Decomposition of Copper Formate Clusters: Insight into Elementary Steps of Calcination and Carbon Dioxide Activation

The decomposition of copper formate clusters is investigated in the gas phase by infrared multiple photon dissociation of Cu(II)_n(HCO₂)_2n+1⁻, n≤8. In combination with quantum chemical calculations and reactivity measurements using oxygen, elementary steps of the decomposition of copper formate are characterized, which play a key role during calcination as well as for the function of copper hydride based catalysts. The decomposition of larger clusters (n > 2) takes place exclusively by the sequential loss of neutral copper formate units Cu(II)(HCO₂)₂ or Cu(II)₂(HCO₂)₄, leading to clusters with n=1 or n=2. Only for these small clusters, redox reactions are observed as discussed in detail previously, including the formation of formic acid or loss of hydrogen atoms, leading to a variety of Cu(I) complexes. The stoichiometric monovalent copper formate clusters Cu(I)_m(HCO₂)_m+1⁻, (m=1,2) decompose exclusively by decarboxylation, leading towards copper hydrides in oxidation state +I. Copper oxide centers are obtained via reactions of molecular oxygen with copper hydride centers, species containing carbon dioxide radical anions as ligands or a Cu(0) center. However, stoichiometric copper(I) and copper(II) formate Cu(I)(HCO₂)₂⁻ and Cu(II)(HCO₂)₃⁻, respectively, is unreactive towards oxygen.     

Post-Nickelation of a Crystalline Trinuclear Copper Organic Framework for Synergistic Photocatalytic Carbon Dioxide Conversion

Rational regulation of electronic structures and functionalities of framework materials still remains challenging. Herein, reaction of 4,4′,4′′-nitrilo-tribenzhydrazide with tris(μ₂-4-carboxaldehyde-pyrazolato-N,N′)-tricopper (Cu₃Py₃) generates the crystalline copper organic framework USTB-11(Cu). Post-modification with divalent nickel ions affords the heterometallic framework USTB-11(Cu,Ni). Powder X-ray diffraction and theoretical simulations reveal their two-dimensional hexagonal structure geometry. A series of advanced spectroscopic techniques disclose the mixed Cu^I/Cu^II state nature of Cu₃Py₃ in USTB-11(Cu,Ni) with a uniform bistable Cu₃⁴⁺(Cu^I₂Cu^II) : Cu₃⁵⁺(Cu^ICu^II₂) (ca. 1 : 3) oxidation state, resulting in a significantly improved formation efficiency of the charge-separation state. This endows the Ni sites with enhanced activity and USTB-11(Cu,Ni) with outstanding photocatalytic CO₂ to CO performance with a conversion rate of 22 130 μmol g⁻¹ h⁻¹ and selectivity of 98 %.     

Cu3(CN)4(NH3)2Hg(CN)2: a novel inter­penetrating framework formed from CuI,CuII, HgII and cyanide bridges

The title compound, poly[diammine­hexa‐μ‐cyano‐di­copper(I)­copper(II)­mercury(II)], [Cu₃Hg(CN)₆(NH₃)₂]_n, has a novel threefold‐inter­penetrating structure of three‐dimensional frameworks. This three‐dimensional framework consists of two‐dimensional network Cu₃(CN)₄(NH₃)₂ complexes and rod‐like Hg(CN)₂ complexes. The two‐dimensional network complex contains trigonal–planar Cu^I (site symmetry m) and octa­hedral Cu^II (site symmetry 2/m) in a 2:1 ratio. Two types of cyanide group form bridges between three coordination sites of Cu^I and two equatorial sites of Cu^II to form a two‐dimensional structure with large hexa­gonal windows. One type of CN⁻ group is disordered across a center of inversion, while the other resides on the mirror plane. Two NH₃ mol­ecules (site symmetry 2) are located in the hexa­gonal windows and coordinate to the remaining equatorial sites of Cu^II. Both N atoms of the rod‐like Hg(CN)₂ group (Hg site symmetry 2/m and CN⁻ site symmetry m) coordinate to the axial sites of Cu^II. This linkage completes the three‐dimensional framework and penetrates two hexa­gonal windows of two two‐dimensional network complexes to form the threefold‐inter­penetrating structure.     

