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).