EFFECT OF POLYETHER LIGANDS ON STABILITIES AND MASS-TRANSPORT PROPERTIES OF A SERIES OF GADOLINIUM(III) BETA-DIKETONATE COMPLEXES

The reaction of [Gd(tmhd)(3)](2) (1) (tmhd-H = 2,2,6,6-tetramethylhept ane-3,5-dione) with a selected range of chelating O-donors such as, mo no- {CH3OCH2CH2OCH3}, di- {CH3(OCH2CH2)(2)OCH3}, tri- {CH3(OCH2CH2)(3) OCH3}, tetra- {CH3(OCH2CH2)(4)OCH3), and heptaglyme {CH3(OCH2CH2)(7)OC H3} in n-hexane at room temperature yielded the compounds [Gd(tmhd)(3) (monoglyme)] (2), [Gd(tmhd)(3)(diglyme)] (3), [{Gd(tmhd)(3)}(2)(trigly me)] (4). [{Gd-(tmhd)(3)}(2)(tetraglyme)] (5), and [(Gd(tmhd)(3)}(2)(h eptaglyme)] (6), respectively. The complexes are either monomers (2, 3 ) or dimers (1, 4-6) and have been characterized by microanalyses, sol ution cryoscopy in benzene, FT IR, mass spectrometry, and sublimation, TGA, and DSC studies. Complexes 1, 2, 5, and 6 have also been charact erized by X-ray crystallography. 1 and 6 both crystallize in the monoc linic space group P2(1)/n, with a = 12.228(2) Angstrom, b = 27.615(2) Angstrom, c = 21.843(11) Angstrom, and beta = 105.37(6)degrees (1) and a = 11.773(2) Angstrom, b = 18.712(3) Angstrom), c = 21.610(3) Angstr om, and beta = 103.53(1)degrees (6). 2 and 5 crystallize in the tricli nic space group P $$($) over bar 1 with a = 10.814(2) Angstrom, b = 12 .141(3) Angstrom, c = 16.534(2) Angstrom, alpha = 83.90(1)degrees, bet a = 88.20(1)degrees, and gamma = 71.85(1)degrees (2) and a = 11.934(2) Angstrom, b = 19.478(4) Angstrom, c = 20.508(10) Angstrom, alpha = 99 .25(1)degrees, beta = 106.94(2)degrees, and gamma = 104.76(1)degrees, (5), The gadolinium ion shows a seven-coordinate distorted monocapped trigonal prismatic geometry in 1 and an eight coordinate square antipr ismatic geometry in the other compounds. In 2 the monoglyme nets as bi dentate chelating ligand. The tetraglyme and heptaglyme molecules in c omplexes 5 and 6, respectively, act as chelating as well as bridging l igands, utilizing four of their available oxygen atoms for coordinatio n. All these compounds are air and water stable. and those with the lo nger glymes have good volatilities and thermal stabilities, as demonst rated by sublimation, TGA, and DSC studies.