Rigid Ligand Research Articles

Controlling Excited-State Dynamics and Chemical Reactivities of Platinum Acetylide Complexes via Self-Threading Ligands with Permethylated α-Cyclodextrin

Abstract Exterting control over the excited-state dynamics and chemical reactivities of transition metal complexes allows an enhancement in their physical properties and the development of their applications to novel materials. Hence, in this study, transition metal complexes were incorporated into a protective environment using permethylated α-cyclodextrin (PM α-CD)-based macrocycles. As a novel design concept for protective ligands in transition metal complexes, the macrocyclic PM α-CDs were efficiently introduced and fixed close to the metal centers via covalent bonding with the self-threading structures of rigid π-conjugated ligands. The protection of the transition metal complexes prevented undesired conformational changes and chemical reactions, thereby enhancing their functional properties and revealing the potential reactivities of the transition metals. In this account, the unique chemical reactivities and optical properties of transition metal complexes protected with PM α-CDs are summarized, with a focus on the distinctive features of platinum acetylide complexes and their applications to polymer materials.

Elucidating the role of synthesis conditions on Zr-MOF properties and yield

Metal-organic frameworks (MOFs) are a new type of ultra-high surface area porous materials with applications in catalysis, energy storage, and gas adsorption. Compared to other MOFs, Zirconium-based MOFs (Zr-MOFs) demonstrate improved stability due to strong bonds between tetravalent zirconium and carboxylate ligands, making them applicable in real world conditions. This study aims to investigate optimal synthesis conditions for the solvothermal fabrication of Zr-MOFs by looking at two promising tetratopic ligand-based MOFs, Zr-TCPP and Zr-TPTC. By systematically investigating the impact of synthesis parameters on yield, crystallinity, and morphological characteristics, both general and specific trends were determined. The present work demonstrated that the ideal reactant ratio was twice the actual Zr:ligand ratio in the final structure. Stronger acid modulators were found to produce more crystalline samples for MOFs with flexible ligands (Zr-TPTC), where formic acid use resulted in more crystalline samples compared to acetic acid; however, this lowered the yield. The effect of temperature on yield was non-linearly dependent on the reactant ratio used for synthesising flexible Zr-TPTC. For MOFs with rigid ligands (Zr-TCPP), increasing synthesis temperature did not affect yield but decreased crystallite size and improved phase selectivity. Stability tests in water and acid were performed on both MOFs to assess the effect on crystallinity and morphology and the results showed expected trends for Zr-MOFs. The optimized synthesis parameters for Zr-TCPP resulted in a superior method of producing PCN-222 with higher yield and crystallinity. On the other hand, a new Zr-TPTC MOF with high yield and crystallinity was synthesised using the optimized parameters. This study thus elucidates the role of synthesis parameters on Zr-MOF properties and yield and furthers the understanding of MOF synthesis mechanisms, expanding the potential for their applicability in industry.

Influence of metal on coordination geometry and solution dynamics in complexes of cis-ethylenebis(diphenylphosphine oxide) and Ln(OTf)3 (Ln = La, Sm, Lu) X-ray crystal structures and NMR titration studies

This paper describes the synthesis and characterization of complexes containing the relatively rigid bisphosphine oxide ligand cis-ethylenebis(diphenylphosphine oxide) with three lanthanide (Ln) triflate salts (Ln = La3+, Sm3+, Lu3+). The complexes were characterized in the solid state by IR and X-Ray crystallography and show bidentate binding of the ligand to each metal center. The complexes were also studied at various Ln-ligand stoichiometries in solutions of CDCl3 using 1H and 31P NMR. These studies revealed that for the complexes where Ln = La3+ and Sm3+ ligand exchange is fast on the 1H and 31P NMR time scales when there are less than four equivalents of ligand in solution but slows when more than four equivalents are present. For the solution studies of complexes with Lu3+, ligand exchange is fast on the 1H NMR but slow on the 31P NMR time scale for all Lu-ligand stoichiometries.

A Cationic Metal Glue Strategy for Expanding Paramagnetic Hetero-Multinuclear Metal-Oxo Clusters within Polyoxometalate Ligands.

