New compounds with bridging dicyanamide and bis-chelating 2,2′-bipyrimidine ligands: syntheses, structural characterisation and magnetic properties of the two-dimensional materials [Fe2(dca)4(bpym)]·H2O and [Fe2(dca)4(bpym)(H2O)2]

Abstract

The new polymeric, two-dimensional compounds [Fe₂(dca)₄(bpym)]·H₂O (1) and [Fe₂(dca)₄(bpym)(H₂O)₂] (2) (dca⁻ = dicyanamide anion and bpym = 2,2′-bipyrimidine) have been synthesised and characterised by infrared spectroscopy and X-ray crystallography. Both compounds consist of two-dimensional networks of octahedrally co-ordinated iron(II) cations, bridged by bis-bidentate 2,2′-bipyrimidine and bridging dicyanamide anions. The metals are in a distorted octahedral environment due to the small bite angle of the bpym ligands [75.3(1)° in 1 and 73.7(1)° in 2]. The main difference between the two structures is the co-ordination mode of the dca ligands. In compound 1, the iron(II) cation is linked by four dca bridging ligands and by one bis-chelating bpym. In compound 2, each iron cation is linked by two trans-bridging dicyanamide ligands, one bis-chelating bpym and two unidentate ligands in a cis arrangement (one terminal dicyanamide and one water molecule). The main consequence of the different dca co-ordination modes is that each metal cation is connected to four neighbouring metals in 1 but to only three in 2. Magnetic measurements reveal a broad maximum in the χ_ms. T plots at ca. 11 K for both compounds, which is characteristic of antiferromagnetic exchange interactions between the high-spin iron(II) centres (J = −1.6 cm⁻¹, g = 2.20 for 1 and J = −1.8 cm⁻¹, g = 2.15 for 2).