A comparison of the structures of RE<sup>3+</sup> with proline

doi:10.1524/zkri.1997.212.8.601

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“…Hitherto, various lanthanide–amino acids coordination complexes have been structurally characterized including: Alanine [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ], proline [ 29 , 30 , 31 , 32 , 33 , 34 ], glycine [ 35 , 36 , 37 , 38 ], valine [ 37 , 39 , 40 ], and glutamic acid [ 41 , 42 , 43 ]; and, sparingly, isoleucine [ 44 , 45 ], leucine [ 46 ], phenylalanine [ 47 ], tyrosine [ 48 ], cysteine, aspartic acid [ 21 ], and histidine [ 49 ]. The amino acid ligands bridge the lanthanide ions forming dimeric, polymeric, or cluster species.…”

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confidence: 99%

Chiral Lanthanide Complexes with l- and d-Alanine: An X-ray and Vibrational Circular Dichroism Study

2020

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A whole series of [Ln(H2O)4(Ala)2]26+ dimeric cationic lanthanide complexes with both l- and d-alanine enantiomers was synthesized. The single-crystal X-ray diffraction at 100 and 292 K shows the formation of two types of dimers (I and II) in crystals. Between the dimer centers, the alanine molecules behave as bridging (μ2-O,O’-) and chelating bridging (μ2-O,O,O’-) ligands. The first type of bridge is present in dimers I, while both bridge forms can be observed in dimers II. The IR and vibrational circular dichroism (VCD) spectra of all l- and d-alanine complexes were registered in the 1750–1250 cm−1 range as KBr pellets. Despite all the studied complexes are exhibiting similar crystal structures, the spectra reveal correlations or trends with the Ln–O1 distances which exemplify the lanthanide contraction effect in the IR spectra. This is especially true for the positions and intensities of some IR bands. Unexpectedly, the ν(C=O) VCD bands are quite intense and their composed shapes reveal the inequivalence of the C=O vibrators in the unit cell which vary with the lanthanide. Unlike in the IR spectra, the ν(C=O) VCD band positions are only weakly correlated with the change of Ln and the VCD intensities at most show some trends. Nevertheless, this is the first observation of the lanthanide contraction effect in the VCD spectra. Generally, for the heavier lanthanides (Ln: Dy–Lu), the VCD band maxima are very close to each other and the mirror reflection of the band of two enantiomers is usually better than that of the lighter Lns. DFT calculations show that the higher the multiplicity the higher the stability of the system. Actually, the molecular geometry in crystals (at 100 K) is well predicted based on the highest-spin structures. Also, the simulated IR and VCD spectra strongly depend on the Ln electron configuration but the best overall agreement was reached for the Lu complex, which is the only system with a fully filled f-shell.

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confidence: 99%

Chiral Lanthanide Complexes with l- and d-Alanine: An X-ray and Vibrational Circular Dichroism Study

2020

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Compounds of Amino Acids and Neutral Salts

Fleck

Petrosyan

2014

Salts of Amino Acids

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In this chapter we present salts composed of amino acids combined with inorganic cations and anions. These salts generally contain amino acids in neutral, i.e., zwitterionic form, with the charges balanced by the cations and anions. However, some of the phases resented here contain cations, anions, and amino acids, but the amino acids are not in neutral form, as, e.g., glycinate À Cu, but for reasons of similarity, they are included in this chapter. The variation of salts (and thus the number of species) is even greater as for salts of amino acids and cations, as a multitude of combinations of amino acids, cations, and anions is possible. Additionally, different hydration states are often found, as well as different ratios of components. Thus, there are several instances of systems containing more than one phase (e.g., the system glycine-zinc-chloride-water). Despite the greater variation, many coordination patterns found in the salts described in the previous chapter recur in the salts reported here. Likewise, the connectivities of units are similar as those found in salts of amino acids and cations. Instances of materials with noteworthy physical properties are presented. Keywords Introducing RemarksAs stated before, this chapter deals with salts of amino acids and neutral, inorganic salts. In these species, the amino acid usually exists in zwitterionic form, but it is still coordinated to a cation. As other anions are present, the amino acids are not the only possible ligands. These anions can act as additional ligands (plus possible water molecules as well). Moreover, in some cases the inorganic anions are not part of the coordination spheres, but located in the interstices between units composed of cations and coordinating amino acids.M. Fleck and A.M. Petrosyan, Salts of Amino Acids: Crystallization, Structure and Properties,

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A comparison of the structures of RE³⁺ with proline

Abstract: The gadolinium complex with L-proline, [Gd

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Chiral Lanthanide Complexes with l- and d-Alanine: An X-ray and Vibrational Circular Dichroism Study

Chiral Lanthanide Complexes with l- and d-Alanine: An X-ray and Vibrational Circular Dichroism Study

Compounds of Amino Acids and Neutral Salts

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A comparison of the structures of RE3+ with proline

Abstract: The gadolinium complex with L-proline, [Gd

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Chiral Lanthanide Complexes with l- and d-Alanine: An X-ray and Vibrational Circular Dichroism Study

Chiral Lanthanide Complexes with l- and d-Alanine: An X-ray and Vibrational Circular Dichroism Study

Compounds of Amino Acids and Neutral Salts

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A comparison of the structures of RE³⁺ with proline