Cubane Core Research Articles

Simplified Nomenclature and Projection Diagrams of Chiral Cubane Analogs.

A simplified nomenclature for chiral cubane analogs is proposed where analogs with a clockwise systematic continuous numbering of the cubane core are designated as (C)-, and analogs with an anticlockwise continuous numbering of the cubane core are designated as (A)-. This method is accurate, allows for the rapid conversion of the chemical name to a structure, and it eliminates the need to designate the stereochemistry of each of the 8 carbons of cubane.

Tetranuclear CoII4O4 Cubane Complex: Effective Catalyst Toward Electrochemical Water Oxidation.

The reaction of Co(OAc)2·6H2O with 2,2'-[{(1E,1'E)-pyridine-2,6-diyl-bis(methaneylylidene)bis(azaneylylidene)}diphenol](LH2) a multisite coordination ligand and Et3N in a 1:2:3 stoichiometric ratio forms a tetranuclear complex Co4(L)2(μ-η1:η1-OAc)2(η2-OAc)2]· 1.5 CH3OH· 1.5 CHCl3 (1). Based on X-ray diffraction investigations, complex 1 comprises a distorted Co4O4 cubane core consisting of two completely deprotonated ligands [L]2- and four acetate ligands. Two distinct types of CoII centers exist in the complex, where the Co(2) center has a distorted octahedral geometry; alternatively, Co(1) has a distorted pentagonal-bipyramidal geometry. Analysis of magnetic data in 1 shows predominant antiferromagnetic coupling (J = -2.1 cm-1), while the magnetic anisotropy is the easy-plane type (D1 = 8.8, D2 = 0.76 cm-1). Furthermore, complex 1 demonstrates an electrochemical oxygen evolution reaction (OER) with an overpotential of 325 mV and Tafel slope of 85 mV dec-1, required to attain a current density of 10 mA cm-2 and moderate stability under alkaline conditions (pH = 14). Electrochemical impedance spectroscopy studies reveal that compound 1 has a charge transfer resistance (Rct) of 2.927 Ω, which is comparatively lower than standard Co3O4 (5.242 Ω), indicating rapid charge transfer kinetics between electrode and electrolyte solution that enhances higher catalytic activity toward OER kinetics.

Synthesis, structure, and magnetic properties of cubane-type tetranuclear Ni(II) and Cu(II) complexes with amide-containing polydentate ligand

Abstract Synthesis, structure, and magnetic properties of a tetranuclear metal complex with a symmetrical polydentate ligand, trans-(±)-1,2-(2-hydroxy-3-methoxybenzamido)cyclohexane (H2L), were characterized. The complexes have tetranuclear cubane cores with the formulae [Ni4(L)2(μ3-OMe)4(CH3OH)4] (1) and [Cu4(L)2(μ3-OMe)4(CH3OH)2] (2), whose cluster units are each composed of chiral ligands [(R, R)- or (S, S)-L]. The magnetic properties of the two compounds were characterized by 1 being ferromagnetic and 2 being antiferromagnetic.

Organo-Functionalized Lacunary Double Cubane Type Oxometallates: Synthesis, Structure, and Properties of [(MIICl)2(VIVO)2{((HOCH2CH2)(H)N(CH2CH2O))(HN(CH2CH2O)2)}2] (M = Co, Zn).

Organofunctionalized tetranuclear clusters [(MIICl)2(VIVO)2{((HOCH2CH2)(H)N(CH2CH2O))(HN(CH2CH2O)2)}2] (1, M = Co; 2, M = Zn) containing an unprecedented oxometallacyclic {M2V2Cl2N4O8} (M = Co, Zn) framework are prepared by solvothermal reactions. The new oxo-alkoxide compounds are fully characterized by spectroscopic methods, magnetic susceptibility measurement, DFT and ab-initio computational methods, and complete single crystal X-ray diffraction structure analysis. The isostructural clusters are formed of edge-sharing octahedral {VO5N} and trigonal bipyramidal {MO3NCl} units. Diethanolamine ligates the bimetallic lacunary double cubane core of 1 and 2 in an unusual two-mode fashion, unobserved previously. In the crystalline state, the clusters of 1 and 2 are joined by hydrogen-bonds to form a three-dimensional network structure. Magnetic susceptibility data indicate weakly antiferromagnetic interactions between the vanadium centers [Jiso(VIV-VIV) = -5.4(1); -3.9(2) cm-1], and inequivalent antiferromagnetic interactions between the cobalt and vanadium centers [Jiso (VIV-CoII) = -12.6 and -7.5 cm-1] contained in 1.

