Some 3dn (4 ≤ n ≤ 7) transition metal compounds exhibit a cooperative transition between a low-spin (LS) and a high-spin (HS) state. This transition is abrupt and occurs with a thermal hysteresis, which confers a memory effect on the system. The intersite interactions and thus the cooperativity are magnified in polymeric compounds such as [Fe(Rtrz)3]A2·nH2O in which the Fe2+ ions are triply bridged by 4-R-substituted-1,2,4-triazole molecules. Moreover, in these compounds, the spin transition is accompanied by a well-pronounced change of color between violet in the LS state and white in the HS state. The transition temperatures of these materials can be fine tuned, using an approach based on the concept of a molecular alloy. In particular, it is possible to design a compound for which room temperature falls in the middle of the thermal hysteresis loop. These materials have many potential applications, for example, as temperature sensors, as active elements of various types of displays, and in information storage and retrieval.

https://science.sciencemag.org/content/sci/279/5347/44.full.pdf

Spin-Transition Polymers: From Molecular Materials Toward Memory Devices

Triazoles and tetrazoles: Prime ligands to generate remarkable coordination materials

Mononuclear, oligonuclear and polynuclear metal coordination compounds with 1,2,4-triazole derivatives as ligands

Spin Transition Molecular Materials for displays and data recording

This article reviews the most relevant chemical and structural aspects that influence the spin-crossover phenomenon (SCO). Special attention is focussed on the recent development of SCO coordination polymers. The different approaches currently being explored in order to achieve multifunctionality in SCO materials are discussed.

Thermal, pressure and light switchable spin-crossover materials

High-spin α low-spin transition in [Fe(NCS)2(4,4′-bis-1,2,4-triazole)2](H2O). X-ray crystal structure and magnetic, mössbauer and EPR properties

A copper(II) dope as a detector for the high-spin .tautm. low-spin transition in the two-dimensional compound [trans-bis(thiocyanato)bis(4,4'-bi-1,2,4-triazole)iron] hydrate

Synthesis, spectroscopy and X-ray structure of hexakis(μ-3-methyl-4-ethyl-1,2,4-triazolo-N1,N2)tetraaquatricopper(II) hexakis(trifluoromethylsulfonate)

Spectroscopic and magnetic properties of a new class of two-dimensional bitriazole compounds: The X-ray structure of poly-bis(thiocyanato-N)-bis-μ-(4,4′-bis-1,2,4-triazole-N1,N1′)-cobalt(II) monohydrate

Spectroscopic and magnetic properties of transition metal(II) triflouromethanesulfonate compounds with bridging asymmetric 3,4-dialkyl substituted 1,2,4-triazole ligands

W. Vreugdenhil

Papers

High-spin α low-spin transition in [Fe(NCS)2(4,4′-bis-1,2,4-triazole)2](H2O). X-ray crystal structure and magnetic, mössbauer and EPR properties

A copper(II) dope as a detector for the high-spin .tautm. low-spin transition in the two-dimensional compound [trans-bis(thiocyanato)bis(4,4'-bi-1,2,4-triazole)iron] hydrate

Synthesis, spectroscopy and X-ray structure of hexakis(μ-3-methyl-4-ethyl-1,2,4-triazolo-N1,N2)tetraaquatricopper(II) hexakis(trifluoromethylsulfonate)

Spectroscopic and magnetic properties of a new class of two-dimensional bitriazole compounds: The X-ray structure of poly-bis(thiocyanato-N)-bis-μ-(4,4′-bis-1,2,4-triazole-N1,N1′)-cobalt(II) monohydrate

Spectroscopic and magnetic properties of transition metal(II) triflouromethanesulfonate compounds with bridging asymmetric 3,4-dialkyl substituted 1,2,4-triazole ligands