First example of chromone-based nickel(II) coordination polymers with tunable magnetic properties

Abstract

We present three novel Ni(II)-based coordination polymers (CPs) formulated as [Ni(L1)(NCS)2]·2H2O (1), [Ni(L2)(NCS)2] (2), and [Ni2(L3)2(dca)3]NO3·2CH3OH (3), where Ln = Schiff bases resulting from the condensation of N1-ethylethane-1,2-diamine (for L1), N1,N1- diethylethane-1,2-diamine (for L2) or N1,N1-dimethylethane-1,2-diamine (for L3) with chromone 3-carboxaldehyde in a 1:1 molar ratio (dca− = dicyanamide = N(CN)2−). Compounds 1 and 2 show similar μ1,3- thiocyanato-bridged regular chains with different interchain interactions due to the different functional groups of L1 and L2. Both compounds are metamagnets at low temperature with critical fields of 8 and 200 mT in 1 and 2, respectively, in agreement with the stronger interchain interactions observed in 2. Compound 1 presents an antiferromagnetic order at 3.2 K for DC fields below 8 mT and a canted antiferromagnetic order for fields above 8 mT. Compound 2 shows an antiferromagnetic order at ca. 3.0 K and a ferromagnetic one for fields above 200 mT. Compound 3, prepared with a slight modification of the Schiff base ligand, is a 2D Ni-based dicyanamide-bridged network that shows a very weak antiferromagnetic Ni−Ni interaction through the 1,5-dca− bridges and a ZFS in the Ni(II) ions. We show that slight changes in a Schiff base ligand lead to important changes in the intermolecular interactions and in the magnetic properties. On the other side, changes in the coligand may induce changes in the dimensionality and also in the magnetic properties.