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Three azobenzenes CN(C 6 H 4 )-NN-(C 5 H 4 N) (py-iso), CN(C 6 H 4 )-NN-(C 6 H 4 )CN (cyano-iso) and CN(C 6 H 4 )-NN-(C 6 H 4 )NC (iso-iso) with good coordinating groups (pyridine, phenylcyano or phenylisocyano) at the ends of the diazenyl unit have been synthesized and fully characterised. These compounds have been used as ligands in the synthesis of water-soluble metallic species by coordination to {Fe II (CN) 5 3- } units, either in one or two of the anchoring groups of the derivatives. Both the azo derivatives and their complexes are photochemically active with respect to their trans -to- cis isomerisation process. Their cis -to- trans reverse thermal reaction has been thoroughly studied as a function of the donor groups, solvent, temperature and pressure, in order to gain insight into the rotation or inversion mechanisms involved in the process. A comparison of the isomerisation mechanism between the iron complexes and the corresponding free ligands revealed an interesting fine tuning of the process on coordination of the {Fe II (CN) 5 3- } moieties, which may even produce, in some cases, non-photoswitchable species containing typically photoactive units.

The crystal structure of Mn(ii) carboxylate with 3-methylbenzoate as a bridging ligand [Mn(3-MeC 6 H 4 COO) 2 (H 2 O) 2 ] n shows a rhomboidal layer, where each pair of neighbor Mn(ii) ions are bridged through only one carboxylate group with a syn-anti conformation. The magnetic exchange between neighbor ions is weakly antiferromagnetic (J = -0.52 cm -1 , g = 2.04), and at low temperature the system shows spin canting with T B = 3.8 K. Computational studies, based on periodic calculations of the energies of the significant spin states on the magnetic cell and some higher supercells, corroborate the weak AF interaction between the adjacent Mn(ii) ions and preclude the negligible effect of frustration caused by very weak interactions between the non-adjacent ions in the magnetic response of the system. The results provide compelling evidence that the observed spin canting is due to the local coordination geometry of the manganese ions leading to two antiferromagnetically coupled subnets with different axial vectors.