Structural Characterization and Magnetic Properties of the First 2,2‘-Bipyrimidine-Containing Iron(III) Complexes

Two new iron(III) complexes of the formulas [Fe(bpm)Cl 3 (H 2 O)]·H 2 O ( 1 ) and [Fe 2 (bpm)Cl 6 (H 2 O) 2 ]·2H 2 O ( 2 ) (bpm = 2,2‘-bipyrimidine) have been synthesized and their crystal structures determined by single-crystal X-ray diffraction. 1 and 2 crystallize in the monoclinic system, space group P 2 1 / n, with a = 8.593(2) Å, b = 17.669(4) Å, c = 8.928(2) Å, β = 102.36(2)°, and Z = 4 for 1 and a = 6.422(3) Å, b = 11.999(4) Å, c = 12.297(6) Å, β = 93.82(4)°, and Z = 2 for 2 . The structure of complex 1 is made up of neutral [Fe(bpm)Cl 3 (H 2 O)] mononuclear units and water molecules of crystallization. The monuclear units are linked through hydrogen bonds involving the coordinated water molecule and one of the chlorine atoms yielding a uniform chain. The iron(III) is hexacoordinate, with two nitrogens of a chelating bpm, three chlorine atoms, and one water molecule building a distorted octahedron around the metal atom. The structure of 2 consists of centrosymmetric bpm-bridged dinuclear [Fe 2 (bpm)(Cl 6 )(H 2 O) 2 ] units and water molecules of crystallization which are linked through hydrogen bonds leading to a three-dimensional network. The geometry of each metal atom in 2 is distorted octahedral as in 1 . The equatorial positions around the metal ion in 1 and 2 are filled by two bpm nitrogens and two chlorine atoms, whereas the axial positions are occupied by a water molecule and a chlorine atom. The shortest intermolecular metal−metal distance in 1 is 5.957(2) Å, and the intramolecular metal−metal separation in 2 is 5.952(1). The magnetic behavior of 1 and 2 has been investigated over the temperature range 1.8−300 K. Significant antiferromagnetic coupling is observed for both compounds, the susceptibility curves exhibiting maxima at 5.0 ( 1 ) and 5.2 K ( 2 ). The pathways of the exchange interaction in 1 (hydrogen bonding) and 2 (hydrogen bonding and bridging bpm) are discussed in the light of their crystal structures, and the values of the coupling constants are compared with those of related systems.