Synthesis, structure and electronic properties are reported on single crystals of Sm4Mo18O32 and Nd4Mo18O32. The triclinic crystal structure has three distinctly different Mo metal atom clusters (Mo-2, Mo-4 and Mo-6), which extend in complex chains. The temperature dependence of the electrical resistivity displays a broad minimum around 150-200 K with a pronounced increase in the 30-50 K range. However, unlike the related monoclinic reduced Mo oxides, A(4)Mo(18)O(32) (A = Y, Gd-Yb), there is no true metal-insulator transition in the Sm and Nd analogs. We discuss these observations in terms of correlations among the Mo clusters. (c) 2006 Elsevier Ltd. All rights reserved.