The Structures And Magnetism Of Copper(Ⅱ)-Azido Compounds Regulated By Aromatic Carboxylic Acids

Metal-azido compounds have attracted researchers’ extensive attention due to their excellent properties in magnetism. Among them, azido-carboxylate compounds with mixed bridges have become a hot research topic. As bridging ligands, azide and carboxylic acid both have a variety of bridging coordination modes, which can effectively transfer the magnetic coupling interaction. In this paper, by introducing aromatic carboxylate as coligands, together with azido ions to construct Cu(II)-azido-carboxylate compounds and study their magneto-structural relationships. The main results are as follows:1. By selecting a series of phenylacetic acids as coligands with related structures and different substitutent groups to give five Cu(II)-azido compounds. Structure analyses reveal that the structure units of these compounds are chain structures based on EO-azido-carboxylate bridges. In compounds [Cu(o-npa)(N3)(H2O)]n (1) and [Cu(p-npa)(N3)(C2H5OH)]n (5)(o-Hnpa=o-nitrophenylacetic acid and p-Hnpa=p-nitrophenylacetic acid), the carboxylate groups taking syn-syn bidentate bridging mode with single EO-azido and bridging water molecule or ethanol molecule bridged neighboring Cu(II) ions forming an infinite one-dimensional chain. Compounds [Cu(p-npa)(N3)]n (2) and [Cu(p-mpa)(N3)]n (3)(p-Hmpa=p-methylphenylacetic acid) are two-dimensional structures. In2, the (μ-EO-N3)(μ-COO) double bridges are further connected by the coordinated p-NO2forming a two-dimensional layer-structure. While in3, the carboxylate groups adopt the μ3-bridging tridentate mode to connect the adjacent Cu(II)-chains forming a two-dimensional network structure. Compound [Cu3(p-mpa)2(N3)4(CH3OH)2]n (4) is a Cu(II)-azido chain composed of alternating (μ-EO-N3)(μ-COO) double bridges and (EO-N3)2double bridges. Weak intermolecular forces also exist in the compounds: compounds1,4and5form the two-dimensional super-molecular structures by interchain hydrogen bonding, while compounds3and6are the two-dimensional super-molecular structures formed by π-π stacking and conjugate interactions. In addition, with the introduction of p-ebz (p-Hebz=p-ethylbenzoic acid) as coligand, we obtained the compound [Cu(p-ebz)2(N3)]n (6), in which carboxylate groups adopt two kinds of coordination modes:syn-syn bidentate and monodentate, together with the single EO-azido forming a one-dimensional Cu(II)-chain.2. Magnetic measurements have been carried out on part of the compounds and the results indicate that these compounds are ferromagnetic. Compound3behaves as a magnet and exhibits the long-range ordering behavior and its phase transition temperature (Tc) is7K. Comparison from the structures and magnetic analysis results, it can be concluded that the ∠Cu-N-Cu angle has an important influence on the coupling constant (J). The Cu(II)-azido compounds which regulated by different substituent phenylacetic acids exhibit different magnetic properties due to their different intrachain and interchain structures. In addition, just changing the position of the same substituent group, we get the Cu(II)-azido compounds with different structures and magnetic properties. All indicate that the type and position of substituent groups both can influence the structures of the compounds, which further regulate their magnetic properties.