X-ray crystallographic, spectroscopic and molecular sensing properties of fac-tricarbonylchloro(di-2-pyridylketonebenzoylhydrazone)rhenium(I) dimethylformamide solvate

Abstract

The molecular sensor fac-[Re(CO) 3(dpkbh)Cl]·DMF ( 1) where DMF= N, N-dimethyl formamide and dpkbh=di-2-pyridylketonebenzoylhydrazone crystallized in the acentric triclinic space group P1. Structural analysis shows two units of ( 1) with rhenium in distorted octahedral geometry, the carbonyl groups are in facial positions with an average C–Re–C angle of 90° and the N, N-bidentate dpkbh forms six-membered metallocyclic ring with rhenium in a boat conformation. The molecular packing shows the binding of DMF to fac-[Re(CO) 3(dpkbh)Cl] and helical strands of ( 1) interlocked via a network of hydrogen bonds. Optical measurements on fac-[Re(CO) 3(dpkbh)Cl] in DMF show the presence of two interlocked charge transfer bands at 440 and 318 nm that are highly sensitive to slight variations in their surroundings. As the concentration decreases, the intensity of the low energy absorption band at 440 nm increases and the reverse is observed when the concentration increases. Thermo-optical measurements on fac-[Re(CO) 3(dpkbh)Cl] in DMF established the reversible interconversion between the high and low energy electronic states of fac-Re(CO) 3(dpkbh)Cl and changes in enthalpy (Δ H ∅) of+17.44±0.40 kJmol −1, entropy (Δ S ∅) of +37.45±0.50 J mol −1 and free energy (Δ G ∅) of +6.27±0.30 kJ mol −1 in DMF were calculated. Acids or bases in concentration as low as 1.0×10 −9 M can be detected and determined using fac-[Re(CO) 3(dpkbh)Cl] in DMF. 1H-NMR measurements on fac-[Re(CO) 3(dpkbh)Cl] in DMF in non-aqueous media reveal high sensitivity to solvent and temperature variations and points to strong solvent-complex interactions. The amide protons and solvate protons show high sensitivity to temperature variations than the aromatic protons pointing to the participation of the amide proton in solvate-complex hydrogen bonds in non-aqueous solutions of fac-[Re(CO) 3(dpkbh)Cl].