Isolation of Elusive Fluoflavine Radicals in Two Differing Oxidation States.

Facile access and switchability between multiple oxidation states are key properties of many catalytic applications and spintronic devices yet poorly understood due to inherent complications arising from isolating a redox system in multiple oxidation states without drastic structural changes. Here, we present the first isolable, free fluoflavine (flv) radical flv(1-•) as a bottleable potassium compound, [K(crypt-222)](flv•), 1, and a new series of organometallic rare earth complexes [(Cp*2Y)2(µ-flvz)]X, (where Cp* = pentamethylcyclopentadienyl, X = [Al(OC{CF3}3)4]- (z = -1), 2; X = 0 (z = -2), 3; [K(crypt-222)]+ (z = -3), 4) comprising the flv ligand in three different oxidation states, two of which are paramagnetic flv1-• and flv3-•. Excitingly, 1, 2, and 4 constitute the first isolable flv1-• and flv3-• radical complexes and, to date, the only isolated flv radicals of any oxidation state. All compounds are accessible in good crystalline yields and were unambiguously characterized via single-crystal X-ray diffraction analysis, cyclic voltammetry, IR-, UV-vis, and variable-temperature EPR spectroscopy. Remarkably, the EPR spectra for 1, 2, and 4 are distinct and a testament to stronger spin delocalization onto the metal centers as a function of higher charge on the flv radical. In-depth analysis of the electron- and spin density via density functional theory (DFT) calculations utilizing NLMO, QTAIM, and spin density topology analysis confirmed the fundamental interplay of metal coordination, ligand oxidation state, aromaticity, covalency, and spin density transfer, which may serve as blueprints for the development of future spintronic devices, single-molecule magnets, and quantum information science at large.

Guanidinate Yttrium Complexes Containing Bipyridyl and Bis(benzimidazolyl) Radicals.

Ancillary ligand scaffolds that sufficiently stabilize a metal ion to allow its coordination to an open-shell ligand are scarce, yet their development is essential for next-generation spin-based materials with topical applications in quantum information science. To this end, a synthetic challenge must be met: devising molecules that enable the binding of a redox-active ligand through facile displacement and clean removal of a weakly coordinating anion. Here, we probe the accessibility of unprecedented radical-containing rare-earth guanidinate complexes by combining our recently discovered yttrium tetraphenylborate complex [{(Me3Si)2NC(NiPr)2}2Y][(µ-η6-Ph)(BPh3)] with the redox-active ligands 2,2'-bipyridine (bpy) and 2,2'-bis(benzimidazole) (Bbim), respectively, under reductive conditions. Our endeavor resulted in the first evidence of guanidinate complexes that contain radicals, namely, a mononuclear bipyridyl radical complex, {(Me3Si)2NC(NiPr)2}2Y(bpy•) (1), and a dinuclear bis(benzimidazolyl) radical-bridged complex, [K(crypt-222)][{(Me3Si)2NC(NiPr)2}2Y]2(µ-Bbim•) (2'). The latter was achieved by an in situ reduction of [{(Me3Si)2NC(NiPr)2}2Y]2(µ-Bbim) (2), which was isolated from a salt metathesis reaction. 1 and 2 were characterized by X-ray crystallography and IR and UV-vis spectroscopy. Variable-temperature electron paramagnetic resonance spectroscopy was applied to gain insight into the distribution of unpaired spin density on 1 and 2'. Density functional theory calculations were conducted on 1 and 2' to elucidate further their electronic structures. The redox activity of 1 and 2' was also probed by electrochemical methods.

Linear, Electron-Rich Erbium Single-Molecule Magnet with Dibenzocyclooctatetraene Ligands.

