Solvent-induced structural transformation from heptanuclear to decanuclear [Co–Ln] coordination clusters: trapping of unique counteranion and understanding of aggregation pathways

The MeCN solvent-induced transformations of heptanuclear LnIII3CoII2CoIII2⁺ cationic aggregates, associated with literature unknown Ln(iii)-pivalate-based counter anions, to decanuclear LnIII3CoII3/2CoIII4/5 clusters have been investigated.

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.

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

Treatment of a digold(I) metalloligand, [Au^I₂(dppe)(d-Hpen)₂] (H₂L^Au; 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: [Co^III₂(L^Au)₂]²⁺, [Ni^IICo^III(L^Au)₂]⁺, and [Ni^II₂(L^Au)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 [Co^III₂(L^Au)₂]²⁺ and [Ni^IICo^III(L^Au)₂]⁺ as a solid solution to form the charge-separation (CS)-type ionic crystals 1_Na, 1_M1, and 1_M2, respectively, while [Ni^II₂(L^Au)₂] independently crystallized as a single species (2). In 1_Na, [Co^III₂(L^Au)₂]²⁺ and [Ni^IICo^III(L^Au)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 1_M1 and 1_M2 are very similar to that of 1_Na, having a CS-type structure composed of cationic supramolecular octahedra with a +12 charge and anionic inorganic clusters with a -10 charge. However, 1_M1 contains M¹ ions in place of the H₃O⁺ ions in 1_Na, 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 1_M2.

Ring-to-Cage Structural Conversion via Template Effect in a Gold(I) Metallosupramolecular System

A unique example of a ring-to-cage structural conversion in a multinuclear gold(I) coordination system with d-penicillamine (d-H2 pen) is reported. The reaction of [Au2 Cl2 (dppe)] (dppe=1,2-bis(diphenylphosphino)ethane) with d-H2 pen in a 1:1 ratio gave [Au4 (dppe)2 (d-pen)2 ] ([1]), in which two [Au2 (dppe)]2+ units are linked by two d-pen S atoms in a cyclic form so as to have two bidentate-N,O coordination arms. The subsequent reaction of [1] with Cu(OTf)2 afforded [Au4 Cu(dppe)2 (d-pen)2 ]2+ ([2]2+ ), in which a CuII ion is chelated by the two coordination arms in [1] to form an AuI4 CuII bicyclic metallocage. A similar reaction using Cu(NO3 )2 was accompanied by the ring expansion of [1] to [Au8 (dppe)4 (d-pen)4 ], leading to the production of [Au8 Cu2 (dppe)4 (d-pen)4 ]4+ ([3]4+ ). In [3]4+ , two CuII ions are each chelated by the two coordination arms to form an AuI8 CuII2 tricyclic metallocage, accommodating a nitrate ion. The use of Ni(NO3 )2 or Ni(OAc)2 instead of Cu(NO3 )2 commonly gave a tricyclic metallocage of [Au8 Ni2 (dppe)4 (d-pen)4 ]4+ ([4]4+ ), but a water molecule was accommodated inside the AuI8 NiII2 metallocage.

Dielectric Jump and Negative Electrostriction in Metallosupramolecular Ionic Crystals

In natural ionic solids, cationic and anionic species are alternately arranged to minimize electrostatic energy. Aggregation of identical ionic species is commonly prohibited due to the repulsive, long-range nature of Coulombic interactions. Recently, we synthesized unique ionic solids, [Au^I₄Co^III₂(dppe)₂(d-pen)₄]X₂·nH₂O (dppe = 1,2-bis(diphenylphosphino)ethane, d-pen = d-penicillaminate), in which complex cations are self-assembled into a cationic supramolecular octahedron, while monovalent or divalent inorganic anions are aggregated into an anomalous anionic cluster accommodating several water molecules. This quite unusual aggregation manner originates from various molecular-level non-Coulombic interactions such as hydrogen bonds and CH-π interactions; thus, this class of ionic solids is referred to as non-Coulombic ionic solids, abbreviated as NCISs. Herein, we report that the NCISs with a peculiar charge-separated (CS) structure in a cubic lattice show a negative, isotropic electrostriction phenomenon that has never been found in any ionic solids, as well as an anomalously large relaxer-like dielectric jump phenomenon reaching to an application level of ε′/ε₀ ~ 10⁵. The appearance of these phenomena was explained by the cooperative dynamics of inorganic anions and dipolar water molecules in the pliable anionic clusters that are surrounded by a rather robust cationic metallosupramolecular framework with a meso-scopic scale.

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

The heterogeneous catalase-like activity of ionic crystals consisting of Au^I₄Co^III₂ complex cations is studied along with their surface morphologies and oxidation states.

Unique heterogeneous catalase-like activity was observed for metallosupramolecular ionic crystals [Au^I₄Co^III₂(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 SO₄^2–) consisting of Au^I₄Co^III₂ complex cations, [1]²⁺, and inorganic anions, X^– or X^2–. 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.

Proton-controlled formation and interconversion of AuI2NiII trinuclear and AuI4NiII3 heptanuclear complexes with mixed thiomalate and bis(diphenylphosphino)ethane

A unique coordination system with linear Au^I and octahedral Ni^II centers, in which two polynuclear structures with different nuclearities are independently formed and inter-converted in response to solution acidities, is reported.

Bis[μ-1,3-bis-(di-phenyl-phosphan-yl)propane-κ(2) P:P']digold(I) tetra-chloridonickelate(II) diethyl ether monosolvate

The title compound, [Au₂(C₂₇H₂₆P₂)₂][NiCl₄]·C₄H₁₀O, consists of a digold(I) complex cation, an [NiCl₄]²⁻ complex anion and a diethyl ether solvent mol­ecule. Two 1,3-bis­(di­phenyl­phosphan­yl)propane (dppp) ligands bridge two Au^I atoms, forming a metallacycle in which each of the Au^I atoms is coordinated in a slightly distorted linear environment by two P atoms. In the complex anion, the Ni^II atom is coordinated by four chloride ligands in a distorted tetra­hedral geometry. The complex cation and the complex anion form a cation–anion pair through two Au⋯Cl contacts of 3.040 (1) and 3.021 (2) Å. One of the phenyl groups of the dppp ligand is disordered over two positions with equal occupancies.