Cubane-type tungsten-iron-sulfur clusters with a nitrogen atom in the core: terminal ligand substitutions and redox behaviors.

The lack of M-Fe-S (M = Mo or W) clusters incorporating a second period (2p) atom in the core has resulted in limited investigations and poor understanding of the physical and chemical properties of the M-Fe-S clusters closely related to the FeMo cofactor. In this work, systematic studies have been carried out to explore the chemical reactivities at the terminal ligand sites and the redox properties of a series of clusters comprising a [WFe3S3N] cubane core, based on the previously developed cluster [(Tp*)WFe3S3(μ3-NSiMe3)Cl3]1-. Substitutions of the terminal chlorides with ethanethiolate, methanethiolate, thiophenolate, p-thiocresolate and azide occurred smoothly, while the replacement of the chlorides with carbene ligands required the reduction of the precursor into [(Tp*)WFe3S3(μ3-NSiMe3)Cl3]2- first. The reduced cluster core could also be supported by thiophenolates as terminal ligands, but not thiolates or azides. It is remarkable that the thiophenolate ligated reduced cluster can be synthesized from the precursor [(Tp*)WFe3S3(μ3-NSiMe3)Cl3]1-via different synthetic routes, either reduction followed by substitution or substitution followed by reduction, either in situ or stepwise. This work indicates that terminal ligands contribute significantly to determine the chemical and physical properties of the clusters, even though they might affect the cluster core to a limited extent from a structural point of view, which raises the possibility of delicate control in regulating the physical/chemical properties of M-Fe-S clusters with a heteroleptic core incorporating 2p atom(s).

Field‐Induced SMM Behaviour of Tetranuclear Coordination Clusters with a Cubane [Ni4O4] Core

AbstractTwo tetranuclear Ni(II) complexes: [Ni4(HL1)4] ⋅ H2O (1) and [Ni4(HL2)4] ⋅ 1.5 dmf (2) where dmf=dimethylformamide, H3L1=4‐(tert‐butyl)‐2‐(((2‐hydroxy‐5‐nitrophenyl)imino)methyl)‐6‐(hydroxymethyl)phenol and H3L2=4‐(tert‐butyl)‐2‐(hydroxymethyl)‐6‐(((2‐hydroxyphenyl)‐imino)methyl)phenol, have been prepared and characterized by single crystal X‐Ray diffraction, elemental analysis and FT‐IR spectroscopy. The solid‐state structures reveal the formation of highly symmetric and asymmetric [Ni4O4] cubane cores in complexes 1 and 2, respectively. Extensive magnetic studies show that both complexes present ferromagnetic exchange interactions between the Ni(II) ions within the cubane core with g=2.113(3), J1=−7.89(8) cm−1, J2=13.3(1) cm−1 and |D|=11.3(4) cm−1 (for 1) and g=2.206(4), J1=1.0(1) cm−1, J2=7.8(1) cm−1 and |D|=8.7(2) cm−1 (for 2). The large anisotropy, high ground spin state (arising from the ferromagnetic coupling) and the good isolation of the clusters provided by the Schiff base ligands, give rise to the first examples of field‐induced single‐molecule magnets (FI−SMM) in Ni4O4 clusters and to the highest energy barrier reported to date in a Ni4O4 cluster.

Syntheses of new high-symmetric polyoxometalates with Mo4O4 cubane core

Presented here are a series of new polyoxometalates (POMs) containing Mo4O4 core. Thanks to the large Mo4O4 cubane template, the new cluster exhibits the same Td symmetry as classic Keggin POM but higher nuclear number and more heterometal atoms. Moreover, the third order nonlinear optical (NLO) properties of them are also researched.

Solvothermal One-Pot Synthesis of a New Family of Chiral [Fe4O4]-Cubane Clusters with Redox Active Cores

The two achiral ligands tris(1-methyl-1H-imidazol-2-yl)methanol ((mim)3COH) and bis(1-methyl-1H-imidazol-2-yl)(3-methylpyridin-2-yl)methanol ((mim)2(mpy)COH) form on reaction with Fe(BF4)2∙6H2O, the octahedral low-spin complexes [Fe((mim)3COH)2](BF4)2∙MeCN (1) and [Fe((mim)2(mpy)COH)2](BF4)2∙0.5MeCN (2). Both octahedral complexes immediately rearrange to the chiral [Fe4O4]-cubane clusters [Fe4(mim)3CO)4](BF4)4 (3) and [Fe4(mim)3CO)4](BF4)4∙CHCl3 (4), whereas the highly symmetrical 3 crystallizes as racemate, 4 resolves based on the asymmetry introduced by the 2-methylpyridine moiety and crystallizes as an enantiomerically pure sample. Both clusters feature redox active [Fe4O4]-cubane cores with up to four individual accessible states, which directs towards a potential application as electron-shuttle.

