Chloride- and Hydrosulfide-Bound 2Fe Complexes as Models of the Oxygen-Stable State of [FeFe] Hydrogenase.

[FeFe] hydrogenases demonstrate remarkable catalytic efficiency in hydrogen evolution and oxidation processes. However, susceptibility of these enzymes to oxygen-induced degradation impedes their practical deployment in hydrogen-production devices and fuel cells. Recent investigations into the oxygen-stable (Hinact) state of the H-cluster revealed its inherent capacity to resist oxygen degradation. Herein, we present findings on Cl- and SH-bound [2Fe-2S] complexes, bearing relevance to the oxygen-stable state within a biological context. A characteristic attribute of these complexes is the terminal Cl-/SH- ligation to the iron center bearing the CO bridge. Structural analysis of the t-Cl demonstrates a striking resemblance to the Hinact state of DdHydAB and CbA5H. The t-Cl/t-SH exhibit reversible oxidation, with both redox species, electronically, being the first biomimetic analogs to the Htrans and Hinact states. These complexes exhibit notable resistance against oxygen-induced decomposition, supporting the potential oxygen-resistant nature of the Htrans and Hinact states. The swift reductive release of the Cl-/SH-group demonstrates its labile and kinetically controlled binding. The findings garnered from these investigations offer valuable insights into properties of the enzymatic O2-stable state, and key factors governing deactivation and reactivation conversion. This work contributes to the advancement of bio-inspired molecular catalysts and the integration of enzymes and artificial catalysts into H2-evolution devices and fuel-cell applications.

Unraveling the Structure-Property-Performance Relationships of Fused-Ring Nonfullerene Acceptors: Toward a C-Shaped ortho-Benzodipyrrole-Based Acceptor for Highly Efficient Organic Photovoltaics.

The high-performance Y6-based nonfullerene acceptors (NFAs) feature a C-shaped A-DA'D-A-type molecular architecture with a central electron-deficient thiadiazole (Tz) A' unit. In this work, we designed and synthesized a new A-D-A-type NFA, termed CB16, having a C-shaped ortho-benzodipyrrole-based skeleton of Y6 but with the Tz unit eliminated. When processed with nonhalogenated xylene without using any additives, the binary PM6:CB16 devices display a remarkable power conversion efficiency (PCE) of 18.32% with a high open-circuit voltage (Voc) of 0.92 V, surpassing the performance of the corresponding Y6-based devices. In contrast, similarly synthesized SB16, featuring an S-shaped para-benzodipyrrole-based skeleton, yields a low PCE of 0.15% due to the strong side-chain aggregation of SB16. The C-shaped A-DNBND-A skeleton in CB16 and the Y6-series NFAs constitutes the essential structural foundation for achieving exceptional device performance. The central Tz moiety or other A' units can be employed to finely adjust intermolecular interactions. The single-crystal X-ray structure reveals that ortho-benzodipyrrole-embedded A-DNBND-A plays an important role in the formation of a 3D elliptical network packing for efficient charge transport. Solution structures of the PM6:NFAs detected by small- and wide-angle X-ray scattering (SWAXS) indicate that removing the Tz unit in the C-shaped skeleton could reduce the self-packing of CB16, thereby enhancing the complexing and networking with PM6 in the spin-coating solution and the subsequent device film. Elucidating the structure-property-performance relationships of A-DA'D-A-type NFAs in this work paves the way for the future development of structurally simplified A-D-A-type NFAs.

Aggregation-induced emission enhancement (AIEE) of tetrarhenium(I) metallacycles and their application as luminescent sensors for nitroaromatics and antibiotics.