Judicious design of ligand scaffolds to highly anisotropic lanthanide ions led to substantial advances in molecular spintronics and single-molecule magnetism. Erbium-based single-molecule magnets (SMMs) are rare, which is attributed to the prolate-shaped ErIII ion requiring an equatorial ligand field for enhancing its single-ion magnetic anisotropy. Here, we present an electron-rich mononuclear Er SMM, [K(crypt-222)][Er(dbCOT)2], 1 (where dbCOT = dibenzocyclooctatetraene), that was obtained from a salt metathesis reaction of ErCl3 and K2dbCOT. The dipotassium salt, K2dbCOT, was generated through a two-electron reduction of the bare dbCOT0 ligand employing potassium graphite and was crystallized from DME to give the new solvated complex, [K(DME)]2[dbCOT]n, 2. 1 was analyzed through crystallography, electrochemistry, spectroscopy, magnetometry, and CASSCF calculations. The structure of 1 consists of an anionic metallocene complex featuring a linear (180.0°) geometry with an ErIII ion sandwiched between dianionic dbCOT ligands and an outer-sphere K+ ion encapsulated in 2.2.2-cryptand. Two pronounced redox events at negative potentials allude to the formation of a trianionic erbocene complex, [Er(dbCOT)2]3-, on the electrochemical time scale. 1 shows slow magnetic relaxation with an effective spin-reversal barrier of Ueff = 114(2) cm-1, which is close in magnitude to the calculated energies of the first and second excited states of 96.9 and 109.13 cm-1, respectively. 1 exhibits waist-constricted hysteresis loops below 4 K and constitutes the first example of an erbocene-SMM bearing fused aromatic rings to the central COT ligand. Notably, 1 comprises the largest COT scaffold implemented in erbocene SMMs, yielding the most electron-rich homoleptic erbium metallocene SMM.

Taming Super-Reduced Bi23- Radicals with Rare Earth Cations.

Here, we report the synthesis of two new sets of dibismuth-bridged rare earth molecules. The first series contains a bridging diamagnetic Bi22- anion, (Cp*2RE)2(µ-η2:η2-Bi2), 1-RE (where Cp* = pentamethylcyclopentadienyl; RE = Gd (1-Gd), Tb (1-Tb), Dy (1-Dy), Y (1-Y)), while the second series comprises the first Bi23- radical-containing complexes for any d- or f-block metal ions, [K(crypt-222)][(Cp*2RE)2(µ-η2:η2-Bi2•)]·2THF (2-RE, RE = Gd (2-Gd), Tb (2-Tb), Dy (2-Dy), Y (2-Y); crypt-222 = 2.2.2-cryptand), which were obtained from one-electron reduction of 1-RE with KC8. The Bi23- radical-bridged terbium and dysprosium congeners, 2-Tb and 2-Dy, are single-molecule magnets with magnetic hysteresis. We investigate the nature of the unprecedented lanthanide-bismuth and bismuth-bismuth bonding and their roles in magnetic communication between paramagnetic metal centers, through single-crystal X-ray diffraction, ultraviolet-visible/near-infrared (UV-vis/NIR) spectroscopy, SQUID magnetometry, DFT and multiconfigurational ab initio calculations. We find a πz* ground SOMO for Bi23-, which has isotropic spin-spin exchange coupling with neighboring metal ions of ca. -20 cm-1; however, the exchange coupling is strongly augmented by orbitally dependent terms in the anisotropic cases of 2-Tb and 2-Dy. As the first examples of p-block radicals beneath the second row bridging any metal ions, these studies have important ramifications for single-molecule magnetism, main group element, rare earth metal, and coordination chemistry at large.

From an Isolable Bismolyl Anion to an Yttrium-Bismolyl Complex with µ-Bridging Bismuth(I) Centers and Polar Covalent Y-Bi Bonds.

The synthesis and first structural characterization of the [K(18-crown-6)] bismolyl Bitet (C4 Me4 Bi) contact ion pair (1) is presented. Notably, according to Natural Resonance Theory calculations, the Bitet anion of 1 features two types of leading mesomeric structures with localized anionic charge and two lone pairs of electrons at the BiI center, as well as delocalized anionic charge in the π-conjugated C4 Bi ring. The lone pairs at Bi enable a unique bridging coordination mode of the bismolyl ligand, as shown for the first rare earth metal bismolyl complex (Cptet 2 Y)2 (µ-η1 -Bitet )2 (2). The latter results from the salt metathesis reaction of KBitet with Cptet 2 Y(BPh4 ) (Cptet =C5 Me4 H). The Y-Bi bonding interaction in 2 of 16.6 % covalency at yttrium is remarkably large.

From an Isolable Bismolyl Anion to an Yttrium-Bismolyl Complex with µ-Bridging Bismuth(I) Centers and Polar Covalent Y-Bi Bonds.

Invited for the cover of this issue is the group of Selvan Demir at the Michigan State University. The cover art depicts the helicopter landing of the first crystallographically characterized bismolyl anion potassium salt in a desert oasis landscape with pyramids of elemental bismuth. Read the full text of the article at 10.1002/chem.202302687.

