Jahn-Teller Switching of a Redox-Active Nickel(III) Center in a Homoleptic Thiolato Metalloligand Environment.

Treatment of nickel(II) nitrate with the iridium(III) metalloligand fac-[Ir(apt)3] (apt = 3-aminopropanethiolate) gave the trinuclear complex [Ni{Ir(apt)3}2](NO3)3 ([1Ir](NO3)3), in which the nickel center has a formal oxidation state of +III. Chemical or electrochemical oxidation and reduction of [1Ir](NO3)3 generated the corresponding trinuclear complexes [Ni{Ir(apt)3}2](NO3)4 ([1Ir](NO3)4) and [Ni{Ir(apt)3}2](NO3)2 ([1Ir](NO3)2) with one-electron oxidated and reduced states, respectively. Single-crystal X-ray crystallography revealed that the nickel center in [1Ir](NO3)3 is situated in a highly distorted octahedron due to Jahn-Teller effect, while the nickel center in each of [1Ir](NO3)4 and [1Ir](NO3)2 adopts a normal octahedral geometry. Crystals of [1Ir](NO3)3·2H2O are dehydrated on heating while retaining their single-crystallinity. The dehydration induces temperature-dependent dynamic disorder of the Jahn-Teller distortion at the nickel(III) center, which is largely quenched upon rehydration of the crystal.

Serendipitous formation of oxygen-bridged CuII6M (M = MnII, CoII) double cubanes showing electrocatalytic water oxidation.

Hydroxido-bridged CuII6M double-cubane clusters (M = MnII, CoII) supported by D-penicillaminedisulfide were unexpectedly formed by treating a D-penicillaminato CuII2PtII2 complex with MBr2 in water. The clusters displayed heterogeneous electrocatalytic activities for water oxidation dependent on the central M shared by two CuII cubane units.

A chromotropic PtIIPdIICoII coordination polymer with dual electrocatalytic activity for water reduction and oxidation.

Here, we present a heterometallic coordination polymer that exhibits heterogeneous electrocatalytic activities for both water reduction and water oxidation. Treatment of the PtII2PdII2 tetranuclear complex [Pd2{Pt(NH3)2(D-pen)2}2] ([1]; D-H2pen = D-penicillamine) with CoX2 (X = Cl, Br) provided (PtII2PdII2CoII2)n coordination polymers [Co2(H2O)6(1)]X4 ([2]X4), in which the PtII2PdII2 units of [1] are linked by [Co2(µ-H2O)(H2O)5]4+ moieties in a 3D network structure. [2]X4 showed a colour change from orange to dark green upon dehydration, reflecting the geometrical conversion of the CoII centres in [Co2(µ-H2O)(H2O)5]4+ from an octahedron to a tetrahedron by the removal of aqua ligands. While both [2]Cl4 and [2]Br4 electrochemically catalysed water reduction to H2 in the solid state due to the presence of PdII active centres, water oxidation to O2 was catalysed only by [2]Br4, which is ascribed to the presence of Br- ions that mediate the catalytic reactions that occurred at CoII active centres.

Highly Porous Ionic Solids Consisting of AuI3CoIII2 Complex Anions and Aqua Metal Cations.

Treatment of Na3[Au3Co2(d-pen)6] (Na3[1]; d-H2pen = d-penicillamine) with M(OAc)2 (M = NiII, MnII) in water gave ionic crystals of [M(H2O)6]3[1]2 (2M) in which [1]3- anions are hydrogen-bonded with [M(H2O)6]2+ cations to form a 3D porous framework with a porosity of ca. 80%. Soaking crystals of 2Ni in its mother liquor afforded crystals of [Ni(H2O)6]2[{Ni(H2O)4}(1)2] (3Ni) in which [1]3- anions are connected to trans-[Ni(H2O)4]2+ and [Ni(H2O)6]2+ cations through coordination and hydrogen bonds, respectively, to form a 1D porous framework with a porosity ca. 60%. Further soaking crystals led to [{Ni(H2O)4}3(1)2] (4Ni), in which [1]3- anions are connected to cis-[Ni(H2O)4]2+ and trans-[Ni(H2O)4]2+ cations through coordination bonds in a dense framework with a porosity of ca. 30%. A similar two-step crystal-to-crystal transformation mediated by solvent proceeded when crystals of 2Mn were soaked in a mother liquor. However, the transformation of 2Mn generated [{Mn(H2O)4}(H1)] (4'Mn) as the final product, in which [H1]2- anions are connected to cis-[Mn(H2O)4]2+ cations through coordination bonds in a very dense framework with a porosity ca. 5% by way of [Mn(H2O)6]2[{Mn(H2O)4}(1)2] (3Mn), which is isostructural with 3Ni. While all the compounds adsorbed H2O and CO2 depending on the degree of their porosity, unusually large NH3 adsorption capacities were observed for 4Ni and 4'Mn, which have dense frameworks.

