Homoleptic Rare‐Earth Carbazolates and the Trends of Their E Ln II/III Redox Potentials: Mixed‐Valent Samarium in 1 ∞ [Sm 2 (Cbz) 5 ](CbzH) (CbzH = carbazole) and Trivalent Thulium, Neodymium and Gadolinium in [Ln 2 (Cbz) 6 ]

The solvent‐free melt reaction of carbazole (CbzH, C 12 H 8 NH) with samarium metal yields 1 ∞ [Sm 2 (Cbz) 5 ](CbzH) ( 1 ), whilst the melt reactions with thulium, neodymium and gadolinium give [Tm 2 (Cbz) 6 ] ( 2 ), [Nd 2 (Cbz) 6 ] ( 3 ) and [Gd 2 (Cbz) 6 ] ( 4 ), respectively. Compounds 1 and 2 were obtained as single crystals and their crystal structures determined by single‐crystal X‐ray analysis, whilst 3 and 4 were obtained as powders. X‐ray powder diffraction studies show that the gadolinium‐containing complex 4 is isotypic to the thulium complex 2 , whereas the neodymium‐containing complex 3 is not. Compound 1 contains alternating Sm II and Sm III cations in a chain structure. Complex 2 only exhibits dimeric units of Tm III . Besides Ln−N coordination, the crystal structures of both compounds show η 6 ‐π interactions with the phenyl rings of the carbazolate ligands. This leads to small coordination polyhedra, such as connected tetrahedra of two nitrogen atoms and two η 6 ‐π‐coordinated phenyl rings around Sm II , and trigonal bipyramids of five nitrogen atoms around Sm III for 1 , as well as tetrahedra of three nitrogen atoms and one η 6 ‐π‐phenyl interaction around Tm III for 2 . From the trend of the E   Ln   II/IIIredox potentials, the complexes of neodymium and gadolinium are also trivalent. For 1 − 4 the results of FIR, MIR and Raman spectroscopy as well as simultaneous DTA/TG analyses are also presented. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)