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

Abstract

In this article, tetranuclear Zn II coordination complexes [Zn 4L(μ 2-OH) 2]·2(NO 3)·6(CH 3OH)·H 2O ( 1) and [Zn 4L(μ 2-OH) 2(H 2O) 2]·( p-bdc)·2(CH 3OH)·3H 2O ( 2), dinuclear Zn II complex [Zn 4L(NH 2-bdc) 2]·2(CH 3OH)·3H 2O ( 3), and trinuclear Cd II complexes [Cd 3L( m-bdc)]·6.5H 2O ( 4) and [Cd 3L(NH 2-bdc)]·5.5H 2O ( 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, NH 2-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 (Zn 2O 2N 4). Moreover, two (Zn 2O 2N 4) clusters within the ring of the L ligand are further bridged by two NH 2-bdc anions in a monodentate fashion. Compound 4 possesses the trinuclear Cd II clusters (Cd 3N 8O 8), 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.