Substituent Effect to Fine-Tune Energy Levels of Atom-Precise [MoOS3]2− Modified Copper(I) Thiolate Clusters Boosting Recyclable Photocatalysis

The propulsion of photocatalytic hydrogen (H₂) production is limited by the rational design and regulation of catalysts with precise structures and excellent activities. In this work, the [MoOS₃]²⁻ unit is introduced into the Cu^I clusters to form a series of atomically-precise Mo^VI−Cu^I bimetallic clusters of [Cu₆(MoOS₃)₂(C₆H₅(CH₂)S)₂(P(C₆H₄−R)₃)₄] ⋅ xCH₃CN (R=H, CH₃, or F), which show high photocatalytic H₂ evolution activities and excellent stability. By electron push-pull effects of the surface ligand, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of these Mo^VI−Cu^I clusters can be finely tuned, promoting the resultant visible-light-driven H₂ evolution performance. Furthermore, Mo^VI−Cu^I clusters loaded onto the surface of magnetic Fe₃O₄ carriers significantly reduced the loss of catalysts in the collection process, efficiently addressing the recycling issues of such small cluster-based catalyst. This work not only highlights a competitively universal approach on the design of high-efficiency cluster photocatalysts for energy conversion, but also makes it feasible to manipulate the catalytic performance of clusters through a rational substituent strategy.     

Poly[tetraamminecopper(II) bis[tris(μ2‐cyanido‐κ2C,N)dicuprate(I)]]: a unique CuI–CuII mixed‐valence complex containing anionic cuprous cyanide layers and [Cu(NH3)4]2+ cations

The title compound, {[Cu(NH₃)₄][Cu(CN)₃]₂}_n, features a Cu^I–Cu^II mixed‐valence CuCN framework based on {[Cu₂(CN)₃]⁻}_n anionic layers and [Cu(NH₃)₄]²⁺ cations. The asymmetric unit contains two different Cu^I ions and one Cu^II ion which lies on a centre of inversion. Each Cu^I ion is coordinated to three cyanide ligands with a distorted trigonal–planar geometry, while the Cu^II ion is ligated by four ammine ligands, with a distorted square‐planar coordination geometry. The interlinkage between Cu^I ions and cyanide bridges produces a honeycomb‐like {[Cu₂(CN)₃]⁻}_n anionic layer containing 18‐membered planar [Cu(CN)]₆ metallocycles. A [Cu(NH₃)₄]²⁺ cation fills each metallocyclic cavity within pairs of exactly superimposed {[Cu₂(CN)₃]⁻}_n anionic layers, but there are no cations between the layers of adjacent pairs, which are offset. Pairs of N—H...N hydrogen‐bonding interactions link the N—H groups of the ammine ligands to the N atoms of cyanide ligands.     

The unprecedented role of a CuII cryptand in the luminescence properties of a EuIII cryptate complex

Abstract  

A Eu^III cryptate complex constructed from a Cu^II cryptand with an L ^tBu ligand, [Eu^IIICu₂^II(L ^tBu)₂(NO₃)₃(MeOH)], and the corresponding Ca^II and Na^I cryptates, [Ca^IICu₂^II(L ^tBu)₂(NO₃)₂(MeOH)₂] and [Na^ICu₂^II(L ^tBu)₂(Me₂CO)](BPh₄), have been synthesized and characterized in order to shed light on the essential role of Cu^II in the luminescence of a Eu^III cryptate. The unprecedented role of a Cu^II cryptand makes it possible to produce lanthanide luminescence in a Eu^III cryptate complex and is successfully elucidated by comparison with the corresponding Ca^II and Na^I cryptates.     