A Pseudorotaxane System Containing γ-Cyclodextrin Formed via Chiral Recognition with an AuI 6 AgI 3 CuII 3 Molecular Cap.

Solvent-mediated crystal-to-crystal transformations of [Au6 Ag3 Cu3 (H2 O)3 (d-pen)6 (tdme)2 ]3+ (d-[1(H2 O)3 ]3+ ; pen2- =penicillaminate, tdme=1,1,1-tris(diphenylphosphinomethyl)ethane) to form unique supramolecular species are reported. Soaking crystals of d-[1(H2 O)3 ]3+ in aqueous Na2 bdc (bdc2- =1,4-benzenedicarboxylate) yielded crystals containing d-[1(bdc)(H2 O)2 ]+ due to the replacement of a terminal aqua ligand in d-[1(H2 O)3 ]3+ by a monodentate bdc2- ligand. When γ-cyclodextrin (γ-CD) was added to aqueous Na2 bdc, d-[1(H2 O)3 ]3+ was transformed to d-[1(bdc@γ-CD)(H2 O)2 ]+ , where a γ-CD ring was threaded by a bdc2- molecule to construct a pseudorotaxane structure. While the use of dicarboxylates with an aliphatic carbon chain instead of bdc2- afforded analogous pseudorotaxanes, such pseudorotaxane species were not formed when crystals of [Au6 Ag3 Cu3 (H2 O)3 (l-pen)6 (tdme)2 ]3+ (l-[1(H2 O)3 ]3+ ) enantiomeric to d-[1(H2 O)3 ]3+ were soaked in aqueous Na2 bdc and γ-CD, affording only crystals containing l-[1(bdc)(H2 O)2 ]+ .

Racemic Tartrate/Malate Anions Combine with Racemic Complex Cations to Form Optically Active Ionic Crystals.

Spontaneous resolution has attracted continuing attention in various research fields since Pasteur's work on the crystallization behavior of racemic tartrate. Here, a unique example of this phenomenon is reported, involving ionic crystals generated from racemic RR/SS- tartrate or R/S-malate and racemic ΔΔ/ΛΛ-[Ag3 Rh2 (2-aminoethanethiolato)6 ]3+ (ΔΔ/ΛΛ-[1]3+ ) in water. RR- and SS-tartrate selectively recognize the ΛΛ and ΔΔ isomers of [1]3+ to produce ionic crystals of (ΛΛ-[1])2 (RR-tartrate)3 and (ΔΔ-[1])2 (SS-tartrate)3 , respectively, which can undergo spontaneous resolution. While spontaneous resolution also occurs when using R/S-malate, R- and S-malate select the opposite isomers of [1]3+ to give ionic crystals of (ΔΔ-[1])2 (R-malate)3 and (ΛΛ-[1])2 (S-malate)3 , respectively. In the presence of S-aspartate, (ΛΛ-[1])2 (R-tartrate)3 and (ΔΔ-[1])2 (S-tartrate)3 are preferentially crystallized from ΔΔ/ΛΛ-[1]3+ and RR/SS-tartrate at solution pH values of 6 and 10, respectively. This finding provides significant insight into the optical resolution of chemical species by spontaneous resolution and the origin of homochirality in nature.

Interconversion between square-planar palladium(ii) and octahedral palladium(iv) centres in a sulfur-bridged trinuclear structure.

Treatment of fac-[Rh(apt)3] (apt = 3-aminopropanethiolate) with Pd2+ gives an S-bridged trinuclear complex, [Pd{Rh(apt)3}2]4+ ([1]4+), which is interconvertible with [Pd{Rh(apt)3}2]2+ ([2]2+). This interconversion is accompanied by a drastic change between the PdIV centre with an S6 octahedral geometry in [1]4+ and the PdII centre with an S4 square-planar geometry in [2]2+.

Dimensional Structures and Electrocatalytic Activities of Platinum(II)-Palladium(II)-Manganese(II) Coordination Polymers Controlled by Chloride versus Bromide.

