Silver 2,4'-Bipyridine Coordination Polymer for the High-Capacity Trapping of Perrhenate, A Pertechnetate Surrogate

Pertechnetate, the most stable form of the radionuclide 99Tc in aerobic aqueous systems, is a hazardous anion present in nuclear waste. Its high mobility in water makes the remediation of the anion challenging. In the past decade, significant effort has been placed into finding materials capable of adsorbing this species. Here, we present the synthesis and high-resolution crystal structure of the coordination polymer [Ag(2,4'-bipyridine)]NO3, which is capable of sequestering perrhenate─a pertechnetate surrogate─through anion exchange to form another new coordination polymer, [Ag(2,4'-bipyridine)]ReO4. Both the beginning and end structures were solved by single-crystal X-ray diffraction and the adsorption reaction was monitored through inductively coupled plasma-optical emission spectroscopy and UV-vis spectroscopy. The exchange reaction follows a pseudo-second-order mechanism and the maximum adsorption capacity is 764 mg ReO4/g [Ag(2,4'-bipyridine)]NO3, one of the highest recorded for a coordination polymer or metal-organic framework. A solvent-mediated recrystallization mechanism was determined by monitoring the ion-exchange reaction by scanning electron microscopy-energy-dispersive spectroscopy and powder X-ray diffraction.

Luminescence turn-on sensor for the selective detection of trace water and methanol based on a Zn(ii) coordination polymer with 2,5-dihydroxyterephthalate

A highly selective detection of trace water in organic solvents is urgently required for the chemical industry. In this work, the simple sonochemical method was used for producing a luminescent sensor, [Zn(H2dhtp)(2,2'-bpy)(H2O)]n (Zn-CP) (H2dhtp2- = 2,5-dihydroxyterephthalate and 2,2'-bpy = 2,2'-bipyridine). Zn-CP exhibits reversible thermally-induced and methanol-mediated structural transformation. Importantly, Zn-CP has exceptional water sensing performance in both dry methanol and dry ethanol, with high selectivity, wide linear ranges, and a low limit of detection (LOD) of 0.08% (v/v). Upon the incremental addition of water, the luminescent intensities enhanced and shifted, along with the emission color changing from green to greenish yellow. In addition, Zn-CP can detect methanol selectively through turn-on luminescence intensity with LODs of 0.28, 0.52, and 0.35% (v/v) in dry ethanol, dry n-propanol, and dry n-butanol, respectively. The excited-state proton transfer of linker H2dhtp2-via enol-keto tautomerism and collaboration with structural transformation could be attributed to the sensing mechanism.

Amide-Driven Secondary Building Unit Structural Transformations between Zn(II) Coordination Polymers

The behavior of coordination polymers (CPs) against external stimuli has witnessed remarkable attention, especially when the resulting CPs present reversible molecular arrays. Accordingly, CPs with these characteristics can lead to differences in their properties owing to these structural differences, being promising for their use as potential molecular switches with diverse applications. Herein, we have synthesized four Zn(II) CPs bearing α-acetamidocinnamic acid (HACA) and 4,4'-bipyridine (4,4'-bipy). The reaction between Zn(OAc)₂·2H₂O, HACA, and 4,4'-bipy yields {[Zn(ACA)₂(4,4'-bipy)]·EtOH} _n (1), which was used for the formation of three CPs through dissolution-recrystallization structural transformations (DRSTs): {[Zn(ACA)₂(4,4'-bipy)]·2MeOH} _n (2), {[Zn₂(μ-ACA)₂(ACA)₂(4,4'-bipy)]·2H₂O} _n (3), and {[Zn₃(μ-ACA)₆(4,4'-bipy)]·0.75CHCl₃} _n (4). The study of the four crystal structures revealed that their secondary building units (SBUs) comprise monomeric, dimeric, and trimeric arrangements linked by 4,4'-bipy ligands. The fundamental role of the utilized solvent and/or temperature, as well as their effect on the orientation of the amide moieties driving the formation of the different SBUs is discussed. Furthermore, the reversibility and interconversion between the four CPs have been assayed. Finally, their solid-state photoluminescence has evinced that the effect of the amide moieties not only predetermine a different SBU but also lead to a different emission in 4 compared with 1-3.

Design of coordination polymers based on combinations of 1,2-diphenylethane-1,2-diyl diisonicotinate with Cu(ii), Zn(ii), Cd(ii) and Co(ii)

Five new supramolecular coordination polymers of different dimensionalities (L-Cu(acac)2, L-Cu(hfac)2, L-ZnCl2, L-CdI2 and L-CoCl2) based on the use of the flexible organic ligand L (1,2-diphenylethane-1,2-diyl diisonicotinate) are reported.

