The metathesis reaction of anhydrous LnCl3(Ln = Y, Dy, Er, Sm, Yb) with the potassium salt KL [L = 2,4,6-Me3C6H2-NC(Me)CHC(Me)N-2,4,6-Me3C6H2], a mesityl-substituted β-diketiminate, is described. Dinuclear complexes with an unusual triple chlorido bridge in the molecule [LClLn(µ-Cl)3LnL(THF)] [Ln = Y (1a) and Dy (1b)] were obtained by recrystallization from a mixture of non-polar solvents (toluene/n-pentane) in low yield. In contrast, the crystallization in the presence of THF led to the isolation of mononuclear complexes [LLnCl2(THF)2] [Ln = Y (2a), Dy (2b), Er (2c), Sm (2d), Yb (2e)] in good yields. Compounds 1b and 2a–e were fully characterized, and the solid-state structures of 1a,b and 2a–c were determined by single-crystal X-ray diffraction. The magnetic properties of 2b were studied in detail.