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Co(CO) 3 (NO) is a stable 18-electron complex in part due to the bonding of the NO ligand in its linear form. The donation of the lone pair on the nitrogen makes this complex ML 4 X, containing 18 electrons. The traditional coordination number here would be 4, while the CBC more accurately describes the bonding with a LBN of 5.
At 100 °C, this number decreases to 3.24 due to the increased molecular motion and decreased density, while at 0 °C, the average number of hydrogen bonds increases to 3.69. [42] Another study found a much smaller number of hydrogen bonds: 2.357 at 25 °C. [43] Defining and counting the hydrogen bonds is not straightforward however.
Dihydrogen complexes are coordination complexes containing intact H 2 as a ligand. They are a subset of sigma complexes. [1] The prototypical complex is W(CO) 3 (PCy 3) 2 (H 2). This class of compounds represent intermediates in metal-catalyzed reactions involving hydrogen. Hundreds of dihydrogen complexes have been reported.
The number of times a polydentate ligand binds to a metal centre is symbolized by "κ n", where n indicates the number of sites by which a ligand attaches to a metal. EDTA 4− , when it is hexidentate, binds as a κ 6 -ligand, the amines and the carboxylate oxygen atoms are not contiguous.
However, these ligands also form dative covalent bonds like the L-type. [2] This type of ligand is not usually used because in certain situations it can be written in terms of L and X. For example, if a Z ligand is accompanied by an L type, it can be written as X 2. Examples of these ligands are Lewis acids, such as BR 3. [3]
Consequently M-H distances are often underestimated, especially in early studies. Often the presence of a hydride ligand was deduced by the absence of a ligand at an apparent coordination site. Classically, the structures of metal hydrides was addressed by neutron diffraction since hydrogen strongly scatters neutrons. [13]
In DNA-ligand binding studies, the ligand can be a small molecule, ion, [1] or protein [2] which binds to the DNA double helix. The relationship between ligand and binding partner is a function of charge, hydrophobicity, and molecular structure. Binding occurs by intermolecular forces, such as ionic bonds, hydrogen bonds and Van der Waals forces.
For example, calculations suggest that Fe 2 (CO) 9 lacks an iron–iron bond by virtue of a 3-center 2-electron bond involving one of three bridging CO ligands. [5] Representations of two kinds of μ-bridging ligand interactions, 3-center, 4-electron bond (left) and 3-center, 2-electron bonding. [5]