Condensation of Rare Earth Pyrazolates: The Dimeric, Trimeric and Polymeric Units [Gd 2 (Pz) 6 (PzH) 4 ], [Nd 3 (Pz) 9 (PzH) 2 ] and $^{1}_{\infty}\rm [Eu(Pz)_{2}(PzH)_{2}]$

Solvent free high‐temperature oxidations of rare earth metals with the heterocycle pyrazole as well as in low to non‐coordinating solvents were investigated to isolate intermediate stages between monomeric and polymeric pyrazolates of the lanthanides. Reaction conditions were tuned according to simultaneous DTA/TG and temperature dependent X‐ray powder diffraction experiments on known monomeric and polymeric pyrazolates, that gave rise to the idea that further structure intermediates could be isolated. Reactions in 1,2,3,4‐tetrahydroquinoline gave the dimeric complex [Gd 2 (Pz) 6 (PzH) 4 ](PzH)(Tech) ( 1 ) as well as the triangular complex [Nd 3 (Pz) 9 (PzH) 2 ](PzH)(Tech) 2 ( 2 ). The solvent free melt synthesis resulted in a new polymeric form of $^{1}_{\infty}\rm [Eu(Pz)_{2}(PzH)_{2}]$ ( 3 ) (pyrazole, PzH = C 3 H 3 NNH; pyrazolate anion, Pz − = C 3 H 3 NN − ; 1,2,3,4‐tetrahydroquinoline, Tech = C 9 H 13 N). All three compounds contain coordinating pyrazolate amide groups and pyrazole molecules the latter decreasing in numbers upon condensation of the building units. According to simultaneous DTA/TG/MS investigations the condensation process can be identified with the release of pyrazole molecules. 1 consists of dimeric molecules containing trivalent gadolinium with a C.N. of eight. The two gadolinium atoms show different coordination polyhedra. Only σ coordination and bridging is found for 1 . 2 consists of trimeric molecules containing trivalent neodymium. The neodymium atoms also exhibit different coordination polyhedra with C.N.s of eight and nine. Both π and σ coordination is found for 2 , the π coordinating pyrazolate ligands acting as lids of the triangular units. Topological analysis of the electron localization function (ELF) for 2 calculated at the scalar‐relativistic DFT level reveals only weakly covalent π donor η 5 ‐Pz–Nd interactions compared to the stronger covalent σ donor Pz–Nd interactions. The topological analysis of both, the ELF and the electron density reveals no significant differences of the respective charges of the Nd atoms. 3 exhibits a one‐dimensional chain structure with Eu II and a C.N of ten. It can thus be addressed the β form of the referring formula with a new arrangement of the coordinating ligands. Like the α form 3 shows σ and π coordination of pyrazole and pyrazolate ligands. Simultaneous DTA/TG analysis reveals that the low‐temperature α form shows a phase transition into the β form between 110 °C and 130 °C. The three compounds were investigated by low‐temperature single crystal X‐ray analysis, Mid IR and Far IR spectroscopy.