Copper(I) Cyanide Networks: Synthesis, Structure, and Luminescence Behavior. Part 2. Piperazine Ligands and Hexamethylenetetramine

Reversible Cu-Nanoparticle Formation in Soft Hydrogel Composites: Towards Write-Erase Displays and Fluorescence Detection

In this study, we introduce a hydrogel-polymer microsphere (HPM) composite material constituted of PVA, glycerin, and polymer microspheres obtained from Pickering emulsions that are capable of adsorbing Cu2+ ions. The obtained HPM composite is soft, flexible, can be fully saturated with Cu2+ ions, and exhibits a reversible color transition from blue to black upon electrode contact or interaction with a reducing agent, due to in situ generation of copper nanoparticles (Cu-NPs). Because of the color contrast between the locally generated Cu-NPs and the background, the HPM can be used as substrate for stamping different shapes or writing text. Further, the surface can be erased by an acidic solution, which makes it interesting as flexible write-erase displays. A second feature of the HPM is that it can function as a fluorescence detector of cyanide ions. An HPM whose surface has been stamped with an electrode, upon contacting an aqueous solution containing cyanide ions, begins fluorescing a yellow-green light around the patterned area. The displayed luminescence is irreversible and is preserved even after HPM's drying or lyophilization. This work lays a foundational framework for future exploration of the HPM composites in various technological applications, for sensing, circuit printing, and flexible displays.

Crystal structures, electron spin resonance, and thermogravimetric analysis of three mixed-valence copper cyanide polymers

The crystal structures of three mixed-valence copper cyanide alkanolamine polymers are presented, together with thermogravimetric analysis (TGA) and electron spin resonance (ESR) data. In all three structures, a CuII moiety on a crystallographic center of symmetry is coordinated by two alkanolamines and links two CuICN chains via cyanide bridging groups to form diperiodic sheets. The sheets are linked together by cuprophilic CuI-CuI interactions to form a three-dimensional network. In poly[bis(μ-3-aminopropanolato)tetra-μ-cyanido-dicopper(I)dicopper(II)], [Cu4(CN)4(C3H8NO)2]n, 1, propanolamine bases have lost their hydroxyl H atoms and coordinate as chelates to two CuII atoms to form a dimeric CuII moiety bridged by the O atoms of the bases with CuII atoms in square-planar coordination. The ESR spectrum is very broad, indicating exchange between the two CuII centers. In poly[bis(2-aminopropanol)tetra-μ-cyanido-dicopper(I)copper(II)], [Cu3(CN)4(C3H9NO)2]n, 2, and poly[bis(2-aminoethanol)tetra-μ-cyanido-dicopper(I)copper(II)], [Cu3(CN)4(CH7NO)2]n, 3, a single CuII atom links the CuICN chains together via CN bridges. The chelating alkanolamines are not ionized, and the OH groups form rather long bonds in the axial positions of the octahedrally coordinated CuII atoms. The coordination geometries of CuII in 2 and 3 are almost identical, except that the Cu-O distances are longer in 2 than in 3, which may explain their somewhat different ESR spectra. Thermal decomposition in 2 and 3, but not in 1, begins with the loss of HCN(g), and this can be correlated with the presence of OH protons on the ligands in 2 and 3, which are not present in 1.

An Insight into nd10 Metal Cyanide-based Coordination Polymers Through ab-initio Calculations: Electronic Properties and Optical Response

Semiconductors are essential for modern life since they are the basis of many current technologies that are related to better living standards. Some of them, characterized by the periodic assembling of metal cyanides with filled d-shell (nd¹⁰ ) constitute an interesting series of cyanide-based coordination polymers with physical properties such like anomalous anisotropic thermal expansion and quantum confinement effects related to the polymer's width that can be exploited for technological applications. Herein, the electronic structure of nd¹⁰ metal cyanide-based systems were studied both experimentally and through Density Functional Theory. The band gap found for one-dimensional (1D) -M-C≡N- (M=Cu, Ag, Au) and tetrahedral M-(C≡N)₂ (M=Zn, Cd, Hg) systems can be attributed to Laporte-allowed π → ${\to }$ π* (Metal to Ligand Charge Transfer mechanism) combined with metal center (d → ${\to }$ s,p) electronic transitions. Aurophilic bonding was found on the AuCN structure, and a new forbidden electronic transition associated to its band gap is reported. Computed effective and reduced masses from carriers revealed that carrier mobility and quantum confinement effects are greater in 1D systems.

