| Abstract: | ![]()
Preparation and Properties of Tetragonal α-Di(phthalocyaninato(1?))praseodymium(III)-polyhalides; Crystal Structure of α-[Pr(Pc?)2]Br1.5 Brown red di(phthalocyaninato(1?))-praseodym(III)-polyhalides [Pr(Pc?)2]Xy (X = Br, I) of variable composition (1 ≤ y ≤ 2.5) are formed by (electro)chemical oxidation of [Pr(Pc2?)2]?. The thermical decomposition of these polyhalides at 250°C yields partially oxidized, green α-[PrPc?Pc2?]. Due to strong spin–spin coupling of the phthalocyanin-π-radicals only PrIII contributes to the magnetic moment of ca. 3.0 B.M. for all complexes. Green metallic prisms of [Pr(Pc?)2]Br1.5 crystallize in the tetragonal α-modification: space group P4/nnc with a = 19.634(5) Å, c = 6.485(2) Å; Z = 2. In the sandwich complex PrIII is eightfold coordinated by the isoindoline N-atoms of the two staggered (41°), nearly planar Pc?- ligands. The quasi-onedimensional character of the structure along [001] is due to the infinite columns of Pc? ligands. The superperiod along [001] is a consequence of the distribution of the Pr atoms onto two incompletely filled crystallographic positions at a distance of c/2 and the disordered chains of the bromine atoms extending in the same direction. Powder diffractograms of Pr(Pc )2Br2, [Pr(Pc?)2]I2 und [PrPc Pc2?] confirm the tetragonal α-modification of these complexes, too. The content of tribromide correlates with the population of the Pr(2)-site. In the UV-VIS-NTR absorption spectrum of a thin film of Pr(Pc )2Br, the intense bands at 13.9 and 19.5 kK are assigned to the B and Q transition, respectively. The D band at 9. kK is characteristic for isolated dimeric Pc?-π-radicals. Due to increasing electron delocalisation as a result of the growing columns the D band is shifted to lower energy appearing successively at 6.05 and 3.3 kK. The mir and resonance Raman (RR) spectra of α-[Pr(Pr?)2]Xy, (X = Br, I) show the well known diagnostic bands for Pc?-π-radicals. Thc RR spectrum of the polyiodide is dominated by the overtone progression of the totally symmetric (I-I) stretching vibration of the triiodide at 108cm?1. The FT-Raman spectra are also marked by the totally symmetric stretching vibration of the polyhalides (Br3 : 145cm 1; 13?:105cm?1; I5? 151 cm?1). |
