Inorganic Chemistry, Vol.59, No.9, 5835-5844, 2020
Adducts of Tris(alkyl) Holmium(III) Showing Magnetic Relaxation
In the series of the adducts of tris(alkyl) Ho" complexes, Ho-III (CH2SiMe3)(3) (THF)(2) (1Ho-THF, Me = methyl) can exhibit slow magnetic relaxation under a zero applied direct current (DC) field with the energy barrier Delta/k(B) of 76 K, which is one of the highest in the non-Kramers ion Ho-III-based single-ion magnets (SIMs). The DC field-dependence of relaxation time for 1Ho-THF indicates the occurrence of direct relaxation process at low temperature under certain DC fields. 1Ho-THF stands out in the series of 1Ln-THF (Ln = Tb, Dy, Ho, Er, Tm), wherein Dy congener is another SIM in the absence of a DC field with the relaxation barrier of 40 K, while Tb and Er congeners are fieldinduced SIMs. Further substitutions of the two trans-THF in 1Ho-THF by other neutral ligands such as quinuclidine, tricyclohexylphosphine oxide, and 3,5-lutidine afforded Ho(CH2SiMe3)(3) (quinuclidine)(2) (2Ho-QN), Ho(CH2SiMe3)(3)(OPCy3)(2) (3Ho-OPCy3), and Ho(CH2SiMe3)(3) (lutidine)(3) (4Ho-Lut), respectively. The former two possess analogous structures to 1Ho-THF with two trans-arranged neutral ligands, and the latter one has three cis-lutidine coordinated. The fast quantum tunneling effect swamps the magnetic relaxation for the above three derivatives, so slow relaxation could not be observed under experimental conditions, even when a certain DC field was applied.