Precise structural design of large hetero-multinuclear metal-oxo clusters is crucial for controlling their large spin ground states and multielectron redox properties for application as a single-molecule magnet (SMM), molecular magnetic refrigeration, and efficient redox catalyst. However, it is difficult to synthesize large hetero-multinuclear metal oxo clusters as designed because the final structures are unpredictable when employing conventional one-step condensation reaction of metal cations and ligands. Herein, we report a "cationic metal glue strategy" for increasing the size and nuclearity of hetero-multinuclear metal-oxo clusters by using lacunary-type anionic molecular metal oxides (polyoxometalates, POMs) as rigid multidentate ligands. The employed method enabled the synthesis of {(FeMn4 )Mn2 Ln2 (FeMn4 )} oxo clusters (Ln=Gd, Tb, Dy, and Lu), which are the largest among previously reported paramagnetic hetero-multinuclear metal-oxo clusters in POMs and showed unique SMM properties. These clusters were synthesized by conjugating {FeMn4 } oxo clusters with Mn and Ln cations as glues in a predictable way, indicating that the "cationic metal glue strategy" would be a powerful tool to construct desired large hetero-multinuclear metal clusters precisely and effectively.

A Cationic Metal Glue Strategy for Expanding Paramagnetic Hetero‐Multinuclear Metal‐Oxo Clusters within Polyoxometalate Ligands

AbstractPrecise structural design of large hetero‐multinuclear metal‐oxo clusters is crucial for controlling their large spin ground states and multielectron redox properties for application as a single‐molecule magnet (SMM), molecular magnetic refrigeration, and efficient redox catalyst. However, it is difficult to synthesize large hetero‐multinuclear metal oxo clusters as designed because the final structures are unpredictable when employing conventional one‐step condensation reaction of metal cations and ligands. Herein, we report a “cationic metal glue strategy” for increasing the size and nuclearity of hetero‐multinuclear metal‐oxo clusters by using lacunary‐type anionic molecular metal oxides (polyoxometalates, POMs) as rigid multidentate ligands. The employed method enabled the synthesis of {(FeMn4)Mn2Ln2(FeMn4)} oxo clusters (Ln=Gd, Tb, Dy, and Lu), which are the largest among previously reported paramagnetic hetero‐multinuclear metal‐oxo clusters in POMs and showed unique SMM properties. These clusters were synthesized by conjugating {FeMn4} oxo clusters with Mn and Ln cations as glues in a predictable way, indicating that the “cationic metal glue strategy” would be a powerful tool to construct desired large hetero‐multinuclear metal clusters precisely and effectively.

Auxiliary linkers-induced assembly of two 2D Co(II)-based coordination polymers with different interpenetrating fashion: Structure and magnetism

The coordination possibilities of rigid aromatic tetracarboxylate ligand with transition metal have been explored. Two new CoII-based coordination polymers with the not fully deprotonated ligand 5,5′-(ethene-1,2-diyl)diisophthalic acid) (H4L) were synthesized and characterized, incorporating different auxiliary ligands, [Co(H2L)(4,4′-bipy)0.5(H2O)]n(1) and {[Co(H2L) (dib)]·2H2O}n(2) (4,4′-bipy = 4,4′-bipyridine, and dib = 1,4-bis(1H-imidazol-1-yl)benzene). The structural analysis related to 1 and 2 illustrated that the auxiliary linkers result in the generation of a fairly 2D (2,3)-connected framework with 4-fold interpenetration for 1 and 2D binodal (2,4)-connected network with 2-fold interpenetration. Magnetic susceptibility measurements demonstrate that 1 and 2 exhibit antiferromagnetic coupling with the corresponding J values of for 1 and 2, respectively.

Self-Assembly and Photothermal Conversion of MetallaRussian Doll and Metalla[2]catenanes Induced via Multiple Stacking Interactions.

