[Fe(phen)(CN)4]−: a suitable metalloligand unit to build 3d–4f heterobimetallic complexes with mixed bpym-cyano bridges (phen = 1,10-phenantroline, bpym = 2,2′-bipyrimidine)

Abstract

The synthesis, crystal structure and magnetic properties of a new series of mixed 3d–4f complexes with the formula [{Fe^III(phen)(CN)₃(μ-CN)}₄Ln₂^III(NO₃)₂(H₂O)₆(μ-bpym)]·nH₂O [Ln = Eu (1), Gd (2), Dy (3) and Ho (4); n = 8 (1, 3 and 4) and 11 (2); phen = 1,10-phenantroline; bpym = 2,2′-bipyrimidine] are discussed here. Compounds 1–4 are centrosymmetric hexanuclear species whose structure is made up of two cyano-bridged {Fe₂^IIILn^III} heterobimetallic moieties which are connected through a bis-bidentate bpym molecule between the two rare-earth centers. The values of the iron–lanthanide distance across the single cyano-bridge are Fe(1)⋯Eu(1) = 5.5587(8) and Fe(2)⋯Eu(1) = 5.4908(8) Å (1), Fe(1)⋯Gd(1) = 5.5456(6) and Fe(2)⋯Gd(1) = 5.4831(6) Å (2), Fe(1)⋯Dy(1) = 5.5223(7) and Fe(2)⋯Dy(1) = 5.4509(7) Å (3) and Fe(1)⋯Ho(1) = 5.5094(12) and Fe(2)⋯Ho(1) = 5.4420(14) Å (4), whereas those of the lanthanide–lanthanide separation through the bpym bridge are 6.8196(8) (1), 6.7971(6) (2), 6.7511(7) (3) and 6.7395(6) Å (4). The two crystallographically independent iron(III) ions in 1–4 are six-coordinated with two nitrogen atoms from a bidentate phen ligand and four carbon atoms from four cyanide groups building somewhat distorted octahedral surroundings. The trivalent lanthanide cations in 1–4 are nine-coordinated with two bpym and two cyano-nitrogen atoms, three water molecules and a chelating nitrate describing distorted monocapped square antiprism environments. Compounds 1–4 are isomorphous species where the neutral hexanuclear motifs are assembled through an extensive network of hydrogen bonds involving all the water molecules to afford a supramolecular three-dimensional structure. Interestingly, the crystal packing of 2 shows the occurrence of unprecedented centrosymmetric twelve-atom water aggregates which are integrated by two interlinked pentanuclear water rings, each one having a dangling water molecule. The investigation of the magnetic properties of 1–4 in the temperature range 1.9–300 K reveals the presence of intramolecular magnetic interactions for 2–4 [antiferro- (through single cyano and bpym bridges) in 2 and ferromagnetic (across single cyano and/or bpym bridges) in 3 and 4] whereas the magnetic behaviour of 1 corresponds to that of the magnetically isolated low-spin iron(III) and europium(III) centers.