The two-dimensional (2D) system [NH,(CH,),NH,]MnCl, is investigated by means of electron spin resonance (ESR) at X-band over the 40 to 300 K temperature range. The linewidth, the g-factor, the spin-lattice relaxation time T I , and their thermal and angular dependences are measured. The data are characteristic of a 2D compound. The angular dependence AH(0) indicates, taking also into account the presence of a half-field line, the diffusive character of the magnetization at long time. The observed thermal dependences are consistent with an antiferromagnetic order at 40 K. The experimental data are interpreted using the Bloembergen and Wang three-reservoir model since a strong exchange interaction is present.

The anisotropies of the EPR linewidth and g-factor were investigated in two-dimensional molecular composites of the type [NH3-R-NH3]MX 4 . Measurements were performed both in single crystals and powders over the temperature range 4.2-290 K. The spin-lattice relaxation time T l was measured using the modulation method, as a function of temperature. The samples exhibit different structures and coupling interactions, according to the nature of the halogen X, the metal M and the organic radical R. We have analysed the influence of these parameters on spin behavior by studying the samples [NH3-(CH)n-NH3]MX 4 with M = Mm, Cu; X = C1, Br, and n = 2, 3, 4, 5. When R is constituted by molecules with unsaturated bonds, these materials can be considered as excellent matrices for selective polymerisation reactions by irradiation or thermal processing. We have performed EPR measurements on the heated complex of propargylamine and cadmium chloride [HC~C-CH2-NH3]2CdC14 . The obtained data are interpreted taking into account the strong exchange interaction and the various coupling interactions in the samples. The thermal dependences of T l are explained by means of the Bloembergen and Wang three-reservoir model. The data show spin diffusion when the metal is manganese, and an antisymmetric exchange interaction modulated by phonons in the case of copper. The nature of the halogen plays ala important role in spin dynamics and namely in spin-lattice relaxation. The results obtained on [HC-C-CH2-NH3]2CdC14 after heating under vaccum show the creation of many paramagnetic centers due to the vanishing of triple bonds and the occurrence of a strong exchange interaction.