Structural and photomagnetic studies of a 1-D bimetallic chain [Mn_2~(II)(L)_2(H_2O)][Mo~(IV)(CN)_8] (centre dot) 5H_2O (L = macrocycle); analogy with the photo-oxidation of K_4[Mo~(IV)(CN)_8] (centre dot) 2H_2O

摘要

A one-dimensional chain [Mn_2~(II)(L)_2(H_2O)][Mo~(IV)(CN)_8] (centre dot) 5H_2O 2 (L = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene, macrocyclic ligand) has been prepared from the reaction of K_4[Mo~(IV)(CN)_8] (centre dot) 2H_2O 1 with the complex [Mn~(II)L(H_2O)_2]Cl_2 (centre dot) 4H_2O and its structure and photomagnetic properties have been studied. The structure of 2 consists of a polymeric zigzag chain of alternating Mn(L) and Mo(CN)_8 units with another Mn(L) unit linked to the Mo as a pendant arm. The paramagnetic compound 2 shows important modifications of its magnetic properties under UV-light irradiation, leading to the formation of ferrimagnetic chains. This non-reversible photomagnetic effect is thought to be caused by an internal photo-oxidation of Mo~(IV) (diamagnetic) to Mo~C (paramagnetic) as observed in the precursor 1. The crystallographic data seem to indicate that the formation of hydrogen bonds between water molecules and nitrogen atoms of non-bridging cyano groups is a key factor to observe the molybdenum photo-oxidation.