Spin crossover in polymeric and heterometallic FeII species containing polytopic dipyridylamino-substituted-triazine ligands.

We report the synthesis and characterisation of the new polytopic ligands, ddta (N,N-di(pyridin-2-yl)-4,6-di(1,4,7,10-tetraoxa-13-azacyclopentadecan-13-yl)-1,3,5-triazin-2-amine) and tptd (N(2),N(2),N(4),N(4)-tetra(pyridin-2-yl)-6-(1,4,7,10-tetraoxa-13-azacyclopentadecan-13-yl)-1,3,5-triazine-2,4-diamine). Each contains N-donor dipyridylamino binding sites as well as separate and distinct mono-aza-15-crown-5 binding sites. The ligand ddta has been used to synthesise the polymeric heterometallic SCO compound trans-[Fe(II)(NCS)(2)(ddta)(2)Na(2)](ClO(4))(2)·4CH(3)CH(2)CH(2)OH, 1, and tptd has been used to synthesise the polymeric SCO compound trans-[Fe(II)(NCS)(2)(tptd)]·CH(3)OH, 2, and the dinuclear compound cis-[(Fe(II))(2)(NCS)(4)(tptd)(2)], 3. Magnetic susceptibility measurements show that 1 and a desolvated sample of 2 each undergo a gradual, one-step spin transition with T(½) values of ~240 K and ~110 K, respectively. The paucity of inter-chain intermolecular interactions, as well as the flexible, covalent bridges between Fe(II) spin crossover sites, are likely to contribute to the gradual nature of the spin transition observed in each case. Variable temperature powder X-ray diffraction studies on 1 show the anisotropic behaviour of the unit cell parameters, where c and the b-c plane are most affected by structural changes occurring as the temperature is lowered.