Spectroscopically Distinct Geometrical Isomers in a Single Crystal. Characterization of the Eight-Coordinate Adducts of Tris(dipivaloylmethanato)lanthanide(III) with 2,9-dimethyl-1,10-phenanthroline
Tris(dipivaloylmethanato)(2,9-dimethyl- 1,10-phenanthroline)lanthanide(III), [L n(DPM)3*DMOP], complexes (Ln = La, Eu, Tb, 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 5Do →FO region are observed which are separated by an unprecedented 35 cm-l. The 5Do →7F1 and 5Do →7F2 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)3DMOP] was solved by single-crystal X-ray diffraction methods. The complex was found to crystallize in the monoclinic space group P21/n with a = 13.941(7) Å, b = 16.512(7) Å, c = 21.626(9) Å, β = 105.13(4)°, and V = 4805.6 Å3. 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 (1) and square (8) 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 Å. 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 P21/n. For [La(DPM)3*DMOP], a = 14.083(4) Å, b = 16.499(3) Å, c = 21.746(9) A, β=106.14(3)°, and V =4 853.7 A3, for [Tb(DPM)3*DMOP],a = 13.897(7) Å, b = 16.508(6) Å, c = 21.621(5) Å, 104.97(4)°, and V = 4792.1 A’, and for [Ho(DPM)p.DMOP], (I = 13.859(9) Å, β = 16.539(5) Å, c = 21.538(12) A, β = 104.78(5)°, and V = 4773.5 Å3. 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 β-diketonate rings spanning s edges and a β-diketonate and a DMOP chelate ring spanning 1 edges.