Controlling Ligand Coordination Spheres and Cluster Fusion in Superatoms

Single-ion magnetism in novel Btp-based cobalt complexes of different charge

The magnetic behavior of single-ion metal complexes may be influenced by the nature and composition of the secondary coordination sphere that can be composed of solvent molecules and counterions bound through non-covalent interactions. However, achieving precise control over the outer-coordination sphere of these magnetic complexes to demonstrate its influence on their magnetic properties presents a challenge. A strategy for varying the number of counterions, while simultaneously preserving the arrangement of the ligand atoms around the metal center without altering its oxidation state, is to adjust the overall formal charge of the complex. This adjustment could lead to changes in the magnetic properties of single-ion metal complexes. In this study, we present two novel ligands featuring the coordinating unit Btp (2,6-bis(1,2,3-triazol-4-yl)pyridine). These ligands are equipped with functional groups that can potentially undergo deprotonation. By carefully selecting the solvents used during the crystallization process of the complexes, we can tune at will the charge of the complexes, thus modifying the composition of the CoII complexes' outer-coordination sphere. We show that, by modifying these conditions, we can tailor the secondary coordination sphere of both charged (mono- and dicationic) and neutral anisotropic CoII metal complexes to show field-induced single-ion magnetism, influencing in turn the size of the barrier to reversal of the magnetization and their slow relaxation process.

Extending the Chevrel-type superatoms to the nitrogen family

Chevrel-type superatoms refer to the ligated transition metal chalcogenide clusters M6E8L6, where the octahedral M6 is face-capped with cubic chalcogen E8 (E = S/Se/Te). Most transition metals can form such superatoms and many organic and inorganic ligands can be substituted in solution reactions, which allows these atomic precision species to be easily functionalized and their properties to be tunable. No test was reported for substituting the chalcogens with pnicogens in this class of materials. In this article, we try to discover if such substitutions are possible. Combining different transition metals and ligands, theoretical computations show that [M6Q8(CN)6]2- (Q = P, As, Sb) for M = Co, Rh, Ir, and Ni, Pd, Pt have closed electronic shells and possess enhanced thermal and chemical stabilities. Analyses of the electronic structures indicate high similarity between the M-M and M-Q/M-S interactions in these species.

Tailoring the Superatomic Characteristics and Optical Behavior of Metal-Free Boron Clusters via Ligand Engineering

It is of great importance to understand how the number and type of ligands influence the properties of clusters through ligand engineering, as this knowledge is crucial for the rational design and optimization of functional materials. Herein, the geometrical structures, binding energies, and electronic properties of nonmetallic Bn (n = 20 and 40) clusters with CO, PEt3, F, NO2, and CN ligands are systematically explored based on density functional theory (DFT) calculations. Our findings demonstrate that the CO ligand acts as an electron donor when attached to these two boron clusters, in contrast to their role as electron acceptors in interactions with metal oxide and metal chalcogenide clusters. This emphasizes the necessity of considering the intrinsic properties of the host cluster when modifying with ligands. Moreover, it was observed that substituting PEt3 with F, NO2, or CN converted the B20 cluster from an electron acceptor to an electron donor, thereby demonstrating the versatility in tuning the redox characteristics of boron clusters by selecting appropriate ligands. Intriguingly, the attachment of the PEt3, F, NO2, and CN ligands to B20 can significantly modulate the electronic properties of B20 to realize the formation of metal-free superalkali (B20(PEt3)n, n = 3-5) and superhalogen (B20F, B20NO2, and B20CN) clusters. Furthermore, the structure, stability, and optical absorption of the charge transfer complex B20(PEt3)3+B20F were analyzed. This complex has been identified as an efficient material for harvesting visible light. Our findings provide insights into the effects of ligand variations on boron cluster functionalities, offering a new perspective for the design of advanced materials with tailored cluster properties through ligand engineering.

Pd8(PDip)6: Cubic, Unsaturated, Zerovalent

Atomically precise nanoclusters hold promise for supramolecular assembly and (opto)electronic- as well as magnetic materials. Herein, this work reports that treating palladium(0) precursors with a triphosphirane affords strongly colored Pd8(PDip)6 that is fully characterized by mass spectrometry, heteronuclear and Cross-Polarization Magic-Angle Spinning (CP-MAS) NMR-, infrared (IR), UV-vis, and X-ray photoelectron (XP) spectroscopies, single-crystal X-Ray diffraction (sc-XRD), mass spectrometry, and cyclovoltammetry (CV). This coordinatively unsaturated 104-electron Pd(0) cluster features a cubic Pd8-core, µ4-capping phosphinidene ligands, and is air-stable. Quantum chemical calculations provide insight to the cluster's electronic structure and suggest 5s/4d orbital mixing as well as minor Pd─P covalency. Trapping experiments reveal that cluster growth proceeds via insertion of Pd(0) into the triphosphirane. The unsaturated cluster senses ethylene and binds isocyanides, which triggers the rearrangement to a tetrahedral structure with a reduced frontier orbital energy gap. These experiments demonstrate facile cluster manipulation and highlight non-destructive cluster rearrangement as is required for supramolecular assembly.

