Molecular sensing behavior of the first Mn(I)-compound of di-2-pyridylketone-p-nitrophenylhydrazone (dpknph), fac-[Mn(CO)3(dpknph)Br]

The reaction between [Mn(CO)5Br] and di-2-pyridylketone-p -nitrophenylhydrazone (dpknph) in diethyl ether under ultrasonic conditions gave fac -[Mn(CO)3(dpknph)Br] in good yield. Optical and thermodynamic measurements on fac -[Mn(CO)3(dpknph)Br] in non-aqueous polar solvents revealed reversible interconversion between two intense charge transfer absorption bands due to π–π* (dpk), followed by dpk → nitro intraligand charge transfer transition (ILCT), mixed with metal ligand charge transfer transition (MLCT) due to View the MathML sourcedπ(Mn)→π(dpk)∗. In non-polar solvents, a single absorption band appeared. Extinction coefficients of 46 200 ± 2000 and 28 400 ± 2000 M−1 cm−1 were calculated in DMSO for the low- and high-energy electronic states of fac-[Mn(CO)3(dpknph)Br] using excess NaBF4. Changes in enthalpy (ΔHø) of +14.0 and −12.1 kJ mol−1, entropy (ΔSø) of +28.65 and −64.30 J mol−1 K−1, and free energy (ΔGø) of +5.48 and +7.08 kJ mol−1 at 298 K were calculated for the interconversion between the high and low energy electronic states of fac-[Mn(CO)3(dpknph)Br]. These results allow for the use of these systems (fac-[Mn(CO)3(dpknph)Br] and surrounding solvent or solute molecules) as optical sensors for a variety of physical and chemical stimuli that include metal ions. Group 12 metal ions in concentrations as low as 1.00 × 10−9 M can be detected and determined using fac-[Mn(CO)3(dpknph)Br] in dmso in the presence and absence of NaBH4.