A variety of organometallic supramolecular architectures have been constructed over the past decades and their properties were also explored via different strategies. However, the synthesis of metalla-Russian doll is still a fascinating challenge. Herein, a series of new coordination supramolecular complexes, including a metalla-Russian doll, metalla[2]catenanes, and metallarectangles, were synthesized by using meticulously selected Cp*Rh (Cp* = η5-C5Me5) building units (E1, E2, and E3) and three rigid anthracylpyridine ligands (L1, L2, and L3) via a self-assembly strategy. While the combination of the short ligand L1 and E1 or E2 generated two metallarectangles, the longer ligand L2 containing an alkynyl group resulted in two new [2]catenanes, most likely due to which the strong electron-donating effect of alkynyl groups causes self-accumulation. Interestingly, an unusual Russian doll assembly was obtained through the reaction of L3 and E3 based on sextuple π···π stacking interactions. Furthermore, the dynamic structural conversion between [2]catenanes and the corresponding metallarectangles could be observed through concentration-, solvent-, and guest-induced effects. The [2]catenane complexes 4b displayed efficient photothermal conversion efficiency in solution (20.2%), in comparison with other organometallic macrocycles. We believe that π···π stacking interactions generate active nonradiative pathways and promote radiative photodeactivation pathways. This study proves the versatility of half-sandwich building units, not only to build complicated supramolecular topologies but also in effective functional materials for various appealing applications.

Trinuclear Dy(III) Single‐Molecule Magnets with Two‐Step Relaxation

Comprehensive SummaryThe reaction of DyCl3⋅6H2O with a rigid diacylhydrazone ligand (H2L) afforded a trinuclear precursor [Dy3L2Cl3(H2O)2(CH3OH)]Cl2⋅3CH3OH (1). The replacement of the Cl– ions and the coordinating solvents by the aryloxides ligands (Lx)– yields three trinuclear complexes [Dy3L2(Lx)5]⋅nsol (x = 1,2‐naphthol (2); x = 2,7‐hydroxycoumarin (3); and x = 3, phenol (4)). In complexes 2—4, two end Dy3+ centers adopt almost identical N4O4 coordination sphere of D6h geometry while the central one adopts N4O5 coordination sphere in Cs geometry. Magnetic measurements reveal weak antiferromagnetic interactions in the hydrated samples 2e—4e and two‐step slow relaxation process under zero dc field with effective energy barriers Ueff of 439 and 91 K, 353 and 40 K, 466 and 89 K for SR and FR in 2e—4e, respectively. Such dynamic magnetic behaviour for 4 persists in the magnetically diluted sample of 4@Y. Complex 4 possesses the short Dy‐Oaryloxide bond distance of 2.055(18) Å, and the largest Ueff among the reported linear trinuclear dysprosium complexes. Moreover, the functionalized aryloxides ligands (Lx)– show photoluminescence via intramolecular energy transfer, making 2e—4e luminescent Dy3+ SMMs with high energy barriers.

Reticular Synthesis of Metal‐Organic Frameworks by 8‐Connected Quadrangular Prism Ligands for Water Harvesting

AbstractUtilization of rigid, highly connected organic linkers is critical for the reticular synthesis of functional metal–organic frameworks (MOFs). However, highly‐stable MOFs (e.g. Al/Cr/Zr‐based MOFs) based on rigid ligands with more than 6 coordinating functions have been rarely achieved thus far. Herein, we describe the construction of two bcu Zr‐based MOFs (named ZrMOF‐1 and ZrMOF‐2) from peripherally extended pentiptycene ligands (H8PEP‐1 and H8PEP‐2) with rigid quadrangular prism shape possessing 8 carboxylic groups at the prism vertices. Particularly, ZrMOF‐1 exhibits microporous structure with large Bruno‐Emmett‐Teller surface area and high water stability, endowing it a promising water harvesting material with a high water uptake capacity of 0.83 gH2O gMOF−1 at P/P0=0.90 and 25 °C, a steep uptake at a low P/P0 of 0.30, and excellent durability over 500 water adsorption‐desorption cycles. Moreover, self‐consistent charge density functional tight‐binding calculations were carried out, rationalizing the water adsorbing process and amount in ZrMOF‐1.

Reticular Synthesis of Metal-Organic Frameworks by 8-Connected Quadrangular Prism Ligands for Water Harvesting.

Utilization of rigid, highly connected organic linkers is critical for the reticular synthesis of functional metal-organic frameworks (MOFs). However, highly-stable MOFs (e.g. Al/Cr/Zr-based MOFs) based on rigid ligands with more than 6 coordinating functions have been rarely achieved thus far. Herein, we describe the construction of two bcu Zr-based MOFs (named ZrMOF-1 and ZrMOF-2) from peripherally extended pentiptycene ligands (H8 PEP-1 and H8 PEP-2) with rigid quadrangular prism shape possessing 8 carboxylic groups at the prism vertices. Particularly, ZrMOF-1 exhibits microporous structure with large Bruno-Emmett-Teller surface area and high water stability, endowing it a promising water harvesting material with a high water uptake capacity of 0.83 gH2O gMOF -1 at P/P0 =0.90 and 25 °C, a steep uptake at a low P/P0 of 0.30, and excellent durability over 500 water adsorption-desorption cycles. Moreover, self-consistent charge density functional tight-binding calculations were carried out, rationalizing the water adsorbing process and amount in ZrMOF-1.

