A series of nonanuclear lanthanide oxo-hydroxo complexes of the general formula [Ln(9)(mu(4)-O)(2)(mu(3)-OH)(8)(mu-BA)(8)(BA)(8)](-)[HN(CH2CH3)(3)](+).(CH3OH)(2)(CHCl3) (BA = benzoylacetone; Ln = Sm, 1; Eu, 2; Gd, 3; Dyt 4: Er, 5) were prepared by the reaction of hydrous lanthanide trichlorides with benzoylacetone in the presence of triethylamine in methanol and recrystallized from chloroform/methanol (1:10) at room temperature. These five compounds are isomorphous. Crystal data for 1: cubic, Pn (3) over barn; T = 180 K; a = 33.8652(4) Angstrom; V = 38838.4(8) Angstrom(3); Z = 6: D-calcd = 1.125 g cm(-3); R1 = 3.37%. Crystal data for 2: cubic, Pn (3) over barn; T = 180 K; a = 33,8252(8) Angstrom; V = 38700.9(16) Angstrom(3); Z = 6; D-calcd = 1.133 g cm(-3); R1 = 4.97%. Crystal data for 3: cubic, Pn (3) over barn; T = 180 K; a = 33.7061(6) Angstrom; V = 38293.5(12) Angstrom(3); Z = 6; D-calcd = 1.157 g cm(-3); R1 = 5.13%. Crystal data for 4: cubic, Pn (3) over barn; T = 180 K; a = 33.5900(7) Angstrom; V = 37899.2(14) Angstrom(3); Z = 6; D-calcd = 1.182 g cm(-3); R1 = 4.03%, Crystal data for 5: cubic, Pn (3) over barn; T = 180 K; a = 33,5054(8) Angstrom; V = 37613.6(16) Angstrom(3); Z = 6; D. Id = 1.202 g cm(-3); R1 = 4,86%. The core of the anionic cluster comprises two vertex-sharing square-pyramidal [Ln(5)(mu(4)-O)(mu(3)-OH)(4)](9-) units. The compounds were characterized by elemental analysis, IR, fast atom bombardment mass spectra, thermogravimetry, and differential scanning calorimetry. The thermal analysis indicated that the nonanuclear species were stable up to 150 degreesC. Luminescence spectra of 2 and magnetic properties of 1-5 were also studied.