The complexes [Ln(terpy)(2)(NCS)(3)] (Ln = Pr (1), Nd (2); terpy = 2,2':6',2"-terpyridine), [Nd(terpY)2(NCS)(3)]-2EtOH (3) and [Ln(phen)3(NCS)3].EtOH (Ln = Pr(4), Nd (5); phen = 1,10-phenanthroline) have been synthesised in high yield by the reaction of [Ln(NO3)(3)].6H(2)O (Ln = Pr, Nd) with KNCS and subsequently with terpy or phen, respectively. The five complexes have been characterised crystallographically, and it is found that the pairs of complexes, I and 2, and 4 and 5 are isomorphous with each other. In all the complexes the lanthanoid ions are nine co-ordinate, and all contain meridionally disposed thiocyanate groups. The molecular geometry of 3 is very similar to that of 2, and the crystal structure differs only in the presence of the two ethanol solvent molecules. In the whole series of complexes the Ln-N(thiocyanate) distances are shorter than the Ln-N(terpy/phen) distances and there is a shortening of all the lanthanoid-ligand bonds in the neodymium complexes compared with the praseodymium, consistent with the expected 'lanthanide contraction' that occurs as additional electrons enter the 4f orbitals. In all the complexes the thiocyanate groups are linear, but there is a significant variation in the angle at the thiocyanate at nitrogen and Ln-N-C angles lie in the range 147-177degrees. (C) 2003 Elsevier Science Ltd. All rights reserved.