No abstract

Complexes [(dpp-BIAN)0CoIII2]·MeCN (I) and [(Py)2CoI2] (II) were synthesized by the reaction between cobalt(II) iodide and 1,2-bis(2,6-diisopropylphenylimino)acenaphthene (dpp-BIAN) or pyridine (Py), respectively. The molecular structures of the complexes were determined by X-ray diffraction. The Co(II) ions in both compounds are in a distorted tetrahedral environment (CoN2I2). The electrochemical behavior of complex I was studied by cyclic voltammetry. Magnetochemical measurements revealed that when an external magnetic field is applied, both compounds exhibit the properties of field-induced single ion magnets.

No abstract

New adducts with the composition [Co2Gd(NO3)(Piv)6L2] (L=2,4‐lutidine (lut) (1), 2‐phenylpyridine (PhPy) (4), 2‐ethynylpyridine (EtPy) (5)) and [Co2Eu(NO3)(Piv)6(EtPy)2] (6) were synthesized. According to X‐ray diffraction data, the molecular complexes comprise two atoms of cobalt(II) and one central atom of gadolinium(III) bridged by carboxylate ligands. The donor base molecules are coordinated to cobalt atoms. Magnetic measurements of the new and previously synthesized complexes with quinoline (2) and pyridine (3) ligands showed the ferromagnetic nature of the coupling between the metal centers in the CoII2GdIII core with JCo‐Gd parameters in the range of 0.15−0.18 cm−1. DFT calculations supported the ferromagnetic type of coupling for these complexes. Simultaneous thermal analysis of 1 and 2 showed the thermal stability of the complexes up to 180 °C and the stepwise nature of thermolysis, which includes the stages of elimination of the donor base molecules and the thermal decomposition of the pivalate moieties in the complex.

A new 1D-coordination polymer [Co(Piv)2(NH2(CH2)6NH2)]n (1, Piv is Me3CCO2− anion) was obtained, the mononuclear fragments {Co(O2CR)2} within which are linked by μ-bridged molecules of hexamethylenediamine (NH2(CH2)6NH2). For this compound, two different monoclinic C2/c (α-1) and P2/n (β-1) phases were found at room temperature by single-crystal X-ray diffraction analysis, with a similar structure of chains and their packages in unit cells. The low-temperature phase (γ-1) of crystal 1 at 150 K corresponds to the triclinic space group P-1. As the temperature decreases, the structural phase transition (SPT) in the α-1 and β-1 crystals is accompanied by an increase in the crystal packing density caused by the rearrangements of both H-bonds and the nearest ligand environment of the cobalt atom (“octahedral CoN2O4 around the metal center at room temperature” → “pseudo-tetrahedral CoN2O2 at 150 K”). The SPT was confirmed by DSC in the temperature range 210–150 K; when heated above 220 K, anomalies in the behavior of the heat flow are observed, which may be associated with the reversibility of SPT; endo effects are observed up to 300 K. The SPT starts below 200 K. At 100 K, a mixture of phases was found in sample 1: 27% α-1 phase, 61% γ-1 phase. In addition, at 100 K, 12% of the new δ-1 phase was detected, which was identified from the diffraction pattern at 260 K upon subsequent heating: the a,b,c-parameters and unit cell volume are close to the structure parameters of γ-1, and the values of the α,β,γ-angles are significantly different. Further heating leads to a phase transition from δ-1 to α-1, which both coexist at room temperature. According to the DC magnetometry data, during cooling and heating, the χMT(T) curves for 1 form a hysteresis loop with ~110 K, in which the difference in the χMT values reaches 9%. Ab initio calculations of the electronic structure of cobalt(II) in α-1 and γ-1 have been performed. Based on the EPR data at 10 K and the ab initio calculations, the behavior of the χMT(T) curve for 1 was simulated in the temperature range of 2–150 K. It was found that 1 exhibits slow magnetic relaxation in a field of 1000 Oe.