Abstract
A novel organic-inorganic chromium(III) hybrid salt, triethylammonium trans-diaquabis(oxalato-κ2O1,O2)chromate(III), (C6H16N)[Cr(C2O4)2(H2O)2] (1), has been synthesized in aqueous solution and characterized by elemental and thermal analyses, FTIR and UV-Vis spectroscopies, and by single crystal X-ray structure determination. Compound 1 crystallizes in the orthorhombic system, Pbcn space group with the unit cell parameters a = 11.1776(10), b = 7.6105(10), c = 17.5654(2) Å, α = β = γ = 90°, V = 1494.24(3) Å3, Z = 4 and Z’ = 1/2. The structure of 1 consists of [Cr(C2O4)2(H2O)2]− mononuclear anions and triethylammonium [(C2H5)3NH]+ cations. In the anionic unit, the CrIII ion is six coordinated, in a distorted octahedral geometry, by four equatorial O atoms of two oxalate anions acting as chelating ligands and two O atoms from trans-coordinated water molecules occupying the apical positions with longer metal-oxygen distances. In the solid, O-H … O and N-H … O intra and inter molecular hydrogen bonding interactions connect the components into a 3D network. The triethylammonium cations are disordered among two possible orientations with occupancies rates around 50% for C4, N1, C1a, C1b, C4ii, N1ii, C1aii, C1bii (ii = −x + 1, y, − z + 1/2). The IR spectrum of 1 is consistent with the presence of the various molecular building constituents. The UV-Vis spectrum shows two absorption bands around 564 and 416 nm which are compatible with an anionic chromium (III) complex in an octahedral environment. Thermal studies carried out in air between 25°C and 700°C confirm the anhydrous character of 1 and show that it is stable up to 210°C.
Highlights
In the recent years, the area of organic-inorganic hybrid salts based on bis(oxalato)chromate(III), has become one of intense research activities due to the need for novel solid-state architectures with potential applications as functional materials in various fields such as catalysis, magnetism, medicine, luminescence, conductivity and even materials science and industrial applications [1]-[6].Up to now, there has been a significant interest in the synthesis and characterization of bis(oxalato)chromate(III) compounds through a synthetic strategy based on supramolecular chemistry and self-assembly processes of two different components
The combination of triethylamine (C2H5)3N with hydrochloric acid and oxalic acid in aqueous solution generates in situ (C6H16N)2C2O4 which reacts with CrCl3·6H2O in water to give, by evaporation of the resulting solution at room temperature after three weeks, the title compound (C6H16N)[Cr(C2O4)2(H2O)2] (1) as violet prismatic crystals. 1 is thermally stable up to 210 ̊C
The FTIR spectrum of 1 (Figure 1) exhibits weak absorption bands centered at 3153 cm−1 attributed to νN−H of triethylammonium cations
Summary
The area of organic-inorganic hybrid salts based on bis(oxalato)chromate(III), has become one of intense research activities due to the need for novel solid-state architectures with potential applications as functional materials in various fields such as catalysis, magnetism, medicine, luminescence, conductivity and even materials science and industrial applications [1]-[6]. To investigate new supramolecular architectures containing molecular building blocks [M(C2O4)3]3− or [Cr(C2O4)2(H2O)2]− (M = Cr, Fe), a lot of work has been devoted to the study of their combination with different organic cations (OrgH+) In this context, heterocyclic aromatic amines (pyridine, pyrazole, imidazole, etc.) rings are often used as organic cations, by protonating their imine groups, leading to 3D hybrid (oxalato)metalate(III) salts with the general formula (OrgH)3[M(C2O4)3]∙nH2O (M = Cr, Fe; n ≥ 0) [7] [8] [9] or A[Cr(C2O4)2(H2O)2]∙nB with A = OrgH+; B = H2O or urea, CO(NH2); n ≥ 0 [10] [11] [12] [13] [14]. By using triethylammonium as organic cation, we have isolated a new hybrid salt: (C6H15NH)[Cr(C2O4)2(H2O)2] and we report its synthesis and structural characterization as well as its spectroscopic and thermal properties
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