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 PT 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 tA depending on the cation. They adopt a distorted dodecahedron with pseudo-D-2d symmetry in the cesium compounds 1 and 2, while a distorted square-antiprism with pseudo-D-4d 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.