SPECTROSCOPICALLY DISTINCT GEOMETRICAL-ISOMERS IN A SINGLE-CRYSTAL - CHARACTERIZATION OF THE 8-COORDINATE ADDUCTS OF TRIS(DIPIVALOYLMETHANATO)LANTHANIDE(III) WITH 2,9-DIMETHYL-1,10-PHENANTHROLINE

Tris(dipivaloylmethanato)(2,9-dimethyl-1,10-phenanthroline)lanthanide(III), [Ln(DPM)3.DMOP], complexes (Ln = La, Eu, Th, Ho) were synthesized from [Ln(DPM)3] and 2,9-dimethyl-1,10-phenanthroline in carbon tetrachloride. The Eu3+ and Tb3+ complexes were characterized spectroscopically by infrared and luminescence techniques. The luminescence spectra of the Eu3+ and Tb3+ adducts were recorded at 77 K. For Eu3+, two transitions in the 5D0 --> F-7(0) region are observed which are separated by an unprecedented 35 cm-1. The 5D0 --> F-7(1) and 5D0 --> F-7(2) spectral regions contain six and eight bands, respectively, indicating two distinct Eu3+ environments. The Eu3+ luminescence spectrum indicates that both Eu3+ environments have local site symmetry C1. The crystal structure of [Eu(DPM)3.DMOP] was solved by single-crystal X-ray diffraction methods. The complex was found to crystallize in the monoclinic space group P2(1)/n with a = 13.941(7) angstrom, b = 16.512(7) angstrom, c = 21.626(9) angstrom, beta -105.13(4)degrees, and V = 4805.6 angstrom3. Two geometrical isomers were found to exist in the unit cell with the ligating atoms forming an eight-coordinate distorted square antiprism. The two isomers differ only in the way the chelate rings span the lateral (l) and square (s) edges of a square antiprism with occupancy factors of 59 and 41%. The average Eu-O and Eu-N bond distances are 2.363 and 2.678 angstrom. X-ray crystallographic occupancy factors were determined for [La(DPM)3.DMOP], [Tb(DPM)3.DMOP], and [Ho(DPM)3.DMOP], and each complex was found to crystallize in the monoclinic space group P2(1)/n. For [La(DPM)3.DMOP], a = 14.083(4) angstrom, b = 16.499(3) angstrom, c = 21.746(9) angstrom, beta = 106.14(3)degrees, and V = 485 3.7 angstrom3, for [Tb(DPM)3.DMOP], a = 13.897(7) angstrom, b = 16.508 (6) angstrom, c = 21.621(5) angstrom, beta = 104.97(4)degrees, and V = 4792.1 angstrom3, and for [Ho(DPM)3.DMOP], a = 13.859(9) angstrom, b = 16.539(5) angstrom, c = 21.538(12) angstrom, beta = 104.78(5)degrees, and V = 4773.5 angstrom3. Each of these adducts contain isomers which exist in 57 to 43%, 58 to 42%, and 55 to 45% ratios for La3+, Tb3+, and Ho3+, respectively. The isomer found more often in each case has all four chelate rings spanning the 1 edges of a square antiprism while the remaining isomer has two beta-diketonate rings spanning s edges and a beta-diketonate and a DMOP chelate ring spanning 1 edges.