Instant Detection of Hydrogen Cyanide Gas and Cyanide Salts in Solid Matrices and Water by using CuII and NiII Complexes of Intramolecularly Hydrogen Bonded Zwitterions.

A series of intramolecularly hydrogen-bonded zwitterionic compartmental ligands HL1-HL4, containing a pendent diamine arm that is monoprotonated and an aldehyde functionality at two different ortho-positions of a 4-halophenoxide, is reported herein. Single-crystal X-ray diffraction (SXRD) provides persuasive evidence for the identification of this class of proton-transferred zwitterions at room temperature. The solid-state photoluminescent nature of these zwitterions remains intact in aqueous and organic solutions. Grinding of HL1 and HL2 with Cu2+ /Ni2+ salts develop turn-on probes 1-4. Compounds 1 and 4 are dinuclear CuII and NiII species, respectively. Compound 2 is a tetranuclear CuII complex. Interestingly, compound 3 is a mononuclear NiII species in which both nitrogen atoms in the pendant diamine arm are protonated and, therefore, not coordinated to the NiII center. All these probes (1-4) display an instant response to the poison gas hydrogen cyanide (HCN) and cyanide salts present in both solid matrices and aqueous (100 % water) solution. Selective and rapid sensing of HCN gas and cyanide salts in solid/soil/water phases, without any interference, by the mechanosynthesized complexes 1-4 can be perceived easily by the naked eye under a hand-held UV lamp.