Tuning the Coordination Geometries and Magnetic Dynamics of [Ln(hfac)4]− through Alkali Metal Counterions

Four lanthanide compounds with formulas [Cs­{Dy­(hfac)4}] (1), [Cs­{Er­(hfac)4}] (2), [K­{Dy­(hfac)4}] (3), and [K­{Er­(hfac)4}] (4) (hfac = hexafluoroacetylacetone) are reported. Compounds 1 and 2 crystallize in the orthorhombic Pbcn space group, while 3 and 4 are in the triclinic P1̅ space group. All display chain structures in which the mononuclear [Ln­(hfac)4]− anions are linked by alkali metal ions. However, the coordination geometries around the Ln atoms are quite different depending on the cation. They adopt a distorted dodecahedron with pseudo-D2d symmetry in the cesium compounds 1 and 2, while a distorted square-antiprism with pseudo-D4d symmetry is adopted in the potassium compounds 3 and 4. The latter compounds show distinct field-induced slow magnetization relaxation. The energy barriers are 23.95 and 20.21 K for compounds 3 and 4, respectively.

本文报道了四种镧系化合物，其化学式分别为[Cs­{Dy­(hfac)₄}] (1)、[Cs­{Er­(hfac)₄}] (2)、[K­{Dy­(hfac)₄}] (3)与[K­{Er­(hfac)₄}] (4)（其中hfac=六氟乙酰丙酮（hexafluoroacetylacetone)）。化合物1和2结晶于正交晶系（orthorhombic）Pbcn空间群，而化合物3和4则结晶于三斜晶系（triclinic）P1̅空间群。所有化合物均呈现链状结构，其中单核[Ln­(hfac)₄]⁻阴离子通过碱金属离子相互连接。不过，Ln原子周围的配位几何构型因阳离子种类的不同而存在显著差异：在含铯的化合物1和2中，Ln原子采取具有拟D₂d对称性的畸变十二面体构型；而在含钾的化合物3和4中，Ln原子则采取具有拟D₄d对称性的畸变四方反棱柱体构型。后两种含钾化合物表现出显著的场诱导慢磁化弛豫行为，其能垒分别为23.95 K（化合物3）与20.21 K（化合物4）。