Here we report the synthesis and structural characterization of heterotrimetallic (PtII2PdII2MnII2)n coordination polymers that show different dimensionalities and electrocatalytic activities depending on chloride and bromide employed in the system. The reaction of the PtII2PdII2 tetranuclear complex [Pd2Pt2(NH3)4(d-pen)4] (1), bearing free carboxylate groups, with Mn2+ in the presence of chloride produced the (PtII2PdII2MnII2)n coordination polymer [Mn2Cl2(H2O)6(1)]Cl2 (2Cl), in which the PtII2PdII2 units of 1 are linked by [MnCl(H2O)3]+ moieties in a 1:2 ratio to form a 2D sheetlike structure. The corresponding reaction in the presence of bromide also gave the (PtII2PdII2MnII2)n coordination polymer [Mn2(H2O)6(1)]Br4 (3Br), but 3Br adopted a 3D network structure via a 1:1 linkage of the PtII2PdII2 units with [Mn2(H2O)6]4+ moieties. These complexes showed appreciably different electrocatalytic activities for H2 evolution.

Charge-Separation-Type Ionic Crystals with Mixed AuI4CoIII2 and AuI4NiIICoIII Hexanuclear Complexes.

Treatment of a digold(I) metalloligand, [AuI2(dppe)(d-Hpen)2] (H2LAu; d-H2pen = d-penicillamine, dppe = 1,2-bis(diphenylphosphino)ethane), with a 1:1 mixture of Co(OAc)2 and Ni(OAc)2 under aerobic conditions resulted in the formation of three types of hexanuclear complexes: [CoIII2(LAu)2]2+, [NiIICoIII(LAu)2]+, and [NiII2(LAu)2]. The addition of NaNO3, M1NO3 (M1 = K, Rb, Cs), and M2(NO3)2 (M2 = Ca, Sr, Ba) to the reaction mixture led to co-crystallization of [CoIII2(LAu)2]2+ and [NiIICoIII(LAu)2]+ as a solid solution to form the charge-separation (CS)-type ionic crystals 1Na, 1M1, and 1M2, respectively, while [NiII2(LAu)2] independently crystallized as a single species (2). In 1Na, [CoIII2(LAu)2]2+ and [NiIICoIII(LAu)2]+ cations assemble in a 1:2 ratio to form a cationic supramolecular octahedron accommodating 4 H3O+ ions, while 10 nitrate ions are packed in each hydrophilic tetrahedral interstice of the crystal to form an anionic adamantane cluster. The overall structures of 1M1 and 1M2 are very similar to that of 1Na, having a CS-type structure composed of cationic supramolecular octahedra with a +12 charge and anionic inorganic clusters with a -10 charge. However, 1M1 contains M1 ions in place of the H3O+ ions in 1Na, and furthermore, a novel rhombic dodecahedron cluster composed of 14 nitrate ions, which encapsulates two M2 ions, is formed in each hydrophilic tetrahedral interstice in 1M2.

Heterochiral-to-Homochiral Structural Transformation in Metallosupramolecular Ionic Crystals.

Here, we report a unique transformation from heterochiral to homochiral structures in ionic crystals composed of complex cations and complex anions. Treatment of an anionic AuI3CoIII2 complex, ΛΛ-[Au3Co2(d-pen)6]3- ([1]3-; H2pen = penicillamine), with M = MnII, CoII, NiII, ZnII in water in the presence of 1,10-phenanthroline (phen) commonly gave ionic crystals formulated as [M(phen)2(H2O)2][Na(H2O)6][{M(phen)2(H2O)}(1)]3 (2M), in which [M(phen)2(H2O)2]2+ and [M(phen)2(H2O)]2+ adopt Δ and Λ configurations, respectively. While 2Co, 2Ni, and 2Zn were all stable in each mother liquor, 2Mn was converted to [Mn(phen)3]3[1]2·phen (3Mn) containing the Λ configurational [Mn(phen)3]3+ under the same conditions. 3Mn showed a water adsorption capacity higher than that of 2Mn, despite its lower porosity of crystal.

Self-assembly of cyclic hexamers of γ-cyclodextrin in a metallosupramolecular framework with d-penicillamine.

