Two new 1D chains of Ni 2 Na 2 heterometallic double half-cubane building units: Synthesis, structures and variable temperature magnetic study

Abstract

An equimolar mixture of Ni(NO3)2·6H2O and pyridine-2-aldehyde with two equivalents of NaN3 in methanol in the presence of NaOMe resulted in the formation of light green precipitate which upon crystallization from dimethylformamide (DMF) yielded light green single crystals [{Ni2Na2(pic)4(N3)2(H2O)2(MeOH)}· MeOH·3H2O]n (1) and [{Ni2Na2(pic)4(N3)2(H2O)4}·2DMF·H2O]n (2) (pic = pyridine-2-carboxylate) at room temperature and high temperature (100°C), respectively. Variable temperature magnetic studies revealed the existence of overall ferromagnetic behaviour with J ≈ +10 cm − 1 and D ≈ − 2 to −7 cm − 1 for 1 and 2, respectively. Negative D values as well as variation of D upon slight distortion of structure by varying reaction temperature were observed. The X-band Electron Paramagnetic Resonance (EPR) spectra of both 2 and 3 were recorded below 50 K. The structural distortion was also implicated from the EPR spectra. Density Functional Theory (DFT) calculations on both complexes were performed in two different ways to corroborate the magnetic results. Considering only Ni\(^{\rm II}_{2}\) dimeric unit, results were J = +20.65 cm − 1 and D = −3.16 cm − 1 for 1, and J = +24.56 cm − 1 and D = −4.67 cm − 1 for 2. However, considering Ni\(^{\rm II}_{2}\)Na\(^{\rm I}_{2}\) cubane as magnetic core the results were J = +16.35 cm − 1 (1), +19.54 cm − 1 (2); D = −3.05 cm − 1 (1), −4.25 cm − 1 (2). Two new 1D chains of Ni2Na2heterometallic double half-cubane building units have been isolated from the reaction of a 1:1 mixture of Ni(NO3)2·6H2O and pyridine-2-aldehyde with two equivalents of NaN3 in the presence of NaOMe and their structures established by X-ray crystallography. The magnetic behaviour of the two complexes has been studied and DFT calculations performed to investigate the exchange mechanism.