Reaction of several lanthanide trichlorides LnCl(3) (Ln = La, Nd, Er, Lu) with 3 or 4 equiv of potassium 2,6-diisopropylphenoxide in THF solution leads to the formation of potassium salts of formula K[Ln(O-2,6-i-Pr2C6H3)(4)] [Ln = Nd (5), Er (6), Lu (7), La(8)]. These salts exhibit unusual solid-state structures involving multihapto potassium-pi-arene interactions. Not all lanthanide trichlorides produce the potassium salt directly from this reaction, and the nature of the product appears to be related to the solubility of the LnCl(3) starting material in THF solution. Compounds 5 and 6 exist in the solid state as pseudo-one-dimensional infinite-chain structures featuring multihapto K-C interactions with phenyl rings from two adjacent [Ln(OAr)(4)](-) units. Compound 8 forms a pseudo-two-dimensional sheet structure, with multihapto K-C interactions linking three neighboring [Ln(OAr)(4)](-) units. Ln-O distances within the tetrahedral [Ln(OAr)(4)](-) units average 2.211(12) (5), 2.084(14) (6) and 2.253(6) Angstrom (8). Potassium-carbon distances of the arene rings are in the ranges 3.097(8)-3.772(11) Angstrom (5), 3.018(8)-3.484(10) Angstrom (6) and 3.089(3)-3.519(4) Angstrom (8). Crystal data for 5 (at -171 degrees C) : monoclinic space group P2(1)/n, a = 12.990(4) Angstrom, b = 18.977(6) Angstrom, c = 18.594(5) Angstrom, beta = 93.94(1)degrees, V = 4572.66 Angstrom(3), d(calc) = 1.296 g cm(-3), Z = 4, R = 0.0538, R(W) = 0.0530. Crystal data for 6 (at -161 degrees C) : monoclinic space group P2(1)/n, a = 10.567(3) Angstrom, b = 20.856(6) Angstrom, c = 20.938(6) Angstrom, beta = 102.72(1)degrees V = 4500.93 Angstrom(3), d(calc) = 1.351 g cm(-3), Z = 4, R = 0.0362, R(W) = 0.0368. Crystal data for 8 (at -171 degrees C) : orthorhombic space group Pcab, a = 19.153(2) Angstrom, b = 20.898(3) Angstrom, c = 22.673(3) Angstrom, V = 9074.66 Angstrom(3), d(calc) = 1.299 g cm(-3), Z = 8, R = 0.0272, R(W) = 0.0281.