Crystal Structure, Second Harmonic Generation, and Vibrational Spectroscopy of K₂Mg₂(SCN)₆·3H₂O

Abstract

Single crystals of K2Mg2(SCN)6·3H2O were obtained by the reaction of the binary compounds MgCl2·xH2O and KSCN at 220° using the Bridgman technique. The compound crystallizes hexagonally with the noncentrosymmetric space group P63 cm (Z = 2, a = 885.2(1) pm, c = 1732.7(3) pm, R1all = 0.1035). In the crystal structure, the Mg2+ ions are coordinated by oxygen and nitrogen atoms while the K+ ions are exclusively surrounded by sulfur atoms. The two crystallographically different Mg2+ ions are linked via common nitrogen atoms to dimers, [Mg2(SCN)6(H2O)3]2-. The K+ ions are connected with each other by two crystallographically different sulfur atoms to hexagonal rings which form layers in the (001) plane. The dimers are connected to these layers in equal orientation leading to the absence of inversion symmetry. Frequency doubling measurements on K2Mg2(SCN)6·3H2O as well as on KDP powder samples were carried out. The second harmonic generation intensity of the rhodanide is about 40% of that of KDP. Furthermore, IR and Raman measurements were performed, and the results were compared to other thiocyanates. The energies of the vibrations of the molecular SCN- ions demonstrate their bridging function in the crystal structure, and the energies and the shapes of the H2O bands indicate hydrogen bonds.

Structural Diversity in Tetrakis(4-pyridyl)porphyrin Supramolecular Building Blocks

“…First, the square-antiprismatic Ba­(II) coordination polyhedra form infinite edge-sharing chains bridged directly by μ 2 -thiocyanate nitrogen atoms. The sulfur atom of one thiocyanate group further links these by coordinating to a separate Ba­(II) center from the nitrogen atom, as observed in the structure of K 2 Mg 2 (SCN) 6 ­·3H 2 O . These one-dimensional Ba­(SCN) 2 tapes run along the crystallographic c- axis and are linked along the (0 1 1) plane by coordination to trans pyridine groups of the TPyP.…”

Ion transport mechanism in anhydrous lithium thiocyanate LiSCN Part I: ionic conductivity and defect chemistry

“…Apart from recently prepared tri-cationic cyanamides with the composition Li 2 MSn 2 (NCN) 6 (M = Mg 45 und Mn 46 ), anhydrous thiocyanates, nitrides or cyanides of lithium and any divalent transition metal are unknown so far, which makes the structure of Mg 1.02 Li 3.96 (SCN) 6 a hitherto unknown structure type (details in the Supporting Information). Mixed alkali and alkaline earth metal pseudo-halides are rare, [47][48][49] and even though Na 4 Mg(SCN) 6 has a very similar composition, its crystal structure is very different. The observation that the new phase Mg 1.02 Li 3.96 (SCN) 6 has a much higher conductivity than even highly doped Li(SCN) is related to the coordination polyhedra of Mg 2+ and Li + in this structure (Supporting Information Figure S3 and S4), and will be discussed later.…”

Synthesis, characterization and thermal behaviour of solid phases in the quasi-ternary system Mg(SCN)2–H2O–THF

“…IR spectroscopy was employed to confirm the presence of thiocyanate and THF as well as to derive information on the coordination of Mg 2+ . Figure 2 14 and various rare earth metal thiocyanate complexes with different solvent molecules. 39 In the last case, the splitting was attributed to the bridging nature of SCNto two cations, enabling both symmetric and asymmetric ν(C≡N) modes.…”

“…[7] 2081 [11] 2083 [12] 2072 [6] 2075 [7] 2034 [8] 1636 [13] 1637 [14] 1606 [15] 1476 [8] 1459 δ(H-C-H) [THF] [16] 1458 [9] 1447 [17] 1372…”

“…10,12 Further structural studies of related Mg 2+ -SCN --phases are only available for mixed cationic systems involving other cations like K + or Cd 2+ . 14,15 In contrast, other MgX2 salts with similar anions (X = CN, N(CN)2) are well known in terms of crystal structures and properties. 16,17 Furthermore, unlike many other thiocyanate salts M(SCN)n (M = Li, Na, K, Ca, Sr, Ba, Ni, Ag, Hg, …, n = 1 or 2), [18][19][20][21][22][23][24][25] it is yet unclear how to obtain the anhydrous form of Mg(SCN) 2 and under what conditions it would be stable.…”