Paddlewheel‐Type Dirhodium Tetrapivalate Based Coordination Polymer: Synthesis, Characterization, and Self‐Assembly and Disassembly Transformation Properties

Lead(II)-Based Coordination Polymer Exhibiting Reversible Color Switching and Selective CO2 Photoreduction Properties

Herein, we report a new photofunctional Pb-S-based coordination polymer (CP) with the formula [Pb(ATAT)(OAc)]n (ATAT = 3-amino-5-mercapto-1,2,4-triazole, OAc = acetate, CP1). Apart from its photoactive one-dimensional (1D) (-Pb-S-)n chain, CP1 is also composed of another 1D (-Pb-O-)n chain that originates from the coordination with acetate. The coordinated acetate can be exchanged with water (H2O) or dimethyl sulfoxide (DMSO), leading to the formation of a CP1-H2O or CP1-DMSO structure that exhibits a distinct change in optical properties, including a white-to-yellow color change. The structural transformation of CP1 to CP1-H2O and CP1-DMSO, and its subsequent recovery to the original CP1 structure could be controlled by the presence or absence of acetic acid vapor; the transformation was completely reversible. CP1 absorbed light with wavelengths shorter than 390 nm, with an estimated bandgap of 3.18 eV. Density functional theory calculations indicated that the valence band of CP1 is mainly formed by N and S orbitals originating from the ATAT unit, whereas the conduction band is composed of the Pb orbitals. Even without any modification, such as the incorporation of a molecular catalyst, CP1 reduced CO2 into formate under UV light with >99% selectivity.

Complexation in situ of 1-methylpiperidine, 1,2-dimethylpyrrolidin, and 1,2-dimethylpiperidine with rhodium(II) tetracarboxylates: Nuclear magnetic resonance spectroscopy, chiral recognition, and density functional theory studies

Complexation in situ of 1-methylpiperidine, racemic 1,2-dimethylpyrrolidin, and racemic 1,2-dimethylpiperidine with rhodium(II) tetracarboxylates in chloroform was studied by ¹ H and ¹³ C nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) methods. As substrates, three dirhodium(II) compounds were applied, tetraacetate, tetrakistrifluoroacetate, and a derivative of optically pure Mosher's acid. Due to conformational flexibility, free and complexed ligands can adopt potentially various conformations. The NMR titration experiments revealed the subsequent formation of 1:1 and 1:2 complexes, depending on the molar ratio of substrate to ligand. Conformations of free and complexed ligands were examined by the comparison of experimental and DFT gauge-independent atomic orbital (GIAO) calculated chemical shifts and by the analysis of the internal energy of the compounds. For some ligand and substrate combinations, a mixture of complexes differing in ligand conformations was formed. Complexes of Mosher's acid derivative of rhodium(II) with racemic 1,2-dimethylpyrrolidin and 1,2-dimethylpiperidine exhibited NMR chiral recognition phenomenon, manifested by splitting of signals in ¹³ C NMR and ¹ H,¹³ C HSQC spectra.

Heteronuclear Dirhodium-Gold Anionic Complexes: Polymeric Chains and Discrete Units

In this article, we report on the synthesis and characterization of the tetracarboxylatodirhodium(II) complexes [Rh2(μ-O2CCH2OMe)4(THF)2] (1) and [Rh2(μ-O2CC6H4-p-CMe3)4(OH2)2] (2) by metathesis reaction of [Rh2(μ-O2CMe)4] with the corresponding ligand acting also as the reaction solvent. The reaction of the corresponding tetracarboxylato precursor, [Rh2(μ-O2CR)4], with PPh4[Au(CN)2] at room temperature, yielded the one-dimensional polymers (PPh4)n[Rh2(μ-O2CR)4Au(CN)2]n (R = Me (3), CH2OMe (4), CH2OEt (5)) and the non-polymeric compounds (PPh4)2{Rh2(μ-O2CR)4[Au(CN)2]2} (R = CMe3 (6), C6H4-p-CMe3 (7)). The structural characterization of 1, 3·2CH2Cl2, 4·3CH2Cl2, 5, 6, and 7·2OCMe2 is also provided with a detailed description of their crystal structures and intermolecular interactions. The polymeric compounds 3·2CH2Cl2, 4·3CH2Cl2, and 5 show wavy chains with Rh-Au-Rh and Rh-N-C angles in the ranges 177.18°-178.69° and 163.0°-170.4°, respectively. A comparative study with related rhodium-silver complexes previously reported indicates no significant influence of the gold or silver atoms in the solid-state arrangement of these kinds of complexes.

