Crystal Structures and Solution Studies of Two Novel Zinc(II) Complexes of a Proton Transfer Compound Obtained from 2, 6‐Pyridinedicarboxylic Acid and 1, 10‐Phenanthroline: Observation of Strong Intermolecular Hydrogen Bonds

Abstract

Abstract The proton transfer compound LH 2 , (phenH + ) 2 (pydc 2— ), has been prepared from 1, 10‐phenanthroline, phen, and 2, 6‐pyridinedicarboxylic acid, (dipicolinic acid), pydcH 2 . Characterization was performed using solution and solid phase CP/MAS 13 C NMR and IR spectroscopy. The reactions of this adduct with ZnSO 4 ·7H 2 O and Zn(NO 3 ) 2 ·4H 2 O give the complexes, [Zn(pydc) 2 ][Zn(phen) 2 (H 2 O) 2 ]·7H 2 O (1) and [Zn(phen) 3 ] 4 (H(Hpydc) 2 )(NO 3 ) 7 ·26H 2 O (2) , respectively. These complexes were characterized by 1 H and 13 C NMR spectroscopy and single crystal X‐ray analysis. The complexes crystallize in the triclinic space group P 1 with Z = 2. The unit cell dimensions for complex 1 and 2 are: a = 9.9838(9) Å, b = 14.7483(13) Å, c = 14.8365(13) Å and a = 12.640(4) Å, b = 15.855(5) Å, c = 21.830(7) Å, respectively. In complex 1 (pydc 2— ) and phen, are tri‐ and bidentate ligands, respectively, and an anionic [Zn(pydc) 2 ] 2— and cationic [Zn(phen) 2 (H 2 O) 2 ] 2+ complex are formed simultaneously. In complex 2 , three phen participate in complexation leaving hydrogen‐bis(pyridine‐2‐carboxylate), (H(Hpydc) 2 ) — as a supramolecular anion. The fragments (H(Hpydc) 2 ) — , 7 NO 3 — , and 26 H 2 O in complex 2 are joined together by extensive and strong H‐bonding; therefore, the structure is composed of [Zn(phen) 3 ] 4 8+ , and an anionic hydrogen bond supramolecular assembly with the formula, {(H(Hpydc) 2 (NO 3 ) 7 ) 8— · 26H 2 O} n . The anionic species (H(Hpydc) 2 ) — has a special position at the inversion center, as well as one of the NO 3 — anions, which is disordered over the inversion center. Most of the hydrogen bonds in complex 2 represent strong H‐bonding. The protonation constants of the building blocks of the pydc‐phen adduct, the equilibrium constants for the reaction of (pydc 2— ) with phenanthroline and the stoichiometry and stability of the Zn II complex with LH 2 on aqueous solution were determined by potentiometric p H titration. The solution study results support self‐association between (pydc 2— ) and (phenH + ) with a stoichiometry for the Zn(II) complex similar to that observed for the isolated crystalline complex.