SOLUTION CHEMISTRY AND CRYSTAL-STRUCTURE OF NICKEL ETRAFLUORO-N,N,N-TRIMETHYL-4-ANILINIUMYL)PORPHYRIN TRIFLUOROMETHANESULFONATE (NITF(4)TMAP(CF3SO3)(4))

The solution chemistry and crystal structure of nickel etrafluoro-N,N, N-trimethyl-4-aniliniumyl)porphyrin (NiTF(4)TMAP(4+)) are reported and compared with analogous chemistry for nickel tetrakis(N-methyl-4-pyri diniumyl)porphyrin (NiT4-N-MePyP(4+)). NiTF(4)TMAP(4+) binds axial lig ands more strongly than most other reported porphyrins. For stronger-f ield ligands such as 1-methylimidazole and tris(n-butyl)phosphine two sequential binding equilibria are observed, whereas with weaker ligand s binding of two axial ligands appears to occur simultaneously. The fo ur coordinate NiTF(4)TMAP(4+) is in equilibrium with the six coordinat e Ni(H2O)(2)TF(4)TMAP(4+) in aqueous solution ([6 coordinate]/[4 coord inate] = 1.6), but the axial waters are readily lost in the presence o f organic substrates such as aromatics (anionic and neutral) and aliph atic ligands (anionic and neutral). The interactions are best explaine d as being predominantly due to the hydrophobic effect. While this eff ect is exacerbated in this fluorinated porphyrin, these results indica te that hydrophobic effects should be considered in any study of porph yrin interactions in aqueous solution. The buffers HEPES and MES cause the porphyrin to be 4-coordinate in their basic form, but the zwitter ionic forms do not interact with the porphyrin. In contrast, hydrogen phthalate displaces the coordinated water more strongly than the dibas ic phthalate. These observations are probably due to increased hydrati on of the substrate. The crystal structure of Ni(TF(4)TMAP)(CF3SO3)(4) . 2CH(3)CN . 2(CH3)(2)-CO (R = 7.59%, R(w) = 7.91%, P ($) over bar 1, Z = 2, a = 14.090(3) Angstrom, b = 15.725(3) Angstrom, c = 19.554(4) Angstrom, alpha = 78.43(3)degrees, beta = 77.26(3)degrees, gamma = 83. 14(3)degrees) showed that the nickel(II) was four coordinate, with no interactions with the anions or lattice solvent.