Crystal structure of catena-poly[[[(2-eth-oxy-pyrazine-κN)copper(I)]-di-μ2-cyanido] [copper(I)-μ2-cyanido]]

In the asymmetric unit of the title coordination compound, {[Cu(CN)(C4H3OC2H5N2)][Cu(CN)]} n , there are two Cu atoms with different coordination environments. One CuI ion is coordinated in a triangular coordination geometry by the N atom of the 2-eth-oxy-pyrazine mol-ecule and by two bridging cyanide ligands, equally disordered over two sites exchanging C and N atoms, thus forming polymeric chains parallel to the c axis. The other Cu atom is connected to two bridging cyanide groups disordered over two sites with an occupancy of 0.5 for each C and N atom, and forming an almost linear polymeric chain parallel to the b axis. In the crystal, the two types of chain, which are orthogonal to each other, are connected by cuprophilic Cu⋯Cu inter-actions [2.7958 (13) Å], forming two-dimensional metal-organic coordination layers parallel to the bc plane. The coordination framework is further stabilized by weak long-range (electrostatic type) C-H⋯π inter-actions between cyano groups and 2-eth-oxy-pyrazine rings.

A novel three-dimensional copper(I) cyanide coordination polymer constructed from various bridging ligands: synthesis, crystal structure and characterization

The cyanide ligand can act as a strong σ-donor and an effective π-electron acceptor that exhibits versatile bridging abilities, such as terminal, μ₂-C:N, μ₃-C:C:N and μ₄-C:C:N:N modes. These ligands play a key role in the formation of various copper(I) cyanide systems, including one-dimensional (1D) chains, two-dimensional (2D) layers and three-dimensional (3D) frameworks. According to the literature, numerous coordination polymers based on terminal, μ₂-C:N and μ₃-C,C,N bridging modes have been documented so far. However, systems based on the μ₄-C:C:N:N bridging mode are relatively rare. In this work, a novel cyanide-bridged 3D Cu^I coordination framework, namely poly[(μ₂-2,2'-biimidazole-κ²N³:N^3')(μ₄-cyanido-κ⁴C:C:N:N)(μ₂-cyanido-κ²C:N)dicopper(I)], [Cu₂(CN)₂(C₆H₆N₄)]_n, (I), was synthesized hydrothermally by reaction of environmentally friendly K₃[Fe(CN)₆], CuCl₂·2H₂O and 2,2'-biimidazole (H₂biim). It should be noted that cyanide ligands may act as reducing agents to reduce Cu^II to Cu^I under hydrothermal conditions. Compound (I) contains diverse types of bridging ligands, such as μ₄-C:C:N:N-cyanide, μ₂-C:N-cyanide and μ₂-biimidazole. Interestingly, the [Cu₂] dimers are bridged by rare μ₄-C:C:N:N-mode cyanide ligands giving rise to the first example of a 1D dimeric {[Cu₂(μ₄-C:C:N:N)]ⁿ⁺}_n infinite chain. Furthermore, adjacent dimer-based chains are linked by μ₂-C:N bridging cyanide ligands, generating a neutral 2D wave-like (4,4) layer structure. Finally, the 2D layers are joined together via bidentate bridging H₂biim to create a 3D cuprous cyanide network. This arrangement leads to a systematic variation in dimensionality from 1D chain→2D sheet→3D framework by different types of bridging ligands. Compound (I) was further characterized by thermal analysis, solid-state UV-Vis diffuse-reflectance and photoluminescence studies. The solid-state UV-Vis diffuse-reflectance spectra show that compound (I) is a wide-gap semiconductor with band gaps of 3.18 eV. The photoluminescence study shows a strong blue-green photoluminescence at room temperature, which may be associated with metal-to-ligand charge transfer.

