253191-59-2Relevant academic research and scientific papers
Four-coordinate, low-spin (S = 0) and six-coordinate, high-spin (S = 1) nickel(II) complexes of tetraphenylporphyrins with β-pyrrole electron-withdrawing substituents: Porphyrin-core expansion and conformation
Duval, Hugues,Bulach, Veronique,Fischer, Jean,Weiss, Raymond
, p. 5495 - 5501 (2008/10/08)
To examine the porphyrin-core expansion and the conformational variations induced by a change in the coordination sphere of nickel(II) from four-coordinate, low-spin (S = 0) to six-coordinate, high-spin (S = 1), several nickel (II) derivatives of tetraphenylporphyrins, substituted in their β-pyrrole positions with electron-withdrawing groups, were isolated and studied by X-ray crystallography. The four-coordinate nickel(II) complex studied, Ni(TPP(Br)4(CN)4) (1), is a derivative of the antipodal β-pyrrole brominated and cyanated macrocycle, 2,3,12,13-tetrabromo-7,8,17,18-tetracyano-5,10,15,20-tetraphenylporphyrin. One of the six-coordinate species is the bis-pyridine nickel(II) adduct, Ni(TPP(Br)4(CN)4)(py)2 (2), of this antipodal β-pyrrole brominated and cyanated ring, whereas the second six-coordinate complex is the bis-1-methylimidazole nickel(II) adduct, Ni(TPP(CN)4)(1-MeIm)2 (3), of the antipodal tetracyanated macrocycle, 7,8,17,18-tetracyano-5,10,15,20-tetraphenylporphyrin. This study confirms that, upon conversion of a four-coordinate, low-spin nickel(II) derivative of a β-pyrrole-substituted tetraphenylporphyrin into a six-coordinate, high-spin complex, a radial expansion of the porphyrin core also takes place. This radial expansion flattens the porphyrin core, inducing more planarity in the conformations of the six-coordinate nickel(II) porphyrin species. The X-ray structure of 1 reveals an average Ni-Np bond distance of 1.920(2) A, similar to that present in tetragonal Ni(OEP) [(Ni-Np)av = 1.929(3) A], the ruffled low-spin nickel(II) (S = 0) porphyrin derivative, and many other low-spin nickel(II) complexes of distorted porphyrins. The conformation of the macrocycle present in 1 is severely saddle-shaped with a small ruffling and a minor doming. The structures of 2 and 3 indicate a clear expansion of the porphyrin cores with two sets of (Ni-Np)av bond lengths of 2.040(2) and 2.073(2) A in 2 and 2.037(2) and 2.068(2) A in 3, which differ significantly from the average Ni-Np distance occurring in 1. Relative to the conformation of the porphyrin ring present in 1, the high-spin complex 2 is less saddle-shaped, but more ruffled. In 3, in which only two opposite pyrrole rings of the porphyrin are substituted by cyano groups, the macrocycle adopts a slightly waved conformation. Crystal data: Ni(TPP(Br)4(CN)4)-2.5(1,2-Cl2C 2H4), [1·2.5(1,2-Cl2C2H4)], triclinic, space group P1, a = 13.741(1) A, b = 14.029(2) A, c = 15.201(2) A, α = 89.037(9)°, β= 70.829(8)°, γ = 67.607(8)°, V = 2539.4(5) A3, T = 20 °C, Z = 2, RF = 0.047 and RwF = 0.067 based on 5341 reflections with I > 3σ(I); Ni(TPP(Br)4(CN)4)(py)2·2.5(1,2-Cl 2C2H4), [2·2.5(1,2-Cl2C2H4)], triclinic, space group P1, a = 11.9472(9) A, b = 14.3651(7) A, c = 19.556(1) A, α = 87.049(5)°, β= 73.181(6)°, γ = 70.613(5)°, V = 3026.8(4) A3, T = 173 K, Z = 2, RF = 0.036, RwF = 0.041 based on 6846 reflections with I > 3σ(I); Ni(TPP(CN)4)(1-MeIm)2·2CH2Cl 2, [3·2(CH2Cl2)], monoclinic, space group C2/c, a = 26.804(8) A, b = 10.948(3) A, c = 19.453(5) A, β= 113.13(2)°, V = 5251.5 A3, T = 20 °C, Z = 4, RF = 0.047, RwF = 0.067 based on 4384 reflections with I > 3σ(I).
