Low-Dimensional 3d–4f Complexes Assembled by Low-Spin [Fe^III(phen)(CN)₄]⁻ Anions

The synthesis, crystal structure, and magnetic properties of four new mixed 3d-4f complexes with formulas [{Fe(III)(phen)(CN)(4)}(4)Gd(2)(III)(bpym)(NO(3))(2)(H(2)O)(4)]·2CH(3)CN·2H(2)O}(n) (1), [{Fe(III)(phen)(CN)(4)}(4)Tb(2)(III)(bpym)(H(2)O)(8)]·(NO(3))(2)·2CH(3)CN}(n) (2), [{Fe(III)(phen)(CN)(4)}(4)Sm(III)(bpym)(NO(3))(2)(H(2)O)(5)]·2CH(3)CN}(n) (3), and [{Fe(III)(phen)(CN)(4)}(2)Pr(2)(III)(bpym)()(NO(3))(4)(H(2)O)(2)](n) (4) (phen = 1,10-phenanthroline and bpym = 2,2'-bipyrimidine) are discussed here. Compounds 1-3 are isomorphous and their structure consists of neutral ladder-like motifs where the rungs are made up by bpym-bridged dilanthanide(III) cations and the rods are defined by [Fe(phen)(CN)(4)](-) units adopting a bis-monodentate coordination mode through two of its four cyanide ligands. The electroneutrality in this family is achieved by either a chelating [at the Gd(III) (1) and Sm(III) (3)] or free [at the Tb(III) (2)] nitrate group and a peripheral [Fe(phen)(CN)(4)](-) entity, which act as a monodentate ligand across one of its four cyanide groups toward the rare-earth cation (1-3). Compound 4 exhibits a neutral two-dimensional structure where (μ-bpym)bis[diaquadi(nitrato-κ(2)-O,O')praseodymium(III)] fragments are interlinked through [Fe(phen)(CN)(4)](-) units adopting a tris-monodentate coordination mode across three of its four cyanide groups. Each iron(III) ion in 1-4 is six-coordinate with two nitrogen atoms from a chelating phen and four cyanide-carbon atoms building a somewhat distorted octahedral environment. The trivalent rare-earth cations are 9- (1-3) and 10-coordinate (4) having in common two nitrogen atoms from a bidentate bpym and three (1-3)/two (4) cyanide nitrogens, the coordination environment being completed by chelating nitrate (1, 3, 4) and water molecules (1-4). Magnetic susceptibility measurements in the 1.9-300 K temperature range show the occurrence of antiferromagnetic interactions in 1 through both the single cyanide- and the bis-bidentate bpym ligands. A weak ferromagnetic interaction is observed for 3 whereas very weak, if any, magnetic interactions would occur in 2 and 4, with the spin-orbit coupling of the low-spin iron(III) ion and the ligand field effects of the Tb(III) (2) and Pr(III) (4) masking their visualization.