Synthesis and Luminescence of Optical Memory Active Tetramethylammonium Cyanocuprate(I) 3D Networks

The structures of three tetramethylammonium cyanocuprate(I) 3D networks [NMe₄]₂[Cu(CN)₂]₂•0.25H₂O (1), [NMe₄][Cu₃(CN)₄] (2), and [NMe₄][Cu₂(CN)₃] (3), (Me₄N = tetramethylammonium), and the photophysics of 1 and 2 are reported. These complexes are prepared by combining aqueous solutions of the simple salts tetramethylammonium chloride and potassium dicyanocuprate. Single-crystal X-ray diffraction analysis of complex 1 reveals {Cu₂(CN)₂(μ₂-CN)₄} rhomboids crosslinked by cyano ligands and D_3h {Cu(CN)₃} metal clusters into a 3D coordination polymer, while 2 features independent 2D layers of fused hexagonal {Cu₈(CN)₈} rings where two Cu(I) centers reside in a linear C_∞v coordination sphere. Metallophilic interactions are observed in 1 as close Cu⋯Cu distances, but are noticeably absent in 2. Complex 3 is a simple honeycomb sheet composed of trigonal planar Cu(I) centers with no Cu^…Cu interactions. Temperature and time-dependent luminescence of 1 and 2 have been performed between 298 K and 78 K and demonstrate that 1 is a dual singlet/triplet emitter at low temperatures while 2 is a triplet-only emitter. DFT and TD-DFT calculations were used to help interpret the experimental findings. Optical memory experiments show that 1 and 2 are both optical memory active. These complexes undergo a reduction of emission intensity upon laser irradiation at 255 nm although this loss is much faster in 2. The loss of emission intensity is reversible in both cases by applying heat to the sample. We propose a light-induced electron transfer mechanism for the optical memory behavior observed.

Synthetic, spectral, structural and catalytic activity of infinite 3-D and 2-D copper(ii) coordination polymers for substrate size-dependent catalysis for CO2 conversion

Two copper(ii) coordination polymers have been synthesized and used as substrate size-dependent catalyst for CO₂ cycloaddition with epoxides.

Adaptive Coordination-Driven Supramolecular Syntheses toward New Polymetallic Cu(I) Luminescent Assemblies

A thermally activated delayed fluorescence (TADF) tetrametallic Cu(I) metallacycle A behaves as a conformationally adaptive preorganized precursor to afford, through straightforward and rational coordination-driven supramolecular processes, a variety of room-temperature solid-state luminescent polymetallic assemblies. Reacting various cyano-based building blocks with A, a homometallic Cu(I) 1D-helical coordination polymer C and Cu₈M discrete circular heterobimetallic assemblies D_M (M = Ni, Pd, Pt) are obtained. Their luminescence behaviors are studied, revealing notably the crucial impact of the spin-orbit coupling offered by the central M metal center on the photophysical properties of the heterobimetallic D_M derivatives.

Crystal structure of bis{catena-poly[(μ2-1,2-bis(4-pyridyl)ethane-κ2 N:N′)silver(I)]} diaqua-bis(5-(4-carboxyphenyl)pyridine-2-carboxylato-κ2 N,O)-(μ2-1,2-bis(4-pyridyl)ethane-κ2 N:N′)disilver(I) octahydrate, C31H35Ag2N4O9

C31H35Ag2N4O9, triclinic, P1̄ (No. 2), a = 8.8351(5) Å, b = 13.1492(6) Å, c = 14.7094(8) Å, V = 1618.76(15) Å3, α = 85.491(4) Å, β = 84.285(5) Å, γ = 72.413(4) Å, Z = 2, R gt(F) = 0.0382, wR ref(F 2) = 0.0796, T = 293(2) K.

Poly[bis(trimethylammonium) [hexa-μ-cyanido-cadmium(II)dicopper(I)]]

The title compound, {(C3H10N)2[CdCu2(CN)6]}n, has been synthesized as an alternative to the high-emitting complexes containing more expensive metals. The CN−ligands make linkages between the CuIand CdIIions to form the coordination polymer, [CdCu2(CN)6]n2−, which is a three-dimensional framework classified as pyrite net (pyr). The net has a void space for accommodating a trimethylammonium ion located on a threefold rotation axis. The CdIIion lies on a special position with site symmetry -3 and is octahedrally coordinated by six N atoms. The CuIion is located on a threefold rotation axis and has a trigonal-planar coordination geometry formed by three C atoms. In the three-dimensional net, two CuIions are arranged closely [Cu...Cu = 3.9095 (5) Å], but the distance is not short enough to suggest a CuI–CuIinteraction. The crystal studied was a merohedral twin (twin operation 2[101]), the refined component ratio being 0.9202 (7):0.0798 (7). A powder of the title compound shows strong luminescence with an emission maximum at 509 nm and a quantum yield of 98% at room temperature.

