Each coordination chain comprises five-coordinate Er III ions of an approximate trigonal bipyramidal geometry and azopy ligands that play the role of molecular bridges. The Er III centers are coordinated by three oxygen atoms of the three BHT ligands located in the equatorial plane and two nitrogen atoms in the approximately axial positions. The Er-O bond lengths (Table ) are 2.154(3), 2.137(3), 2.090(3) Å with the average value of 2.127(3) Å -similar to compound 1 and other reported lanthanide-arylozide complexes. The Er-N bonds are significantly longer due to the neutral character of the azopy ligands with values of 2.462(8) and 2.503(6) Å. Again, these values are similar to those discussed for compound 1. The N-Er-N angle is 152.6(2)° meaning that the trigonal bipyramid is noticeably bent from the 180°. The length of the N3-N4 bond in the azopy molecular bridge is 1.227(8) Å, which is slightly smaller than the corresponding bond of the uncoordinated molecule 1.249(1) Å. This confirms that the N-N bond in the coordinated azopy is still a double bond. Interestingly, compound 2 exhibits orientational disorder of the azopy ligand with ca. 10% mirrored along its long axis. This suggests pedal motions at room temperature, which become frozen during the flash cooling of the crystal in the cryostream -similar behavior was reported for the azobenzene molecule. The shortest interchain ErEr distance is 11.040(1) Å while the intrachain one is considerably longer 13.938(1) Å. Figure presents the packing diagram of the -(Er-azopy)-chains.