Reaction of [Ln(NCS)(3)(THF)(4)](2) or [Yb(NCS)(3)(THF)(4)] with 18-crown-6 yields the moisture-stable [Ln(NCS)(3)(18-crown-6)] (Ln = La, Nd, Dy, Yb) complexes. Although the Ln contraction does not affect the coordination number, the crown ether is decreasingly folded with decreasing ion size. (C) 2012 Elsevier Ltd. All rights reserved.