Tetranuclear Hydroxo Complexes of Rare-Earth Elements with the Cubane Core as Products of Self-Controlled Hydrolysis

Tetranuclear hydroxo complexes [La4(Deta)4(OH)4(Tfa)3(DetadcH)2](HTfa)(H2O)7(Tfa)3 (I) and [Nd4(Deta)4(OH)4(Tfa)3(DetadcH)2](H2O)n(Tfa)3 (II) with diethylene-N,N′-dicarbamate anions (DetadcH–) are synthesized for the first time by the reactions of lanthanum trifluoroacetate and neodymium trifluoroacetate with a solution of diethylenetriamine (Deta) in air under the self-controlled hydrolysis conditions and are characterized by X-ray diffraction, powder X-ray diffraction, IR spectroscopy, and elemental analysis. Compounds I and II contain the same-type complex cationic fragment with the cubane metal–oxygen core stabilized due to four chelate Deta ligands and two bridging DetadcH– ligands. The DFT calculations of the geometry and vibrational spectrum of the [La4(Deta)4(OH)4(Tfa)3(DetadcH)2]3+ complex cation are performed.

Stepwise Construction of Mo–Fe–S Clusters Using a LEGO Strategy

The rational synthesis of iron-sulfur clusters with excellent control of the core ligands has been a significant challenge in biomimetic chemistry. In this work, the rational construction of versatile Mo-Fe-S cubane clusters was realized using a LEGO strategy. (LEGO is a line of plastic construction toys consisting of various interlocking plastic bricks which can be assembled and connected in different ways to construct versatile objects. Herein we use "LEGO strategy" as an analogy for the stepwise synthetic methodology, and we use "brick" to represent a corner atom of the cubane structure.) Through careful synthetic control, the ⟨Fe⟩, ⟨S⟩, and ⟨Cl⟩ bricks were mounted piece-by-piece onto the basic ⟨MoS3⟩ frame to stepwise construct the incomplete cubane core ⟨MoFe2S3Cl⟩ and the complete cubane core ⟨MoFe3S3Cl⟩. The significantly elongated Fe-Cl bonds for the bridging chlorides in the ⟨MoFe2S3Cl⟩ and ⟨MoFe3S3Cl⟩ cores permit ligand metatheses to introduce 2p donors at the bridging sites, which used to be a challenge in traditional iron-sulfur chemistry. Therefore, in subsequent controlled reactions, the bridging ⟨Cl⟩ bricks of the ⟨MoFe2S3Cl⟩ and ⟨MoFe3S3Cl⟩ frames could be easily replaced by ⟨N⟩ , ⟨O⟩, or ⟨S⟩ bricks to generate the ⟨MoFe2S3N⟩, ⟨MoFe2S3O⟩, ⟨MoFe3S3N⟩, and ⟨MoFe3S4⟩ cluster cores, demonstrating more choices for the LEGO synthetic strategy. The series of Mo-Fe-S clusters and their derivatives, together with related synthetic strategies, offers a good platform and methodology for biomimetic chemistry in relation to nitrogenase, especially the FeMo cofactor.

In Situ Assembled Polynuclear Zinc Oxo Clusters Using Modified Schiff Bases as Ligands.

A series of different cores and nuclearity zinc metal clusters 1–5 have been synthesized using Zn(ClO4)2·6H2O, Schiff-base primary ligands, and dibenzoyl methane (DBM) or monoethanolamine (MEA) as co-ligand in a room-temperature reaction. The structure of the complexes is characterized using single-crystal X-ray diffraction. Among them, (1) [Zn(L1)(DBM)] is mononuclear; (2) [Zn4(L2)2(DBM)4], (3) [Zn4(L2)4(H2O)2(ClO4)2]·2CH2Cl2, and (4) [Zn4(L3)2(DBM)4] have a cubane core; and (5) [Zn4(L4)4(MEA)2(ClO4)2] has a ladderlike core structure. Compounds 1–5 have also been characterized using UV–vis absorption and emission spectroscopies. For an in-depth understanding of the absorption spectra of 1 and 3, density functional theory (DFT) calculations have been performed, which suggest that the transitions correspond to the π → π* intraligand charge transfer (ILCT) transitions.

