[Na(THF)2Cr(N3N)]:: The first trigonal monopyramidal chromium(II) complex

Reduction of [Cr(N3N)] (1) {(N3N)(3-) = ((SiMe3NCH2CH2)(3)N)(3-)} with sodium powder in THF affords the yellow, extremely air-sensitive amidochromate(II) [Na(THF)(2)Cr(N3N)] (2) in good yield. Complex 2 has an effective magnetic moment of 5.1 mu(B) indicative of a d(4) high-spin electronic configuration. H-1 NMR spectroscopy in solution and single-crystal X-ray crystallography show that compound 2 is composed of idealized C, symmetric contact ion pairs, in which trigonal-monopyramidal [Cr-II(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.