Syntheses, structures and photoelectronic properties of a series of tri- and tetra-nuclear metal complexes based on a 36-membered tetraphenol macrocyclic ligand

In this article, tetranuclear Zn^II coordination complexes Zn₄L(μ₂-OH)₂]·2(NO₃)·6(CH₃OH)·H₂O (1) and Zn₄L(μ₂-OH)₂(H₂O)₂]·(p-bdc)·2(CH₃OH)·3H₂O (2), dinuclear Zn^II complex Zn₄L(NH₂-bdc)₂]·2(CH₃OH)·3H₂O (3), and trinuclear Cd^II complexes Cd₃L(m-bdc)]·6.5H₂O (4) and Cd₃L(NH₂-bdc)]·5.5H₂O (5), based on a tetraphenol 36-membered macrocycle (L) having four ethylenediamine and four 2,6-diformyl-4-methylphenol functionalities, have been synthesized at room temperature (p-bdc = 1,4-benzenedicarboxylate, NH₂-bdc = 5-aminoisophthalate and m-bdc = 1,3-benzenedicarboxylate). In 1 and 2, four Zn^II centers are bridged by phenoxide and hydroxy atoms of the L ligands to form tetranuclear Zn^II complexes. The inorganic and organic anions in 1 and 2 do not coordinate to Zn^II centers, but act as counter anions. In 3, two Zn^II centers are bridged by two phenoxide O atoms to form a Zn^II cluster (Zn₂O₂N₄). Moreover, two (Zn₂O₂N₄) clusters within the ring of the L ligand are further bridged by two NH₂-bdc anions in a monodentate fashion. Compound 4 possesses the trinuclear Cd^II clusters (Cd₃N₈O₈), which has a similar structure to compound 5. The trinuclear Cd^II clusters are bridged by the dicarboxylate anions to yield an infinite coordination polymers chain. The photoelectric transfer properties of complexes 1, 2 and 4 were investigated by surface photovoltage spectroscopy (SPS) and the field-induced surface photovoltage spectra (FISPS) techniques. The results reveal that the complexes exhibit positive surface photovoltage (SPV) responses in the range of 300-600 nm, possessing the p-type semiconductor characteristics. So far, the surface photovoltage properties of the macrocycle complexes based on tetraphenol macrocyclic ligands were investigated for the first time. Moreover, elemental analyses, IR spectra, and luminescent properties of these compounds were also studied.