Structural Investigations on Mono- and Di-Acrolein Substituted Ni(II) Porphyrins and a Ni(II) Benzochlorin. Model Compounds for Photosensitizers in Photodynamic Therapy

The structures of four Ni complexes and a free base related to tetrapentanoporphyrin (TC₇P) and octaethylporphyrin (OEP) have been determined by X-ray crystallograpic methods. The Ni(II) complexes exhibit considerable S₄-ruffling induced by coordination hole contraction due to the low spin Ni(II). The degree of conformational distortion is enhanced by one or two additional acrolein substituents at the meso positions. The steric strain imposed by interaction of the meso substituent with the neighboring β-pyrrole substituents leads to a significant displacement from the mean plane of the molecule of the meso carbon(s) involved. Increasing non-planarity of the macrocycles is correlated with shifts to longer wavelenghts in the absorption spectra. Ring closures of the acrolein group to afford benzochlorin type pigments results in further bathochromic shifts and a very non-planar molecular conformation. Long wavelength absorbing pigments such as benzochlorins are useful photosensitizers for photodynamic therapy and thus one criterion for a good photosensitizer might be its conformational distortion. Crystal data – 3. C₄₀H₄₆N₄·CH₂Cl₂, M_r = 667.7, triclinic, P I, a = 7.776(5)Å, b = 8.556(4)Å, c = 14.509(8)Å, α = 73.96(1)°, β = 82.04(2)°, γ = 82.58(2)°, V = 914.5(9)ų, Z = 1, D_x = 1.212 Mg/m³, (MoKα) λ = 0.71069Å, μ = 0.209mm^-1, F(000) = 356, 130 K, R = 0.082 for 2217 reflections with I > 1.5σr(I). Ni4. C₄₄H₄₀N₄NiO·CH₂Cl₂, Mr = 770.4, triclinic, P I, a = 11.283(3)Å, b = 11.800(4)Å, c = 15.871(7)Å, α = 79.28(3)°, β = 88.95(2)°, γ = 62.41(1)°, V = 1838.8(11)ų, Z = 2, D_x = 1.391 Mg/m³, (MoKα), μ = 0.715 mm^-1, F(000) = 804, 130 K, R = 0.072 for 5309 reflections with I > 2.0σ(I). Ni5. C₄₆H₂₈N₄NiO₂·CH₂Cl₂, M_r = 812.4, triclinic, P I, a = 8.959(4)Å, b = 14.420(7)Å, c = 15.471(5)Å, α = 102.73(4)°, β = 101.83(4)°, γ = 92.01(5)°, V = 1901.3(14)ų, Z = 2, D_x = 1.419 Mg/m³, (MoKα), μ = 0.679 mm^-1, F(000) = 836, 130 K, R = 0.059 for 4197 reflections with I > 1.75σ(I). Ni7. C₄₃H₄₅N₄NiO₂·CH₂Cl₂, M_r = 793.5, triclinic, P I, a = 8.948(3)Å, b = 13.855(3)Å, c = 15.451(3)A, α = 82.43 (2)°, β = 78.79(2)°, γ = 81.24(2)°, V = 1846.7(8)Å, Z = 2, D_x = 1.427 Mg/m³, (CuKα) λ = 1.54178Å, μ = 2.448 mm^-1, F(000) = 834, 126 K, R = 0.09 for 4039 reflections with I > 2.0σ(I). Ni8. C₄₂H₄₈N₄NiO, M_r = 683.6, monoclinic, P2₁/n, a = 15.168(6)Å, b = 14.796(3)Å, c = 15.983(4)Å, β = 97.17(3)°, V = 3552(2)ų, Z = 4, D_x = 1.278 Mg/m³, (MoKα), μ = 0.584 mm^-1, F(000) = 1456, 130 K, R = 0.042 for 5904 reflections with I > 2.5σ(I).