Syntheses and crystal structures of two heterometallic iodoplumbates containing mixed‐valence copper(I/II)

Mixed‐valence copper(I/II) atoms have been introduced successfully into a Pb/I skeleton to obtain two heterometallic iodoplumbates, namely poly[bis(tetra‐n‐butylammonium) [bis(μ₃‐dimethyldithiocarbamato)dodeca‐μ₃‐iodido‐hexa‐μ₂‐iodido‐tetracopper(I)copper(II)hexalead(II)]], {(C₁₆H₃₆N)₂[Cu₄^ICu^IIPb₆(C₃H₆NS₂)₂I₁₈]}_n , (I), and poly[[μ₃‐iodido‐tri‐μ₂‐iodido‐iodido[bis(1,10‐phenanthroline)copper(I)]copper(I)copper(II)lead(II)] hemiiodine], {[Cu^ICu^IIPbI₅(C₁₂H₈N₂)₂]·0.5I₂}_n , (II), under solution and solvothermal conditions, respectively. Compound (I) contains two‐dimensional anionic layers, which are built upon the linkages of Cu^II(S₂CNMe₂)₂ units and one‐dimensional anionic Pb/I/Cu^I chains. Tetra‐n‐butylammonium cations are located between the anionic layers and connected to them via C—H…I hydrogen‐bonding interactions. Compound (II) exhibits a one‐dimensional neutral structure, which is composed of [PbI₅] square pyramids, [Cu^II₄] tetrahedra and [Cu^IIN₄I] trigonal bipyramids. Face‐to‐face aromatic π–π stacking interactions between adjacent 1,10‐phenanthroline ligands stabilize the structure and assemble compound (II) into a three‐dimensional supramolecular structure. I₂ molecules lie in the voids of the structure.     

Intermolecular interaction and magnetic coupling mechanism of a mixed-valence CuIICuI tetranuclear complex with iodide bridge

A tetranuclear Cu^ICu^II mixed oxidation state complex, [Cu^II ₂(μ-I)₂Cu^I ₂(μ-I)₂(phenP)₂I₂] (phenPE: 2-(1H-pyrazol-1-yl)-1,10-phenanthroline), has been prepared and its crystal structure is determined by X-ray crystallography. In the complex, Cu^II is a distorted square pyramid and Cu^I is a distorted trigonal planar coordination environment; Cu^II and Cu^I are bridged by iodide. It is rare to form a Cu^II-iodide bond and for Cu^II and Cu^I to be bridged by iodide. In the crystal, there is a slipped π–π stacking between adjacent Cu^II complexes, which resulted in the formation of the 1-D chain along the c axis. The fitting for the variable-temperature magnetic susceptibility data gave magnetic coupling constant 2J?=??1.16?cm^?1 and it may be ascribed to the intermolecular π–π magnetic coupling pathway.     

A mixed‐valence chair‐like tetranuclear copper(I,II) cluster with three linking modes of the 3,5‐bis(2‐pyridyl)‐1,2,4‐triazole ligand

In the tetranuclear copper complex tetrakis[μ‐3,5‐bis(2‐pyridyl)‐1,2,4‐triazolido]bis[3,5‐bis(2‐pyridyl)‐1,2,4‐triazolido]dicopper(I)dicopper(II) dihydrate, [Cu^I₂Cu^II₂(C₁₂H₈N₅)₆]·2H₂O, the asymmetric unit is composed of one Cu^I center, one Cu^II center, three anionic 3,5‐bis(2‐pyridyl)‐1,2,4‐triazole (2‐BPT) ligands and one solvent water molecule. The Cu^I and Cu^II centers exhibit [Cu^IN₄] tetrahedral and [Cu^IIN₆] octahedral coordination environments, respectively. The three independent 2‐BPT ligands adopt different chelating modes, which link the copper centers to generate a chair‐like tetranuclear metallomacrocycle with metal–metal distances of about 4.4 × 6.2 Å disposed about a crystallographic inversion center. Furthermore, strong π–π stacking interactions and O—H...N hydrogen‐bonding systems link the tetracopper clusters into a two‐dimensional supramolecular network.     