Linear, Electron-Rich, Homoleptic Rare Earth Metallocene and Its Redox Activity.

The first homoleptic sandwich complex of dibenzocyclooctatetraene (dbCOT), representing a large cyclooctatetraene (COT) ligand with two fused benzene moieties, for any metal was accessed through salt metathesis of YCl3 with K2dbCOT in the presence of 2.2.2-cryptand. Single-crystal X-ray diffraction analysis on red-brown [K(crypt-222)][Y(dbCOT)2], 1, revealed a remarkably linear anionic yttrocene complex featuring a centroid-yttrium-centroid angle of 180.0°. The anionic moiety adopts a pseudo D2d geometry, where the carbon atoms of the central COT ring exhibit a staggered geometry. In total, 36 π-electrons are stored on both dbCOT anions, rendering it the largest isolated sandwich complex containing only fused aromatic rings. The solution-state structure of 1 was probed through a series of techniques involving cyclic voltammetry, UV-vis, and 1D and 2D nuclear magnetic resonance (NMR) spectroscopy, including 89Y NMR. The density functional theory (DFT) and natural bond orbital (NBO) analysis uncovered an ionic bonding interaction between the (dbCOT)2- ligands and YIII ion. NICS calculations support the experimentally observed aromatic character of 1, despite the deviation from planarity found in the dbCOT moieties. The cyclic voltammograms allude to the accessibility of a radical oxidation state, dbCOT3-•, based on a quasi-reversible feature. Excitingly, the chemical one-electron reduction of 1 through exposure to potassium graphite yielded a paramagnetic molecule, which was detected by electron paramagnetic resonance (EPR) techniques. Notably, this EPR spectrum is the first one for any sandwich complex containing a COT radical. Remarkably, 1 is thermally stable, and its isolation may provide access to mono- and multinuclear complexes comprising heavier metals with applications in small-molecule activation, single-molecule magnetism, and molecular nanowires.

Pyrrolyl-Bridged Metallocene Complexes: From Synthesis, Electronic Structure, to Single-Molecule Magnetism.

The π- and σ-basicity of the pyrrolyl ligand affords several coordination modes. A sterically encumbering coordination sphere around metal centers may foster new coordination modes for the pyrrolyl ligand. Here, we present three dinuclear rare earth complexes [Cp*2RE(µ-pyr)]2, [RE = Y (1), La (2), Dy (3); Cp* = pentamethylcyclopentadienyl, pyr = pyrrolyl], which were synthesized through a protonolysis reaction between allyl complexes and H-pyrrole. Each metal is ligated by two Cp* ligands and the N atom of the pyrrolyl ring while interacting with the π-system of the other pyrrolyl ligand, yielding an unprecedented coordination mode for pyrrolyl best described as [((η5-Cp*)2RE)2(µ-1η2-pyr-2κN)(µ-2η2-pyr-1κN)]. The steric congestion implemented by the Cp* ligands forces this asymmetric coordination of the pyrrolyl ligand. 1-3 were characterized by crystallography, electrochemistry, and spectroscopy. Density functional theory calculations on 1 uncovered the bonding situation between the pyrrolyl ligand and the yttrium(III) ion. Excitingly, 3 displays slow magnetic relaxation under zero dc field with Ueff = 98.9(7) cm-1 and τo = 6.7(1) × 10-8 s, placing it among coveted dinuclear metallocene single-molecule magnets. CASSCF calculations provided the energy of the crystal field states of DyIII and confirmed the barrier height.

Heteroleptic Rare-Earth Tris(metallocenes) Containing a Dibenzocyclooctatetraene Dianion.

