H-1-NMR SPECTROSCOPIC STUDY OF PARAMAGNETIC LANTHANIDE(III) TEXAPHYRINS - EFFECT OF AXIAL LIGATION

Paramagnetic Ce(III), Pr(III), Nd(III), Sm(III), Eu(III), Tb(III), Dy( III), Ho(III), Er(III), Tm(III), and Yb(III) texaphyrins were studied in solution using H-1 NMR spectroscopic techniques. Key spectroscopic features for the dinitrate complexes LnTx(NO3)(2) were assigned on the basis of 1D NOE, COSY, and ROESY experiments as well as line width an d isotropic shift analysis. The observed isotropic shifts can be fit t o theoretical models, assuming dipolar contributions are dominant for all but the imino protons. The resulting calculated values are consist ent with highly rhombic magnetic susceptibility tensors for those para magnetic lanthanide texaphyrins in which one of the molecular magnetic axes is roughly perpendicular to the macrocycle plane. For the dinitr ate complexes, a change in the magnetic anisotropy was observed betwee n the Ho(III) and Er(III) texaphyrin complexes, a phenomenon that is c onsidered reflective of the changes in metal-centered axial ligation t hat occur as the lanthanide series is transversed. The derived contact shifts of the imino protons were found to follow well the expected th eoretical dependence on (S-z). Exchange of both axial nitrate anions f or phosphate-type ligands, confirmed by solution phase titration studi es, brings about a drastic change in the observed spectral patterns. T hese changes can be accounted for fully by altering the magnetic susce ptibility tenser so as to accommodate what are presumed to be changes in the effective crystal field parameters. Conformation of phosphate c oordination in the solid state came from a single crystal X-ray diffra ction analysis of the bis(diphenyl phosphate) adduct of Dy(III) texaph yrin. Crystals of (C34H38N5O2)DY((C6H5)(2)-PO4)(2) . 0.64(CH3OH) (DyTx (P1)(2)), obtained by diffusion of diphenyl phosphate into methanolic DyTx(NO3)(2) solution, were triclinic, space group P ($) over bar 1, w ith a = 14.482(3), b = 14.664(3), and c 15.580(3) Angstrom, alpha = 69 .544(15), beta= 65.695(15), and gamma = 70.377(15)degrees, V = 2751.1( 11) Angstrom(3), Z = 2, rho(calc) = 1.48 g/cm(-3). The structure refin ed to a final R(F-2) = 0.109 for 644 parameters using 8390 reflections . The Dy(III) ion is seven-coordinate with five donor atoms being prov ided by the texaphyrin ligand and two by monodentate diphenyl phosphat e ions. The Dy(III) ion is only 0.073 Angstrom from the plane through the five nitrogen atoms of the macrocycle. The Dy(III)-O bond lengths are equivalent and average 2.228(5) Angstrom. The Dy-N-pyrole bond len gths average 2.363(3) Angstrom while the Dy-N-imine bond lengths avera ge 2.448(4) Angstrom.