polymers 1–4 in DMF solution by using 8 ns laser pulses at 532 nm, and find that 1 and 4 exhibit different NLO properties from fcz and both 2 and 3 show similar NLO properties to fcz. 1 possesses strong NLO refractive effects and large NLO absorptive behaviors. 2, 3 and fcz exhibit strong refractive effects, but their NLO absorptive behaviors are weaker than that of 1. The NLO effects of 4 are very weak. The study of optical limiting (OL) effects by using 40 ps laser pulses at 532 nm shows that fcz and polymer 3 possess a strong OL effect. The optical limiting threshold values of 0.15 J cm⁻² for fcz and 0.16 J cm⁻² for 3 are comparable to those of many heterothiometallate clusters. Polymers 1, 2 and 4 show a weak OL effect. The fluorescent spectra in DMF solution (concentration: 1 × 10⁻⁴ mol dm⁻³) show that polymers 1–4 exhibit different luminescence properties from fcz. The maximum wavelength of polymers 1–3 are blue shifted gradually by 2–12 nm while polymer 4 exhibits a fluorescent self-quenching phenomenon. These results demonstrate that metal ions play an important part in the NLO and fluorescent properties of coordination polymers.