Ligand-Driven Self-Assembly of Iodine-Based Cd(II) Complexes via Dissolution-Recrystallization Structural Transformation

The iodo-cadmium(II) complexes with a diversity of crystalline architectures have been prepared via a combination of a Cd(II) precursor and varied iodine solutions. The iodo-Cd(II) complexes with 1,10-phenantroline were assembled...

Post-synthetic modification mechanism for 1D spin crossover coordination polymers

Suitable solvent os crucial to achieve a quantitative PSM reaction. Then, this method is not restricted to porous materials.

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⁺ ; pen^2- =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 (bdc^2- =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 bdc^2- 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 bdc^2- molecule to construct a pseudorotaxane structure. While the use of dicarboxylates with an aliphatic carbon chain instead of bdc^2- 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 ]⁺ .

Solvent-Induced Structural Transformation and Luminescence Response in a Dumbbell-Shaped Crystalline Molecular Rotor

Crystalline molecular rotors constitute a new class of stimuli-responsive molecular materials owing to inherent molecular dynamics. However, beyond the molecular level, the role of molecular packings on the bulk structures and related properties has yet to be fully understood. Herein, we report a crystalline molecular rotor showing solvent-induced structural transformation and luminescence response. The molecular rotor has a dumbbell shape with two plates as the stators and one axial bridging ligand as the rotator. The crystals adopt solvated and desolvated forms with strikingly different packing structures. The solvated forms can easily transform into the desolvated form. During the structure transformation, the butterfly-like conformation of the stator undergoes a drastic dihedral angle change of about 30°, resulting in a luminescent change of about 10 nm. These findings afford a new aspect for functional molecular rotor materials.

Coordination-Bond-Driven Dissolution-Recrystallization Structural Transformation with the Expansion of Cuprous Halide Aggregate

Metal-organic frameworks (MOFs) with cuprous-halide-aggregates have shown superiority as organic LED (OLED) and semiconductor materials, while engineering MOF flexibility by involving the expansion of cuprous aggregates remains a great challenge. In this particular work, a dissolution-recrystallization structural transformation (DRST) with the dramatic growth of Cu^I-I aggregates, from 2D NJNU-100 to 3D NJNU-101 has been successfully realized. The unsaturated coordination nodes (2-positional nitrogen atoms) in NJNU-100 have been demonstrated to be the driven force for DRST to NJNU-101 via the formation of coordination bonds. The structural transformation process was irreversible and observed with optical microscopy and powder XRD. The expansion of Cu^I-I aggregates was also computational simulated accompanying with the rotation of the neutral tripodal TTTMB ligand (1,3,5-tris(1,2,4-triazol-1-ylmethyl)-2,4,6-trimethylbenzene) and the reduction of Cu^II to Cu^I. Moreover, the intermediate product NJNU-102 was captured by adding the planar molecular anthrancene to shut down the reaction, where only partial 2-positional nitrogen atoms coordinated to the aggregates and the anthrancene was oxidized to anthraquinone. NJNU-102 has further confirmed that DRST involved the breakage and recombination of coordination bonds and the electron transfer. NJNU-100 and NJNU-101 could be applied as semiconductor and OLED materials. This work has provided insights for crystal engineering, especially for the construction of the Cu^I_xX_y aggregates, and illustrated that DRST could be controlled with a rational design (as the unsaturated coordination modes).

Enhanced Passivation and Carrier Collection in Ink-Processed PbS Quantum Dot Solar Cells via a Supplementary Ligand Strategy

Solution-processed semiconductors have opened promising avenues for next-generation semiconductor and optoelectronic industries. Colloidal quantum dots (QDs) as one of the most typical materials are widely utilized for the design and development of light-emitting diodes, photodetectors, and solar cells. Recently, an emerging process of PbS QD ink has been employed to attain world record power conversion efficiency by surface passivation using a PbI₂ ligand to form PbI₂-PbS and the process optimization in the field of photovoltaics. However, the bonding and debonding of the ligands on the surface of PbS QDs are dynamic reversible processes in an ink environment. The uncoordinated Pb²⁺ defects induced by unbonded PbS QDs serve as the recombination sites. Thus, the present ink process leaves much room for the enhancement by surface passivation of PbS QDs. Herein, we devise an efficient strategy with a supplementary phenethylammonium iodide (PEAI) ligand for the formation of the PEAI-PbS interface in PbS QD ink-processed solar cells. This newly developed method can not only improve the passivation on the QD surface by iodine ions but also simultaneously enhance the carrier collection efficiency by a graded energy alignment between PbI₂-PbS and PEAI-PbS layers. The corresponding power conversion efficiency of the optimized device has significantly increased by approximately 20% more than the control device. As a result, such a robust and efficient method regarded as a strategic candidate can overcome the bottleneck of imperfect passivation caused by a large specific surface area and loose bonding ligands, eventually promoting the industrial application of QDs.

