[Mn2(bipym)(H2O)8]4+ and [Fe(bipy)(CN)4]− as building blocks in designing novel bipym- and cyanide-bridged heterobimetallic complexes (bipym = 2,2′-bipyrimidine and bipy = 2,2′-bipyridine)

Abstract

Two new cyano complexes, K[Fe(bipy)(CN)₄]·H₂O (1) and (μ-bipym)[Mn(H₂O)₃{Fe(bipy)(CN)₄}]₂[Fe(bipy)(CN)₄]₂·12H₂O (2), have been synthesised and their structures determined by single-crystal X-ray diffraction. Complex 1 is made up of mononuclear [Fe(bipy)(CN)₄]⁻ anions, potassium cations and water molecules of crystallization. The iron(III) is six-coordinated, being surrounded by two nitrogen atoms of a chelating bipy and four carbon atoms of four cyanide groups [Fe–N and Fe–C 1.991(3)–1.990(3) and 1.958(5)–1.914(5) Å, respectively]. Complex 2 consists of centrosymmetric tetranuclear (μ-bipym)[Fe(H₂O)₃{Fe(bipy)(CN)₄}]₂²⁺ cations, [Fe(bipy)(CN)₄]⁻ anions and water molecules of crystallization. The cyano-containing iron(III) complex of 1 is present in 2 but in the latter it acts not only as a counterion but also as a monodentate ligand towards the manganese atom through one of its four cyanide groups. Bond lengths and angles around the iron atoms in 2 are practically identical to those observed in 1. The manganese atom in 2 is six-coordinated with two bipym- and one cyanide-nitrogen atoms and three mer-water molecules comprising a distorted octahedral environment [Mn–N(bipym) 2.35(1) and 2.29(1) Å, Mn–N(cyanide) 2.19(2) and Mn–O 2.21(1)–2.12(2) Å]. The manganese–manganese and manganese–iron separations across the bis-chelating bipym and single-cyano bridge are 6.131(6) and 5.092(4) Å, respectively. Studies of the magnetic behaviour of 1 and 2 in the temperature range 1.9–300 K reveal that compound 1 is a magnetically isolated low-spin iron(III) complex with an important orbital contribution whereas significant antiferromagnetic interactions occur in 2 between the manganese(II) ions across bis-chelating bipym (J = −1.2 cm⁻¹) and between the manganese(II) and iron(III) ions through the single-cyano bridge (j = −3.0 cm⁻¹). The use of [Fe^III(AA)(CN)₄]⁻ (AA = bidentate ligand) as a ligand towards metal ions appears very promising in designing new cyano-bridged polynuclear compounds.