Synthesis, spectroscopic, and X-ray crystallographic analysis of manganese compounds of di-2-pyridyl ketone thiophene-2-carboxylic acid hydrazone (dpktch): The reaction of Mn(CO)5Br with dpktch

The ultrasonic radiation of a mixture of [Mn(CO)5Br], di-2-pyridyl ketone thiophene-2-carboxylic acid hydrazone (dpktch) and diethyl ether in air gave fac-[Mn(CO)3(η2-N,N-dpktch)Br]. Under refluxing conditions [MnBr2(η3-N,N,O-dpktch)] and [Mn(η3-N,N,O-dpktch-H)2] were isolated from a mixture of Mn(CO)5Br, dpktch, and CH3CN. The infrared spectra of the isolated compounds divulge the facial coordination of the carbonyl (CO) groups in fac-[Mn(CO)3(η2-N,N-dpktch)Br], the absence of the carbonyl (CO) groups in [MnBr2(η3-N,N,O-dpktch)] and [Mn(η3-N,N,O-dpktch-H)2], and the coordination of dpktch/dpktch-H. The electronic absorption spectra of the isolated compounds show two intra-ligand charge transfer (ILCT) transitions that are sensitive to changes in their surroundings. The interconversion between fac-[Mn(CO)3(η2-N,N-dpktch)Br] and its conjugate base fac-[Mn(CO)3(η2-N,N-dpktch-H)Br] in protophilic solvents was demonstrated using stoichiometric amounts of an acid or a base. Acids or bases in concentrations as low as 1.00 × 10−6 M can be detected and determined using protophilic solutions of fac-[Mn(CO)3(η2-N,N-dpktch)Br]. X-ray crystallographic analysis done on crystals of [MnBr2(η3-N,N,O-dpktch)] and [Mn(η3-N,N,O-dpktch-H)2] confirmed their identity and show tetragonal (square pyramidal) coordination about manganese in [MnBr2(η3-N,N,O-dpktch)] and octahedral coordination about manganese in [Mn(η3-N,N,O-dpktch-H)2]. The extended structures of [MnBr2(η3-N,N,O-dpktch)] and [Mn(η3-N,N,O-dpktch-H)2] revealed digitated units of [MnBr2(η3-N,N,O-dpktch)], and anti-parallel stacks of [Mn(η3-N,N,O-dpktch-H)2] locked via a network of hydrogen bonds. Analysis of solvent accessible areas in the solid state of [MnBr2(η3-N,N,O-dpktch)] and [Mn(η3-N,N,O-dpktch-H)2] show the unit cell of the former to be void free while the latter to contain several voids.