Lanthanide Contraction in Lanthanide Organic Frameworks: A Theoretical and Experimental Study.

Area of Science:

• Solid-state chemistry
• Inorganic chemistry
• Materials science

Background:

• Lanthanide contraction is a well-known phenomenon affecting atomic radii across the lanthanide series.
• Understanding lanthanide contraction is crucial for predicting and designing materials containing these elements.
• Lanthanide organic frameworks (LOFs) offer a versatile platform for studying fundamental lanthanide properties in the solid state.

Purpose of the Study:

• To investigate the lanthanide contraction phenomenon in three-dimensional lanthanide organic frameworks (LOFs).
• To analyze the impact of lanthanide contraction on Ln-O bond lengths and O-O distances within the coordination polyhedra.
• To evaluate the accuracy of semiempirical quantum mechanical models in reproducing lanthanide contraction in these structures.

Main Methods:

• Studied an isostructural series of 14 lanthanide organic frameworks (LOFs) with the formula [Ln2(C4H4O4)3(H2O)2]·H2O.
• Analyzed the sum of all Ln-O bond lengths (∑Ln-O) and the sum of all O-O distances (∑O-O) within coordination polyhedra.
• Employed different semiempirical quantum mechanical models, including Sparkle/PM3 and Sparkle/RM1, for calculations.

Main Results:

• The phenomenon of lanthanide contraction was clearly observed in the studied LOF series.
• Both ∑Ln-O and ∑O-O values exhibited a predictable trend that could be fit to a second-order polynomial.
• The semiempirical Sparkle/PM3 and Sparkle/RM1 models effectively reproduced the lanthanide contraction phenomenon.

Conclusions:

• Lanthanide contraction is demonstrably present in the solid-state structures of these lanthanide organic frameworks.
• The chosen semiempirical models provide reliable predictions for lanthanide contraction effects on bond lengths.
• This study validates the use of LOFs as model systems for investigating lanthanide chemistry and aids in the development of accurate computational methods.