Research Article: Synthesis, decom­position studies and crystal structure of a three-dimensional CuCN network structure with protonated N-methyl­ethano­lamine as the guest cation

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.

Partial Text

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.




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