Abstract
The reaction of hot (~95 °C) aqueous solutions of Tl2CO3 with solid HL (HL = NC-C(=N-OH)-R is a cyanoxime, and R is an electron-withdrawing group; 37 ligands are known up-to-date) leads to crystalline yellow/orange TlL. Similarly, the reaction between AgNO3 and ML (M = K+, Na+; L = anion of the monodeprotonated cyanoxime) this time at room temperature in mixed ethanol/aqueous solutions leads to sparingly soluble, colored AgL in high-yield. All synthesized monovalent Tl and Ag complexes were characterized using a variety of spectroscopic methods and X-ray analysis, which revealed the formation of primarily 2D coordination polymers of different complexity. In all cases cyanoxime mono-anions act as bridging ligands. Thallium(I) cyanoximates adopt in most cases a double-stranded motif that is originated from centrosymmetric (TlL)2 dimers in which two Tl2O2 rhombs are fused into infinite “ladder-type” structure. There are very short (3.65–3.85 Å) intermetallic distances in (TlL)n, which are close to that (3.46 Å) in metallic thallium. This opens the possibility for the electrochemical or chemical generation of mixed valence Tl(I)/Tl(III) polymers that may exhibit electrical conductivity. Synthesized silver(I) compounds demonstrate a very significant (for multiple years!) stability towards visible light. There are three areas of potential practical applications of these unusual complexes: (1) battery-less detectors of UV-radiation, (2) non electrical sensors for gases of industrial importance, (3) antimicrobial additives to light-curable acrylate polymeric glues, fillers and adhesives used during introduction of indwelling medical devices. Chemical, structural, technological and biological aspects of application of Tl(I) and Ag(I) cyanoximes-based coordination polymers are reviewed.
Highlights
Coordination polymers are different from conventional organic polymers because of at least two reasons
In this work we summarize up-to-date results of our studies of coordination polymers based on cyanoximes—a new class of small organic molecules that exhibit properties of excellent anionic ligands that bind a variety of metal ions [4,5,6,7,8,9]
In recent years we were interested in synthesis and subsequent investigations of rather unique and interesting complexes of cyanoximes based on monovalent silver and thallium
Summary
Coordination polymers are different from conventional organic polymers because of at least two reasons. In recent years we were interested in synthesis and subsequent investigations of rather unique and interesting complexes of cyanoximes based on monovalent silver and thallium These compounds turned out to be coordination polymers of different complexity in which anionic cyanoximes act as bridging ligands sometimes showing unusual binding modes. As a main group III element, monovalent thallium has a 6s2 lone pair, which always defines its stereochemistry and significantly distorts the shape of the Tl(I) coordination polyhedron and, respectively, its compounds The latter, coupled with a fairly large size of Tl(I) ion (1.64 Å for six-coordinate environment [27]) and its polarizability leads to an interesting general trend in the structural chemistry of this metal: there are typically 2–3 short distances between the metal center and oxygen atoms in complexes, and 2–3 much longer electrostatic contacts with other donor atoms. Tl(CCO) [19]—all other investigated TlL complexes do not exhibit appreciable emission properties
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