Three new single paramagnetic lanthanide-based complexes, [Ln(L)(LOEt)] (Ln(3+) = Dy(3+), Tb(3+), and Ho(3+)), are synthesized with the multidentate calix[4]arene ligand H2L (H2L = 5,11,17,23-tetrakis(1,1-dimethylethyl)-25,27-dihydroxy-26,28-dimethoxycalix[4]arene) and Kläui's tripodal ligand LOEt(-) (LOEt(-) = (η(5)-cyclopentadienyl)tris(diethylphosphito-p)cobaltate(III)). All of the complexes have been characterized by single crystal X-ray diffraction analysis, thermal stability, absorption spectra, and magnetization measurements. The magnetic properties and magnetostructural correlation in this seven-coordinated system are investigated. The dysprosium complex 1 shows typical single-molecule magnetic behavior with characteristic magnetic hysteresis loops and the slow relaxation of magnetization.