New concepts for molecular magnets

Abstract

Miller and Epstein (1994) define molecular magnets as magnetic materials which are prepared by the low-temperature methods of the preparative chemistry. This definition includes molecular crystals of neutral radicals, radical salts and charge transfer complexes as well as metal complexes and polymers with unpaired spins (Dormann 1995). The challenge of molecular magnets consists in tailoring magnetic properties by specific modifications of the molecular units. The combination of magnetism with mechanical or electrical properties of molecular compounds promise materials of high technical interest (Gatteschi 1994a, Mo È hwald 1996 and both the chemical synthesis of new molecular materials with magnetic properties as well as the physical investigation and explanation of these properties is important, in order to achieve any progress. This work deals with the physical characterization of the magnetic properties of molecular materials. It is organized as follows. In the first part molecular crystals of neutral radicals are studied. After briefly discussing the general magnetic properties of these materials and after an overview over the physical principles of exchange interaction between organic radicals I focus on the interplay between the crystallographic structure and the magnetic properties of various derivatives of the verdazyl and nitronyl nitroxide radicals. The magnetic properties of metal complexes are the subject of the second part. After an overview over the experimental and theoretical tools which are used for the investigation of the magnetic properties I shortly discuss the exchange coupling of transition metal ions and the magnetic properties of complexes of two and three metal ions. Special emphasis is given to spin cluster compounds. Spin cluster denote complexes of many magnetic ions. They are attractive as building blocks of molecular magnets as well as magnetic model compounds for the study of spin frustration, molecular super-paramagnetism and quasi one-dimensional magnets.

Electronic structure of the molecule-based magnet CuPM(NO3)2(H2Doll1, Wolter2, Klauß3 2007Phys. Rev. B4120View full textAdd to dashboardCite

“…Other interesting research directions are spin state transitions [6], or tuning of the magnetic coupling and the design of ferromagnets (see, e.g. [7,8]). This has led to an interdisciplinary effort in physics and chemistry, and by experimentalists and theoreticians.…”

Formazans in the synthesis of heterocycles. II. Synthesis of azines (Review)

“…This substituent, e.g., an alkyl group, is either present in the precursor or is introduced during the reaction. The accessibility of the initial formazans and the high stability of the verdazyl radicals have attracted and are still attracting the attention of chemists, biologists, and physicists [2][3][4][5][6][7][8][9][10][11][12][13][14][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. New verdazyls [15-17, 19, 33] and their complexes with metals [16, 21-25, 27, 28, 30] and with π-acceptors [26,29,31,32] are regularly being synthesized, new characteristics of known verdazyls are being studied, and new aspects of their application are being sought, as in the creation of linear and helical polymers, organic magnetic materials, semiconductors, luminophores, etc.…”

“…New verdazyls [15-17, 19, 33] and their complexes with metals [16, 21-25, 27, 28, 30] and with π-acceptors [26,29,31,32] are regularly being synthesized, new characteristics of known verdazyls are being studied, and new aspects of their application are being sought, as in the creation of linear and helical polymers, organic magnetic materials, semiconductors, luminophores, etc. [20,21,25,27,30]. The verdazyls 4 are reduced reversibly to leucoverdazyls 2 and are oxidized to verdazyl cations 5 and form complexes with benzene, benzoquinones, and other n-and π-acceptors [2-4, 7, 26, 29-33], making it possible to use them for the solution of many problems of organic chemistry, including the study of one-electron transfer processes.…”

Ultrafast primary processes of the stable neutral organic radical, 1,3,5-triphenylverdazyl, in liquid solution

“…Scheme 1), and we focused particularly on the dynamics in liquid solution. [19][20][21][22][23] 18 Owing to an extensive delocalization of the spin density across a 1,2,4,5tetrazine moiety, verdazyls are so stable that they can be isolated and stored for years safely just like closed-shell organic compounds.…”