Hydrothermal synthesis of three new 3-D framework rare-earth mellitates

Hydrothermal reaction of rare-earth ions and mellitic acid [MEL-H-6 = C-6(COOH)(6)] has been carried out to determine the effects of metal size and ancillary aquation on polymer architecture. Three new 3-D framework rare-earth mellitate polymer types are formed with reduced aquation levels compared to ambient phases, Larger ions Ln = La to Er form 9-coordinate [Ln(2)(MEL)(H2O)(6)] I (orthorhombic, Pnnm, for La a = 13.642(2), b = 6.769(1), c = 10.321(2) Angstrom, V = 953.1 Angstrom (3)) and smaller ions Ln Tm to Lu form the 7-coordinate [Ln, (MEL) (H2O)]H2O 2 (tetragonal, P4/ncc, for Tm a = 18.443(3), c = 10.374(2) Angstrom, V = 3529 Angstrom (3)). In the case of Ln = Er, Tm a third type with mu -aqua groups is found [Ln(2)(MEL)(mu -H2O)(2)(H2O)(2)] 3 (monoclinic P2(1)/c, for Tm a = 5.781(1), b = 14.840(1), c = 8.920(1) Angstrom, beta = 93.46(1)degrees, V = 763.8 Angstrom (3)) This 8-coordinate phase is favored over I at higher temperature (200 degreesC) for Er and favored over 2 at lower temperatures (160 degreesC) for Tm. (C) 2001 Elsevier Science BN. All rights reserved.