Magnetostructural behaviour of the complex [MnL(H2O)2]Cl2·4H2O at variable temperature studied by electron spin resonance (L = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene)

Abstract

The molecular and crystal structure of the complex [MnL(H₂O)₂]Cl₂·4H₂O 1 (L = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene) have been determined, the solid state and solution electronic spectra recorded and the thermogravimetric analysis as well as an ESR analysis at different temperatures performed. The structure shows that the cation displays a distorted pentagonal-bipyrimidal co-ordinated geometry, with the macrocycle in the pentagonal plane and two water molecules in the axial positions. From the UV/VIS spectra it can be seen that the electronic structure of 1 is very sensitive to surroundings. The 300 K ESR spectrum of 1 consists of five fine-structure lines centred at g = 2.111, showing anisotropy. A sequence of spectra neatly shows that the compound has a clear magnetic dependence on temperature. Spectral analysis and theoretical calculations give the best 300 K zero-field splitting parameters as D = 0.07 cm^–1, E = 0.008 cm^–1, λ = E/D = 0.1142. The 77 K zero-field splitting parameters increase to D = 0.074 cm^–1 and E = 0.012 cm^–1, thus indicating an increasing rhombic distortion as the temperature decreases. The Q-band spectra at 300 and at 77 K are isotropic, and the zero-field effects are very small. The theoretical Q-band spectra were calculated on the basis of the X-band parameters. The temperature variation of the crystal-field parameters is interpreted as a smooth magnetostructural temperature dependence of the compound.