Syntheses, crystal structure and magnetic properties of an unprecedented one-dimensional coordination polymer derived from an {(NiL)₂Ln} node and a pyrazine spacer (H₂L = N,N′-Bis(salicylidene)-1,3-propanediamine, Ln = Gd, Tb and Dy)

Abstract

In order to investigate the coordinative interaction of the [Ni^IIL] metalloligand with lanthanides (H₂L = N,N′-bis(salicylidene)-1,3-propanediamine or H₂salpn) and the building block potential of the resultant unstable {(Ni^IIL)₂Ln^III} (Ln^III = Lanthanides) complex with a short spacer pyrazine (pyz), three heterometallic coordination polymers of formulae [{(NiL)₂Ln(NO₃)₃}pyz]_n⋅1.5nH₂O [Ln = Gd (1), Tb (2) and Dy (3)] have been synthesized. In these compounds the central Ln^III ion is connected to two terminal [NiL] metalloligands through µ_1,1-diphenoxido bridges to form the trinuclear node with three nitrato coligands (LnO₉ monocapped square-antiprism). The coordinative preference of pyrazine ligand towards the Ni^II-centre of the trinuclear units leads to the formation of these tailored 1D-zigzag coordination polymers with transoidtrinuclear nodes. The magnetization at 1.8 K for 1 (10.4 μ_B at 7 T) indicates the presence of Gd−Ni ferromagnetic coupling through the phenoxido bridges. The exchange parameter was determined to be +0.179(4) K from the magnetic susceptibility measurement. Both in-phase and out-of-phase ac magnetic measurements under an applied dc magnetic field reveal temperature dependence of the susceptibility at different frequencies below 5 K for compound 3, characteristic of Single Molecule Magnets (SMMs) or polymeric aggregates of SMMs.