Heterometallic CeIV/ VV Oxo Clusters with Adjustable Catalytic Reactivities.

Heterometallic CeIV/M oxo clusters are underexplored yet and can benefit from synergistic properties from combining cerium and other metal cations to produce efficient redox catalysts. Herein, we designed and synthesized a series of new Ce12V6 oxo clusters with different capping ligands: Ce12V6-SO4, Ce12V6-OTs (OTs: toluenesulfonic acid), and Ce12V6-NBSA (NBSA: nitrobenzenesulfonic acid). Single crystal X-ray diffraction (SCXRD) for all three structures reveals a Ce12V6 cubane core formulated [Ce12(VO)6O24]18+ with cerium on the edges of the cube, vanadyl capping the faces, and sulfate on the corners. While infrared spectroscopy (IR), ultraviolet-visible spectroscopy (UV-vis), electrospray ionization mass spectrometry (ESI-MS), and proton nuclear magnetic resonance (1H NMR) proved the successful coordination of the organic ligands to the Ce12V6 core, liquid phase 51V NMR and small-angle X-ray scattering (SAXS) confirmed the integrity of the clusters in the organic solutions. Furthermore, functionalization of the Ce12V6 core with organic ligands both provides increased solubility in term of homogeneous application and introduces porosity to the assemblies of Ce12V6-OTs and Ce12V6-NBSA in term of heterogeneous application, thus allowing more catalytic sites to be accessible and improving reactivity as compared to the nonporous and less soluble Ce12V6-SO4. Meanwhile, the coordinated ligands also influenced the electronic environment of the catalytic sites, in turn affecting the reactivity of the cluster, which we probed by the selective oxidation of 2-chloroethyl ethyl sulfide (CEES). This work provides a strategy to make full use of the catalytic sites within a class of inorganic sulfate capped clusters via organic ligand introduction.

Solvent mediated synthesis of homoleptic tri and tetranuclear nickel complex derived from [Ni2(µ-SeC5H4N)2(dppe)2]2+ and theoretical studies

In the present report, the reactivity of the binuclear complex [Ni2(µ-SeC5H4N)2(dppe)2]2+ towards dichloromethane and methanol has been studied. The complex [Ni2(µ-SeC5H4N)2(dppe)2]2+ in the presence of chlorinated solvent resulted in selenido bridged trinuclear complex of composition [Ni3(µ-Se)2(dppe)2]2+ (1) whereas in the presence of methanol hydrolyzed product having cubane core [Ni4{(C5H4N)2Se}4(μ3OH)4(C6H5COO)(HCOO)]2+ (2) was isolated. Both the complexes were characterized by elemental analysis, IR, 1H, and 31P{1H} NMR spectroscopy. An attempt has also been made to investigate their thermal studies. The molecular structure of both the complex [Ni3(µ-Se)2(dppe)2]2+ (1) and [Ni4{(C5H4N)2Se}4(μ3OH)4(C6H5COO)(HCOO)]2+ (2) were established by single-crystal X-ray diffraction analysis. Broken-symmetry density functional theory (BS-DFT) calculations were carried out on complex 2 to investigate the electronic structure and nature of magnetic exchange interaction. BS-DFT reveals the existence of three different J values i.e. -8.9 cm−1, +18.7 cm−1 and +1.8 cm−1 between different Ni(II) pairs. A strong ferromagnetic interaction was observed between formate/phenylacetate bridged Ni(II) centers. An antiferromagnetic interaction between the ferromagnetically coupled formate and phenylacetate bridged Ni(II) dimers result in isolation of S = 0 spin ground state for complex 2. Molecular orbital, spin-density analyses were performed on the X-ray and optimized geometries to probe the electronic structure of complex 2.

