Synthesis and molecular and solid state structural characterization of mixed CH3–CF3 and CH3–C2F5 fluoroalkyl pyrazoles and a new, TpC2F5,CH3TpC2F5,CH3 ligand

We report a new mixed methyl-fluoroalkyl (Rf) 3,5-substituted pyrazole, PzRf,CH3PzRf,CH3, with Rf = C2F5. An X-ray structural comparison of PzRf,CH3PzRf,CH3 (Rf = CF3 and C2F5) reveals a similar boat-type H-bonded tetrameric architecture, dominated by the 3,5 tautomers. The tetramers compactness could be compared by computing the volume of the tetrahedron defined by the geometric centers of the four pyrazole rings. Using this criterion the C2F5 group is found to induce a tighter intratetrameric packing relative to CF3, in addition to exhibiting a possibly higher degree of N–H proton delocalization.The new TpRf,CH3TpRf,CH3 (Rf = C2F5) sodium scorpionate is also reported. The X-ray structure of NaTpC2F5,CH3NaTpC2F5,CH3(H2O) shows discrete mononuclear units. The Na-coordinated H2O exhibits weak, 2.6 Å intermolecular Na–O–H···F contacts leading to the formation of a head-to-tail chain assembly. In contrast, the NaTpCF3,CH3NaTpCF3,CH3 (H2O) complex forms dimers in solid-state, supported by Na-bridging water ligands and intermolecular Na···F interactions.The presence of metal-bonded H2O in the sodium complex of TpC2F5,CH3TpC2F5,CH3 as well as the formation of discrete complexes when CF3 is replaced by C2F5 in TpRf,CH3TpRf,CH3 reflect both the strong σ electronic acceptor nature of the ligand and its enhanced steric bulkiness.

Graphical abstractThe new Rf pyrazole, PzRf,CH3PzRf,CH3, yields NaTpRf,CH3NaTpRf,CH3, Rf = C2F5 scorpionate. Both PzRf,CH3PzRf,CH3, Rf = CF3 and C2F5, exhibit similar tetrameric architecture in solid state and 3,5 tautomers. The NaTpCF3,CH3NaTpCF3,CH3(H2O) complex forms Na(H2O) bridged dimers in solid-state, but NaTpC2F5,CH3NaTpC2F5,CH3(H2O) crystallizes as mononuclear units, linked by weak intermolecular Na–O–H···F contacts in a head-to-tail chain. The presence of Na-bonded H2O in TpC2F5,CH3TpC2F5,CH3 as well as the formation of discrete complexes when CF3 is replaced by C2F5 in TpRf,CH3TpRf,CH3 reflect both the strong σ electronic acceptor nature of the ligand and its enhanced steric bulkiness.Figure optionsDownload full-size imageDownload as PowerPoint slide