Cyclodextrins are widely used cyclic oligosaccharides of d-glucose whose hydrophilic exterior is covered by hydroxyl groups and whose hydrophobic interior is surrounded by lipophilic moieties. Because of this structural feature, cyclodextrin molecules commonly aggregate into dimensional structures via intermolecular hydrogen bonds, and their aggregation into closed oligomeric architectures has been achieved only via the attachment of functional substituent groups to the cyclodextrin rings. Here, we report the first structurally characterized self-assembly of non-substituted γ-cyclodextrin molecules into cyclic hexamers, which was realized in a chiral coordination framework composed of complex-anions with d-penicillamine rather than l- or dl-penicillamine. The self-assembly is accompanied by the 3D-to-2D structural transformation of porous coordination frameworks to form helical hexagonal cavities that accommodate helical γ-cyclodextrin hexamers. This finding provides new insight into the development of cyclodextrin chemistry and host-guest chemistry based on chiral recognition and crystal engineering processes.

Influence of catalyst nuclearity on copper-catalyzed aerobic alcohol oxidation.

Reactions of CuX with the bis(triazolyl) ligand Hbtm [bis(1-benzyl-1H-1,2,3-triazol-4-yl)phenylmethanol] in CH2Cl2 afforded trinuclear copper(ii) complexes with a core structure (µ-X)Cu3(µ-κ3-N,O,N-btm)3(L)2+ [X = Cl, L = CH3OH (1); X = Br, L = H2O (2)], while a similar reaction of [Cu(CH3CN)4](PF6) with the mono(triazolyl) ligand HPhtm [(1-benzyl-1H-1,2,3-triazol-4-yl)diphenylmethanol] resulted in the mononuclear complex [Cu(κ2-N,O-Phtm)(κ2-N,O-HPhtm)(κ1-N-HPhtm)][PF6] (3). The structural characterization of these complexes was made by single-crystal X-ray crystallography in combination with elemental and ESI mass analyses. Catalytic studies toward aerobic oxidation of benzyl alcohol to benzaldehyde revealed that the trinuclear 1 and 2 exhibited higher activities than the mononuclear 3 in both CH3CN and EtOH/H2O solvent systems.

Controlled Formation of Thiol-Thiolate Hydrogen versus Disulfide Bonds between Two Iridium(III) Centers.

Here, we report an iridium(III) coordination system with 2-aminoethanethiolate (aet), which shows the formation of S-H⋅⋅⋅S hydrogen and S-S disulfide bonds in a controlled manner. Treatment of fac-[Ir(aet)3 ] with aqueous HBF4 under aerobic conditions gave dinuclear [Ir2 (aet)4 (cysta)]2+ ([1]2+ ; cysta=cystamine) with a single S-S disulfide bond, while dimeric [Ir2 (aet)3 (Haet)3 ](BF4 )3 ([2](BF4 )3 ) with a triple S-H⋅⋅⋅S hydrogen bond was formed by similar treatment under anaerobic conditions. Upon exposure to air, [2]3+ was converted to dinuclear [Ir2 (aet)2 (Haet)2 (cysta)]4+ ([3]4+ ), in which two IrIII centers are spanned by a double S-H⋅⋅⋅S hydrogen bond and a single S-S disulfide bond. Complex [3]4+ was interconvertible with [1]2+ via the removal/addition of protons on S donors, accompanied by the intermolecular exchange of the fac-[Ir(aet)3 ] units. Complexes [1]2+ , [2]3+ , and [3]4+ , isolated as BF4 - salts, were fully characterized by single-crystal X-ray crystallography.

Complex Phase Behaviour and Structural Transformations of Metal-Organic Frameworks with Mixed Rigid and Flexible Bridging Ligands.

Two new heteroleptic metal-organic framework materials show strong adsorption of H2 and ethanol. [Co2 (L1)(bdc)2 ], where L1=N1 ,N4 -bis(4-pyridinylmethyl)-2,5-dimethylbenzene-1,4-diamine and bdc is benzene-1,4-dicarboxylate, has a twofold interpenetrating pillared layer structure with pcu topology. It has a stepped, hysteretic EtOH adsorption that can be related to complicated phase and structural transformation behaviour that occurs on de-solvation and re-solvation, including major conformational changes to the geometry of the flexible L1 ligand. [Co2 (L1)(bpdc)2 ], where bpdc=biphenyl-4,4'-dicarboxylate, has a unique six-connected self-catenating framework structure. Solvation changes occur without significant structural change and a partially-hydrolysed material binds its own decomposition products as guests.

Heterogeneous catalytic water oxidation controlled by coordination geometries of copper(ii) centers with thiolato donors.

