Coordination Complexes and Networks with Cyano-Substituted Azolates

Abstract

Cyanoazolates are derivatives of the azolates, in which all of the C-H hydrogen atoms are replaced by the C≡N groups. Their functionality is mainly dominated by the present cyano group(s), which are strongly electron withdrawing. In this way cyanoazolate molecules are electron deficient owing to the extensive negative charge delocalization across the anion’s structure and own higher number of coordination sites. Although cyanoazolates have been known for a long time, many structural investigations are still missing.<br /> Consequently, this work provides the first example of a systematic study on the cyanoazolate series [C_2nN₅]^– (n = 0, 2, 3, 4) with significant contribution of the crystal structures of 5-cyanotetrazolate, 4,5-dicyano-1,2,3-triazolate, 2,4,5-tricyanoimidazolate and tetracyanopyrrolide obtained as various organic salts used later as a starting materials. The research is completed by the preparation of new cyanoazolate-based coordination materials of first-row transition metal ions (Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺). The magnetic properties of diverse complexes and coordination polymers are analyzed using magnetic models based on the Heisenberg model principle in order to estimate the strength of magnetic exchange interactions in the magnetic systems. A variety of cooperative phenomena (ferro-, antiferro-, and ferrimagnetism) are detected at low temperatures, whereas mainly isolated ion behavior is observed at high temperatures.<br /> In the presence of water, the C≡N groups of cyanotetrazole and tetracyanopyrrole undergo hydrolytic transformation forming the C(O)NH₂ carboxamide yielding tetrazolate-5-carboxamide and 3,4,5-tricyanopyrrole-2-carboxamide trapped in copper(II) complexes.<br /> The project has been extended to a new class of 2D and 3D coordination polymers based on <i> N,N´,N´´</i>-tricyanoguanidinate dianion, which serves as triply connecting, trigonal building block with a rare alternating carbon-nitrogen connectivity. Also in this case the magnetic investigations are undertaken to check for a possible magnetic exchanges mediated through the large π-conjugated linkers.