Dirhodium Coordination Polymers for Asymmetric Cyclopropanation of Diazooxindoles with Olefins: Synthesis and Spectroscopic Analysis

A facile approach is reported for the preparation of dirhodium coordination polymers [Rh₂ (L1)₂ ]_n (Rh₂ -L1) and [Rh₂ (L2)₂ ]_n (Rh₂ -L2; L1=N,N'-(pyromellitoyl)-bis-L-phenylalanine diacid anion, L2=bis-N,N'-(L-phenylalanyl) naphthalene-1,4,5,8-tetracarboxylate diimide) from chiral dicarboxylic acids by ligand exchange. Multiple techniques including FTIR, XPS, and ¹ H→¹³ C CP MAS NMR spectroscopy reveal the formation of the coordination polymers. ¹⁹ F MAS NMR was utilized to investigate the remaining TFA groups in the obtained coordination polymers, and demonstrated near-quantitative ligand exchange. DR-UV-vis and XPS confirm the oxidation state of the Rh center and that the Rh-single bond in the dirhodium node is maintained in the synthesis of Rh₂ -L1 and Rh₂ -L2. Both coordination polymers exhibit excellent catalytic performance in the asymmetric cyclopropanation reaction between styrene and diazooxindole. The catalysts can be easily recycled and reused without significant reduction in their catalytic efficiency.

Coordination-Induced Self-Assembly of a Heteroleptic Paddlewheel-Type Dirhodium Complex

A novel heteroleptic paddlewheel-type dirhodium (Rh2) complex [Rh2(O2CCH3)3(PABC)] (1; PABC = para-aminobenzenecarboxylate), which has an amino group as a potential donor site for coordination with the metal ion, was synthesized and characterized by 1H NMR, ESI-TOF-MS, infrared spectra, and elemental analysis. The slow evaporation of N,N-dimethylformamide (DMF)-dissolved 1 produces the purple-colored crystalline polymeric species [Rh2(O2CCH3)3 (PABC)(DMF)]n (1P). Single-crystal and powder X-ray diffraction analyses, as well as thermo-gravimetric analysis, clarified that 1P formed a one-dimensional polymeric structure, in which the two axial sites of the Rh2 ion in 1P are coordinated by a DMF molecule and an amino group of the PABC ligand of the neighboring molecule 1, by coordination-induced self-assembly (polymerization) with an Rh-amino bond. The reversible structural change (self-assembly and disassembly transformations) between the discrete species [Rh2(O2CCH3)3(PABC)(DMF)2] (1D; green solution) and the polymeric species 1P (purple solid) was accompanied by a color change, which easily occurred by the dissolution and evaporation procedures with DMF.

Linear One-Dimensional Coordination Polymers Constructed by Dirhodium Paddlewheel and Tetracyanido-Metallate Building Blocks

In this article, we describe the preparation of anionic heteronuclear one-dimensional coordination polymers made by dirhodium paddlewheels and tetracyanido-metallatate building blocks. A series of complexes of (PPh4)2n[{Rh2(µ-O2CCH3)4}{M(CN)4}]n (M = Ni (1), Pd (2), Pt (3)) formulae were obtained by reaction of [Rh2(μ-O2CCH3)4] with (PPh4)2[M(CN)4] in a 1:1 or 2:1 ratio. Crystals of 1−3 suitable for single crystal X-ray diffraction were grown by slow diffusion of a dichloromethane solution of the dirhodium complex into a chloroform solution of the corresponding tetracyanido–metallatate salt. Compounds 1 and 2 are isostructural and crystallize in the triclinic P-1 space group, while compound 3 crystallizes in the monoclinic P21/n space group. A detailed description of the structures is presented, including the analysis of the packing of anionic chains and PPh4+ cations.

Synthesis, Characterization, Absorption Properties, and Electronic Structures of Paddlewheel-Type Dirhodium(II) Tetra-μ-(n-naphthoate) Complexes: An Experimental and Theoretical Study

The reactions of [Rh₂(O₂CCH₃)₄(OH₂)₂] with n-naphthalenecarboxylic acids (n = 1: 1-HNC, n = 2: 2-HNC) afford the dirhodium tetra-μ-(n-naphthoate) complexes [Rh₂(1-NC)₄] (1) and [Rh₂(2-NC)₄] (2), respectively. Single crystal X-ray diffraction analyses of [1(OCMe₂)₂] and [2(OCMe₂)₂], which were obtained by recrystallization from acetone (OCMe₂) solutions of 1 and 2, reveal that the dirhodium cores are coordinated by four equatorially bridging naphthoate ligands and two axial OCMe₂ ligands. Density functional theory (DFT) calculation confirmed that (i) the single Rh⁻Rh bond is formed between the two Rh ions and (ii) the electronic structures between two Rh ions in [1(OCMe₂)₂] and [2(OCMe₂)₂] are best described as π⁴δ²σ²δ*²π*⁴ and δ²π⁴σ²δ*²π*⁴, respectively. Time-dependent DFT (TDDFT) calculations clarify the absorption band characters of [1(OCMe₂)₂] and [2(OCMe₂)₂]; the former shows the bands due to d⁻d and metal⁻to⁻metal-ligand charge transfer (MMLCT) excitations in the visible light region, whereas the latter shows the bands due to only d⁻d excitations in the same region. The electrochemical properties and thermal stabilities of [1(OCMe₂)₂] and [2(OCMe₂)₂] were also investigated in this study.

