Coordination cluster nuclearity decreases with decreasing rare earth ionic radius in 1:1 Cr/Ln N-butyldiethanolamine compounds: a journey across the lanthanide series from Cr4(III)La4–Cr4(III)Tb4 via Cr3(III)Dy3 and Cr3(III)Ho3 to Cr2(III)Er2–Cr2(III)Lu2.

Reactions of the N-substituted diethanolamine ligand N-n-butyldiethanolamine with chromium(II) and lanthanide(III)/rare earth salts (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y) in the presence of coligands give access to three series of isostructural 1:1 3d(Cr(III))/4f(Ln(III)) coordination cluster compounds that can be designated in terms of octanuclear "square-in-square" (Ln = La-Tb), hexanuclear "triangle-in-triangle" (Ln = Dy, Ho, Y) and tetranuclear "butterfly" or defect dicubane core (Ln = Er-Lu) topologies as revealed by single-crystal X-ray crystallographic analysis. The bulk magnetic properties were also measured. The influences of the various components in the reaction system on the final topology and the role of the ionic radius are discussed.