Synthesis And Characterization Of Nitrosyl Or Nitrate Manganese Porphyrins

The interactions between metalloporphyrins and various nitrogen oxides NOX have been considered to be of great biological significance.Metalloporphyrins compounds coordinated by nitric oxide(NO)or nitrate ions(NO3-)have been involved in many key physiological processes,such as nitrogen cycling,mammalian nerve signaling,vasodilation,and platelet aggregation.In this work,in order to study the structure and properties of nitrogen oxides coordinated metalloporphyrin complexes,several nitric oxides or nitrate coordinated manganese porphyrin complexes with[Mn(TPP)]as starting materials are prepared and investigated by X-ray single-crystal diffraction,UV-vis,FT-IR,Raman spectroscopy,In-situ diffuse reflectance infrared spectroscopy,and electron paramagnetic resonance spectroscopies.The main research results are as follows:We have successfully synthesized and isolated the six-coordinate manganese bis(nitrosyl)porphyrin[Mn(TPP)(NO)2],which is the first {Mn(NO)}7 crystal structure with the two trans NO ligands.Compared to the known complex[Mn(TTP)(NO)],[Mn(TPP)(NO)2]has longer Mn-NNo bond(1.641(2)vs.1.877(9)?).Electron paramagnetic resonance spectroscopies indicate that the central metal manganese(3d5)is low-spin state S=1/2.The NO stretching vibration of[Mn(TPP)(NO)2]is found at 1760 cm-1 by FT-IR.By means of in-situ diffuse Fourier transform infrared spectroscopy,we tentatively determined a five-coordinate[Mn(TPP)(NO)]intermediate in the formation of[Mn(TPP)(NO)2].The research result provides a new understanding of the coordination number of nitric oxide-coordinated manganese porphyrins,which fills a gap in the field.We have synthesized and isolated three kinds of mixed hexacoordinate manganese porphyrins containing nitric oxide that is Mn(TPP)(1-MeIm)(NO)],[Mn(TPP)(1,2Me2Im)(NO)]and[Mn(TPP)(C4H8O)(NO)].As can be seen from their single crystal structures,the Mn-N-O moieties of these compounds are approximately linear(173.5(3)～178.7(3)°).Meanwhile,the bond lengths of Mn-NNo in compounds[Mn(TPP)(1-MeIm)(NO)]and[Mn(TPP)(1,2-Me2Im)(NO)]are 1.629(2)and 1.631(2)? respectively,shorter than that of[Mn(TPP)(C4H8O)(NO)](1.659(3)?),which implies the stronger back π bonding for the former two.In addition,the silent EPR of[Mn(TPP)(1-MeIm)(NO)]and[Mn(TPP)(1,2Me2Im)(NO)]indicates the antiferromagnetic coupling between low-spin manganese(Ⅱ)(S=1/2)and NO(S=1/2).The study of the crystal structures and spectroscopic characteristics of the above series of compounds has provided an experimental and theoretical basis for an indepth understanding of the physiological significance of NO and histidine-coordinated heme bonding in living organisms.We have isolated two polymorphic nitrate manganese(Ⅲ)porphyrins[Mn(TPP)(NO3)](P1 and Pccn).The monodentate NO3 in the two new crystal structures show longer Mn-O bond distances than those of the bidentate NO3 ligands(2.097(3)and 2.1246(18)vs.1.938(3)～1.996(3)?).The N-O stretching vibration peaks of[Mn(TPP)(NO3)]axial ligand(NO3)are at 1286,1385 and 1474 cm-1 in the FT-IR spectrum.