Binding of Cu+ and Cu2+ with peptides: Peptides = oxytocin,Arg8‐vasopressin,bradykinin, angiotensin‐I,substance‐P,somatostatin, and neurotensin

The intrinsic binding ability of 7 natural peptides (oxytocin, arg⁸‐vasopressin, bradykinin, angiotensin‐I, substance‐P, somatostatin, and neurotensin) with copper in 2 different oxidation states (Cu^I/II) derived from different Cu^+/2+ precursor sources have been investigated for their charge‐dependent binding characteristics. The peptide‐Cu^I/II complexes, [M − (n‐1)H + nCu^I] and [M − (2n‐1)H + nCu^II], are prepared/generated by the reaction of peptides with CuI solution/Cu‐target and CuSO₄ solution and are analyzed by using matrix‐assisted laser desorption/ionization (MALDI) time‐of‐flight mass spectrometry. The MALDI mass spectra of both [M − (n‐1)H + nCu^I] and [M − (2n‐1)H + nCu^II] complexes show no mass shift due to the loss of ─H atoms in the main chain ─NH of these peptides by Cu⁺ and Cu²⁺ deprotonation. The measured m/z value indicates the reduction of Cu^I/II oxidation state into Cu⁰ during MALDI processes. The number and relative abundance of Cu⁺ bound to the peptides are greater compared with the Cu²⁺ bound peptides. Oxytocin, arg⁸‐vasopressin, bradykinin, substance‐P, and somatostatin show the binding of 5Cu⁺, and angiotensin‐I and neurotensin show the binding of 7Cu⁺ from both CuI and Cu targets, while bradykinin shows the binding of 2Cu²⁺, oxytocin, arg⁸‐vasopressin, angiotensin‐I, and substance‐P; somatostatin shows the binding of 3Cu²⁺; and neurotensin shows 4Cu²⁺ binding. The binding of more Cu⁺ with these small peptides signifies that the bonding characteristics of both Cu⁺ and Cu²⁺ are different. The amino acid residues responsible for the binding of both Cu⁺ and Cu²⁺ in these peptides have been identified based on the density functional theory computed binding energy values of Cu⁺ and the fragment transformation method predicted binding preference of Cu²⁺ for individual amino acids.     

The unprecedented role of a Cu<Superscript>II</Superscript> cryptand in the luminescence properties of a Eu<Superscript>III</Superscript> cryptate complex

Abstract  A Eu^III cryptate complex constructed from a Cu^II cryptand with an L ^tBu ligand, [Eu^IIICu₂^II(L ^tBu)₂(NO₃)₃(MeOH)], and the corresponding Ca^II and Na^I cryptates, [Ca^IICu₂^II(L ^tBu)₂(NO₃)₂(MeOH)₂] and [Na^ICu₂^II(L ^tBu)₂(Me₂CO)](BPh₄), have been synthesized and characterized in order to shed light on the essential role of Cu^II in the luminescence of a Eu^III cryptate. The unprecedented role of a Cu^II cryptand makes it possible to produce lanthanide luminescence in a Eu^III cryptate complex and is successfully elucidated by comparison with the corresponding Ca^II and Na^I cryptates. Graphical abstract   Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Facially Dispersed Polyhydride Cu9 and Cu16 Clusters Comprising Apex‐Truncated Supertetrahedral and Square‐Face‐Capped Cuboctahedral Copper Frameworks

By using a linear tetraphosphine, meso‐bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm), nona‐ and hexadecanuclear copper hydride clusters, [Cu₉H₇(μ‐dpmppm)₃]X₂ (X=Cl ( 1 a ), Br ( 1 b ), I ( 1 c ), PF₆ ( 1 d )) and [Cu₁₆H₁₄(μ‐dpmppm)₄]X₂ (X₂=I₂ ( 2 c ), (4/3) PF₆?(2/3) OH ( 2 d )) were synthesized and characterized. They form copper‐hydride cages of apex‐truncated supertetrahedral {Cu₉H₇}²⁺ and square‐face‐capped cuboctahedral {Cu₁₆H₁₄}²⁺ structures. The hydride positions were estimated by DFT calculations to be facially dispersed around the copper frameworks. A kinetically controlled synthesis gave an unsymmetrical Cu₈H₆ cluster, [Cu₈H₆(μ‐dpmppm)₃]²⁺ ( 3 ), which readily reacted with CO₂ to afford linear Cu₄ complexes with formate bridges, leading to an unprecedented hydrogenation of CO₂ into formate catalyzed by {Cu₄(μ‐dpmppm)₂} platform. The results demonstrate that new motifs of copper hydride clusters could be established by the tetraphosphine ligands, and the structures influence their reactivity.     

