Syntheses, supramolecular structures, magnetic and photochromic properties of six lanthanide complexes based on the 5-azotetrazolyl salicylic acid ligandElectronic supplementary information (ESI) available: Cartesian coordinates of π−-π stacking interaction in 1-6, the results of π−-π stacking interaction energies calculation of 1-6, the atomic labelling diagram and crystal packing diagram of 3 and 5, the diagram of hydrogen bonds in 1-6, plots of χM−1vs. T for 5, UV-vis spectra of 2-6 in alkali

Six lanthanide complexes based on the 5-azotetrazolyl salicylic acid (H 3 ASA) ligand of {[Er(H 2 ASA)(HASA)(H 2 O) 6 ]·6H 2 O} ( 1 ), {[Ln(H 2 ASA)(HASA)(H 2 O) 4 ] 2 ·6H 2 O} [Ln = Er ( 2 ), Ho ( 3 )], [Ln(H 2 ASA)(HASA)(H 2 O) 4 ] [Ln = Nd ( 4 ), Gd ( 5 )] and {[Dy(ASA)(H 2 O) 5 ]·5H 2 O} ( 6 ) have been synthesized and characterized by single crystal X-ray diffraction analysis. In 1-6 , the carboxyl group acts in different coordinating or bridging modes resulting in a mononuclear structure for 1 , two dinuclear structures for 2 and 3 and three one-dimensional structures for 4-6 , and the unusual π − -π stacking between tetrazolate anions and phenyl rings and various hydrogen bonding interactions are observed. The energies for π − -π stacking interactions were calculated and demonstrated at the MP 2 level using the Gaussion 09 suite. The magnetic properties of 2-6 and photochromism for aqueous solutions of 1-6 were investigated. Six lanthanide complexes based on 5-azotetrazolyl salicylic acid were synthesized and their crystal structures, magnetic and photochromic properties were reported.