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

The synthesis, crystal structure, and magnetic properties of four new mixed 3d–4f complexes with formulas [{FeIII(phen)­(CN)4}4Gd2III(bpym)­(NO3)2(H2O)4]·2CH3CN·2H2O}n (1), [{FeIII(phen)­(CN)4}4Tb2III(bpym)­(H2O)8]·(NO3)2·2CH3CN}n (2), [{FeIII(phen)­(CN)4}4SmIII(bpym)­(NO3)2(H2O)5]·2CH3CN}n (3), and [{FeIII(phen)­(CN)4}2Pr2III(bpym)(NO3)4(H2O)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-κ2-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.