Thermal Expansion Behavior of MI[AuX2(CN)2]-Based Coordination Polymers (M = Ag, Cu; X = CN, Cl, Br)

Two sets of trans-[AuX₂(CN)₂]^--based coordination polymer materials-M[AuX₂(CN)₂] (M = Ag; X = Cl, Br or M = Cu; X = Br) and M[Au(CN)₄] (M = Ag, Cu)-were synthesized and structurally characterized and their dielectric constants and thermal expansion behavior explored. The M[AuX₂(CN)₂] series crystallized in a tightly packed, mineral-like structure featuring 1-D trans-[AuX₂(CN)₂]^--bridged chains interconnected via a series of intermolecular Au···X and M···X (M = Ag, Cu) interactions. The M[Au(CN)₄] series adopted a 2-fold interpenetrated 3-D cyano-bound framework lacking any weak intermolecular interactions. Despite the tight packing and the presence of intermolecular interactions, these materials exhibited decreased thermal stability over unbound trans-[AuX₂(CN)₂]^- in [ⁿBu₄N][AuX₂(CN)₂]. A significant dielectric constant of up to ε_r = 36 for Ag[AuCl₂(CN)₂] (1 kHz) and a lower ε_r = 9.6 (1 kHz) for Ag[Au(CN)₄] were measured and interpreted in terms of their structures and composition. A systematic analysis of the thermal expansion properties of the M[AuX₂(CN)₂] series revealed a negative thermal expansion (NTE) component along the cyano-bridged chains with a thermal expansion coefficient (α_CN) of -13.7(11), -14.3(5), and -11.36(18) ppm·K^-1 for Ag[AuCl₂(CN)₂], Ag[AuBr₂(CN)₂], and Cu[AuBr₂(CN)₂], respectively. The Au···X and Ag···X interactions affect the thermal expansion similarly to metallophilic Au···Au interactions in M[Au(CN)₂] and AuCN; replacing X = Cl with the larger Br atoms has a less significant effect. A similar analysis for the M[Au(CN)₄] series (where the volume thermal expansion coefficient, α_V, is 41(3) and 68.7(19) ppm·K^-1 for M = Ag, Cu, respectively) underscored the significance of the effect of the atomic radius on the flexibility of the framework and, thus, the thermal expansion properties.

A convenient synthesis of 1-aralkyl-4-benzylpiperazine derivatives

An efficient two-step route was developed for the synthesis of 1-aralkyl-4-benzylpiperazine derivatives by a Blanc reaction and alkylation. The key intermediate, N-benzylpiperazine, was prepared in an excellent yield by direct benzylation of commercially available piperazine under metal-free conditions.

Efficient synthesis and antioxidant activities of N-heterocyclyl substituted Coenzyme Q analogues

A new strategy for the efficient synthesis of C-5 heterocyclyl substituted Coenzyme Q analogues was developed by N-alkylation of bromomethylated quinone 11 with a series of amines 12 under metal-free conditions. In vitro antioxidant activities of these Coenzyme Q analogues were evaluated and compared with commercial antioxidant Coenzyme Q10 by employing DPPH assay. All these N-heterocyclyl substituted Coenzyme Q analogues are found to be exhibiting good antioxidant properties and may be used as potent antioxidants for combating oxidative stress.