Isolable heteroleptic tris(metallocenes) containing five-membered and larger rings remain extremely scarce. The utilization of tripositive rare-earth-metal ions with ionic radii >1 Šallowed access to unprecedented and sterically congested dibenzocyclooctatetraenyl (dbCOT) metallocenes, [K(crypt-222)][Cptet2RE(η2-dbCOT)] (RE = Y (1), Dy (2); Cptet = tetramethylcyclopentadienyl), through a salt metathesis reaction involving Cptet2RE(BPh4) and the potassium salt of the dbCOT dianion. The solid-state structures were investigated by single-crystal X-ray diffraction, magnetometry, and IR spectroscopy and provided evidence for the first crystallographically characterized (dbCOT)2- anion in a complex containing d- or f-block metals. Remarkably, the (Cptet)- ligands force a distortion from planarity within the (dbCOT)2- moiety, engendering a rare η2-bonding motif, as opposed to the classical η8 conformation observed in complexes bearing a (COT)2- ion. The η2 coordination mode was proven crystallographically between 100 and 298 K and computationally (DFT and NBO). Furthermore, nucleus independent chemical shift (NICS) calculations uncovered significant ring current within the dbCOT ligand. The solution-state properties of 1 and 2 were analyzed via cyclic voltammetry, NMR, and UV-vis spectroscopy. Cyclic voltammograms of 1 and 2 exhibit a quasi-reversible feature indicating the accessibility of complexes with dbCOT in two oxidation states (dbCOT2-/3-•). Importantly, the dysprosium congener, 2, is a zero-field single-molecule magnet (SMM).

Slow Magnetic Relaxation in Mono- and Bimetallic Lanthanide Tetraimido-Sulfate S(NtBu)4 2- Complexes.

Lanthanide ions are particularly well-suited for the design of single-molecule magnets owing to their large unquenched orbital angular momentum and strong spin-orbit coupling that gives rise to high magnetic anisotropy. Such nanoscopic bar magnets can potentially revolutionize high-density information storage and processing technologies, if blocking temperatures can be increased substantially. Exploring non-classical ligand scaffolds with the aim to boost the barriers to spin-relaxation are prerequisite. Here, the synthesis, crystallographic and magnetic characterization of a series of each isomorphous mono- and dinuclear lanthanide (Ln=Gd, Tb, Dy, Ho, Er) complexes comprising tetraimido sulfate ligands are presented. The dinuclear Dy complex [{(thf)2 Li(NtBu)2 S(tBuN)2 DyCl2 }2 ⋅ ClLi(thf)2 ] (1c) shows true signatures of single-molecule magnet behavior in the absence of a dc field. In addition, the mononuclear Dy and Tb complexes [{(thf)2 Li(NtBu)2 S(tBuN)2 LnCl2 (thf)2 ] (2b,c) show slow magnetic relaxation under applied dc fields.

Slow Magnetic Relaxation in Mono- and Bimetallic Lanthanide Tetraimido Sulfate S(NtBu)4 2- Complexes.

Invited for the cover of this issue are Selvan Demir and co-worker from the Michigan State University at East Lansing, and Dietmar Stalke and co-workers from the Georg-August Universität at Göttingen. The image illustrates the first coordination of a tetraimido sulfate ligand via two of its nitrogen donors to a lanthanide ion producing mono- and bimetallic lanthanide complexes where specifically the dysprosium congeners, benefitting from the intrinsic oblate-shaped electron density, feature single-molecular magnet behavior as indicated by the observed slow magnetic relaxation. Read the full text of the article at 10.1002/chem.202101076.

Substituent Effects on Exchange Coupling and Magnetic Relaxation in 2,2'-Bipyrimidine Radical-Bridged Dilanthanide Complexes.

Systematic analysis of related compounds is crucial to the design of single-molecule magnets with improved properties, yet such studies on multinuclear lanthanide complexes with strong magnetic coupling remain rare. Herein, we present the synthesis and magnetic characterization of the series of radical-bridged dilanthanide complex salts [(Cp*2Ln)2(µ-5,5'-R2bpym)](BPh4) (Ln = Gd, Dy; R = NMe2 (1), OEt (2), Me (3), F (4); bpym = 2,2'-bipyrimidine). Modification of the substituent on the bridging 5,5'-R2bpym radical anion allows the magnetic exchange coupling constant, JGd-rad, for the gadolinium compounds in this series to be tuned over a range from -2.7 cm-1 (1) to -11.1 cm-1 (4), with electron-withdrawing or -donating substituents increasing or decreasing the strength of exchange coupling, respectively. Modulation of the exchange coupling interaction has a significant impact on the magnetic relaxation dynamics of the single-molecule magnets 1-Dy through 4-Dy, where stronger JGd-rad for the corresponding Gd3+ compounds is associated with larger thermal barriers to magnetic relaxation (Ueff), open magnetic hysteresis at higher temperatures, and slower magnetic relaxation rates for through-barrier processes. Further, we derive an empirical linear correlation between the experimental Ueff values for 1-Dy through 4-Dy and the magnitude of JGd-rad for the corresponding gadolinium derivatives that provides insight into the electronic structure of these complexes. This simple model applies to other organic radical-bridged dysprosium complexes in the literature, and it establishes clear design criteria for increasing magnetic operating temperatures in radical-bridged molecules.