Metal-Organic Frameworks and Metal-Organic Cages - A Perspective

The fields of metal-organic cages (MOCs) and metal-organic frameworks (MOFs) are both highly topical and continue to develop at a rapid pace. Despite clear synergies between the two fields, overlap is rarely observed. This article discusses the peculiarities and similarities of MOCs and MOFs in terms of synthetic strategies and approaches to system characterisation. The stability of both classes of material is compared, particularly in relation to their applications in guest storage and catalysis. Lastly, suggestions are made for opportunities for each field to learn and develop in partnership with the other.

Anion-Induced Structural Diversity of Zn and Cd Coordination Polymers Based on Bis-9,10-(pyridine-4-yl)-anthracene, Their Luminescent Properties, and Highly Efficient Sensing of Nitro Derivatives and Herbicides

Luminescent coordination polymers (CPs) of Zn²⁺ or Cd²⁺ and bis-9,10-(pyridine-4-yl)-anthracene (BA) show different 1D and 2D topologies depending on the anion used in the precursor. Compounds {[Zn(μ₂-BA)(MeOH)₂(p-Tos)₂]} _n (1) and {[Zn(μ₂-BA)(MeOH)₂(CF₃CO₂)₂]} _n (2) form linear structures and {BA@[Zn(μ₂-BA)(MeOH)₂(H₂O)₂](CF₃SO₃)₂} _n (3) featuring intercalation of uncoordinated BA molecules into linear ribbons. Cd-based CPs {[Cd(μ₂-BA)₂(ClO₄)₂]· n(DCM)} _n (4) and {[Cd(μ₂-BA)(MeOH)₂(Dioxane)(η₂-SiF₆)]·mDioxane} _n (5) form porous structures with 2D lattices. All complexes exhibit strong blue emission in the solid state with average lifetimes between 8 and 13 ns. The emission of compound 4 is sensitive to the presence of nitro aromatics, simazine, and trichloroanisole (TCA) and demonstrates nonlinear Stern-Volmer quenching kinetics. Limits of detection (LOD) of 15 and 16 ppb for picric acid and TCA were achieved, respectively.

Successful Decontamination of 99 TcO4 - in Groundwater at Legacy Nuclear Sites by a Cationic Metal-Organic Framework with Hydrophobic Pockets

⁹⁹ Tc contamination at legacy nuclear sites is a serious and unsolved environmental issue. The selective remediation of ⁹⁹ TcO₄ ^- in the presence of a large excess of NO₃ ^- and SO₄ ^2- from natural waste systems represents a significant scientific and technical challenge, since anions with a higher charge density are often preferentially sorbed by traditional anion-exchange materials. We present a solution to this challenge based on a stable cationic metal-organic framework, SCU-102 (Ni₂ (tipm)₃ (NO₃ )₄ ), which exhibits fast sorption kinetics, a large capacity (291 mg g^-1 ), a high distribution coefficient, and, most importantly, a record-high TcO₄ ^- uptake selectivity. This material can almost quantitatively remove TcO₄ ^- in the presence of a large excess of NO₃ ^- and SO₄ ^2- . Decontamination experiments confirm that SCU-102 represents the optimal Tc scavenger with the highest reported clean-up efficiency, while first-principle simulations reveal that the origin of the selectivity is the recognition of TcO₄ ^- by the hydrophobic pockets of the structure.

Solvent-mediated structural transformations of copper(II) coordination polymers induced by different short-chain alcohols

A three-dimensional copper(II) coordination polymer (CP), {Cu(L-F)(N₃)}_n (1), was synthesized by reacting Cu(NO₃)₂ with 5-fluoronicotinic acid (HL-F) and NaN₃ in a water medium. Complex (1) shows a 3D network, in which the 1D [Cu₂(COO)N₃]_n chains are interconnected via L-F ligands. By immersing (1) into different short-chain alcohols (CH₃OH, C₂H₅OH and HOC₂H₄OH), three different CPs were isolated, including {Cu₃(L-F)₄(N₃)₂(CH₃OH)₂}_n (2), {Cu₃(L-F)₄(N₃)₂(C₂H₅OH)₂}_n (3) and {Cu_2.5(L-F)₃(N₃)₂(HOC₂H₄OH)_0.5}_n (4). CPs (2) and (3) display a similar structure, in which trinuclear subunit [Cu₃(COO)₂(N₃)₂(solvent)₂] is generated. Furthermore, such entities are interconnected via L-F ligands to give rise to a 3D network. As for (4), there are trinuclear [Cu₃(COO)₂(N₃)₂] and binuclear [Cu₂(COO)N₃] units, which are interconnected by L-F ligands to generate a 3D network. Notably, in (2) and (3), the coordination modes of CH₃OH and C₂H₅OH solvents are monodentate; whereas for (4), the HOC₂H₄OH solvent adopts a bridging mode to link two Cu atoms. Of further interest, these processes are solvent-mediated structural transformations, with obvious colour changes in the crystals. Structural changes and mechanisms of transformation are discussed in detail.