Two new metal-organic frameworks based on nitrogen-containing rigid tetracarboxylic acid ligand: Synthesis, crystal structure, characterization and DFT study

Two nickel metal-organic frameworks (Ni-MOFs) based on a nitrogen-containing rigid tetracarboxylic acid ligand had been synthesized by the hydrothermal method, namely {[Ni(H4L1)0.5(4,4′-bibp) (H2O)]·1.5H2O}n (1) and {[Ni(H4L1)(H2O)2]·H2O}n (2) (H4L1 = 5,5′-(1H-1,2,4-triazole-3,5-diyl)diisophthalic acid, 4,4′-bibp = 4,4′-di (1H-imidazol-1-yl)-1,1′-biphenyl). Crystal structure analysis revealed that the two complexes exhibited varied structures in the presence or absence of the auxiliary N-donor ligand 4,4′-bibp: the complex 1 was a three-dimensional (3D) metal-organic framework with a (1,2,4,5)-connected {4.64.8}2{42.64}3{6}2 topology. In the complex 2, the carboxylate ligand was used as a junction point to form a 2D layered structure with Ni(II). The results showed that the addition of the 4,4′-bibp has a very important effect on the structure of the complexes. Some conventional characterizations were carried out, such as: Infrared (IR) spectroscopy, powder X-ray diffraction (PXRD) and thermogravimetric (TGA) analyses. Moreover, the ORCA program was used to perform density functional theory (DFT) calculations to investigate the molecular properties of the two complexes.

Reactions of Group VIB metal carbonyls with two novel rigid macrocyclic Schiff base ligands incorporating acridine inter-crossing group

Two new rigid macrocyclic Schiff base ligands incorporating acridine inter-crossing group [1,1′-(acridine-3,6-diylbis(azaneylylidene))bis(methaneylylidene))bis(naphthalen-2-ol), L1, and N,N'-(acridine-3,6-diyl)bis(1-(quinolin-2-yl)methanimine), L2, were synthesized and fully characterized. The X-ray single crystal analysis of L1 explored that the compound crystallized in a monoclinic crystal system with a space group P21/c. The compound was crystalized with five water molecules. Interestingly, L1 occurred as a double zwitterion, where the hydrogen of the OH group of the hydroxynaphthalene transferred to the azomethine nitrogen to form NH+ and O− moieties with the presence of hydrogen bonding between them. Hirshfeld surface analysis of the L1 was also investigated. Reactions of the two ligands with the Group VIB metal carbonyls in air were investigated. In order to characterize the novel compounds, various analytical and spectroscopic methods were used. The analysis revealed that the complexes were formed as oxo derivatives with unique structural features. The presented compounds conducted fluorescence quenching investigations, viscosity evaluations, antimicrobial and antioxidant properties. It was concluded that the binding interaction with DNA was electrostatic binding mode rather than intercalative mode. Molecular docking of L1 and its complexes were investigated versus three macromolecular receptors (PDB: 4BJP, 1BQB and 1BNA). These targets were selected to compare the experimental biological data with the results of the docking analysis.

Supramolecular Self-Assembly of Engineered Polyproline Helices.

The ability to rationally design biomaterials to form desired supramolecular constructs presents an ever-growing research field, with many burgeoning works within recent years providing exciting results; however, there exists a broad expanse of promising avenues of research yet to be investigated. As such we have set out to make use of the polyproline helix as a rigid, tunable, and chiral ligand for the rational design and synthesis of supramolecular constructs. In this investigation, we show how an oligoproline tetramer can be specifically designed and functionalized, allowing predictable tuning of supramolecular interactions, to engineer the formation of supramolecular peptide frameworks with varying properties and, consequently, laying the groundwork for further studies utilizing the polyproline helix, with the ability to design desired supramolecular structures containing these peptide building blocks, having tunable structural features and functionalities.

