Metal-Chelating N,N'-Bis(4-dimethylaminophenyl)acetamidinyl Radical: A New Chromophore for the Near-Infrared Region

A new non-innocent ligand redox system, N,N'-bis(4-dimethylaminophenyl) substituted acetamidinato/acetamidinyl, has been designed and described by example of structurally and spectroscopically characterized ruthenium complexes. The hitherto unreported ligand is responsible for rather intense and narrow absorptions in the near-infrared region of the one- and two-electron oxidized forms. The spectroscopic, computational, and first structural characterization of an amidinyl radical complex adds to the list of established N-based radical ligands.

Manifestations of noninnocent ligand behavior

The potential of redox-active ligands to behave "noninnocently" in transition-metal coordination compounds is reflected with respect to various aspects and situations. These include the question of establishing "correct" oxidation states, the identification and characterization of differently charged radical ligands, the listing of structural and other consequences of ligand redox reactions, and the distinction between barrierless delocalized "resonance" cases M(n)/L(n) ↔ M(n+1)L(n-1) versus separated valence tautomer equilibrium situations M(n)/L(n) ⇌ M(n+1)L(n-1). Further ambivalence arises for dinuclear systems with radical bridge M(n)(μ-L(•))M(n) versus mixed-valent alternatives M(n+1)(μ-L(-))M(n), for noninnocent ligand-bridged coordination compounds of higher nuclearity such as (μ(3)-L)M(3), (μ(4)-L)M(4), (μ-L)(4)M(4), or coordination polymers. Conversely, the presence of more than one noninnocently behaving ligand at a single transition-metal site in situations such as L(n)-M-L(n-1) or L(•)-M-L(•) may give rise to corresponding ligand-to-ligand interaction phenomena (charge transfer, electron hopping, and spin-spin coupling) and to redox-induced electron transfer with counterintuitive oxidation-state changes. The relationships of noninnocent ligand behavior with excited-state descriptions and perspectives regarding material properties and single-electron or multielectron reactivity are also illustrated briefly.

Unconventional mixed-valent complexes of ruthenium and osmium

Recent developments have helped to extend the repertoire of mixed-valent ruthenium and osmium complexes beyond conventional systems. This extension has been achieved by using sophisticated ligands and by creating more variegated coordination patterns. The strategies employed include the use of multidentate ligands (which give rise to multinuclear and chelate complexes) and the use several redox active components (non-innocent ligands and oxidation-state ambivalence). The results offer enhanced chemical insight into metal-ligand electron-transfer situations and suggest that mixed-valent materials may eventually be exploited in molecular electronics and molecular computing.

Construction of Copper(I) Coordination Polymers of 1,2,4,5-Tetracyanobenzene with Zigzag Sheet and Porous Frameworks

This paper describes two copper(I) supramolecules with the same anion and cation but quite different topologies and properties. The reaction of [Cu(CH(3)CN)(4)]PF(6) and 1,2,4,5-tetracyanobenzene (TCNB) leads to two novel polymeric coordination compounds, [Cu(2)(TCNB)(3)](PF(6))(2)(Me(2)CO)(4)( )()(1) and [Cu(2)(TCNB)(3)](PF(6))(2) (2), depending on the solvents used. The crystal structures have been determined by single-crystal X-ray diffraction. Crystal data are as follows. 1: C(21)H(15)N(6)O(2)CuPF(6), monoclinic, P2(1)/a, a = 11.553(4) Å, b = 16.135(7) Å, c = 15.046(3) Å, beta = 108.08(2) degrees, Z = 4. 2: C(15)H(3)N(6)CuPF(6), orthorhombic, Cmcm, a = 28.282(3) Å, b = 10.337(3) Å, c = 16.285(4) Å, Z = 16. In both polymers, copper(I) ions have similar pseudotetrahedral environments and the four coordination sites are fully occupied by the four bridging ligands, two &mgr;(2)-TCNB and two &mgr;(4)-TCNB groups. Polymer 1, obtained in acetone, revealed a two-dimensional zigzag sheet network between copper(I) ions, whereas 2, synthesized in methylethyl ketone, displayed a three-dimensional porous framework with different functional groups (or atom) in different cavities. The redox, magnetic, and conductive behaviors of both complexes are discussed. It is demonstrated that the two complexes give different physicochemical properties.