An unexpected bonding interaction between d_(xy) and axial cyanide mediated by porphyrin deformation

摘要

Through density functional calculation and NMR spectroscopy, an unexpected bonding interaction between d_(xy) and axial cyanides is revealed to account for the lower shielding of axial cyanide of ruffled [Fe(TRP)(CN)_2]~- complexes with the contribution of the unusual low-spin electronic structure (d_(xz)d_(yz))4(d_(xy)).rnAxial ligands coordinated directly to the paramagnetic central metal are particularly useful NMR probes to the electronic environment of the complexes. The ~(13)C NMR signal of iron-bound ~(13)CN shifting from -3540 ppm to -4145 ppm in ferric hemoprotcins has been demonstrated to be sensitive to the nature of the proximal trans ligand. In the bis(cyanide) (meso-tetraalkylporphyrinato-iron(Ⅲ)) complexes, [Fe(TRP)-(CN)_2]~-, the lower shielding signal of ~(13)CN has been correlated with the contribution of the unusual low-spin state d_(xz,yz)~4d_(xy)~1 that is induced by ruffled deformation.