Synthesis and Characterization of Iron Bispyridine Bisdicyanamide, Fe[C5H5N]2[N(CN)2]2

Fe[C₅H₅N]₂[N(CN)₂]₂ (1) was synthesized from a reaction of stoichiometric amounts of NaN(CN)₂ and FeCl₂·4H₂O in a methanol/pyridine solution. Single-crystal and powder diffraction show that 1 crystallizes in the monoclinic space group I2/m (no. 12), different from Mn[C₅H₅N]₂[N(CN)₂]₂ (P2₁/c, no. 14) due to tilted pyridine rings, with a = 7.453(7) Å, b = 13.167(13) Å, c = 8.522(6) Å, β = 114.98(6)° and Z = 2. ATR-IR, AAS, and CHN measurements confirm the presence of dicyanamide and pyridine. Thermogravimetric analysis shows that π-stacking interactions of the pyridine rings play an important role in structural stabilization. Based on DFT-optimized structures, a chemical bonding analysis was performed using a local-orbital framework by projection from a plane-wave basis. The resulting bond orders and atomic charges are in good agreement with the expectations based on the structure analysis. SQUID magnetic susceptibility measurements show a high-spin state Fe^II compound with predominantly antiferromagnetic exchange interactions at lower temperatures.

Syntheses and Characterization of Two Dicyanamide Compounds Containing Monovalent Cations: Hg2[N(CN)2]2 and Tl[N(CN)2]

Crystals of Hg2[N(CN)2]2 were grown by a slow diffusion-reaction between aqueous Hg2(NO3)2·2H2O and Na[N(CN)2]. Hg2[N(CN)2]2 adopts the triclinic space group P 1 ¯ (no. 2) with a = 3.7089(5), b = 6.4098(6), c = 8.150(6) Å, α = 81.575(6)°, β = 80.379(7)°, γ = 80.195(7)°, and Z = 1. Crystals of Tl[N(CN)2] were obtained from the reaction of TlBr with Ag[N(CN)2] in water. Single-crystal structure analyses evidence that Tl[N(CN)2] is isotypic to α-K[N(CN)2] and adopts the orthorhombic space group Pbcm (no. 57) with a = 8.5770(17), b = 6.4756(13), c = 7.2306(14) Å, and Z = 4. Regarding volume chemistry, the dicyanamide anion occupies ca. 44 cm3·mol−1, and so it corresponds to a large pseudohalide. The IR spectra of both compounds exhibit vibrational modes that are characteristic of the dicyanamide anion.

Syntheses, single-crystal structures, vibrational spectra and DSC/TG analyses of orthorhombic and trigonal Ag[N(CN)2]

Colorless powders of orthorhombic Ag[N(CN)2] were synthesized by blending aqueous solutions Ag[NO3] with stoichiometric amounts of Na[N(CN)2] equally dissolved in water. Single crystals of both modifications of Ag[N(CN)2] could be obtained by recrystallizing the powder with aqueous ammonia. Non-isothermal evaporation of the solvent at room temperature within a few hours yielded the orthorhombic modification as the main product crystallizing in the space group Pnma (no. 62) with the unit-cell parameters a = 1612.45(12), b = 361.58(3) and c = 599.02(4) pm (Z = 4). Upon evaporating the solvent much more slowly, isothermally within a few days, mainly thin hexagonal platelets of the trigonal modification of Ag[N(CN)2] were obtained, crystallizing in the space group P3121 (no. 152) with the lattice constants a = 359.86(3) and c = 2285.91(17) pm (Z = 3). Both results corroborate earlier structure determinations, but show higher precision. The vibrational spectra confirm the presence of the dicyanamide anion [N(CN)2]−, but exhibit slight differences to literature data. Differential scanning calorimetry/thermogravimetry (DSC/TG) analyses were performed to further characterize the two modifications.