Nitrate complexes lanthanide

Complexes of alcohols like methanol, ethanol, 2-propanol and n-butanol (116-122), and ethers like Diox (47,120,123-125) and THF (126-128) have been prepared. The bonding between these ligands and the metal ions is considered to be very weak. In recent years, complexes of the lanthanides with a few macrocyclic polyethers have been reported. Cassol et al. (129) have prepared the complexes of benzo-15-crown-5 and dibenzo-18-crown-6 with lanthanide nitrates and isothiocyanates. King and Heckley (130) have also reported the complexes of these ligands with lanthanide nitrates. The heavier lanthanide nitrate complexes of dibenzo-18-crown-6... 

Substitution at the 2-position of the pyridine ring in PyO introduces steric hindrance to coordination as is evident from the formation of Heptakis-2-MePyO complexes with lanthanide perchlorates (167) and pentakis-2-MePyO complexes with the corresponding bromides (168), iodides (162) and chlorides (169). The lanthanide nitrate complexes prepared by Ramakrishnan and Soundararajan (170) have the formula Ln(2-MePy0)3(N03)3 -xH20in which all the nitrate groups are bidentate. 

Interaction of the nitrate ion with lanthanide(III) in acetonitrile solution was studied by conductivity, vibrational spectroscopy and luminescence spectroscopy. Bidentate nitrate with approximate C2V local symmetry was detected. FT-IR spectral evidence for the formation of [La(N03)5]2, where La = Nd, Eu, Tb and Er with coordination number 9.9 has been obtained [128]. Two inequivalent nitrate ions bound to lanthanides were detected by vibrational spectroscopy. The inequivalent nature varied with different lanthanides. For example three equivalent nitrate groups for La and Yb, one nitrate different from the other two for Eu ion were detected. Vibrational spectral data point towards strong La-NC>3 interaction in acetonitrile [129]. Stability constants for lanthanide nitrate complexes are given in Table 4.10. 

TABLE 4.10 Stability constants of lanthanide-nitrate complexes in various solvents. ... 

Electronic spectral data (cm 1) and related bonding parameters of lanthanide nitrate complexes of MBAAP. Ref. [299]. 

In contrast to the alkali metals, the lanthanides do not form crown ether complexes readily in aqueous solution, due to the considerable hydration energy of the Ln + ion. These complexes are, however, readily synthesized by operating in non-aqueous solvents. Because many studies have been made with lanthanide nitrate complexes, coordination numbers are often high. Thus 12-coordination is found in La(N03)3(18-crown-6) (Eigure 4.4), 11 coordination in La(N03)3(15-crown-5), and 10 coordination is found in La(N03)3(12-crown-4). Other complexes isolated include Nd(18-crown-6)o.75(N03)3, which is in fact [ Nd(18-crown-6)(N03)2 +]3 psid(N03)6]. Other lanthanide salts complex with crown ethers small crowns like 12-crown-4 give 2 1 complexes with lanthanide perchlorates, though the 2 1 complexes are not obtained with lanthanide nitrates where the anion can... 

Choppin and Strazik (16) have shown that lanthanide nitrate complexes are outer-sphere in nature, meaning that there is a monolayer of water molecules separating the nitrate and lanthanide. This layer of water acts as a dielectric and reduces the strength of the ionic bond that forms the complex. For this reason it is assumed that the neutral species (M(N03)3) is present only at lanthanide nitrate concentrations approaching the solubility limit. Since all of the solutions studied in this work were below the solubility limit, the existence of the neutral species (M (N03) 3) is neglected. 

The chemistry of lanthanide nitrate complexes of terpy is complicated various formulae occur, dependiug not... 

A very detailed study has been made of lanthanide nitrate complexes of 4-amino-bis(2,6-(2-pyridyl))-l,3,5-triazine (abptz). Many of these compounds resemble corresponding terpy complexes and gradually a picture is being built up of how the structure and stoichiometry depend on factors such as the radius of the metal ion, composition of the reaction mixture, and the solvent employed. Complexes [La(abptz)(N03)3(H20)2] (11-coordinate), [Ln(abptz)-... 

Figure 98 Mesomorphism of a series of lanthanide nitrate complexes of ligand L H.

Changes in the composition of complexes formed can also occur as a result of the lanthanide contraction. For example, lanthanide nitrate complexes of (Me0)2P(0)CH2C(=CH2)P(0)(0Me)2 = L form two... 

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