Structural and magnetic properties of Co(II) complexes with tridentate ONO pincer-type ligands

Pincer type ligand 2,6-pyridinedimethanol was used as a useful tool in the preparation of the Co(II) pseudoctahedral complex together with 3,5-dinitrobenzoate counteranion. New complex of the composition [Co(pydm)(2)](3,5-dnbz)(2) (pydm = 2,6-pyridinedimethanol, and 3,5-dnbz = 3,5-dinitrobenzoate anion) has been prepared and characterized. Its XRD structure revealed pseudooctahedral {CoN2O4} chromophore around the cobalt atom with Co-N distances significantly shorter (Co-N-av = 2.038 angstrom) in comparison to the Co-O ones (Co-O-av = 2.142 angstrom), which was probably the reason of its relatively high zero-field splitting parameter (D/hc = 43.6 cm(-1)). Positive value of the D parameter causes slow relaxation process typical for Co(II) SMM behavior. The 3,5-dinitrobenzoate counteranions are strongly bonded to the [Co(pydm)(2)] cation via rather strong hydrogen bonds (O center dot center dot center dot O-av = 2.568 angstrom) forming "quasi molecular" units. Solid state structure allowed different pi-pi stacking interactions of neighboring "molecular" unit aromatic rings probally leading to observation of the additional relaxation mode.