Synthesis and Structural Characterization of a Series of One-Dimensional Heteronuclear Dirhodium-Silver Coordination Polymers

Herein, we describe the preparation of heteronuclear dirhodium-silver complexes by reaction between molecular Rh(II)-Rh(II) compounds [Rh₂(μ-O₂CR)₄L₂] (R = Me, Ph (1), CH₂OEt (2); L = solvent molecules) with paddlewheel structure and PPh₄[Ag(CN)₂]. One-dimensional coordination polymers of (PPh₄)n[Rh₂(μ-O₂CR)₄Ag(CN)₂]n (R = Me (3), Ph (4), CH₂OEt (5)) formula have been obtained by replacement of the two labile molecules in the axial positions of the paddlewheel structures by a [Ag(CN)₂]- bridging unit. The crystal structures of 3⁻5 display a similar arrangement, having anionic chains with a wavy structure and bulky (PPh₄)⁺ cations placed between the chains. The presence of the (PPh₄)⁺ cations hinders the existence of intermolecular Ag-Ag interactions although several C-H····π interactions have been observed. A similar reaction between [Rh₂(μ-O₂CCMe₃)₄(HO₂CCMe₃)₂] and PPh₄[Ag(CN)₂] led to the molecular compound (PPh₄)₂{Rh₂(μ-O₂CCMe₃)₄[Ag(CN)₂]₂} (6) by replacement of the axial HO₂CCMe₃ ligands by two [Ag(CN)₂]- units. The trimethylacetate ligand increases the solubility of the complex during the crystallization favouring the formation of discrete heteronuclear species.

Reversible transformation between Cu(i)-thiophenolate coordination polymers displaying luminescence and electrical properties

The direct self-assembly between CuI with thiophenol produces two different 1D coordination polymers (CPs) with multifunctional properties; the ratio CuI in acetonitrile is the key factor determining the reversible conversion between both CPs.

Experimental and theoretical study of dimer-of-dimers-type tetrarhodium(ii) complexes bridged by 1,4-benzenedicarboxylate linkers

Two dimer-of-dimers-type tetrarhodium complexes, [Rh4(piv)6(BDC)] ([1]; piv = pivalate) and [Rh4(piv)6(F4BDC)] ([2]), in which two paddlewheel-type dirhodium units are linked by 1,4-benzenedicarboxylate (BDC) and 1,4-tetrafluorobenzenedicarboxylate (F4BDC), respectively, have been synthesized and characterized via single-crystal X-ray diffraction analyses, ESI-MS, 1H NMR, infrared spectroscopy, Raman spectroscopy, and elemental analyses. Crystal structure analyses of [1(THF)4] and [2(THF)4], which are crystallized from THF solutions of [1] and [2], respectively, revealed that dihedral angles (φ) between two -CO2 units and phenyl rings of the BDC linker in [1(THF)4] are almost co-planar (φ = 2.8°), whereas those of the F4BDC linker in [2(THF)4] are largely inclined (φ = 78.3°). Density functional theory calculations clarified that (i) their dihedral angles of optimized geometries of [1(THF)4] and [2(THF)4] are almost the same as their experimental geometries, and (ii) the rotation energy barriers of phenyl moieties in [1(THF)4] and [2(THF)4] estimated by potential energy surface analyses are 12.0 and 8.4 kcal mol-1, respectively, indicating that hydrogen bondings are formed between two -CO2 units and four hydrogen atoms of phenyl rings of the BDC linker in [1(THF)4], whereas two -CO2 units and four fluorine groups on the phenyl ring of the F4BDC linker in [2(THF)4] are electrostatically and sterically repulsed. Electrochemical properties and electronic structures of [1(THF)4] and [2(THF)4] are strongly influenced by the electronic states of dicarboxylate linkers, whereas absorption spectra are strongly influenced by the dihedral angles between two -CO2 units and phenyl rings of dicarboxylate linkers.

Self-assembly of metal-organic polyhedra into supramolecular polymers with intrinsic microporosity

Designed porosity in coordination materials often relies on highly ordered crystalline networks, which provide stability upon solvent removal. However, the requirement for crystallinity often impedes control of higher degrees of morphological versatility, or materials processing. Herein, we describe a supramolecular approach to the synthesis of amorphous polymer materials with controlled microporosity. The strategy entails the use of robust metal–organic polyhedra (MOPs) as porous monomers in the supramolecular polymerization reaction. Detailed analysis of the reaction mechanism of the MOPs with imidazole-based linkers revealed the polymerization to consist of three separate stages: nucleation, elongation, and cross-linking. By controlling the self-assembly pathways, we successfully tuned the resulting macroscopic form of the polymers, from spherical colloidal particles to colloidal gels with hierarchical porosity. The resulting materials display distinct microporous properties arising from the internal cavity of the MOPs. This synthetic approach could lead to the fabrication of soft, flexible materials with permanent porosity.

Porosity in metal–organic materials typically relies on highly ordered crystalline networks, which hinders material processing and morphological control. Here, the authors use metal–organic polyhedra as porous monomers in supramolecular polymerization to produce colloidal spheres and gels with intrinsic microporosity.