Nitrite and Nitric Oxide Interconversion at Mononuclear Copper(II): Insight into the Role of the Red Copper Site in Denitrification

Nitrite (NO₂⁻) and nitric oxide (NO) interconversion is crucial for maintaining optimum NO flux in mammalian physiology. Herein we demonstrate that [ L ₂Cu^II(nitrite)]⁺ moieties (in 2 a and 2 b ; where, L = Me₂PzPy and Me₂PzQu ) with distorted octahedral geometry undergo facile reduction to provide tetrahedral [ L ₂Cu^I]⁺ (in 3 a and 3 b ) and NO in the presence of biologically relevant reductants, such as 4-methoxy-2,6-di-tert-butylphenol (4-MeO-2,6-DTBP, a tyrosine model) and N-benzyl-1,4-dihydronicotinamide (BNAH, a NAD(P)H model). Interestingly, the reaction of excess NO gas with [ L ₂Cu^II(MeCN)₂]²⁺ (in 1 a ) provides a putative {CuNO}¹⁰ species, which is effective in mediating the nitrosation of various nucleophiles, such as thiol and amine. Generation of the transient {CuNO}¹⁰ species in wet acetonitrile leads to NO₂⁻ as assessed by Griess assay and ¹⁴N/¹⁵N-FTIR analyses. A detailed study reveals that the bidirectional NO_x-reactivity, namely, nitrite reductase (NIR) and NO oxidase (NOO), at a common Cu^II site, is governed by the geometric-preference-driven facile Cu^II/Cu^I redox process. Of broader interest, this study not only highlights potential strategies for the design of copper-based catalysts for nitrite reduction, but also strengthens the previous postulates regarding the involvement of red copper proteins in denitrification.     

Electrochemical and quantum chemical investigation of the CuI and CuII complexes with biquinolyl monomer and polymer ligands

Structural reorganization of polyamide (PA) and low-molecular-weight Cu^I and Cu^II complexes with biquinolyl (biQ) ligands during their mutual redox transformations in solution was studied using the electrochemical methods (cyclic voltammetry and preparative electrolysis) and quantum chemical DFT calculations. The influence of electronic factors and geometry distortions in the complexes on the ionization energy on going from Cu^I to Cu^II was evaluated in comparison. The catalytically active form of the [Cu^I(PA)L₂]BF₄ complex can be synthesized in situ from the stable tetrahedral complex [Cu^I(PA)₂]BF₄ by the series of successive redox transitions Cu^I → Cu^II → Cu^I accompanied by the loss of one biQ-containing macroligand. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1331–1340, July, 2007.     

Encapsulation of tricopper cluster in a synthetic cryptand enables facile redox processes from CuICuICuI to CuIICuIICuII states

One-pot reaction of tris(2-aminoethyl)amine (TREN), [Cu^I(MeCN)₄]PF₆, and paraformaldehyde affords a mixed-valent [TREN₄Cu^IICu^ICu^I(μ₃-OH)](PF₆)₃ complex. The macrocyclic azacryptand TREN₄ contains four TREN motifs, three of which provide a bowl-shape binding pocket for the [Cu₃(μ₃-OH)]³⁺ core. The fourth TREN caps on top of the tricopper cluster to form a cryptand, imposing conformational constraints and preventing solvent interaction. Contrasting the limited redox capability of synthetic tricopper complexes reported so far, [TREN₄Cu^IICu^ICu^I(μ₃-OH)](PF₆)₃ exhibits several reversible single-electron redox events. The distinct electrochemical behaviors of [TREN₄Cu^IICu^ICu^I(μ₃-OH)](PF₆)₃ and its solvent-exposed analog [TREN₃Cu^IICu^IICu^II(μ₃-O)](PF₆)₄ suggest that isolation of tricopper core in a cryptand enables facile electron transfer, allowing potential application of synthetic tricopper complexes as redox catalysts. Indeed, the fully reduced [TREN₄Cu^ICu^ICu^I(μ₃-OH)](PF₆)₂ can reduce O₂ under acidic conditions. The geometric constraints provided by the cryptand are reminiscent of Nature''s multicopper oxidases (MCOs). For the first time, a synthetic tricopper cluster was isolated and fully characterized at Cu^ICu^ICu^I (4a), Cu^IICu^ICu^I (4b), and Cu^IICu^IICu^I (4c) states, providing structural and spectroscopic models for many intermediates in MCOs. Fast electron transfer rates (10⁵ to 10⁶ M⁻¹ s⁻¹) were observed for both Cu^ICu^ICu^I/Cu^IICu^ICu^I and Cu^IICu^ICu^I/Cu^IICu^IICu^I redox couples, approaching the rapid electron transfer rates of copper sites in MCO.

