Synthesis, crystal structure and magnetic properties of the manganese(II) chains [Mn(bipym)(NO3)2] and [Mn(bipym)(NCO)2] (bipym = 2,2′-bipyrimidine)

Abstract

Two new manganese(II) chains of formula [Mn(bipym)(NO ₃ ) ₂ ] 1 and [Mn(bipym)(NCO) ₂ ] 2 (bipym = 2,2′-bipyrimidine) have been synthesized and their structures determined by single-crystal X-ray diffraction. Their structures consist of zigzag chains of bipym-bridged manganese(II) ions where electroneutrality is achieved by monodentate and chelating nitrate groups (1) and by N-bonded terminal cyanate ligands (2). The manganese atom in 1 is seven-co-ordinated being surrounded by four bipym nitrogens and three nitrato-oxygens [Mn–N and Mn–O 2.362(2)–2.330(2) and 2.205(2)–2.392(2) Å, respectively]. The manganese atom in 2 is six-co-ordinated with four bipym- and two cyanato-nitrogen atoms in cis position comprising a distorted-octahedral environment [average Mn–N (cyanato) and Mn–N (bipym) bond distances 2.097(3) and 2.355(3) Å, respectively]. In both structures the bipym group acts as a bis(bidentate) ligand forming two five-membered chelate rings, the values of the bite angle at the bipym being 69.5(1) and 69.3(1)° in 1 and 69.5(1)° in 2. The intrachain metal–metal separations are 6.239(1) and 6.247(1) Å in 1 and 6.234(1) Å in 2. Variable-temperature magnetic susceptibility data in the temperature range 290–4.2 K show the occurrence of a significant intrachain antiferromagnetic coupling between the local high-spin manganese(II) ions, the values of the exchange coupling parameter J being -0.93 (1) and -1.1 (2) cm ^-1 . The efficiency of bis(chelating) ligands such as bipym and oxalate in mediating antiferromagnetic coupling between manganese(II) ions is analysed and discussed in the light of available magnetostructural data.