Synthesis, crystal structure and magnetic properties of a two-dimensional cyanide-based heterometallic coordination polymer with cationic piperazinium ligands: poly[aquatetra-μ2-cyanido-κ(8)C:N-dicyanido-κ(2)C-(piperazinium-κN(4))cobalt(III)copper(II)]

Cyanide as a bridge can be used to construct homo- and heterometallic complexes with intriguing structures and interesting magnetic properties. These ligands can generate diverse structures, including clusters, one-dimensional chains, two-dimensional layers and three-dimensional frameworks. The title cyanide-bridged Cu(II)-Co(III) heterometallic compound, [Cu(II)Co(III)(CN)6(C4H11N2)(H2O)]n, has been synthesized and characterized by single-crystal X-ray diffraction analysis, magnetic measurement, thermal study, vibrational spectroscopy (FT-IR) and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM-EDS). The crystal structure analysis revealed that it has a two-dimensional grid-like structure built up of [Cu(Hpip)(H2O)](3+) cations (Hpip is piperazinium) and [Co(CN)6](3-) anions that are linked through bridging cyanide ligands. The overall three-dimensional supramolecular network is expanded by a combination of interlayer O-H...N and N-H...O hydrogen bonds involving the coordinated water molecules and the N atoms of the nonbridging cyanide groups and monodentate cationic piperazinium ligands. A magnetic investigation shows that antiferromagnetic interactions exist in the title compound.

Electronic, bonding, and optical properties of 1d [CuCN]n (n = 1-10) chains, 2d [CuCN]n (n = 2-10) nanorings, and 3d [Cun (CN)n ]m (n = 4, m = 2, 3; n = 10, m = 2) tubes studied by DFT/TD-DFT methods

The electronic, bonding, and photophysical properties of one-dimensional [CuCN](n) (n = 1-10) chains, 2-D [CuCN](n) (n = 2-10) nanorings, and 3-D [Cu(n)(CN)(n)](m) (n = 4, m = 2, 3; n = 10, m = 2) tubes are investigated by means of a multitude of computational methodologies using density functional theory (DFT) and time-dependent-density-functional theory (TD-DFT) methods. The calculations revealed that the 2-D [CuCN](n) (n = 2-10) nanorings are more stable than the respective 1-D [CuCN](n) (n = 2-10) linear chains. The 2-D [CuCN](n) (n = 2-10) nanorings are predicted to form 3-D [Cun (CN)(n)](m) (n = 4, m = 2, 3; n = 10, m = 2) tubes supported by weak stacking interactions, which are clearly visualized as broad regions in real space by the 3D plots of the reduced density gradient. The bonding mechanism in the 1-D [CuCN](n) (n = 1-10) chains, 2-D [CuCN](n) (n = 2-10) nanorings, and 3-D [Cu(n)(CN)(n)](m) (n = 4, m = 2, 3; n = 10, m = 2) tubes are easily recognized by a multitude of electronic structure calculation approaches. Particular emphasis was given on the photophysical properties (absorption and emission spectra) of the [CuCN](n) chains, nanorings, and tubes which were simulated by TD-DFT calculations. The absorption and emission bands in the simulated TD-DFT absorption and emission spectra have thoroughly been analyzed and assignments of the contributing principal electronic transitions associated to individual excitations have been made.

Design and Synthesis of Piperazine-Based Task-Specific Ionic Liquids for Liquid–Liquid Extraction of CuII, NiII, and CoII from Water

The novel synthesis of task-specific ionic liquids (TSILs) introducing piperazine substructures was described. Piperazine functional groups were easily grafted onto an imidazolium cationic derivative via a simple four-step process starting from available materials such as imidazole, ethylene glycol, and 1-butylamine or 3-dimethylaminopropylamine. Effects of pH, temperature, and structure of functional groups on the performance of liquid–liquid extraction of Cu2+, Ni2+, and Co2+ from water were investigated. It was found that TSILs were efficient for removal of these metal ions in mild acid solutions. The TSIL with an extra nitrogen atom showed a higher capability to separate metal ions, especially for Cu2+. This may be ascribed to the intrinsic structure of the functional groups – the more coordination sites, the higher the affinity for the metal ions. Furthermore, the thermodynamics indicated that the extraction process was exothermic and spontaneous in nature.

Two novel topological structures of [Cu(CN)] coordination polymers modified by flexible triazole ligands

Triazole ligands have been introduced into the {Cu(CN)} skeleton to produce appealing polymers, which exhibit certain thermal stability and fluorescence properties.

Theoretical insights into the effect of amine and phosphine decoration on the photoluminescence of copper(i) and silver(i) coordination polymers

Ligand decoration shifts the excitation and emission spectra of coinage metal cyanides. DFT and TD-DFT calculations are used to identify the MOs involved the transitions that contribute to photoluminescence.