dad Compounds of Niobium and Tantalum: Examples of the Structural Flexibility of dad Ligands

New uses for dad! Ideal examples of the flexible coordination of 1,4‐diaza‐1,3‐butadiene (dad) ligands are the novel niobium and tantalum (dad) complexes 1 and 2 . As a result of the unusual μ‐η 2 ,η 2 bridging function of two dad ligands in 1a, b , the lithium ions are located within the ligand sphere of the complexes. Irrefutable evidence of the different coordination modes is provided by 2 : three types are represented in this one dinuclear niobium complex.\documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}$${\begin{array}{ll}[(\eta^4\hbox{-dad}){\rm M}(\mu\hbox{-}\eta^2,\eta^2\hbox{-dad})_2{\rm Li}]\\{\bf 1a},{\rm M}={\rm Nb};{\bf 1b},{\rm M}={\rm Ta}\end{array}}$$\end{document}