Monodentate ligands coordination modes

NMR measurements also provide information on the coordination of the ligands in the uranyl polymers. Solid-state I c-NMR confirms the coordination modes of the carboxylate ligands to the uranyl ion that is, both monodentate and bidentate carboxylate coordination modes are evident. The uranyl dicarboxyl ate polymers which possess two moles of coordinated DMSO exhibit two carbon-13 carbonyl resonances, one at about 175 ppm downfield from tetramethylsilane (TMS) and one at about 185 ppm. The polymers which possess only one mole of coordinated DMSO exhibit only the carbonyl peak near 185 ppm. Based on other known coordination compounds, the 175 ppm peak can be assigned to monodentate carboxylate and the 185 ppm peak to bidentate carboxylate. Thus, 7-coordination predominates in the polymers with either one or two moles of solvent coordinated to the uranyl ion, which is consistent with the infrared results reported elsewhere (5). 

Pyrazolate as a ligand can exhibit various coordination modes, inter alia, monodentate, exo-bidentate, and endo-bidentate. Several review articles have been published in the field.556-559 The use of pyrazole in the modeling of biological systems was also reviewed.560,561 The most common application of pyrazole ligands is to use its exo-bidentate coordination mode linking two metal centers that may be identical or different (compare Section 6.3.4.12.6). Polypyrazolylborates and related ligands are covered in the subsequent section. 

With P-donors a variety of different structures are formed. Two complexes (359a,b) with a five-coordinate square pyramidal geometry and one S-donor in the apical position are reported.934,933 In a related complex (360) the nickel center reveals a distorted square planar geometry, because one xanthate ligand switched to a monodentate coordination mode. 6 By reaction of [NiL2] complexes with Ph2P(CH2)2P(Ph)(CH2)2PPh2, compound (362) is formed, which consists of a five-coordinate cation and a hexacoordinate anion. 7... 

Although, in principle, the chemistry here reported should be centered on the late transition metals, sometimes we will jump the frontier between late and middle or early transition metal since this line could be more or less diffuse and could change as a function of the history. At least seven different coordination modes have been identified (I-VII, Scheme 3) as the main bonding modes. In modes I and II the ylide behaves as neutral and monodentate, bonded exclusively through the Ca atom (kC mode) this is the case for simple ylides and carbodipho-sphoranes. Mode 111 covers the variants of a metallated ylide, that is, a situation in which the metal replaces a substituent of the ylide and transforms it into an anionic ligand. 

Carboxylates exhibit diverse coordination modes (Fig. 9) from monodentate, where the ligand is part of a chelate ring (Fig. 9, top left), through symmetrical or asymmetrical bidentate, to bridging via syn and/or anti linkages. 

Carboxylate anions are versatile ligands that are found in a variety of coordination modes including unidentate, chelate, and a number of bis(monodentate) bridging modes.1 Such versatility makes the chemistry of carboxylate complexes particularly interesting. It is now also apparent that the diverse catalytic activity shown by many metal carboxylates may be rationalized in terms of the chemistry of the carboxylato ligand.2 In general though, few rational syntheses of metal carboxylates are known.1 This... 

Whilst what has been termed the real scientific advancement in this area took place in 1967,5 complexes of alkali and alkaline earth metal cations (M"+) with simple monodentate ligands can be traced back, through the metal-ammonias , to Faraday.10 It was not until almost a century later, however, that precise determinations of the stoichiometries of the M"+—NH3 products were realized and the term coordination was introduced to describe the bonding mode of the ligand.11"13 The alkali metals themselves were first noted to dissolve in liquid ammonia in 186314 and since that time it has been found that the metals also dissolve in amines and ethers.15... 

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