Date Published: May 01, 2020
Publisher: International Union of Crystallography
Author(s): Christopher Koenigsmann, Leena N. Rachid, Christina M. Sheedy, Peter W. R. Corfield.
The crystal structure is reported of a three-dimensional anionic CuICN network with noncoordinated protonated N-methylethanolamine cations providing charge neutrality. Pairs of cuprophilic Cu atoms are bridged by μ3-cyanide groups which link these units into 43 spirals along the c axis, and these are linked together by other cyanide groups. On heating the compound to 280 °C, a CuCN residue is formed, while further heating leaves a residue of elemental copper, isolated as the oxide.
Copper cyanide networks have been studied extensively in light of their interesting and unpredictable topologies, their photoluminescence, and the possible applications of their physical properties (see, for example: Grifasi et al., 2016 ▸; Pike 2012 ▸; Dembo et al., 2010 ▸; Tronic et al., 2007 ▸). The CuICN–base networks in the literature either involve the base coordinated to Cu or the CuCN network carrying a net negative charge, requiring a cation in the network to provide neutrality. Our program of structural studies on mixed-valence copper cyanide complexes has sought to prepare neutral CuCN networks by incorporating divalent copper ions into CuI networks, the CuII atoms being stabilized by coordination to one or more chelating ligands in the form of nitrogen bases. The synthesis and structural analysis of the title compound, poly[2-hydroxy-N-methylethan-1-aminium [μ3-cyanido-κ3C:C:N-di-μ-cyanido-κ4C:N-dicuprate(I)]], (I), arose from an initial attempt to prepare such a neutral mixed-valence complex by partial reduction of Cu2+(aq) with the cyanide ion in the presence of N-methylethanolamine (meoen) as the stabilizing chelating ligand, a method which has previously produced crystalline products when chelating diamines were used (see, for example: Corfield & Sabatino, 2017 ▸). After many unsuccessful attempts, mixtures containing crystalline compound (I) resulted, as described in the Experimental (§2) section. Although we have been unable so far to prepare a crystalline mixed-valence copper cyanide compound involving this base, we developed modified procedures to synthesize pure compound (I) in light of its interesting structural properties. Detailed thermogravimetric analyses of (I) were carried out in order to understand the structure further. Prompted by this work, our laboratory is now carrying out similar studies on a number of other CuCN networks based upon N-alkylethanolamines.
Reagents were used as supplied by the manufacturers without further purification. IR spectra were obtained with a Thermo Scientific Nicolet iS50 FT–IR instrument, while thermal degradation studies were carried out under nitrogen with a TA Instruments TGA-Q500 instrument. Scanning electron microscopy images were obtained with a Zeiss EVO MA-10 instrument equipped with an LaB6 filament. Images were collected with an accelerating voltage of 15 kV in variable pressure mode with a system vacuum of 40 Pa. SEM samples were prepared by drop-casting the powders dispersed in hexanes onto ultraflat p-doped Si wafers, which were dried under vacuum before analysis. Powder X-ray diffraction measurements were made with a Bruker D8 Advance Eco instrument. Elemental analyses were performed by Robertson–Microlit Laboratories, Ledgewood, NJ, USA.