Treatment of a penicillaminato platinum(ii) metalloligand with Cu2+ gave an S-bridged PtII2CuII2 complex, which reacted with Zn2+ to produce 1D and 3D (PtII2CuII2ZnII)n coordination polymers, depending on the counter anions. These compounds increased heterogeneous electrocatalytic activities for water oxidation in proportion to the number of vacant coordination sites at thiolato dicopper(ii) cores.

A stable thiolato-CuI-thiolato triple linkage that bridges two cobalt(iii) centres.

Treatment of Λ-fac-[Co(d-pen-N,S)3]3- (d-H2pen = d-penicillamine) with Cu+ in water gave a stable CoCu complex, ΛΛ-[Co2Cu3(d-pen)6]3- ([1]3-), having three thiolato-copper(i)-thiolato moieties that bridge two cobalt(iii) centres. Complex [1]3- was isolated as a coordination polymer of Na3[1], which was converted to a complex salt of [Cr(H2O)6][1] by treatment with Cr(NO3)3.

Creation of Optically Pure Crystals from a Meso-Type Gold(I) Metalloligand with d- and l-Amino Acids: A Coordination Trick.

A unique example of a coordination system that creates optically pure crystals from a meso compound with d- and l-amino acids is reported. The 1:1 reaction of a newly prepared meso digold(I) complex, [Au2 (dcpe)(d-Hpen)(l-Hpen)] ([H2 1]), with Co(OAc)2 under aerobic conditions yielded a cationic AuI2 CoIII trinuclear complex, [Au2 Co(dcpe)(d-pen)(l-pen)]+ [2]+ , in which [1]2- acts as a hexadentate-N2 ,O2 ,S2 metalloligand to a CoIII center. Similar reactions with M(OAc)2 (M=Ni and Zn) produced analogous but neutral AuI2 MII complexes, [Au2 M(dcpe)(d-pen)(l-pen)] ([3M ]). Complexes [2]+ and [3M ] are chiral (C vs. A) at the octahedral CoIII and MII centers due to the arrangement of the N2 ,O2 ,S2 donor set. In addition, through spontaneous resolution, [3M ] gave optically pure C-[3M ] and A-[3M ] crystals, showing the creation of homochirality from meso-[1]2- and achiral M2+ through crystallization. Such a phenomenon was not observed for [2]+ , which gave a racemic compound containing both C-[2]+ and A-[2]+ .

Valence Interconversion of Octahedral Nickel(II/III/IV) Centers.

Three oxidation states (+2, +3, +4) of an octahedral nickel center were stabilized in a newly prepared RhNiRh trinuclear complex, [Ni{Rh(apt)3 }2 ]n+ (apt=3- aminopropanethiolate), in which the nickel center was bound by six thiolato donors sourced from two redox-inert fac-[RhIII (apt)3 ] octahedral units. The three oxidation states of the octahedral nickel center were fully characterized by single-crystal X-ray crystallography, as well as spectroscopic, electrochemical, and magnetic measurements; all three were interconvertible, and the conversion was accompanied by changes in color, magnetism, and Jahn-Teller distortion.

Heterogeneous catalase-like activity of gold(i)-cobalt(iii) metallosupramolecular ionic crystals.

Unique heterogeneous catalase-like activity was observed for metallosupramolecular ionic crystals [AuI4CoIII2(dppe)2(d-pen)4]X n ([1]X n ; dppe = 1,2-bis(diphenylphosphino)ethane; d-pen = d-penicillaminate; X n = (Cl-)2, (ClO4-)2, (NO3-)2 or SO42-) consisting of AuI4CoIII2 complex cations, [1]2+, and inorganic anions, X- or X2-. Treatment of the ionic crystals with an aqueous H2O2 solution led to considerable O2 evolution with a high turnover frequency of 1.4 × 105 h-1 for the heterogeneous cobalt complexes, which was dependent on their size and shape as well as the arrangement of cationic and anionic species. These dependencies were rationalized by the presence of cobalt(ii) centers on the crystal surface and their efficient exposure on the (111) plane rather than the (100) plane based on morphological and theoretical studies.

A platinum(ii)-palladium(ii)-nickel(ii) heterotrimetallic coordination polymer showing a cooperative effect on catalytic hydrogen evolution.

Stepwise construction of a 1D heterotrimetallic coordination polymer containing all three group 10 metal ions via an ammineplatinum(ii) metalloligand with d-penicillamine is reported. This system showed a significant enhancement in heterogeneous catalytic activity for electrochemical hydrogen evolution by the stepwise introduction of PdII and NiII into the PtII metalloligand.