“…In 2022, the highest record of T B,100s , the temperature at which the relaxation time τ = 100 s, was 72 K in mixed-valence di-lanthanide complexes (Cp iPr5 ) 2 Dy 2 I 3 with a thermal barrier to magnetic relaxation of 1631(25) cm −1 reported by Long et al 17 In general, rare-earth SMMs characterized with shielded 4f orbitals by the external ones and unquenched orbital angular momentum, L possess stronger magnetic anisotropies than transition–metal (TM) SMMs, which usually have quenched L . However, a series of two-coordinate TM compounds, such as Cr(SAr*) 2 , 18 Fe( ii )[C(SiMe 3 ) 3 ] 2 ( U eff = 181 cm −1 ), 19 FeL 2 (L = N(SiMe 3 )(Dipp), N(H)Ar′, N(H)Ar*), 19 [Fe( i )(C(SiMe 3 ) 3 ) 2 ] − ( U eff = 226 cm −1 ), 20 V{N-(SiMePh 2 ) 2 } 2 , 21 Cr{N(SiMe 2 Ph) 2 } 2 , 21 [Ni(MDABCO) 2 Cl 3 ]ClO 4 , 22 [(NHC)CoNDmp] ( U eff = 413 cm −1 ), 23 Co(C(SiMe 2 ONaphthyl) 3 ) 2 ( U eff = 450 cm −1 ), 24 [K(18-crown-6)][Fe{N(SiMe 3 ) 2 } 2 ], 25 [Co{κ 6 - N , N , N , N ′, N ′, N ′-PhB[ONC(Me)C 3 N 2 H] 3- }Cl] ( U eff = 152 cm −1 ), 26 and [Ni(NHC) 2 ]Br, 27 have remarkable magnetic performance and are excellent candidates of SMMs. Among them, Co II -based systems exhibit superior magnetic relaxation properties compared to the others.…”