The self-assembly of tetrarhenium metallacycles [{Re(CO)3}2(µ-dhaq)(µ-N-N)]2 (3a, N-N = 1,3-bis(1-butylbenzimidazol-2-yl)benzene; 3b, N-N = 1,3-bis(1-octylbenzimidazol-2-yl)benzene), (H2-dhaq = 1,4-dihydroxy-9,10-anthraquinone) and [{Re(CO)3}2(µ-thaq)(µ-N-N)]2 (4, N-N = 1,3-bis(1-butylbenzimidazol-2-yl)benzene), (H2-thaq = 1,2,4-trihydroxy-9,10-anthraquinone) under solvothermal conditions is described. The metallacycles 3a,b and 4 underwent aggregation-induced emission enhancement (AIEE) in THF upon the incremental addition of water. TEM images revealed that metallacycle 3a in a 60% aqueous THF solution formed rectangular aggregates with a wide size distribution, while a 90% aqueous THF solution resulted in the formation of a mixture of nanorods and amorphous aggregates due to rapid and abrupt aggregation. UV-vis and emission spectral profiles supported the formation of nanoaggregates of metallacycles 3a,b and 4 upon the gradual addition of water to a THF solution containing metallacycles. Further studies indicated that these nanoaggregates were excellent probes for the sensitive and selective detection of nitro group containing picric acid (PA) derivatives as well as antibiotics.

Luminescent Pt(II) Complexes Containing (1-Aza-15-crown-5)dithiocarbamate and (1-Aza-18-crown-6)dithiocarbamate: Mechanochromic and Solvent-Induced Luminescence.

The strong tendency to stack in the solid state and rich luminescence for the Pt(II) complexes makes them potential candidates as new mechanochromic materials and sensing applications. Six mononuclear complexes [Pt(ppy)(O4NCS2)] (1), [Pt(bpy)(O4NCS2)]ClO4 (2), [Pt(ppy)(O5NCS2)] (3), [Pt(phen)(O4NCS2)]ClO4·CH3OH (5a), [Pt(phen)(O4NCS2)]ClO4 (5b), and [Pt(phen)(O5NCS2)]ClO4 (6a), one dinuclear complex [Pt2(phen)2(NaO5NCS2)2(ClO4)3]ClO4 (6b), and one one-dimensional (1-D) coordination polymer {[Pt2(bpy)2(NaO5NCS2)2(ClO4)2](ClO4)2}n (4) were synthesized by reacting [Pt(ppy)Cl]2, Pt(bpy)Cl2, and Pt(phen)Cl2 (ppy = 2-phenylpyridine, bpy = 2,2'-bipyridine, and phen = 1,10-phenanthroline) with (1-aza-15-crown-5)dithiocarbamate (O4NCS2) or (1-aza-18-crown-6)dithiocarbamate (O5NCS2), respectively, which have been isolated and structurally characterized by X-ray diffraction. Neutral complexes 1 and 3 contain no intermolecular Pt(II)···Pt(II) contact, whereas cationic complexes 2, 5a, 5b, and 6a with ClO4- as counteranions show alternative intermolecular Pt(II)···Pt(II) contacts of 3.535/4.091, 3.480/5.001, 3.527/4.571, and 3.446/4.987 Å in the solid state, respectively. Interestingly, complex 4 forms a 1-D coordination polymer through coordination between the encapsulated Na+ ions inside the azacrown ether rings of O5NCS2 and ClO4- anions with respective intra- and intermolecular Pt(II)···Pt(II) contacts of 3.402 and 3.847 Å in crystal lattices, whereas a dinuclear complex 6b was surprisingly formed and also connected by the encapsulated Na+ ions and ClO4- anions with alternative intra- and intermolecular Pt(II)···Pt(II) contacts of 3.650 and 3.677/4.4.372 Å, respectively. Upon excitation, complexes 1 and 3 showed similar vibronic luminescence at 507, 534, and 502, 532 nm, respectively, and the other complexes 2 and 4-6 showed broad luminescence with maxima at 537-567 nm. The B3LYP/LanL2DZ calculation was carried out and used to clarify their excited-state properties. In addition, the powder samples for complexes 1-4 almost showed no energy shift for the luminescence and significantly those of complexes 5-6 exhibited the mechanochromic luminescence upon grinding. It is noted that complexes 5a and 6a only showed minor red shifts (i.e., from 544 to 556 nm for complex 5a and from 551 to 565 nm for complex 6a), whereas complex 6b exhibited a remarkable red shift from 558 to 603 nm upon grinding. Besides, their luminescence reversibility was also examined toward various solvents.

A linear Di-coordinate boron radical cation.

