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

The new polymeric, two-dimensional compounds [Fe-2(dca)(4)(bpym)].H2O (1) a nd [Fe-2(dca)(4)(bpym)(H2O)(2)] (2) (dca(-)=dicyanamide anion and bpym=2,2' -bipyrimidine) have been synthesised and characterised by infrared spectros copy and X-ray crystallography. Both compounds consist of two-dimensional n etworks of octahedrally co-ordinated iron(II) cations, bridged by bis-biden tate 2,2'-bipyrimidine and bridging dicyanamide anions. The metals are in a distorted octahedral environment due to the small bite angle of the bpym l igands [75.3(1)degrees in 1 and 73.7(1)degrees in 2]. The main difference b etween 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 unident ate ligands in a cis arrangement (one terminal dicyanamide and one water mo lecule). The main consequence of the different dca co-ordination modes is t hat 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 chi (m ) vs. T plots at ca. 11 K for both compounds, which is characteristic of an tiferromagnetic exchange interactions between the high-spin iron(II) centre s (J=-1.6 cm(-1), g=2.20 for 1 and J=-1.8 cm(-1), g=2.15 for 2).