Spin Crossover and Field‐Induced Single‐Molecule Magnet Behaviour in Co(II) Complexes Based on Terpyridine with Tetrathiafulvalene Analogues

Two new TTF-based ligands involving terpyridine moiety (L-1=4-(4 '-Methyl-phenyl-2,2 : 6',2''-terpyridine -4-ylmethylthio)-5-(2-cyanoethylthio)-4 ',5 '-bis(methylthio)tetrathiafulvene and L-2=4-(4 '-Methyl-phenyl-2,2 : 6',2''-terpyridine -4-ylmethylthio)-5-(2-cyanoethylthio)-4 ',5 '-bis(propylthio)tetrathiafulvene) have been synthesized and seven related mononuclear complexes were isolated as single crystals. The 2 : 1 (ligand : metal) complexes of formula [Co(L-1)(2)](NO3)(2) (2) and [Co(L-1)(2)](BF4)(2) (3) displayed thermal spin crossover transition while the 1 : 1 complexes of formula [CoCl2(L-1)](DMF)(2) (4), [CoBr2(L-1)] . (DMF) (5), [CoCl2(L-2)] . (DMF) . 0.5(Et2O) (6) and [CoBr2(L-2)] . (DMF) (7) displayed slow magnetic relaxation through either Raman or Raman/Direct combination processes. A relationship between the structure and the nature of the magnetic relaxation processes is proposed.