The Synthesis, Structures and Magnetism of Copper Azide Compounds Regulated by Benzoic Acids with Different Substituent Groups
|Keywords||azide substituent benzoic acid ferromagnetic metamagnetic long-rangeferromagnetic ordering|
The structures and magnetic properties of azide polymers have drawn much interest because different coordination modes of azide give different magnetic couplings. The modes of azide are expected to change when suitable coligands are introduced, and as a result the structures and magnetic properties of the azide compounds can be tuned.The aromatic carboxylic acid has been one of the most common structural components. It has been a main strategy to ultize the carboxylic acid with bidentate mode to assemble magnetic compounds.In this paper, based on the system of Cu+-N3-, a series of magnetic compounds have been constructed by introducing the coligands of benzoic acids with different substituent groups (R-Benzoic acid). The structures and magnetic properties of the compounds are studied, and the main conclusions are as follows.①Six azide compounds based on Cu(II) have been constructed by six benzoic acids with different substituent groups. All the six compounds are chains linked by both azide and carboxylate. When R=4-NO2, compound [Cu1.5(4-NO2-Benzoate)(N3)2(H2O)]n(1) is a chain with alternating (u-EO-N3)(μ-COO) bridges and (EO-N3)2bridges.1is further connected by hydrogen bonds to form a three-dimensional superastructure. When R=4-OH,4-CH3,4-C1,3-NO2,2-NO2, compounds2-6are all chains with (μ-EO-N3)(μ-COO) bridges. Compared with [Cu(4-CH3-Benzoate)(N3)]n (3) and [Cu(3-NO2-Benzoate)(N3)n·nH2O (5),[Cu(4-OH-Benzoate)(N3)(H2O)]n·nH2O (2),[Cu(4-Cl-Benzoate)(N3)]n (4) and [Cu(2-NO2-Benzoate)(N3)(H2O)]n (6) are connected with hydrogen bonds or π-π stacking interactions to form superstructures. The structural analysis revealed that different overall structures of azide polymers are formed with different substituent benzoic acids as coligands, which indicates the structure effects of the uncoordinated groups. In addition, compound [Cu(4-NO2-Benzoate)(N3)(Phen)]·H2O (7) has been obtained by introducing the chelate ligand Phen. the azide ligands adopt double EO mode to connect the adjacent metal centers to form a binuclear unit while coaboxylate adopts monodentate mode.②Magnetic measurements have been carried out on crystalline samples of the compounds and all the compounds are ferromagnetic, which is consistant with the reported results that azide with EO mode often gives ferromagnetic coupling interaction. Compound1is metamagnetic. Compound2shows long-range ferromagnetic ordering, while compound3is ferromagnetic without long-range ferromagnetic ordering. It can be concluded that the angle∠M-N-M has important influence on the coupling constant (J). Moreover, azide compounds regulated by different benzoic acid with different substituent groups show different magnetic properties due to the different coordination geometry of metal centers and their different superamolecular interactions. This indicates the regulation effect of the substituent groups on magnetism of the compounds.