2-Cyano-2-isonitrosoacetamide and its Ag(i) complexes. Silver(i) cyanoximate as a non-electric gas sensor

Abstract

The 2-cyano-2-isonitrosoacetamide, NC-C(N=OH)-C(O)NH(2) (1), its Na(+), Cs(+) salts and four silver(I) complexes with N-donor ligands were synthesized and characterized using a variety of techniques including IR, UV-vis spectroscopy, solid state photoluminescence, X-ray analysis, and solution electrical conductivity. All four reported here Ag(I) complexes were crystallographically characterized and revealed completely different structures. Thus, the combination of chelate and bridging function of the cyanoxime anion in Ag{NC-C(N=O)-C(O)NH(2)} (complex 6) leads to a unique layered 2D coordination polymer of silver(i) with pronounced argentophilic interactions at 3.194 A. The structure of Ag{NC-C(N=O)-C(O)NH(2)} x 2Pic (Pic = 2-methylpyridine; complex 7) represents the monomeric complex containing bidentate chelate anion 1(-). The crystal structure of monomeric Ag{NC-C(N=O)-C(O)NH(2)} x 2NH(3) (complex 8) reveals the formation of a linear Ag(NH(3))(2)(+) cation non bonded to the metal cyanoxime anion 1(-). This is the first structure of a silver(i) diammine cation with an oxime-based anion. Similarly to 8, the crystal structure of Ag(14ane[N(4)]){NC-C(N=O)-C(O)NH(2)} x CH(3)CN with tetraaza-meso(macrocyclic) ligand (complex 9) contains a metal center not bound to the cyanoxime ligand as well. Instead, the agostic interaction at 2.591 A between the methylene group of the macrocyclic ligand and silver(I) center was found in 9. This is the shortest CH(2)-Ag distance between an aliphatic group and metal observed so far in non-organometallic silver complexes with neutral ligands. We also documented a remarkable visible-light insensitivity of complex 6. Room temperature solid state photoluminescence of this compound was examined in details, including studies of its emission in the presence of several gases of industrial importance: H(2), CO, NO, NH(3), SO(2), acetylene C(2)H(2) and ethylene C(2)H(4). A significant sensitization of to visible light after the exposure was observed, which is a useful property that may be utilized in development of battery-less colorimetric sensors for these gases.

An Excursion into the Intriguing World of Polymeric Tl(I) and Ag(I) Cyanoximates

“…However, there is a large group of 13 visible light insensitive AgL complexes, namely with L = CCO (Figure 3), which are stable to day light for years of continuous exposure (ESI 14). This property has several important practical implications [19][20][21] which will be briefly discussed further in this work.…”

“…Yields are typically above 90%. However, silver(I) cyanoximates with thioamides TCO − and TDCO − (4 and 5, Figure 3) cannot be obtained due to the fast decomposition to black Ag 2 S. Some physical-chemical characteristics and crystal data for characterized up-to-date AgL are presented in [20] are formed similarly to those generated from silver(I) halides [35]. This turned to be an important property for the equipment and glassware clean-up for the last two reagents.…”

“…The deprotonation of cyanoximes with the base (typically NaOH, or K 2 CO 3 ) leads to yellow solutions of respective conjugated anions [19,20,50], which rapidly, within seconds react with aqueous AgNO 3 to form silver(I) cyanoximates of AgL composition. In all cases resulting complexes are thick, sparingly soluble in aqueous solutions precipitates of various colors that and can be easily separated from the reaction mixture by filtration, washed with water and cold methanol and dried in vacuum desiccator over H 2 SO 4 (c).…”

“…These compounds turned out to be coordination polymers of different complexity in which anionic cyanoximes act as bridging ligands sometimes showing unusual binding modes. Silver(I) polymeric cyanoximates showed quite remarkable stability towards visible light, which can be utilized in several practical applications [19][20][21], while polymeric thallium(I) cyanoximates are attractive building blocks and templates [22] for the preparation of mixed valence Tl(I)/Tl(III) systems that may exhibit electrical conductivity. This is an important property in design of molecular wires and in other molecular electronics applications [23].…”

Competing hydrogen-bond donors: phenols vs. cyanooximes

“…6 However, cyanooximes, 7 where the oxime nitrogen atom is a 25 particularly weak hydrogen-bond acceptor due to the presence of the electron-withdrawing -CN moiety, 8,9 tend to act as a single point hydrogen-bond donors similar to an -OH group. 10 The latter functionality is ubiquitous in biological systems, and is also heavily utilized in applications such as templated covalent 30 synthesis, 11 nonlinear optics 12 and sensors.…”