Ba[C(CN) ₃ ] ₂ and Pb[C(CN) ₃ ] ₂ : Two Remarkably Different Heavy Main‐Group Metal Bistricyanomethanides

Metathesis reactions of either barium dichloride, BaCl 2 , or lead dichloride, PbCl 2 , respectively, with Ag[C(CN) 3 ] in water yielded single crystals of anhydrous Ba[C(CN) 3 ] 2 and Pb[C(CN) 3 ] 2 . Ba[C(CN) 3 ] 2 crystallizes in the monoclinic space group P 2 1 / n (no. 14) with the lattice parameters a = 437.98(3) pm, b = 1685.36(11) pm, c = 1398.87(9) pm, β = 96.541(3)° for Z = 4, while Pb[C(CN) 3 ] 2 adopts the non‐centrosymmetric trigonal space group P 31 m (no. 157) featuring a = 1414.53(9) pm and c = 411.64(3) pm with c/a = 0.291 for Z = 3. Both crystal structures exhibit M 2+ cations in ninefold coordination of nitrogen atoms from the star‐shaped planar tricyanomethanide anions [C(CN) 3 ] – (≡ tcm – ), but the distances in the respective tricapped trigonal prisms are rather unlike: d (Ba–N) = 277.7–299.9 pm versus d (Pb1–N) = 254.2–294.4 pm and d (Pb2–N) = 265.2–290.1 pm. For Ba[C(CN) 3 ] 2 (≡ Ba(tcm) 2 ) a cotunnite‐like arrangement according to Ba(tcmA) 4/4 (tcmB) 5/5 is observed, while Pb[C(CN) 3 ] 2 (≡ Pb(tcm) 2 ) avoids this orthorhombic PbCl 2 ‐type structure. Most probably due to the stereochemical lone‐pair activity of the Pb 2+ cations, the best Niggli description of its unique non‐centrosymmetric crystal structure, which is confirmed by a strong second harmonic generation response, seems to be {(Pb1)[(tcmA) 3/3 (tcmB) 6/6 ] 1/3 (Pb2)[(tcmA) 6/6 (tcmB) 3/3 ] 2/3 }. Moreover, a blue lone‐pair luminescence from the Pb 2+ cations can be detected for Pb[C(CN) 3 ] 2 , and the same holds for Pb[N(CN) 2 ] 2 , displaying a similar ninefold nitrogen coordination for Pb 2+ . Raman spectra were recorded for both Ba[C(CN) 3 ] 2 and Pb[C(CN) 3 ] 2 to verify the presence of discrete tricyanomethanide anions [C(CN) 3 ] – .