Geometric constraints and site isolation provided by the cryptand enable reversible redox of tricopper μ-oxo cluster.     

Synthesis and antimicrobial evaluation of coordination compounds containing 2,2′-bis(3-aminopyridyl) diselenide as ligand

The reaction between 2,2′-bis(3-aminopyridyl) diselenide (L) and metal transition salts results in the formation of molecular or cluster complexes. The structural elucidation of the synthesized complexes [CuCl₂(L)] ( 1 ), [Cu(3-NH₂PySeO₂)₂]·2H₂O ( 2 ), [Cu₄(3-NH₂PySe)₄]·dimethylformamide ( 3 ), [CoCl₂(L)] ( 4 ), [ZnCl₂(L)] ( 5 ), and [Ag₆(3-NH₂PySe)₆] ( 6 ) demonstrates the coordination of nitrogen atoms to Cu^II, Co^II, and Zn^II, and that of the selenium atoms to Cu^I and Ag^I, which agrees with Pearson’s hard and soft acids and bases (HSAB) theory. Furthermore, the oxidation of selenium with the formation of 3-aminopyridylseleninate [3-NH₂PySeO₂]⁻ bonded to the copper atom was observed in complex 2 . The antimicrobial action of complexes 1 , 2 , 4 , and 5 was evaluated against Mycobacterium fortuitum, Mycobacterium massiliense, and Mycobacterium abscessus. It was observed that all these complexes have potential antimicrobial activity compared with the free ligand and metal salts used in the synthesis.     

A three‐dimensional mixed‐valence CuII/CuI coordination polymer constructed from biphenyl‐3,4′,5‐tricarboxylate and 1,4‐bis(1H‐imidazol‐1‐yl)benzene ligands

Coordination polymers (CPs) built by coordination bonds between metal ions/clusters and multidentate organic ligands exhibit fascinating structural topologies and potential applications as functional solid materials. The title coordination polymer, poly[diaquabis(μ₄‐biphenyl‐3,4′,5‐tricarboxylato‐κ⁴O³:O^3′:O^4′:O⁵)tris[μ₂‐1,4‐bis(1H‐imidazol‐1‐yl)benzene‐κ²N³:N^3′]dicopper(II)dicopper(I)], [Cu^II₂Cu^I₂(C₁₅H₇O₆)₂(C₁₂H₁₀N₄)₃(H₂O)₂]_n, was crystallized from a mixture of biphenyl‐3,4′,5‐tricarboxylic acid (H₃bpt), 1,4‐bis(1H‐imidazol‐1‐yl)benzene (1,4‐bib) and copper(II) chloride in a water–CH₃CN mixture under solvothermal reaction conditions. The asymmetric unit consists of two crystallographically independent Cu atoms, one of which is Cu^II, while the other has been reduced to the Cu^I ion. The Cu^II centre is pentacoordinated by three O atoms from three bpt³⁻ ligands, one N atom from a 1,4‐bib ligand and one O atom from a coordinated water molecule, and the coordination geometry can be described as distorted trigonal bipyramidal. The Cu^I atom exhibits a T‐shaped geometry (CuN₂O) coordinated by one O atom from a bpt³⁻ ligand and two N atoms from two 1,4‐bib ligands. The Cu^II atoms are extended by bpt³⁻ and 1,4‐bib linkers to generate a two‐dimensional network, while the Cu^I atoms are linked by 1,4‐bib ligands, forming one‐dimensional chains along the [20] direction. In addition, the completely deprotonated μ₄‐η¹:η¹:η¹:η¹ bpt³⁻ ligands bridge one Cu^I and three Cu^II cations along the a (or [100]) direction to form a three‐dimensional framework with a (10³)₂(10)₂(4².6.10².12)₂(4².6.8².10)₂(8) topology via a 2,2,3,4,4‐connected net. An investigation of the magnetic properties indicated a very weak ferromagnetic behaviour.     

