MAGNETOSTRUCTURAL BEHAVIOR OF THE COMPLEX [MNL(H2O)(2)]CL-2.4H(2)O ATVARIABLE-TEMPERATURE STUDIED BY ELECTRON-SPIN-RESONANCE BICYCLO[12.3.1]OCTADECA-1(18),2,12,14,16-PENTAENE)

The molecular and crystal structure of the complex [MnL(H2O)(2)]Cl-2 . 4H(2)O 1 (L = bicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene) have been determined, the solid state and solution electronic spectra reco rded 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, wit h the macrocycle in the pentagonal plane and two water molecules in th e axial positions. From the UV/VIS spectra it can be seen that the ele ctronic structure of 1 is very sensitive to surroundings. The 300 K ES R 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 anal ysis and theoretical calculations give the best 300 K zero-field split ting parameters as D = 0.07 cm(-1), E = 0.008 cm(-1), lambda = 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 dis tortion 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 th eoretical Q-band spectra were calculated on the basis of the X-band pa rameters. The temperature variation of the crystal-field parameters is interpreted as a smooth magnetostructural temperature dependence of t he compound.