Automated structure validation was introduced in chemical crystallography about 12 years ago as a tool to assist practitioners with the exponential growth in crystal structure analyses. Validation has since evolved into an easy-to-use checkCIF/PLATON web-based IUCr service. The result of a crystal structure determination has to be supplied as a CIF-formatted computer-readable file. The checking software tests the data in the CIF for completeness, quality and consistency. In addition, the reported structure is checked for incomplete analysis, errors in the analysis and relevant issues to be verified. A validation report is generated in the form of a list of ALERTS on the issues to be corrected, checked or commented on. Structure validation has largely eliminated obvious problems with structure reports published in IUCr journals, such as refinement in a space group of too low symmetry. This paper reports on the current status of structure validation and possible future extensions.

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Structure validation in chemical crystallography

The results of a single-crystal structure determination when in CIF format can now be validated routinely by automatic procedures. In this way, many errors in published papers can be avoided. The validation software generates a set of ALERTS detailing issues to be addressed by the experimenter, author, referee and publication journal. Validation was pioneered by the IUCr journal Acta Crystallographica Section C and is currently standard procedure for structures submitted for publication in all IUCr journals. The implementation of validation procedures by other journals is in progress. This paper describes the concepts of validation and the classes of checks that are carried out by the program PLATON as part of the IUCr checkCIF facility. PLATON validation can be run at any stage of the structure refinement, independent of the structure determination package used, and is recommended for use as a routine tool during or at least at the completion of every structure determination. Two examples are discussed where proper validation procedures could have avoided the publication of incorrect structures that had serious consequences for the chemistry involved.

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Single-crystal structure validation with the program PLATON

The literature has shown numerous contributions on the synthesis and physicochemical properties of persistent organic radicals but there are a lesser number of reports about their use as building blocks for obtaining molecular magnetic materials exhibiting an additional and useful physical property or function. These materials show promise for applications in spintronics as well as bistable memory devices and sensing materials. This critical review provides an up-to-date survey to this new generation of multifunctional magnetic materials. For this, a detailed revision of the most common families of persistent organic radicals—nitroxide, triphenylmethyl, verdazyl, phenalenyl, and dithiadiazolyl—so far reported will be presented, classified into three different sections: materials with magnetic, conducting and optical properties. An additional section reporting switchable materials based on these radicals is presented (257 references).

Playing with organic radicals as building blocks for functional molecular materials

Review of purely 4f and mixed-metal nd-4f single-molecule magnets containing only one lanthanide ion

The first family of rare-earth-based single chain magnets is presented. Compounds of general formula [M(hfac)3(NITPhOPh)], where M = Eu, Gd, Tb, Dy, Ho, Er, or Yb, and PhOPh is the nitronyl-nitroxide radical (2,4'-benzoxo-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), have been structurally characterized and found to be isostructural. The characterization of both static and dynamic magnetic properties of the whole family is reported. Dy, Tb, and Ho compounds display slow relaxation of the magnetization, and ac susceptibility shows a thermally activated regime with energy barriers of 69, 45, and 34 K for Dy, Tb, and Ho compounds, respectively, while only a frequency-dependent susceptibility is observed for Er below 2.0 K. In Gd and Yb derivatives, antiferromagnetic interactions dominate. The pre-exponential factors differ by about 4 orders of magnitude. Finite size effects, due to naturally occurring defects, affect the static and dynamic properties of the compounds differently.

A Family of Rare-Earth-Based Single Chain Magnets: Playing with Anisotropy

Numerous molecular compounds in which a paramagnetic Ln(III) ion is in interaction with a second spin carrier such as a transition metal ion or an organic radical have been described. However, except for the isotropic Gd(III) ion, very little is known concerning the nature (ferro- or antiferromagnetic) and mechanism of the interaction involving a Ln(III) ion. This study addresses the problem of the interaction between the Ln(III) ions displaying spin−orbit coupling and an organic radical. The magnetic properties of a series of isostructural compounds, {Ln(organic radical)2(NO3)3}, comprising a Ln(III) ion (Ln = Ce to Dy) surrounded by two N,O-chelating aminoxyl radicals (3-nitronyl nitroxide-4,5-dimethyltriazole) have been investigated. The experimental approach used to get insight into the {Ln-Radical} coupling occurring within these compounds is based on the knowledge of the intrinsic paramagnetic contribution of the metal ion. This contribution has been deduced from the corresponding {Ln(Nitrone)2(NO3)...

Systematic Investigation of the Nature of The Coupling between a Ln(III) Ion (Ln = Ce(III) to Dy(III)) and Its Aminoxyl Radical Ligands. Structural and Magnetic Characteristics of a Series of {Ln(organic radical)2} Compounds and the Related {Ln(Nitrone)2} Derivatives

Systematic Investigations of the Nature of the Coupling between a Ln(III) Ion (Ln = Ce(III) to Dy(III)) and Its Aminoxyl Radical Ligands. Structural and Magnetic Characteristics of a Series of {Ln(organic radical)2} Compounds and the Related {Ln(Nitrone)2} Derivatives [J. Am. Chem. Soc. 2000, 122, 3413−3421].

and Olivier Kahn

Papers

Systematic Investigation of the Nature of The Coupling between a Ln(III) Ion (Ln = Ce(III) to Dy(III)) and Its Aminoxyl Radical Ligands. Structural and Magnetic Characteristics of a Series of {Ln(organic radical)2} Compounds and the Related {Ln(Nitrone)2} Derivatives