The pursuit of di-coordinate boron radical has been continued for more than a half century, and their stabilization and structural characterization remains a challenge. Here we report the isolation and structural characterization of a linear di-coordinate boron radical cation, achieved by stabilizing the two reactive atomic orbitals of the central boron atom by two orthogonal π-donating and π-accepting functionalities. The electron deficient radical cation undergoes facile one-electron reduction to borylene and binds Lewis base to give heteroleptic tri-coordinate boron radical cation. The co-existence of half-filled and empty p orbitals at boron also allows the CO-regulated electron transfer to be explored. As the introduction of CO promotes the electron transfer from a tri-coordinate neutral boron radical to a boron radical cation, the removal of CO under vacuum furnishes the reverse electron transfer from borylene to yield a solution consisting of two boron radicals.

Stable Bimetallic FeII/{Fe(NO)2}9 Moiety Derived from Reductive Transformations of a Diferrous-dinitrosyl Species.

A dimeric dithiolate-bridged species, [Fe(NO)(PS2)]2 (1) containing two {FeNO}7 units, can be isolated by treating [Fe(CO)2(NO)2] with PS2H2 (PS2H2 = bis(2-dimercaptophenyl)phenylphosphine). Crystallographic studies reveal the syn-configuration of NO units and the bridging thiolates in the butterfly shape of the 2Fe2S core. Addition of PPh3 to the solution of dinuclear 1 leads to the formation of mononuclear {FeNO}7 [Fe(NO)(PS2)(PPh3)] (2) that shows electrochemical responses similar to those of 1. One-electron reduction of 1 with Cp*2Co or KC8 results in the isolation of thiolate-bridged bimetallic DNIC, [(PS2)Fe(µ-PS2)Fe(NO)2]- ([3]-), confirmed by several spectroscopies including single-crystal X-ray diffraction studies. The bimetallic DNIC [3]- is a rare example obtained from the one-electron reduction of a dinuclear Fe-NO {FeNO}7 model complex. With the assistance of redox behaviors of 2, electrochemical studies imply that the reduction of 1 leads to the formation of a mononuclear {FeNO}8 [Fe(NO)(PS2)(THF)]- intermediate, which involves disproportionation or NO- transfer to yield [3]-. Based on IR data and magnetic properties, the electronic structure of [3]- can be described as a FeII/{Fe(NO)2}9 state. Isolation of the {Fe(NO)2}9 moiety coordinated by the Fe ancillary complex lends strong support to the NO scrambling behavior in the effectiveness of the activity of flavodiiron nitric oxide reductases (FNORs).

Supramolecular assembly and structural transformation of d10-metal complexes containing (aza-15-crown-5)dithiocarbamate.

The reaction of potassium (aza-15-crown-5)dithiocarbamate (KO4NCS2) and (Me2S)AuCl gave the dinuclear complex [Au(O4NCS2)]2, which underwent structural transformation upon heating to rearrange into the hexanuclear complex [Au(O4NCS2)]6. Under similar reaction conditions, KO4NCS2 reacted with AgNO3 or [Cu(CH3CN)4]ClO4 to give the 1-D coordination polymer [Ag(O4NCS2)]n (1) and the tetranuclear complex [Cu(O4NCS2)]4 (2), respectively. It is noted that upon heating a similar structural transformation process occurs from tetranuclear complex 2 to the octanuclear complex [Cu(O4NCS2)]8 (2'), connected by a weak Cu⋯S contact of 2.846 Å, and it has been isolated and corroborated by powder and single-crystal X-ray diffraction studies as well. Moreover, a variety of MO4NCS2 salts (M = Li+, Na+, K+ and Rb+) were used to react with AgNO3 to construct a series of coordination architectures: [LiAg(O4NCS2)2(µ-H2O)0.5]2 (3), {Na[Ag(O4NCS2)2]}n (4), {K[Ag(O4NCS2)2]}n (5) and {Rb[Ag(O4NCS2)2]}n (6). The smallest Li+ ion only coordinates with four oxygen atoms from the same azacrown ether ring and one H2O molecule, leading to a 1-D hydrogen-bonded chain with another azacrown ether ring for complex 3. The larger Na+ ion coordinates with seven oxygen atoms from two different crown ether rings, leading to a 1-D chain for complex 4. However, the largest K+ and Rb+ ions constitute a 1-D framework, except that each metal ion coordinates with eight oxygen atoms from two different crown ether rings, featuring a 1-D helical chain for complexes 5 and 6. Hence, the different sizes of alkaline metal ions exert a dramatic effect on the structural motifs of complexes 3-6. Remarkably, the dithiocarbamate moieties adopt µ2-bridging ([Au(O4NCS2)]2 and [Au(O4NCS2)]6), µ3- and µ4-bridging (1-2) and chelate forms (3-6) in the structural backbones.

