[Na(THF)2Cr(N3N)]: The First Trigonal Monopyramidal Chromium(II) Complex

Reduction of [Cr(N3N)] (1) {(N3N)3- = ((SiMe3NCH2CH2)3N)3-} with sodium powder in THF affords the yellow, extremely air-sensitive amidochromate(II) [Na(THF)2Cr(N3N)] (2) in good yield. Complex 2 has an effective magnetic moment of 5.1 (mu)B indicative of a d4 high-spin electronic configuration. 1H NMR spectroscopy in solution and single-crystal X-ray crystallography show that compound 2 is composed of idealized Cs symmetric contact ion pairs, in which trigonal-monopyramidal [CrII(N3N)]- anions are linked to the [Na(THF) 2]+ countercations by two bridging amide ligands. DFT calculations of 1, 2, and the anion [Cr(N3N)]- at the RI-BP86/TZVPP level of theory provide in combination with extended Huckel calculations a rationale for the observed structural changes from 1 to 2.