Hydrogen bonding induced polymorphism in the scandium(III) complex with ε-caprolactam

Abstract

Two polymorphs of [Sc(cpl) 6 ][Cr(NCS) 6 ] (cpl = ε-C 6 H 11 NO), trigonal and monoclinic, form purple elongated narrow plates and brownish-purple prisms and are formed concomitantly irrespectively of the crystallization conditions. In the trigonal polymorph both cation and anion possess C 3i site symmetry while in the monoclinic form cation and anion lie on inversion centre and 2-fold axis respectively. The nature of the polymorphism traces back to a redistribution of inter-and intramolecular hydrogen bonds that causes different conformation of the complex cations, different hydrogen bonding and different molecular packings. The [Sc(cpl) 6 ] 3+ cations in the structure of the trigonal polymorph form intermolecular N(H)…S, and in the monoclinic form both N(H)…S inter-and N(H)… O intramolecular hydrogen bonds with NCS groups of [Cr(NCS) 6 ] 3− and cpl ligands. This aggregation leads to chains, where the cations and the anions alternate, in the trigonal modification and to layers, in which each ion is surrounded by four counterions, in the monoclinic form. Both polymorphs possess thermochromic properties, and a reversible color change from light purple to dark green takes place at 470-475 K.

High Surface Area of Polyhedral Chromia and Hexagonal Chromium Sulfide by the Thermolysis of Cyclohexylammonium Hexaisothiocyanatochromate(III) Sesquihydrate

“…The bending vibration of the NÀ CÀ S band, δ(NCS), was observed as a strong band at 480 cm À l . [32,33,35,[37][38][39][41][42][43][44][45][46][47][48][49]57,[85][86][87][88] The coordination of hard Cr(III) ion center by the hard N-terminal of thiocyanate ligand is consistent with Pearson's concept of hard and soft acids and bases (HSAB). [34,44,57,85,86] Furthermore, structural studies by single X-ray diffraction confirmed the binding of N-terminal to Cr(III) in [Cr(NCS) 6 ] 3À .…”

“…[32,33,35,[37][38][39][41][42][43][44][45][46][47][48][49]57,[85][86][87][88] The coordination of hard Cr(III) ion center by the hard N-terminal of thiocyanate ligand is consistent with Pearson's concept of hard and soft acids and bases (HSAB). [34,44,57,85,86] Furthermore, structural studies by single X-ray diffraction confirmed the binding of N-terminal to Cr(III) in [Cr(NCS) 6 ] 3À . [21,[24][25][26][27][28][29][30][31][32][33][34][35][36][37][39][40][41][42][43][44][45][46][47][48]…”

“…[21] Among the thiocyanate metal complexes is the anionic complex of hexaisothiocyanatochromate(III) [Cr-(NCS) 6 ] 3À , which was used broadly to construct various supramolecular structures with either organic cations [22][23][24][25][26][27][28][29][30] or metal cations, [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] partially, because both of thiocyanate nitrogen and sulfur terminals are hydrogen acceptors when forming hydrogen bonds. [14,20,25,[27][28][29][31][32][33][34][35][36][37][39][40][41][42][43][44][45]…”

“…[24,26,27,30] The metal salts of [Cr(NCS) 6 ] 3À are classified as bimetallic complexes or double complex salts. [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] They are able to form molecular magnets. [32] They are useful precursors for the synthesis of various functional materials, polymetallic systems, catalysts, nanocomposites, and reversible thermochromic materials.…”

“…[31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] The [Cr(NCS) 6 ] 3À , as an inert bulky ion, is a precipitating agent for lanthanide ions in organic-aqueous medium. [34][35][36]39,41,42,44,[46][47][48][49] In addition, [Cr(NCS) 6 ] 3À is a very good reagent for the gravimetric analysis of heavy metal ions, such as copper, silver, cadmium, mercury, lead, thallium, and bismuth, in the aqueous medium, even in the microscale range. [50][51][52][53][54][55][56] The thermolysis, under air, of double complex salts of lanthanides, complexed by the neutral ε-caprolactam, and [Cr(NCS) 6 ] 3À results in a mixture of the corresponding lanthanide oxide (Ln 2 O 3 ) and chromia (Cr 2 O 3 ) nanoparticles due to their relatively low temperatures of decomposition.…”