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Coordination polymers; cluster; Ni$^{\text{II}}_2$ , 1D chain; magnetism; DFT.

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}$\cdot$2DMF$\cdot$H₂O]$_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 $J \approx +10$ cm^-1 and $D \approx −2$ 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$^{\text{II}}_2$ 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$^{\text{II}}_2$Na$^I_2$ 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).

Kartik Chandra Mondal¹ Bappaditya Gole¹ You Song² Stuart R Batten³ David R Turner³ Partha Sarathi Mukherjee¹

1. Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, India
2. State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, China
3. School of Chemistry, Monash University, Australia

Published

November 2011

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