Slow Magnetic Relaxation in a Dysprosium Ammonia Metallocene Complex.

We report the serendipitous discovery and magnetic characterization of a dysprosium bis(ammonia) metallocene complex, [(C5Me5)2Dy(NH3)2](BPh4) (1), isolated in the course of performing a well-established synthesis of the unsolvated cationic complex [(C5Me5)2Dy][(µ-Ph)2BPh2]. While side reactivity studies suggest that this bis(ammonia) species owes its initial incidence to impurities in the DyCl3(H2O)x starting material, we were able to independently prepare 1 and its tetrahydrofuran (THF) derivative, [(C5Me5)2Dy(NH3)(THF)](BPh4) (2), from the reaction of [(C5Me5)2Dy][(µ-Ph)2BPh2] with ammonia in THF. The low-symmetry complex 1 exhibits slow magnetic relaxation under zero applied direct-current (dc) field to temperatures as high as 46 K and notably exhibits an effective barrier to magnetic relaxation that is more than 150% greater than that previously reported for the [(C5Me5)2Ln][(µ-Ph)2BPh2] precursor. On the basis of fitting of the temperature-dependent relaxation data, magnetic relaxation is found to occur via Orbach, Raman, and quantum-tunneling relaxation processes, and the latter process can be suppressed by the application of a 1400 Oe dc field. Field-cooled and zero-field-cooled dc magnetic susceptibility measurements reveal a divergence at 4 K indicative of magnetic blocking, and magnetic hysteresis was observed up to 5.2 K. These results illustrate the surprises and advantages that the lanthanides continue to offer for synthetic chemists and magnetochemists alike.

A Trinuclear Radical-Bridged Lanthanide Single-Molecule Magnet.

Assembly of the triangular, organic radical-bridged complexes Cp*6 Ln3 (µ3 -HAN) (Cp*=pentamethylcyclopentadienyl; Ln=Gd, Tb, Dy; HAN=hexaazatrinaphthylene) proceeds through the reaction of Cp*2 Ln(BPh4 ) with HAN under strongly reducing conditions. Significantly, magnetic susceptibility measurements of these complexes support effective magnetic coupling of all three LnIII centers through the HAN3-. radical ligand. Thorough investigation of the DyIII congener through both ac susceptibility and dc magnetic relaxation measurements reveals slow relaxation of the magnetization, with an effective thermal relaxation barrier of Ueff =51 cm-1 . Magnetic coupling in the DyIII complex enables a large remnant magnetization at temperatures up to 3.0 K in the magnetic hysteresis measurements and hysteresis loops that are open at zero-field up to 3.5 K.

Large spin-relaxation barriers for the low-symmetry organolanthanide complexes [Cp*2 Ln(BPh4 )] (Cp*=pentamethylcyclopentadienyl; Ln=Tb, Dy).

Single-molecule magnets comprising one spin center represent a fundamental size limit for spin-based information storage. Such an application hinges upon the realization of molecules possessing substantial barriers to spin inversion. Axially symmetric complexes of lanthanides hold the most promise for this due to their inherently high magnetic anisotropies and low tunneling probabilities. Herein, we demonstrate that strikingly large spin reversal barriers of 216 and 331 cm(-1) can also be realized in low-symmetry lanthanide tetraphenylborate complexes of the type [Cp*2 Ln(BPh4 )] (Cp*=pentamethylcyclopentadienyl; Ln=Tb (1) and Dy (2)). The dysprosium congener showed hysteretic magnetization data up to 5.3 K. Further studies of the magnetic relaxation processes of 1 and 2 under applied dc fields and upon dilution within a matrix of [Cp*2 Y(BPh4 )] revealed considerable suppression of the tunneling pathway, emphasizing the strong influence of dipolar interactions on the low-temperature magnetization dynamics in these systems.

Implementation of 2,2'-azobispyridine radical mono- and dianions in dinuclear rare earth metal complexes.

