Synonyms for diars or Related words with diars
Examples of "diars"
is a bidentate ligand used in coordination chemistry. It was first described in 1939, but was popularized by R. S. Nyholm for its ability to stabilize metal complexes with unusual oxidation states and coordination numbers, e.g. TiCl(
). High coordination numbers arise because
is fairly compact and the As-M bonds are long, which relieves crowding at the metal center. In terms of stabilizing unusual oxidation states,
stabilizes Ni(III), as in [NiCl(
Of historical interest is the supposedly diamagnetic [Ni(
)](ClO), obtained by heating nickel perchlorate with
. Octahedral "d" complexes characteristically have triplet ground states, so the diamagnetism of this complex was puzzling. Later by X-ray crystallography, the complex was shown to be pentacoordinate with the formula [Ni(triars)(
)](ClO), where triars is the tridentate ligand [CHAs(CH]As(CH), arising from the elimination of trimethylarsine.
It is a colorless liquid. Oxygen converts
to the dioxide, CH(As(CH)O).
One of Nyholm’s early successes was the preparation of an octahedral complex of trivalent nickel [Ni(
)Cl]Cl, by aerial oxidation of the red salt of bivalent nickel [Ni(
)]Cl. He also described stable complexes of quadrivalent nickel such as the deep blue [Ni(
)Cl] [ClO], by nitric acid oxidation of the trivalent complex. This stabilisation of higher oxidation states became significant in the Nyholm-Rail reaction where the ditertiary arsine,
undergoes a condensation reaction to a tritertiary arsine, triars. Nyholm prepared examples of divalent octahedral complexes of the type M(
)X, where X is Cl, Br or I, and M is Cr, Mn, Fe, Co, Ni, Mo, Tc, Ru, Pd, W, Re, Os, and Pt.
is prepared by the reaction of "ortho"-dichlorobenzene and sodium dimethylarsenide:
) is the organoarsenic compound with the formula CH(As(CH)). The molecule consists of two dimethylarsino groups attached to adjacent carbon centers of a benzene ring. It is a chelating ligand in coordination chemistry. This colourless oil is commonly abbreviated "
Related, but non-chelating organoarsenic ligands include triphenylarsine and trimethylarsine. Work on
preceded the development of the chelating diphosphine ligands such as dppe, which are now prevalent in homogeneous catalysis.
Symmetrical organoarsenic(III) compounds, e.g. trimethylarsine and triphenylarsine, are commonly used as ligands in coordination chemistry. They behave like phosphine ligands, but are less basic. The diarsine CH(As(CH)), known as
, is a chelating ligand. Thorin is an indicator for several metals.
Many of these divalent complexes are sensitive to aerial oxidation. The chromium complex is oxidized by water. Indeed, previous attempts to prepare Cr(
)X had failed. The chromium compounds were eventually synthesized by his co-worker Anthony Nicholl Rail only a month before Nyholm’s death, using rigorous air-free techniques.
Nyholm's research in inorganic chemistry was primarily concerned with the preparation of transition metal compounds, particularly those involving organo-arsenic ligands. His interest in organoarsenic chemistry was fostered at the University of Sydney by George Joseph Burrows (1888–1950). Using the strong chelating ligand
, Nyholm demonstrated a range of oxidation states and coordination numbers for several of the transition metals. Nyholm noted that the term ‘unusual valence state’ had an ‘historical, but not chemical significance.’ ‘The definition of usual oxidation state refers to oxidation states that are stable in environments made up of those chemical species that were common in classical inorganic compounds, e.g. oxides, water and other simple oxygen donors, the halogens, excluding fluorine, and sulphur. Nowadays, however, such species constitute only a minority of the vast number of donor atoms and ligands that can be attached to metal.’
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