Syntheses, Structures, and Photoluminescence Properties of Two New Zinc(II) Coordination Polymers Constructed by Rigid Carboxylic Acid Ligand

Syntheses, Structures, and Photoluminescence Properties of Two New Zinc(II) Coordination Polymers Constructed by Rigid Carboxylic Acid Ligand

Six novel Zn(II)/Cd(II) coordination polymers based on a rigid tridentate imidazolyl terpyridine ligand fine-tuned by different carboxylates: Syntheses, structural diversities and luminescence properties

Six novel coordination polymers (CPs) based on a rigid tridentate ligand, 4′-(4-(imidazol-1-yl)phenyl)-4,2′:6′,4′'-terpyridine (imphtpy), namely {[Zn2(imphtpy)2(p-bdc)2]·(H2O)}n (1), [Zn(imphtpy)(m-bdc)]n (2), {[Zn(imphtpy)(qda)1.5]·(H2O)}n (3), [Cd2(imphtpy)2(m-bdc)2]n (4), [Cd(imphtpy)(abtc)0.5]n (5) and [Cd(imphtpy)(qda)]n (6), (p-H2bdc = 1,4-benzenedicarboxylic acid, m-H2bdc = 1,3-benzenedicarboxylic acid, H2qda = hydroquinone-o,o'-diacetic acid and H4abtc = 3,3′,5,5′-azobenzenetetracarboxylic acid), have been solvothermally synthesized and characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction (PXRD), thermogravimetric (TG) analysis and single-crystal X-ray diffraction. Complex 1 displays a pseudo four-fold interpenetration of dia network in a [2 + 2] mode. Complex 2 exhibits a 2D → 2D polycatenane of two-fold interpenetrated network with the sql topology. Complex 3 shows a interdigitated 2D layer with the sql topology, which is further extended into a 3D supramolecular framework through π-π interactions and hydrogen bonds. Complex 4 features a two-fold interpenetrated (4,4)-connected 3D + 3D → 3D framework with the bbf topology. Complex 5 reveals a 2D network constructed by binuclear Cd2(CO2)4 secondary building unit (SBU) with the sql topology which is further packed into a 3D supramolecular framework through π-π interactions. Complex 6 is a 3D network constructed by binuclear Cd2(CO2)2O2 SBU with the uninodal 6-c pcu topology. These results indicate that the versatile coordination networks of imphtpy and various polycarboxylate ligands play crucial roles in modulating the structural topologies of coordination networks. In addtion, photoluminescence properties have been explored for complexes 1–6 in the solid state at room temperature, which are derived from metal perturbed intraligand charge transfer (ICT) or ligand-to-ligand charge transfer.

Cyclic Homo- and Heterohalogen Di-λ3-diarylhalonium Structures.

In the context of the ever-growing interest in the cyclic diaryliodonium salts, this work presents synthetic design principles for a new family of structures with two hypervalent halogens in the ring. The smallest bis-phenylene derivative, [(C6H4)2I2]2+, was prepared through oxidative dimerization of a precursor bearing the ortho-disposed iodine and trifluoroborate groups. We also report, for the first time, the formation of cycles containing two different halogen atoms. These present two phenylenes linked by hetero-(I/Br) or -(I/Cl) halogen pairs. This approach was also extended to the cyclic bis-naphthylene derivative [(C10H6)2I2]2+. The structures of these bis-halogen(III) rings were further assessed through X-ray analysis. The simplest cyclic phenylene bis-iodine(III) derivative features the interplanar angle of ∼120°, while a smaller angle of ∼103° was found for the analogous naphthylene-based salt. All dications form dimeric pairs through a combination of π-π and C-H/π interactions. As the largest member of the family, a bis-I(III)-macrocycle was also assembled using the quasi-planar xanthene backbone. Its geometry enables the two iodine(III) centers to be bridged intramolecularly by two bidentate triflate anions. In a preliminary manner, the interaction of the phenylene- and naphthalene-based bis-iodine(III) dications with a new family of rigid bidentate bis-pyridine ligands was studied in solution and the solid state, with an X-ray structure showing the chelating donor bonding to just one of the two iodine centers.

