Hexahalorhenate() salts of protonated ciprofloxacin: antibiotic-based single-ion magnets

Two novel Re IV compounds of formula [H 2 cip][Hcip][ReCl 6 ]Cl·H 2 O ( 1 ) and [Hcip] 2 [ReBr 6 ] ( 2 ) [(H 2 cip) 2+ /(Hcip) + = ciprofloxacindiium cation/ciprofloxacinium cation] have been synthesized and studied structurally and magnetically. 1 crystallizes in the monoclinic system with space group P 2 1 / c , whereas 2 crystallizes in the orthorhombic system with space group Pbca. 1 and 2 are hexahalorhenate( iv ) salts obtained with the protonated ciprofloxacin antibiotic. In their crystal lattice, the [ReX 6 ] 2− [X = Cl( 1 ) and Br( 2 )] anions are well separated from each other through the protonated ciprofloxacindiium ( 1 ) and ciprofloxacinium ( 1 and 2 ) cations, which are arranged without generating intermolecular Re−X X−Re interactions between the paramagnetic centers. In both compounds, intermolecular π π ( 1 ) and π F ( 2 ) type interactions [the shortest centroid centroid and centroid fluorine distance being approximately 3.49(1) and 2.95(1) Å, respectively], as well as hydrogen bonds ( 1 and 2 ), are present. The self-assembly of these protonated organic cations and Re IV complexes generate novel supramolecular structures based on this paramagnetic 5d metal ion. The study of their magnetic properties through variable-temperature dc magnetic susceptibility measurements reveals a magnetic behaviour typical of noninteracting mononuclear Re IV complexes ( S Re = 3/2), with magnetically isolated spin quartets and high values of their zero-field splitting (ZFS), for 1 and 2 . In addition, AC magnetic susceptibility measurements in the presence of external dc fields show slow relaxation of the magnetization, which is a behavior compatible with the occurrence of the field-induced single-ion magnet (SIM) phenomenon for 1 and 2 . This is the first magnetostructural study performed on salts based on protonated ciprofloxacin antibiotic and a paramagnetic 5d ion. In the crystal lattice of two novel Re IV compounds, the paramagnetic [ReCl 6 ] 2− and [ReBr 6 ] 2− anions are well separated from each other through two protonated forms of the antibiotic ciprofloxacin. These compounds behave as single-ion magnets (SIMs).