XAFS study of gadolinium and samarium bisporphyrinate complexes

The comparative X-ray absorption spectroscopy study of gadolinium and samar ium bisporphyrinate complexes represented by the formulas (GdH)-H-III(oep)( tpp), Gd-III(oep)(2), (GdH)-H-III(tpp)(2) and (SmH)-H-III(oep)(tpp), Sm-III (oep)(2), (SmH)-H-III(tpp)(2) is reported. The XAFS spectra are recorded on the LURE-DCI storage ring (Orsay, France) in transmission mode on the micr ocrystalline samples at the Gd and Sin L-3 edges. The local environment for Ln(3+) ions has been reconstructed applying one-shell and two-shell XAFS a nalysis procedures. The protonated and nonprotonated bisporphyrinate comple xes present different XAFS features. After our analysis on the title deriva tives, the gadolinium ion (at 80 K) is found to be bonded: (i) to eight nit rogen atoms at R(Gd-N) 2.50 Angstrom, for (GdH)-H-III(oep)(2) [Debye-Waller (DW) factor 0.004 Angstrom (2)]; (ii) to Seven nitrogen atoms at R(Gd-N) 2 .49 Angstrom, for (GdH)-H-III(oep)(tpp) [DW factor 0.005 Angstrom (2)] and one nitrogen at long distance; and (iii) to six nitrogen atoms at R(Gd-N) 2 .50 Angstrom [DW factor 0.006 Angstrom (2)] and two nitrogen atoms at Iona distance for (GdH)-H-III(tpp)(2). A similar coordination sphere has been de tected for the corresponding Sm derivatives. So, the samarium ion (at room temperature) is bonded: (i) to eight nitrogen atoms at R(Sm-N) 2.53 Angstro m, for Sm-III(oep)(2) [DW factor 0.006 Angstrom (2)]; (ii) to seven nitroge n atoms at R(Sm-N) 2.53 Angstrom, for (SmH)-H-III(oep)(tpp) [DW factor 0.00 6 Angstrom (2)] and one nitrogen at long distance; and (iii) to six nitroge n atoms at R(Sm-N) 2.50 Angstrom, for (SmH)-H-III(tpp)(2) [DW factor 0.006 Angstrom (2)] and two nitrogen atoms at long distance. As far as concerns L n(III)(oep)(2) complexes, the increase of Ln-N distance in the series Gd3< Eu3+ < Sm3+ reflects an increase in the ionic radii, which are in good ag reement with previously published XRD data on Eu-III(oep)(2). Moreover, the protonated, Ln(III)H(oep)(tpp) and Ln(III)H(tpp)(2) complexes possess syst ematically shorter distances of about 0.02 Angstrom between the XAFS and XR D data. This difference is attributed to the asymmetry of the distribution concerning Ln-N distances.