The Triply Deprotonated Acetonitrile Anion CCN³⁻ Stabilized in a Solid

Abstract

The unprecedented, fully deprotonated form of acetonitrile, the acetonitriletriide anion CCN , is experimentally realized for the first time in the stabilizing bulk host framework of the Ba [TaN ][C N] nitridometalate via a one-pot synthesis from the elements under moderate conditions (920 K). The molecular structure of this long-sought acetonitrile derivative is confirmed by X-ray diffraction, as well as NMR, IR, and Raman spectroscopy. The anion is isoelectronic to the CO molecule, and, in contrast to acetonitrile (H C-C≡N), the electron pairs are shifted towards two double bonds, that is, [C=C=N] .

Sr4N[CN2][C2N]: The First Carbodiimide Acetonitriletriide

“…These distances are somewhat larger than in carbodiimide anions NCN 2– of other ternary strontium containing structures, see Table . Distances observed for CCN 3– in Ba 5 [TaN 4 ][C 2 N] ( d (C–C) = 133(2) pm, d (C–N) = 124(2) pm) differ to those obtained here, especially regarding the carbon–carbon bond. In order to resolve this, additional structural models for the overlapping anions containing slightly shifted split positions for all atoms, were tested.…”

“…The low site symmetry ( C 1 ) of the anions together with factor group splitting cause the observed splitting of valence and deformation modes of both anions. Stretching frequencies of C 2 N 3– in Sr 4 N[CN 2 ][C 2 N] ( ν as = 1765–1809 cm –1 , ν s = 1150–1152 cm –1 ) are very similar to those observed in Ba 5 [TaN 4 ][C 2 N] . Multiple bands observed in the region 497–715 cm –1 in IR and Raman spectra represent deformation modes of both anions.…”

“…In this respect, the nitrogen partial pressure is a crucial synthesis parameter as already observed for syntheses of related nitridometalates containing carbon (e.g. (Sr 6 N)[CoN 2 ][CN 2 ] 2 , Ba 3 [Co(CN) 3 ], or Ba 5 [TaN 4 ][C 2 N]) . Best quality samples with only small amounts of impurities (see Supporting Information) were obtained by employing Sr 2 N, NaCN, and graphite as starting materials.…”

“…The first experimental realization of the fully deprotonated acetonitrile anion CCN 3– in the nitridometalate host of Ba 5 [TaN 4 ][C 2 N], raised the question, whether this CO 2 ‐isoelectronic anion could be stabilized in a pure cationic environment as well. Since similar molecular anions, such as CN 2 2– carbodiimide or BN 2 3– boronitride form various crystal structures as alkaline earth salts, ternary acetonitriletriide salts were explored.…”

“…(Sr 6 N)[CoN 2 ][CN 2 ] 2 . At lower partial pressure of the oxidizing agent nitrogen, highly reduced cyanometalates such as Ba 3 [Co(CN) 3 ] and Sr 2 [NNi(CN)], as well as the above mentioned nitridometalate‐acetonitriletriide Ba 5 [TaN 4 ][C 2 N] were obtained.…”