Facially Dispersed Polyhydride Cu9 and Cu16 Clusters Comprising Apex-Truncated Supertetrahedral and Square-Face-Capped Cuboctahedral Copper Frameworks

By using a linear tetraphosphine, meso-bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm), nona- and hexadecanuclear copper hydride clusters, [Cu₉H₇(μ-dpmppm)₃]X₂ (X=Cl ( 1 a ), Br ( 1 b ), I ( 1 c ), PF₆ ( 1 d )) and [Cu₁₆H₁₄(μ-dpmppm)₄]X₂ (X₂=I₂ ( 2 c ), (4/3) PF₆⋅(2/3) OH ( 2 d )) were synthesized and characterized. They form copper-hydride cages of apex-truncated supertetrahedral {Cu₉H₇}²⁺ and square-face-capped cuboctahedral {Cu₁₆H₁₄}²⁺ structures. The hydride positions were estimated by DFT calculations to be facially dispersed around the copper frameworks. A kinetically controlled synthesis gave an unsymmetrical Cu₈H₆ cluster, [Cu₈H₆(μ-dpmppm)₃]²⁺ ( 3 ), which readily reacted with CO₂ to afford linear Cu₄ complexes with formate bridges, leading to an unprecedented hydrogenation of CO₂ into formate catalyzed by {Cu₄(μ-dpmppm)₂} platform. The results demonstrate that new motifs of copper hydride clusters could be established by the tetraphosphine ligands, and the structures influence their reactivity.     

Synthesis and characterization of mononuclear copper(II) and dinuclear cadmium(II) complexes with di-(2-picolyl)sulfide

The reaction of CuCl₂ · 2H₂O and CdCl₂ with di-(2-picolyl)sulfide (dps) leads to the formation of mononuclear copper(II) and binuclear cadmium(II) complexes, [Cu(dps)Cl₂] · H₂O (1) and [(dps)(Cl)Cd^II(μ-Cl)₂Cd^II(Cl)(dps)] (2). The copper atom in (1) is coordinated to one sulfur and two nitrogen atoms from the dps ligand and two chlorides in a distorted square-pyramidal environment. Complex (2) has two distorted octahedra sharing the basal edge that contain the bridging chloro ligands, each of which resides at a center of inversion. Cyclic voltammetric data show that (1) undergoes two reversible one-electron waves corresponding to Cu^II/Cu^III and Cu^II/Cu^I processes. However, cyclic voltammetry of (2) gives two irreversible reduced waves.     

Visualizing Biological Copper Storage: The Importance of Thiolate-Coordinated Tetranuclear Clusters

Bacteria possess cytosolic proteins (Csp3s) capable of binding large quantities of copper and preventing toxicity. Crystal structures of a Csp3 plus increasing amounts of Cu^I provide atomic-level information about how a storage protein loads with metal ions. Many more sites are occupied than Cu^I equiv added, with binding by twelve central sites dominating. These can form [Cu₄(S-Cys)₄] intermediates leading to [Cu₄(S-Cys)₅]⁻, [Cu₄(S-Cys)₆]²⁻, and [Cu₄(S-Cys)₅(O-Asn)]⁻ clusters. Construction of the five Cu^I sites at the opening of the bundle lags behind the main core, and the two least accessible sites at the opposite end of the bundle are occupied last. Facile Cu^I cluster formation, reminiscent of that for inorganic complexes with organothiolate ligands, is largely avoided in biology but is used by proteins that store copper in the cytosol of prokaryotes and eukaryotes, where this reactivity is also key to toxicity.