A Comprehensive Study on the Full Series of Alkali‐Metal Selenocyanates A^I[SeCN] (A^I=Li−Cs)

Abstract

The full series of quasibinary alkali‐metal selenocyanates was synthesized either by oxidation of the respective cyanides (A=Li−Rb) or by metathesis (A=Cs). For Li[SeCN] only ball‐milling and subsequent annealing led to the isolation of the quasibinary selenocyanate. Their structures were refined from single‐crystal and powder X‐ray data. The respective solid‐state IR and Raman spectra were interpreted with the aid of solid‐state quantum‐mechanical calculations and DSC‐TGA measurements allowed for extraction of melting points. Only for Li[SeCN] a possible phase transition was observed that is discussed on the basis of VT‐PXRD experiments. It is also the only quasibinary selenocyanate to form a hydrate (Li[SeCN] ⋅ 2H2O).

Synthesis and Stability of Ammonium Selenocyanate [NH4][SeCN] and Its Reactivity toward Ag[SeCN]

“…Noteworthy are additional short Ag–Ag contacts ( d Ag–Ag = 3.6323(13), 3.2770(13), and 3.1586(12) Å) that, together with the aforementioned tetrahedron, form a distorted pentagonal bipyramid. The [SeCN] − -anions are almost linear with ≺ Se–C–N = 179.4(9)° and exhibit interatomic distances d Se–C = 1.838(10), and d C–N = 1.148(13) Å, which is in accordance with other quasi-binary selenocyanates . Two tetrahedra are connected via a shared edge forming a bow-tie motif with the Ag–Se distances of the bridging Se atoms being the shorter ones (see Figure b).…”

“…The Raman spectrum of [NH 4 ]­[SeCN] (Figure ) is dominated by the ν2 “antisymmetric” stretching vibration ( B g + A g ) of the [SeCN] − anion at 2081 cm –1 (calc. 2194–2202 cm –1 ), which is similar to the related alkali metal selenocyanates . A corresponding ν1 “symmetric” stretching vibration ( B g + A g ) was observed at 582 cm –1 (calc.…”

“…The selenocyanate anion is essentially linear (≺(Se–C–N) = 179.38(15)°) with interatomic distances d (Se–C) = 1.810(2) and d (C–N) = 1.158(2) Å. These values compare well to those of the alkali metal selenocyanates and Hg­[SeCN] 2 . , In comparison, interatomic distances d (C–N) = 1.205(7) Å as obtained from solid-state powder nuclear magnetic resonance spectroscopy are significantly longer . During the refinement of single-crystal data, hydrogen atom positions were located from Fourier difference maps, and subsequently, the N–H distances within the cation were restrained to 0.87 Å (σ = 0.02).…”

“…THF- d 8 was dried over a molecular sieve (4 Å) and degassed prior to use. Potassium selenocyanate was prepared by using the literature procedure . Organic solvents were dried and degassed by standard procedures and subsequently stored under Argon over activated 3 Å molecular sieves .…”

“…Especially the solid-state chemistry of the quasi-binary selenocyanates has been given scant attention. While the structures for K­[SeCN] and Hg­[SeCN] 2 have been reported some decades ago, , we only recently reported the full series of alkali metal selenocyanates A [SeCN] ( A = Li–Cs) . Especially notable is the absence of thorough investigations regarding ammonium selenocyanate.…”