Second sphere coordination in anion binding: Synthesis, characterization, X-ray structure of tris(1,10-phenanthroline)cobalt(III)2,4-dinitrophenolate tetrahydrate, [Co(phen)3](dnp)3·4H2O where dnp = 2,4-dinitrophenolate

A new cobalt(III) complex salt, [Co(phen)3](dnp)3·4H2O has been synthesized in an effort to utilize [Co(phen)3]3+ cation as a new host for di-substituted phenolate (2,4-dinitrophenolate) anion. This cobalt (III) complex salt has been characterized by elemental analyses and spectroscopic techniques (UV/visible, IR, NMR and conductance measurements). Single crystal X-ray structure determination confirmed the composition [Co(phen)3](dnp)3·4H2O. A strong network of hydrogen bonding interactions C–H...O (phenolate), C–H…O (nitro) involving second sphere coordination and O–H…O hydrogen bonding interactions stabilize the crystal lattice. The formation of a complex salt of definite composition along with solubility product data suggests that [Co(phen)3]3+ present in [Co(phen)3]Cl3 may be used as an anion receptor for 2,4-dinitrophenolate ion.