Structure of (5,10,15,20-tetraphenylporphinato)cadmium(II)

Helicity Modulation in NIR-Absorbing Porphyrin-Ryleneimides

Peripheral substitution of a π‐extended porphyrin with bulky groups produces a curved chromophore with four helical stereogenic units. The curvature and stereochemistry of such porphyrins can be controlled by varying the substituents, coordinated metal ions, and apical ligands. In particular, when the achiral saddle‐shaped free bases are treated with large metal ions, i.e., Cd^II or Hg^II, the resulting complexes convert to chiral propeller‐like configurations. X‐ray diffraction analyses show that apical coordination of a water molecule is sufficient to induce a notable bowl‐like distortion of the cadmium complex, which however retains its chiral structure. For phenyl‐ and tolyl‐substituted derivatives, the conversion is thermodynamically controlled, whereas complexes bearing bulky 4‐(tert‐butyl)phenyl groups transform into their chiral forms upon heating. In the latter case, the chiral Hg porphyrin was converted into the corresponding free base and other metal complexes without any loss of configurational purity, ultimately providing access to stable, enantiopure porphyrin propellers.

A critical evaluation of homo- and hetero-leptic cadmium complexes using bond valence sums

The effect of the donor atoms in Cd complexes on the determination of R0 values for the bond valence sum (BVS) is reported. A total of 1321 CdXmYn fragments with X and Y = O, N, S, Cl, Br, and I were used to calculate the R0 values for Cd—X bonds from both homoleptic and heteroleptic fragments. The R0 values determined from mixed CdXmYn fragments agree with those determined from the homoleptic species, with no significant differences in the values as a function of either electronegativity or hard–soft character of the atoms. The new R0 values derived from the homoleptic series recommended for use in calculating the BVS are as follows: Cd(II)—O of 1.875(13) Å, Cd(II)—N of 1.951(15) Å, Cd(II)—S of 2.279(7) Å, Cd(II)—Cl of 2.216(17) Å, Cd(II)—Br of 2.334(7) Å, and Cd(II)—I of 2.525(7) Å. These R0 values can be used to calculate the oxidation state of Cd in complexes where Cd is bonded to any combination of O, N, S, Cl, Br, and I donor atoms. Cases where the BVS does not agree with the expected oxidation state are discussed. In particular, the planarity of Cd porphyrins is discussed in terms of the BVS.Key words: bond valence sums, cadmium complexes, cadmium porphyrins, cadmium distances.

A multiphase 113Cd NMR investigation of metalloporphyrin reorientation in cadmium-substituted myoglobin

113Cd NMR spectroscopy in both the solution and solid state has been used to investigate the role of the metal ion and the proximal histidine on metalloporphyrin reorientation in myoglobin. Heme disorder has been known to exist for many years but understanding its mechanism has proved difficult due to the short-lived nature of the minor porphyrin isomer in native myoglobin. Cadmium-substituted myoglobin can be generated in one form which contains different insertion isomers or in another form which contains predominantly only one of these species. This allows for direct investigation of heme disorder in metal-substituted myoglobin.