Investigating cubane formation and effect of co-crystallization agents in oxo-bridged Co complexes using X-ray absorption spectroscopy

• Cubane core in Co-oxo complexes studied using XAS to probe its spectroscopic nature. • XANES shows presence of octahedrally coordinated Co 3+ ions in cubane structure. • EXAFS confirm octahedral Co with 6 O/N, 3 Co-Co backscattering forming cubane core. • XANES simulation indicate interaction with co-crystallizing salts NaNO 3 and NaClO 4 . • Formation of defect dicubane with Co 2+ /Co 3+ ions predicted by XANES simulation. The formation of cubane core and effect of co-crystallization agent have been studied in the oxo-bridged Co complexes using X-ray absorption spectroscopy. XAFS at Co K-edge have been measured in the oxo-bridged Co complexes [Co 4 O 4 (O 2 CCH 3 ) 4 (C 5 H 5 N) 4 ]( 1 ), 1 .0.5NaNO 3 ·8H 2 O( 2 ), 1 .NaClO 4 ·3·5H 2 O( 3 ) and [Co 4 O 4 (O 2 CCH 3 ) 4 (NH 3 ) 4 ]( 4 ). Complexes 2 and 3 actually contain the same complex 1 co-crystalized by NaNO 3 and NaClO 4 moieties. While 1 and 4 are in powder form, 2 and 3 are in crystalline form. Different XANES features have been correlated to the coordination around the absorbing Co atom in all the complexes. EXAFS analysis has been performed to determine coordination environment around the Co atoms to confirm the formation of the oxo-cubane structure in these complexes. For each of the Co centers present at the four different positions of the cubane core in complexes 2 and 3, XANES spectra have been theoretically simulated and simultaneously p-DOS calculated to examine the effect of co-crystallizing moieties interactions with the individual Co centres present in these two complexes. After preliminary indication by EXAFS analysis, XANES simulations were also performed to examine the presence of defect dicubane structure in 4. The study can be helpful in the detection of these structures during in-situ/operando studies of these catalytically active complexes.

Ortho-C-H Acetoxylation of Cubane Enabling Access to Cubane Analogues of Pharmaceutically Relevant Scaffolds.

A novel method of introducing an oxygen functionality into a cubane core was developed using a transition-metal-catalyzed directed acetoxylation methodology via C-H activation. The obtained compounds were derivatized into cubane analogues of pharmaceutically relevant structural motifs, namely, acetylsalicylic acid and coumarin motifs, which could potentially act as bioisosteres of these scaffolds.

Flexibility Enhances Reactivity: Redox Isomerism and Jahn-Teller Effects in a Bioinspired Mn4O4 Cubane Water Oxidation Catalyst.

Understanding how water oxidation to molecular oxygen proceeds in molecular metal-oxo catalysts is a challenging endeavor due to their structural complexity. In this report, we unravel the water oxidation mechanism of the highly active water oxidation catalyst [Mn4V4O17(OAc)3]3–, a polyoxometalate catalyst with a [Mn4O4]6+ cubane core reminiscent of the natural oxygen-evolving complex. Starting from the activated species [Mn44+V4O17(OAc)2(H2O)(OH)]1–, we scrutinized multiple pathways to find that water oxidation proceeds via a sequential proton-coupled electron transfer (PCET), O–O bond formation, another PCET, an intramolecular electron transfer, and another PCET resulting in O2 evolution, with a predicted thermodynamic overpotential of 0.71 V. An in-depth investigation of the O–O bond formation process revealed an essential interplay between redox isomerism and Jahn–Teller effects, responsible for enhancing reactivity in the catalytic cycle. This is achieved by redistributing electrons between metal centers and weakening relevant bonds through Jahn–Teller distortions, introducing flexibility to the otherwise rigid cubane core of the catalyst. These mechanistic insights are expected to advance the design of efficient bioinspired Mn cubane water-splitting catalysts.

Bifunctional W/NH Cuboidal Aminophosphino W3S4 Cluster Hydrides: The Puzzling Behaviour behind the Hydridic‐Protonic Interplay

AbstractThe novel [W3S4H3(edpp)3]+ (edpp=(2‐aminoethyl)diphenylphosphine) (1+) cluster hydride with an acidic −NH2 functionality has been synthetized and studied. Its crystal structure shows the characteristic incomplete W3S4 cubane core with the outer positions occupied by the P and N atoms of the edpp ligands. Although no signal due to the hydride ligands is observed in the 1H NMR spectrum, hydride assignment is supported by 1H‐15N HSQC techniques, the changes in the 31P{1H} NMR chemical shift, and FT‐IR spectra in the W−H region of the deuterated [W3S4D2H(edpp)3]+ (1+‐d2) samples. Moreover, all NMR evidences suggest that one of the hydrogen atoms of the NH2 group in 1+ is rapidly exchanging with the hydride. The reaction of 1+ with acids (HCl, HBr and DCl) features complex polyphasic kinetics with zero‐order dependence with respect to the acid concentration, being also independent of the solvent nature. This behavior differs from that of their diphosphino analogues, suggesting a different mechanism.