Accessing Ta/Cu Architectures via Metal-Metal Salt Metatheses: Heterobimetallic C-H Bond Activation Affords μ-Hydrides

We employ a metal-metal salt metathesis strategy to access low-valent tantalum-copper heterometallic architectures (Ta-μ2 -H2 -Cu and Ta-μ3 -H2 -Cu3 ) that emulate structural elements proposed for surface alloyed nanomaterials. Whereas cluster assembly with carbonylmetalates is well precedented, the use of the corresponding polyarene transition metal anions is underexplored, despite recognition of these highly reactive fragments as storable sources of atomic Mn- . Our application of this strategy provides structurally unique early-late bimetallic species. These complexes incorporate bridging hydride ligands during their syntheses, the origin of which is elucidated via detailed isotopic labelling studies. Modification of ancillary ligand sterics and electronics alters the mechanism of bimetallic assembly; a trinuclear complex resulting from dinuclear C-H activation is demonstrated as an intermediate en route to formation of the bimetallic. Further validating the promise of this rational, bottom-up approach, a unique tetranuclear species was synthesized, featuring a Ta centre bearing three Ta-Cu interactions.

A general method for metallocluster site-differentiation

The deployment of metalloclusters in applications such as catalysis and materials synthesis requires robust methods for site-differentiation: the conversion of clusters with symmetric ligand spheres to those with unsymmetrical ligand spheres. However, imparting precise patterns of site-differentiation is challenging because, compared with mononuclear complexes, the ligands bound to clusters exert limited spatial and electronic influence on one another. Here, we report a method that employs sterically encumbering ligands to bind to only a subset of a cluster's coordination sites. Specifically, we show that homoleptic, phosphine-ligated Fe-S clusters undergo ligand substitution with N-heterocyclic carbenes (NHCs) to give heteroleptic clusters in which the resultant clusters' site-differentiation patterns are encoded by the steric profile of the incoming NHC. This method affords access to every site-differentiation pattern for cuboidal [Fe4S4] clusters and can be extended to other cluster types, particularly in the stereoselective synthesis of site-differentiated Chevrel-type [Fe6S8] clusters.

Octahedral Rhenium Cluster Complexes with 1,2-Bis(4-pyridyl)ethylene and 1,3-Bis(4-pyridyl)propane as Apical Ligands

A series of eight new octahedral rhenium cluster complexes with the general formula trans-[{Re₆Q₈}L₄X₂] (Q = S or Se; L = 1,2-Bis(4-pyridyl)ethylene (bpe) or 1,3-Bis(4-pyridyl)propane (bpp); X = Cl or Br) was synthesized and investigated. While bpe is a ligand with a conjugated aromatic system, bpp represents a molecule of opposite type and has independent aromatic systems of the two pyridine rings. It was shown that this difference in the electronic structure of the ligands has a fundamental effect on the electronic structure, electrochemical and luminescent properties of the corresponding cluster complexes. Specifically, the [{Re₆Q₈}(bpe)₄X₂] complexes in solutions show multiple quasi-reversible electrochemical transitions associated with reduction of the organic ligands. At the same time, the trans-[{Re₆Q₈}(bpp)₄X₂] complexes show multielectron quasi-irreversible reduction processes, which correlate with the mixed character of the lowest unoccupied molecular orbitals of these complexes. All the obtained new compounds exhibit red photoluminescence. The photophysical parameters (emission lifetimes and quantum yields) measured for the bpp complexes exceed those revealed for bpe complexes by more than an order of magnitude.

Gas-phase fragmentation of single heteroatom-incorporated Co5MS8(PEt3)6+ (M = Mn, Fe, Co, Ni) nanoclusters

Functionalization of metal-chalcogenide clusters by either replacing core atoms or by tuning the ligand is a powerful technique to tailor their properties. Central to this approach is understanding the competition between the strength of the metal-ligand and metal-metal interactions. Here, using collision-induced dissociation of atomically precise metal sulfide nanoclusters, Co5MS8L6+ (L = PEt3, M = Mn, Fe, Co, Ni) and Co5-xFexS8L6+ (x = 1-3), we study the effect of a heteroatom incorporation on the core-ligand interactions and relative stability towards fragmentation. Sequential ligand loss is the dominant dissociation pathway that competes with ligand sulfide (LS) loss. Because the ligands are attached to metal atoms, LS loss is an unusual dissociation pathway, indicating significant rearrangement of the core prior to fragmentation. Both experiments and theoretical calculations indicate the reduced stability of Co5MnS8L6+ and Co5FeS8L6+ towards the first ligand loss in comparison with their Co6S8L6+ and Co5NiS8L6+ counterparts and provide insights into the core-ligand interaction.