Magnets composed of molecular species or polymers and prepared by relatively low‐temperature organic synthetic methodologies are a focus of contemporary materials science research. The anticipated properties of such molecular‐species‐based magnetic materials, particularly in combination with other properties associated with molecules and polymers, may enable their use in future generations of electronic, magnetic, and/or photonic/photronic devices ranging from information storage and magnetic imaging to static and low‐frequency magnetic shielding. A tutorial of typical magnetic behavior of molecular materials is presented. The three distinct models (intramolecular spin coupling through orthogonal orbitals in the same spatial region within a molecule/ion, intermolecular spin coupling through pairwise “configuration interaction” between spin‐containing moieties, and dipole—dipole, through‐space interactions) which enable the design of new molecular‐based magnetic materials are discussed. To achieve the required spin couplings for bulk ferro‐ or ferrimagnetic behavior it is crucial to prepare materials with the necessary primary, secondary, and tertiary structures akin to proteins. Selected results from the worldwide effort aimed at preparing molecular‐based magnetic materials by these mechanisms are described. Some organometallic solids comprised of linear chains of alternating metallocenium donors (D) and cyanocarbon acceptors (A) that is, …︁D•+ A•− D•+ A•−…︁, exhibit cooperative magnetic phenomena. Bulk ferromagnetic behavior was first observed below the critical (Curie) temperature Tc of 4.8 K for [FeIII(C5Me5)2]•+ [TCNE]•− (Me = methyl; TCNE = tetracyanoethylene). Replacement of FeIII with MnIII leads to a ferromagnet with a Tc of 8.8 K in agreement with mean‐field models developed for this class of materials. Replacement with CrIII, however, leads to a ferromagnet with a Tc lowered to 3.65 K which is at variance with this model. Extension to the reaction of a vanadium(o) complex with TCNE leads to the isolation of a magnet with a Tc ≈ 400 K, which exceeds the thermal decomposition temperature of the material. This demonstrates that a magnetic material with a Tc substantially above room temperature is achievable in a molecule/organic/polymeric material. Finally, a new class of one‐dimensional ferrimagnetic materials based on metalloporphins is discussed.

The reaction of bis(benzene)vanadium with tetracyanoethylene, TCNE, affords an insoluble amorphous black solid that exhibits field-dependent magnetization and hysteresis at room temperature. The critical temperature could not be estimated as it exceeds 350 kelvin, the thermal decomposition temperature of the sample. The empirical composition of the reported material is V(TCNE)x.Y(CH(2)Cl(2)) with x approximately 2 and Y approximately 1/2. On the basis of the available magnetic and infrared data, threedimensional antiferromagnetic exchange of the donor and acceptor spins resulting in ferrimagnetic behavior appears to be the mode of magnetic coupling.

The conclusions reached by a diverse group of scientists who attended an intense 2-day workshop on hybrid organic-inorganic perovskites are presented, including their thoughts on the most burning fundamental and practical questions regarding this unique class of materials, and their suggestions on various approaches to resolve these issues.

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The development, characterization, and exploitation of novel materials based on the assembly of molecular components is an exceptionally active and rapidly expanding field. For this reason, the topic of molecule-based materials (MBMs) was chosen as the subject of a workshop sponsored by the Chemical Sciences Division of the United States Department of Energy. The purpose of the workshop was to review and discuss the diverse research trajectories in the field from a chemical perspective, and to focus on the critical elements that are likely to be essential for rapid progress. The MBMs discussed encompass a diverse set of compositions and structures, including clusters, supramolecular assemblies, and assemblies incorporating biomolecule-based components. A full range of potentially interesting materials properties, including electronic, magnetic, optical, structural, mechanical, and chemical characteristics were considered. Key themes of the workshop included synthesis of novel components, structural control, characterization of structure and properties, and the development of underlying principles and models. MBMs, defined as ªuseful substances prepared from molecules or molecular ions that maintain aspects of the parent molecular frameworkº are of special significance because of the capacity for diversity in composition, structure, and properties, both chemical and physical. Key attributes are the ability in MBMs to access the additional dimension of multiple length scales and available structural complexity via organic chemistry synthetic methodologies and the innovative assembly of such diverse components. The interaction among the assembled components can thus lead to unique behavior. A consequence of the complexity is the need for a multiplicity of both existing and new tools for materials synthesis, assembly, characterization, and theoretical analysis. For some technologically useful properties, e.g., ferro-or ferrimagnetism and superconductivity, the property is not a property of a molecule or ion; it is a cooperative solid-state (bulk) propertyÐa property of the entire solid. Hence, the desired properties are a consequence of the interactions between the molecules or ions, and understanding the solidstate structure as well as methods to predict, control, and modulate the structure are essential to understanding and manipulating such behaviors. As challenging as this is, molecules enable a substantially greater ability of control than atoms as building blocks for new materials and thus are well positioned to contribute significantly to new materials. The diversity of components and processes leads to the recognition of the critical role of cross-disciplinary research, including not only that between traditionally different areas within chemistry, but also between chemistry and biochemistry, physics, and a number of engineering disciplines. Enhancing communication and active collaboration between these groups was seen as a critical goal for the research area.

Magnets composed of molecular components that provide both electron spins and spin-coupling pathways can stabilize bulk magnetic ordering. This was first reported for the ionic, zero-dimensional (0-D) electron transfer salt [Fe(C(5)Me(5))(2)](+)[TCNE]˙(-) (TCNE = tetracyanoethylene), which orders as a ferromagnet at T(c) = 4.8 K. Later V[TCNE](x) (x ∼ 2) was characterized to order above room temperature at 400 K (127 °C). Subsequently, numerous examples of organic- and molecule-based magnets have been characterized. In this critical review, after a discussion of the important aspects of magnetism pertaining to molecule-based magnets, including the determination of the magnetic ordering temperature (T(c)) these magnetically ordered materials are reviewed from a perspective of the structural dimensionality (208 references).

Conference Reports: Joel Miller of Du Pont describes activities at a recent NATO Advanced Research workshop on molecular magnetic materials held in Italy, and Siegmar Roth of the Max Planck Institute for Solid State Research in Stuttgart reports on a conference on synthetic metals held in southern Germany.

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