Experimental and theoretical interpretation of the magnetic behavior of two Dy(iii) single-ion magnets constructed through β-diketonate ligands with different substituent groups (-Cl/-OCH 3 ).

Two Dy(iii) single-ion magnets, formulated as [Dy(Phen)(Cl-tcpb) 3 ] (Cl-1) and [Dy(Phen)(CH 3 O-tmpd) 3 ] (CH 3 O-2) were obtained through β-diketonate ligands (Cl-tcpb = 1-(4-chlorophenyl)-4,4,4-trifluoro-1,3-butanedione and CH 3 O-tmpd = 4,4,4-trifluoro-1-(4-methoxyphenyl)-1,3-butanedione) with different substituent groups (-Cl/-OCH 3 ) and auxiliary ligand, 1,10-phenanthroline (Phen). The Dy(iii) ions in Cl-1 and CH 3 O-2 are eight-coordinate, with an approximately square antiprismatic (SAP, D 4d ) and trigonal dodecahedron ( D 2d ) N 2 O 6 coordination environment, respectively, in the first coordination sphere. Under zero direct-current (dc) field, magnetic investigations demonstrate that both Cl-1 and CH 3 O-2 display dynamic magnetic relaxation of single-molecule magnet (SMM) behavior with different effective barriers ( U eff ) of 105.4 cm -1 (151.1 K) for Cl-1 and 132.5 cm -1 (190.7 K) for CH 3 O-2, respectively. As noted, compound CH 3 O-2 possesses a higher effective barrier than Cl-1. From ab initio calculations, the energies of the first excited state (KD 1 ) are indeed close to the experimental U eff as 126.7 cm -1 vs. 105.4 cm -1 for Cl-1 and 152.8 cm -1 vs. 132.5 cm -1 for CH 3 O-2. The order of the calculated energies of KD 1 is same as that of the experimental U eff . The superior SIM properties of CH 3 O-2 could have originated from the larger axial electrostatic potential (ESP (ax) ) felt by the central Dy(iii) ion when compared with Cl-1. The larger ESP (ax) of CH 3 O-2 arises from synergic effects of the more negative charge and shorter Dy-O distances of the axial O atoms of the first sphere. These charges and distances could be influenced by functional groups outside the first sphere, e.g. , -Cl and -OCH 3 .