Hydrogen bond-induced abrupt spin crossover behaviour in 1-D cobalt(II) complexes - the key role of solvate water molecules

The magnetic properties and structural aspects of the 1-D cobalt(II) complexes, [Co(pyterpy)Cl-2]center dot 2H(2)O (1.2H(2)O; pyterpy = 4 '-(4 '''-pyridyl)-2,2 ':6 ',2 ''-terpyridine) and [Co(pyethyterpy)Cl-2]center dot 2H(2)O (2.2H(2)O; pyethyterpy = 4 '-((4 '''-pyridyl)ethynyl)-2,2 ':6 ',2 ''-terpyridine) are reported. In each complex the central cobalt(II) ion displays an octahedral coordination environment composed of three nitrogen donors from the terpyridine moiety, a nitrogen donor from a pyridyl group and two chloride ligands which occupy the axial sites. 1.2H(2)O exhibits abrupt spin-crossover (SCO) behaviour (T-1/2 down arrow = 218 K; T-1/2 up arrow = 227 K) along with a thermal hysteresis loop, while 2.2H(2)O and the dehydrated species 1 and 2 exhibit high-spin (HS) states at 2-300 K as well as field-induced single-molecule magnet (SMM) behaviour attributed to the presence of magnetic anisotropic HS cobalt(II) species (S = 3/2). 1.2H(2)O exhibited reversible desorption/resorption of its two water molecules, revealing reversible switching between SCO and SMM behaviour triggered by the dehydration/rehydration processes. Single crystal X-ray structural analyses revealed that 1.2H(2)O crystalizes in the orthorhombic space group Pcca while 2 and 2.2H(2)O crystallize in the monoclinic space group P2/n. Each of the 1-D chains formed by 1.2H(2)O in the solid state are bridged by hydrogen bonds between water molecules and chloride groups to form a 2-D layered structure. The water molecules bridging 1-D chains in 1.2H(2)O interact with the chloride ligands occupying the axial positions, complementing the effect of Jahn-Teller distortion and contributing to the abrupt SCO behaviour and associated stabilization of the LS state.

Automated summary

The magnetic properties and structural aspects of 1-D cobalt(II) complexes were studied, revealing different magnetic behaviors in different compounds. The presence of water molecules was found to have an impact on the magnetic properties of the complexes.