Synthesis, characterization and nonlinear optical effects of M4(µ4-O) core complexes with large two-photon absorption cross-section

Four tetranuclear 2-mercaptobenzothiazole cluster compounds [M4O(MBT)6] (M = Fe, Co, Ni, Cu; MBT = 2-mercaptobenzhothiazole) were synthesized and characterized by elemental analyses, IR and UV–vis spectra, and single crystal X-ray crystallography. The crystal structures of [M4O(MBT)6] (M = Fe, Co, Ni) confirm that the four metal(II) atoms locate four capsheaves of a tetrahedral skeletal structure and a tetracoordinate O2− as an interstitial atom occupies the centre position of this tetrahedron. The metal atoms all possess slightly distorted tetrahedral geometry. The thermal gravimetry data indicate that these clusters all have good thermal stability. The nonlinear absorption of four cluster solutions (in DMF) were measured by open-aperture Z-scan technique at a 532 nm wavelength. The results of Z-scan experiments show that these clusters all have remarkable and very strong nonlinear optical absorption effects. The largest two-photon absorption cross-section is 172880 GM for cluster [Fe4O(MBT)6].