The straightforward synthesis of N-coordinated ruthenium 4-aryl-1,2,3-triazolato complexes by [3 + 2] cycloaddition reactions of a ruthenium azido complex with terminal phenylacetylenes and non-covalent aromatic interactions in structures.

The straightforward preparation of N-coordinated ruthenium triazolato complexes by [3 + 2] cycloaddition reactions of a ruthenium azido complex [Ru]-N3 (1, [Ru] = (η5-C5H5)(dppe)Ru, dppe = Ph2PCH2CH2PPh2) with a series of terminal phenylacetylenes is reported. The reaction products, N(2)-bound ruthenium 4-aryl-1,2,3-triazolato complexes such as [Ru]N3C2H(4-C6H4CN) (2), [Ru]N3C2H(4-C6H4CHO) (3), [Ru]N3C2H(4-C6H4F) (4), [Ru]N3C2H(Ph) (5) and [Ru]N3C2H(4-C6H4CH3) (6) were produced from 4-ethynylbenzonitrile, 4-ethynylbenzaldehyde, 1-ethynyl-4-fluorobenzene, phenylacetylene and 4-ethynyltoluene, respectively, at 80 °C or above under an atmosphere of air. To the best of our knowledge, this is the first example of the preparation of N-coordinated ruthenium aryl-substituted 1,2,3-triazolato complexes by the [3 + 2] cycloaddition of a metal-coordinated azido ligand and a terminal aryl acetylene, less electron-deficient terminal aryl alkynes. All of the compounds have been fully characterized and the structures of complexes 2, 3, 5 and 6 were confirmed by single-crystal X-ray diffraction analysis. Each compound participates in non-covalent aromatic interactions in the solid-state structure which can be favorable in the binding of DNA/biomolecular targets and has shown great potential in the development of biologically active anticancer drugs.

Surficial grafting of organoimido moieties enhances the capacity performance of oxometallic clusters.

Molybdenum trioxide (MoO3) with a theoretical specific capacity of 1117 mA h g-1 is widely considered a promising anode material for lithium-ion batteries. However, the irreversible conversion reactions, low electrical conductivity, and detrimental volume expansion upon Li intercalation between the one-dimensional layered structures of MoO3 hinder its practical implementation. Herein, we report a facile synthetic protocol that allows surficial modification by replacing the terminal and bridging oxo groups of molybdenum oxide clusters. Successful organoimido functionalization resulted in a large cathodic shift in Mo(VI/V) reduction by 0.6 V, pronounced electronic communication between the organic moiety and the metal-oxide unit, and significant increase in electrical conductivity (80-100 Ω interfacial charge-transfer resistance). Combined with the enlarged active surface area due to the structural hindrance induced by the organic functionality, the steady specific capacity of the organoimido-modified molybdenum oxide clusters was greater than 1200 mA h g-1 at 900 mA g-1 at the end of 360 cycles, where the best value of 1653 mA h g-1 was achieved for the nitroaniline-substituted species. The steady capacity of 480 mA h g-1 was achieved in the fast charge-discharge process (3000 mA g-1) over 1400 cycles. The results indicate that the surficial modification of metal oxides with organo moieties using our facile synthetic method has broad application potential for metal oxides to be used as high-capacity electrode materials in the future.

Stereoselective Cyclization Cascade of Dihydroquinoxalinones by Visible-Light Photocatalysis: Access to the Polycyclic Quinoxalin-2(1H)-ones.

An intriguing stereoselective visible-light photocatalysis of dihydroquinoxalinone derivatives has been realized via cyclization with or without the solvolysis cascade. The reactions provided the polycyclic ring structures with efficient formation of multiple bonds and with high stereoselectivity. X-ray crystallography unequivocally determined the structures of five polycyclic products.