Synthesis and structure of dimeric anthracene-9-carboxylato bridged dinuclear erbium(III) complex, [Er2(9-AC)6(DMF)2(H2O)2]

We study the influence of the bulky aromatic rings, e.g. anthracence-9-carboxylic acid (9-ACA) with a large conjugated π-system on the structure and spectroscopic properties of [Er2(9-AC)6(DMF)2(H2O)2] complex where 9-AC = anthracence-9-carboxylato and DMF = N,N′-dimethylformamide. The complex has been prepared from the erbium chloride and 9-ACA in the mixture of H2O:DMF solution (4:1, v/v) followed by pH adjustment to 6. The complex is crystallized in a monoclinic system with space group P21/n. The two Er(III) ions are double bridged by the deprotonated carboxyl groups of two 9-AC anions (O1 and O1A), forming an eight-coordination number. The chelating bidentate (O,O), chelating-bridging tridentate (O,O,O′) and monodentate of 9-AC anions are observed in the dinuclear [Er2(9-AC)6(DMF)2(H2O)2] complex. The Er-Er distance is 4.015 Å in the dimeric unit. Intramolecular O-H⋯O and C-H⋯O hydrogen bonds as well as numerous of intermolecular C-H⋯π interactions between the anthracene rings by edge-to-face interactions linked the dinuclear dimeric units into two-dimensional supramolecular network in a propeller-arrangement. Electronic absorption spectra of the Er(III) complex and its salt were measured. The emission spectrum of the complex is composed of a broad band due to the emission of intraligand π* → π transition from the 9-AC anions and a shoulder peak originating from the 4f-4f emission transition of the Er(III) ions. The complex has a high thermal stability which can be attributed to the effectively increase the rigidity of the 9-AC anions.