The seminal isolation of a dinuclear rare earth metal complex comprising a bridging 2,2'-azobispyridyl radical anion, [(Cptet2Y)2(µ-abpy˙)](BPh4), is presented, which was obtained from a one-electron chemical oxidation of [(Cptet2Y)2(µ-abpy)]. The unprecedented compounds were characterized by crystallography, spectroscopy and DFT computations. The radical character was proven by EPR spectroscopy.

Introducing the Bis(mesitoyl)phosphide Ligand into Dinuclear Trivalent Rare Earth Metal Coordination Chemistry.

Anionic ancillary ligands play a critical role in the construction of rare earth (RE) metal complexes due to the large influence on the stability of the molecule and engendering emergent electronic properties that are of interest in a plethora of applications. Supporting ligands comprising oxygen donor atoms are highly pursued in RE chemistry owing to the high oxophilicity innate to these ions. The scarcely employed bis(acyl)phosphide (BAP) ligands feature oxygen coordination sites and contain a phosphide backbone rendering it attractive for RE-coordination chemistry. Here, we integrate bis(mesitoyl)phosphide (mesBAP) as an ancillary ligand into REIII chemistry to generate the first dinuclear trivalent RE complexes containing BAP ligands; [{mesBAP}2RE(THF)(µ-Cl)]2 (RE=Y, (1), Gd (2), and Dy (3); THF=tetrahydrofuran). Each RE center is ligated to two monoanionic mesBAP ligands, one THF molecule and one chloride ion. All three molecules were characterized through single-crystal X-ray diffraction, 31P NMR, IR and UV-Vis spectroscopy. 31P, 1H and 13C NMR on the diamagnetic yttrium congener 1 confirm asymmetric ligand coordination. DFT calculations conducted on 2 provided insight into the electronic structure. The magnetic properties of 2 and 3 were investigated via SQUID magnetometry. The GdIII ions exhibit weak antiferromagnetic coupling, corroborated by DFT results.

Construction of intermolecular σ-hole interactions in rare earth metallocene complexes using a 2,3,4,5-tetraiodopyrrolyl anion.

The generation of noncovalent intermolecular interactions represents a powerful method to control molecular vibrations and rotations. Combining these with the axial ligand field enforced by the metallocene ligand scaffold provides a dual-pronged approach in controlling the magnetic-relaxation pathways for dysprosium-based single-molecule magnets (SMMs). Here, we present the first implementation of 2,3,4,5-tetraiodopyrrole (TIPH) in its anionic form [TIP]- as a ligand in three isostructural rare-earth metal complexes Cp*2RE(TIP) (1-RE, RE = Y, Gd, and Dy; Cp* = pentamethylcylopentadienyl), where the TIP ligand binds through the nitrogen and one iodine atom κ2(N,I) to the metal centre. The shallow potential energy surface of the intermolecular σ-hole interaction yields distortions of the interatomic distances at elevated temperatures which were investigated by variable-temperature SCXRD. 1-RE constitute the first crystallographically characterized molecules containing TIP as a ligand for any metal ion, and 1-Dy is the first SMM that employs the TIP ligand. The structural dependence on temperature allowed the mechanism of magnetic relaxation to be explored through ab initio calculations at different temperatures. The electronic influence of the coordinated iodine substituent was probed via magnetometry and cw-EPR spectroscopy on 1-Gd. To further scrutinize the impact of the iodine substituents on the physical properties, a second set of new complexes Cp*2RE(DMP) (2-RE, RE = Y, and Dy) where DMP = 2,5-dimethylpyrrolyl were synthesized. Here, the DMP ligand binds similarly to the TIP ligand and represents an all-hydrocarbon analogue to 1-RE. 2-Dy constitutes the first SMM bearing a DMP ligand.

Modulation of Fe-Fe distance and spin in diiron complexes using tetradentate ligands with different flanking donors.

Here we report the synthesis and characterization of diiron complexes containing triaryl N4 and N2S2 ligands derived from o-phenylenediamine. The complexes display significant differences in Fe-Fe distances and magnetic properties that depend on the identity of the flanking NMe2 and SMe donor groups.

Isolation of an organometallic yttrium bismuth cluster and elucidation of its electronic structure.

A rare organometallic yttrium bismuth cluster complex with a heterometallocubane structure at the core was isolated and characterised by single-crystal X-ray diffraction analysis and UV-Vis spectroscopy. The anionic Bi66- core is best described as a Zintl ion. Computational exploration of its electronic structure reveals polarised Y-Bi bonds alongside delocalisation of the Bi-Bi bonds.