PAPER www.rsc.org/dalton | Dalton Transactions Lanthanide–3d cyanometalate chains Ln(III)–M(III) (Ln = Pr, Nd, Sm, Eu, Gd, Tb; M = Fe) with the tridentate ligand 2,4,6-tri(2-pyridyl)-1,3,5-triazine (tptz): evidence of ferromagnetic interactions for the Sm(III)–M(III) compounds (M = Fe, Cr)†‡ Hanhua Zhao, Nazario Lopez, Andrey Prosvirin, Helen T. Chifotides and Kim R. Dunbar* Received 3rd November 2006, Accepted 19th December 2006 First published as an Advance Article on the web 18th January 2007 DOI: 10.1039/b616016f A series of cyanide-bridged chain mixed Fe(III)/Ln(III) (Ln = Pr, Nd, Sm, Eu, Gd, Tb) complexes with the tridentate ligand 2,4,6-tri(2-pyridyl)-1,3,5-triazine (tptz) used as a capping group has been prepared. Reactions of tptz and LnCl 3 with K 3 Fe(CN) 6 yield a family of air-stable 1-D compounds {[Pr(tptz)- (H 2 O) 4 Fe(CN) 6 ]·8H 2 O} ∞ (1), {[Nd(tptz)(H 2 O) 4 Fe(CN) 6 ]·8H 2 O} ∞ (2), {[Sm(tptz)(H 2 O) 4 Fe(CN) 6 ]· 8H 2 O} ∞ (3), {[Eu(tptz)(H 2 O) 4 Fe(CN) 6 ]·6H 2 O} ∞ (4), {[Gd(tptz)(H 2 O) 4 Fe(CN) 6 ]·6H 2 O} ∞ (5), and {[Tb(tptz)(H 2 O) 4 Fe(CN) 6 ]·8H 2 O} ∞ (6). Temperature dependent magnetic susceptibility studies of 1–6 reveal that in 3, the Sm(III) and Fe(III) ions are ferromagnetically coupled with 3-D ordering occurring below 3.5 K. The appearance of the frequency dependent out-of-phase signal is explained in terms of an ordering with a spin glass-like behavior. To compare the magnetic behavior of 3 with related compounds, {[Sm(tptz)(H 2 O) 4 Co(CN) 6 ]·8H 2 O} ∞ (7) and {[La(tptz)(DMF)(H 2 O) 3 Fe(CN) 6 ]·5H 2 O} ∞ (8), {[Sm(tmphen)(DMF) 3 (H 2 O)Fe(CN) 6 ]·2H 2 O} ∞ (9), {[Sm(tmphen) 2 (H 2 O) 2 Fe(CN) 6 ]·MeOH· 13H 2 O} ∞ (10) and {[Sm(tmphen) 2 (H 2 O) 2 Cr(CN) 6 ]·MeOH·9H 2 O} ∞ (11) with 3,4,7,8-tetramethyl-1, 10-phenanthroline (tmphen) were also prepared. Introduction Research aimed at designing multi-dimensional cyanide-bridged bimetallic assemblies of transition metals with interesting ar- chitectures and magnetic properties has been increasing in recent years. 1–3 Conversely, analogous efforts with rare-earth ions have been comparatively fewer, 4 despite the rather large anisotropic magnetic moments inherent to most lanthanide(III) ions. This lack of attention is attributed to the relatively weak interactions between lanthanide ions, due to the effective shielding by the outer-shell electrons, which may be enhanced, however, when the f electrons interact with the more expanded d electrons of transition metal ions. 5 The most well investigated compounds with magnetically coupled 4f–3d block ions are Gd(III)–Cu(II) or Gd(III)–organic radical systems. 5 Recently, various cyanide bridged networks comprising 4f ions and polycyanometallates 6 have been studied, including 3-D arrays of Fe(III), Co(III), Cr(III), 7,8 2-D structures of Cr(III) and Fe(III), 9–11 and 1-D structures of Fe(III), Co(III), Cr(III) and Mn(III) 12–24 as well as those of the diamagnetic ions [M(CN) 4 ] 2− (M = Ni, Pd, Pt). 25–29 Compounds with three spin carriers including a rare earth ion 30,31 and discrete 3d–4f molecular complexes 17,32–35 have also shown promising magnetic or photo-induced magnetic behavior. 36,37 Department of Chemistry, Texas A & M University, P. O. Box 30012, College Station, TX, 77842-3102, USA. E-mail: dunbar@mail.chem.tamu.edu; Fax: +1 (979) 845-7177; Tel: +1 (979) 845-5235 † The HTML version of this article has been enhanced with colour images. ‡Electronic supplementary information (ESI) available: Fig. S1–S13; Tables S1–S5. See DOI: 10.1039/b616016f The quest for molecules or molecular chains that exhibit slow paramagnetic relaxation, referred to as ‘single molecule magnets’ or ‘single chain magnets’ respectively, has fueled in- creasing interest in lanthanide ions as components of molecular materials. Although the field is still in its nascence, a number of lanthanide containing ‘single molecule magnets’ 38,39,40–50 and ‘single chain magnets’, 51–53 have been reported which indicate promising possibilities for this research. Herein, we report the preparation of a series of cyanide-bridged mixed chain compounds Ln(III)/Fe(III) (Ln = Pr, Nd, Sm, Eu, Gd, Tb) with the tridentate ligand 2,4,6-tri (2-pyridyl)-1,3,5-triazine (tptz; Chart 1a) as a capping group. 54–56 The present homologous series of 3d–4f transition metal chain compounds provides an opportunity to correlate 1-D magnetic behavior with the corresponding structural frameworks. To compare the magnetic behavior of the tptz Sm(III)/Fe(III) complex 3, the cyanide-bridged Sm(III)/Fe(III) and Sm(III)/Cr(III) chain compounds with the bidentate ligand 3,4,7,8-tetramethyl- 1,10-phenanthroline (tmphen; Chart 1b) were also prepared. By applying the strategy of diamagnetic substitution, 9,20,21,57–59 the isostructural tptz Sm(III)–Co(III) and La(III)–Fe(III) com- pounds were also prepared in order to obtain information on the signs of the Sm(III)/Fe(III) and Sm(III)/Cr(III) magnetic interactions. Results and discussion Syntheses and properties In most reported examples of chain compounds containing cyano- bridged 3d–4f paramagnetic transition metal ions, the coordina- tion sphere of the lanthanide ion consists of two molecules of a 878 | Dalton Trans., 2007, 878–888 This journal is © The Royal Society of Chemistry 2007