Interactions between amphiphilic nanoparticles coated with striped hydrophilic/hydrophobic ligands and a lipid bilayer

Due to their unique physicochemical properties, nanoparticles play an important role in the fields of nanomedicine and so on. In this paper, the interactions between the nanoparticles coated with striped hydrophilic and hydrophobic ligands and a lipid bilayer are investigated by using the coarse-grained molecular dynamics simulation. This study focuses on the effects of the density of the ligands, the ratio of the hydrophilic ligands to the hydrophobic ligands, and the rigidity of the ligands on the interactions of the nanoparticles with the lipid bilayer. The results show that the nanoparticles interact with the lipid bilayer in two different ways. The nanoparticle with a small size, a large ratio of hydrophilic ligands to the hydrophobic ligands, and flexible ligands can readily be inserted into the lipid bilayer, and the nanoparticle rotation is very crucial to the insertion of the nanoparticle into the bilayer. However, the nanoparticle with a large size, a small ratio of hydrophilic ligands to hydrophobic ligands, and rigid ligands can only be adsorbed on the surface of the lipid bilayer. This work provides an effective method to modulate the interactions of the amphiphilic nanoparticles with the lipid bilayers and some insights into the applications of the nanoparticles in drug delivery, cell imaging, etc.

Structural Self-Assembly and Applications of Metal-Organic Molecular Containers with Flexible Backbones.

Supramolecular chemistry has become an interdisciplinary discipline of chemistry, physics, and biology. As a huge subunit of supramolecular compounds, the functional metal-organic supramolecular systems with well-defined cavities which are able to accommodate size-suitable guests via benign host-guest behavior, have been known as "metal-organic molecular containers" (MOMCs) and attracted much attentions for their rich chemical properties and wide potential applications in molecular recognition, catalysis, bio-medical and other fields. In particular, the MOMCs with flexible backbones exhibit a unique feature both in the aspect of structural construction and applications, due to the free rotation and self-adaptively of the specific functional groups in the skeletons. In this paper, we review several selected examples of the coordination-driven metal-organic supramolecular systems from the aspects of self-assembly construction to the various applications. The self-assembly strategies, especially the different choice of organic ligands with flexible backbones during the construction, leading to quite diverse configurations compared to the rigid ligands, have been also discussed to show a different perspective of metal-organic system construction.

Self-Assembled Cobalt–Nickel Bimetallic-Organic Framework Materials with High Supercapacitor Performance

Two new metal–organic frameworks (MOFs), [Co(bcpp)(bbip)]·H2O (Co-MOF) and [Ni(bcpp)(bbip)]·H2O (Ni-MOF), have been generated based on a V-type flexible carboxylic ligand 3,5-bis(4-carboxyl phenoxy) pyridine (H2bcpp) and a rigid N-donor ligand 1,1′-(1,4-phenylene)bis(1H-benzimidazole) (bbip) by a solvothermal method. Co-MOF and Ni-MOF are isostructural with a 2-fold interpenetrated layered structure. Moreover, a series of bimetallic CoxNiy-MOFs (x/y = 1:1, 2.5:1, 2.75:1, 3:1, 3.25:1, and 3.5:1) were obtained by using one-pot synthesis. Owing to their mixed metallic components and internal layered structure, the bimetallic CoxNiy-MOFs possess a remarkable electrochemical storage property. Significantly, the Co2.75Ni1-MOF has high specific capacitance (699 F g–1) at 0.5 A g–1 and good cycling durability (retained 72.7% over 3100 turns). Additionally, an asymmetrical ultra-capacitor based on Co2.75Ni1-MOF and activated carbon (AC) delivers a maximum energy density of 20.44 Wh kg–1 at 387.49 W kg–1 and a high cycle-to-cycle stability with 85.4% of the primary capacitance over 15,000 turns.

Synthesis and isolation of a triplet bismuthinidene with a quenched magnetic response.

Large spin-orbit coupling (SOC) is an intrinsic property of the heavy elements that directly affects the electronic structures of the compounds. In this work, we report the synthesis and characterization of a monocoordinate bismuthinidene that features a rigid and bulky ligand. All magnetic measurements [superconducting quantum interference device (SQUID), nuclear magnetic resonance (NMR)] point to a diamagnetic compound. However, multiconfigurational quantum chemical calculations predict the ground state of the compound to be dominated (76%) by a spin triplet. The apparent diamagnetism is explained by an extremely large SOC-induced positive zero-field splitting of more than 4500 wavenumbers that leaves the MS = 0 magnetic sublevel thermally isolated in the electronic ground state.