Effect of structural variation on enzymatic activity in tetranuclear (Cu4) clusters with defective cubane core

The stimulus to the modeling of enzyme functioning sites comes from their potential to give insight into the natural enzyme’s mechanistic pathways, ascertain the role of that different metal ion in the active site and construct better catalysts motivated by nature. The presence of metal ion leads to the activation of molecular oxygen in the metalloenzymes. The metalloenzymes such as the catechol oxidase (CO) enzyme that oxidizes the catechol to corresponding quinones which eventually protect damage tissues from plant and pathogen. Thus, the design and characterization of catalysts used as selectively and efficiently oxidation reactions have grown to be unique challenges for modern inorganic chemists. In this work, two novel tetranuclear complexes (1 and 2) have been synthesized in excellent yield. The complexes were characterized using various spectroscopic techniques such as FTIR, UV–Visible and PXRD pattern. The structure of 1 and 2 was elucidated by SC-XRD (single crystal X-ray diffraction) analysis. The magnetic study reveals the presence of the antiferromagnetic nature of 1 and 2. Both 1 and 2 shows a very good catecholase-like activity by oxidizing the catechol to analogous quinone in methanolic solution. Thus, a structure-activity relationship can further help us design other substituted tetranuclear complexes with enhanced catecholase like activity. Communicated by Ramaswamy H. Sarma

Synthesis, structural characterization, DNA cleavage studies, antimicrobial activities, and time‐killing kinetics of tetranuclear Cu (II) with partial cubane Cu4O4 cores and mononuclear Co (II) and Ni (II) complexes of a new acylhydrazone ligand

In the present study, a new acyl hydrazone N′‐(3‐ethoxy‐2‐hydroxybenzylidene)isobutyrohydrazide (ehbbhH2) and its metal complexes [Co (ehbbhH)2] (1), [Ni (ehbbhH)2] (2), and [Cu4(ehbbh)4]·4H2O (3) were prepared. The structure of the ligand was characterized using elemental analysis, GC‐MS, electronic, IR, 1H, and 13C NMR spectra. The structure of the prepared complexes was investigated by spectral, analytical, thermal, and magnetic susceptibility measurements. The results revealed that complexes 1 and 2 were formed in a 1 M:2 L mole ratio, whereas Complex 3 was formed in a 1:1 mole ratio. Spectral studies showed that the ligand in complexes 1 and 2 bonded to the metal ion in a monoanionic tridentate fashion through the azomethine nitrogen atom, carbonyl, and phenolic oxygen atoms. In Complex 3, ligand acted as dianionic tetradentate through the azomethine nitrogen atom, enolic, phenolic, and ethoxy oxygen atoms. The molecular structures of the ligand and Complex 3 were also established using single‐crystal X‐ray diffraction. The X‐ray structures of Complex 3 revealed that they contained a distorted Cu4O4 cubane core. The present study investigated the cleavage activities of the ligand and its complexes on supercoiled pBR322 DNA. Complex 3 was determined to be the most effective compound on pBR322 plasmid DNA in the presence of hydrogen peroxide. The antimicrobial activities of all compounds were investigated against two Gram‐positive bacteria, two Gram‐negative bacteria, and one eukaryote. The results showed that Complex 3 exhibited better antimicrobial activity than other complexes. Finally, time‐killing assays of Complex 3, which was the most effective complex, were carried out.

A new 1-1-4 pattern of magnetic exchange interactions in a cubane core tetranuclear copper (II) complex

The dependence on structure of the magnetic exchange coupling between copper (II) ions in complexes containing Cu4O4 cubane units has been the subject of several previous studies. A new example of a tetranuclear copper (II) complex, [{Cu(OH)(phen)}4]∙(ClO4)4 (1), having a Cu4O4 cubane core is reported here. 1 was synthesized hydrothermally at 80 °C using 1,10-phenanthroline (phen) as a ligand in a mildly acidic water/ethanol solution (pH = 4.8–5.3) and structurally characterized by single crystal X-ray crystallography. The best fit to the magnetic data in the 2–300 K temperature range was obtained with a previously unreported 1 + 1 + 4 model for the exchange coupling among the copper (II) ions with J1 = − 28.0 cm−1, J2 = +72.2 cm−1, and J3 = − 15.3 cm−1. The model corresponds to one medium, one short, and four long exchange pathways. The overall predominant antiferromagnetic exchange leads to a singlet total spin ground state.