For over two decades there have been intense efforts aimed at the development of alternatives to conventional magnets, particularly materials comprised in part or wholly of molecular components. Such alternatives offer the prospect of realizing magnets fabricated through controlled, low-temperature, solution-based chemistry, as opposed to high-temperature metallurgical routes, and also the possibility of tuning magnetic properties through synthesis. However, examples of magnetically ordered molecular materials at or near room temperature are extremely rare, and the properties of these materials are often capricious and difficult to reproduce. Here we present a versatile solution-based route to a new class of metal-organic materials exhibiting magnetic order well above room temperature. Reactions of the metal (M) precursor complex bis(1,5-cyclooctadiene)nickel with three different organics A-TCNE (tetracyanoethylene), TCNQ (7,7,8,8-tetracyanoquinodimethane) or DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone)--proceed via electron transfer from nickel to A and lead to materials containing Ni(II) ions and reduced forms of A in a 2:1 Ni:A ratio--that is, opposite to that of conventional (low Curie temperature) MA(2)-type magnets. These materials also contain oxygen-based species within their architectures. Magnetic characterization of the three compounds reveals spontaneous field-dependent magnetization and hysteresis at room temperature, with ordering temperatures well above ambient. The unusual stoichiometry and striking magnetic properties highlight these three compounds as members of a class of stable magnets that are at the interface between conventional inorganic magnets and genuine molecule-based magnets.
Ferrocene-containing polymers with one and two ferrocenes per repeat unit have been prepared via hydrosilylation polymerization of dialkynes and ferrocene-containing bis-enynes with 1,1′-bis(dimethylsilyl)ferrocene (1) using Karstedt's catalyst (platinum-divinyltetramethyldisiloxane) and Rh(PPh 3 ) 3 I. Addition of equivalent amounts of 1 and various dialkynes {RCtC-X-CtCR (R ) H, SiMe 3 , X ) C 6 H 4 (1,4-and 1,3-); R ) H, X ) SiMe 2 ; R ) Ph, X ) nothing)} gave polymers 2a-f with varying regiochemical distributions. All polymers were characterized using 1 H, 13 C, and 29 Si NMR spectroscopy, MALDI-TOF mass spectrometry, and elemental analyses. Novel ferrocene-containing bis-enynes (4a,b) were prepared by hydrosilylation addition of 1 to 2 equiv of 1,4-bis(trimethylsilyl)butadiyne and 1,4-bis-(trimethylsilylethynyl)benzene, respectively. Desilylation of 4a,b gave ferrocene-containing bis(enyne)s (5a,b) that were used as monomers for the synthesis of polymers with two ferrocenes per repeat unit (6a,b). The X-ray crystal structure of the bis(enyne) 4a has also been described, and the redox behavior of polymers 2a-e (Pt), 2a (Rh), and 2c (Rh) were studied using cyclic voltammetry. In all cases a single reversible redox wave was observed, attributed to the Fe(II)-Fe(III) redox couple of the ferrocene center.
A series of conjugated ferrocene-based organosilicon complexes with one, two, or three ferrocene units have been prepared via hydrosilylation of alkynes with ferrocenylsilanes using Karstedt's catalyst (platinum-divinyltetramethyldisiloxane) and Rh(PPh 3 ) 3 I. Reaction of 1,1′-bis(dimethylsilyl)ferrocene (1) with 2 equiv of RCtCRFc complexes (type 2), again with varying regiochemical distributions. The platinum-promoted hydrosilylations resulted in β-(E) and R-regioisomers, whereas the rhodium-catalyzed reactions gave primarily β-(Z) species with minor amounts of the β-(E) isomer. X-ray crystallographic studies of the predominant adducts obtained from 1 and Me 3 SiCtCPh as well as 2 and Me 3 Si-CtC-C 6 H 4 -CtC-SiMe 3 (1,4-) using Karstedt's catalyst are described. Cyclic voltammetry shows single redox waves for most systems indicative of no interaction between the Fe-Fe centers. One complex, Fc(Me) 2 Si(CdCH 2 )-Fc′-Si(CdCH 2 )(Me) 2 Fc, shows two reversible waves for the two different types of ferrocene center.
Double condensation of 2-acetylpyridine with 1,3-diaminobenzene-4,6-dicarboxaldehyde affords 2,7-bis(2-pyridyl)-1,8-diazaanthracene, which was subsequently oxidized to the corresponding quinone. Electrochemical studies indicate two reversible reduction processes corresponding to semiquinone and hydroquinonate formation. Electron-withdrawing pyridine groups and the nitrogen atoms make this somewhat more easily reduced than anthraquinone. This compound is redox-active and can be reduced to its radical anion, a potential spin-bearing ligand for the construction of [2 × 2] metallo-grid structures.Key words: quinone, grid, supramolecular, bistridentate, electrochemistry, metallosupramolecular chemistry.
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