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.

Mechanisms of Solvent-Mediated Structural Transformations for Dynamic Crystals of Supramolecular Coordination Systems

Thus far, reports about the transformations for dynamic crystals of supramolecular coordination systems mainly include single-crystal-to-single-crystal reactions, and solvent-mediated processes. This Concept focuses on the mechanisms for solvent-mediated structural transformations of dynamic crystals, which can be classified into two categories, that is, core-on-shell and core-to-core. The core-on-shell mechanism means that the core of the new crystal is generated from the shell of original crystal, being concomitant with the dissolution of the mother crystal. In contrast, for the core-to-core case, the growth of new crystal core and the dissolution of original crystal core will proceed simultaneously, but they are physically separated. Herein, the two mechanisms are elucidated in detail, with some typical examples from recent advances.

A Water-Stable Luminescent ZnII Metal-Organic Framework as Chemosensor for High-Efficiency Detection of CrVI -Anions (Cr2 O72- and CrO42- ) in Aqueous Solution

A new luminescent Zn^II -MOF with 1D triangular channels along the b axis, namely NUM-5, has been successfully assembled and well characterized, which features good stability, especially in aqueous solution. Interestingly, this compound exhibits a fast, sensitive and selective luminescence quenching response towards Cr^VI (Cr₂ O₇^2- /CrO₄^2- ) in aqueous solution. The detection limits towards Cr₂ O₇^2- and CrO₄^2- ions are estimated to be 0.7 and 0.3 ppm, respectively, which are among the lowest detection limits reported for the MOF-based fluorescent probes that can simultaneously detect Cr₂ O₇^2- and CrO₄^2- in aqueous environment. The possible detection mechanism has been discussed in detail. Moreover, it can be easily regenerated after detection experiments, indicative of excellent recyclability. All these results suggest NUM-5 to be a highly selective and recyclable luminescent sensing material for the quantitative detection of Cr^VI anions in aqueous solution.

Single-crystal-to-single-crystal (SCSC) transformation and dissolution–recrystallization structural transformation (DRST) among three new copper(ii) coordination polymers

Three new copper(ii) complexes with single-crystal-to-single-crystal (SCSC) transformation and dissolution–recrystallization structural transformation (DRST) have been synthesized and fully characterized.

Water-Mediated Structural Transformations of CuII 5-Halonicotinates Coordination Networks with Distinct Mechanisms

Currently, no unequivocal evidence is given for elucidation of "black box" during the structural transformations of dynamic crystalline materials. Here, three types of mechanisms are revealed for such transformations through X-ray diffraction and optical microscopy; namely, single-crystal to single-crystal (SC-SC), as well as "core-to-core" and "core-on-shell" processes. As confirmed by time-lapse optical microscopy, the latter two cases can be properly ascribed as partial recrystallization processes, while the former one is a continuous process with two different crystal lattices simultaneously maintained in one single crystal. Interestingly, these three distinct pathways can be exquisitely realized by changing only the halogen substituent (from -F, -Cl, to -Br) of the organic ligands in the coordination supramolecular systems.

Anion exchange dynamics in the capture of perchlorate by a cationic Ag-based MOF

We report a detailed study of the host-guest interaction for a cationic metal-organic framework that can reversibly capture perchlorate. The structural transformation and flexibility of silver 4,4'-bipyridine nitrate (SBN) upon formation of silver 4,4'-bipyridine perchlorate (SBP) was evaluated by monitoring the anion exchange dynamics using a combination of powder X-ray diffraction (PXRD) with multinuclear 13C, 15N and 109Ag solid-state NMR spectra at different time intervals of the anion exchange. The structural transformation from SBN to SBP is complete within 70 minutes and was determined to take place by a solvent-mediated process. This pathway is confirmed by the morphological changes of the two crystalline materials observed by SEM. This key understanding may lead to application of this material towards perchlorate capture.

Efficient and Selective Uptake of TcO4- by a Cationic Metal-Organic Framework Material with Open Ag+ Sites

⁹⁹Tc is one of the most problematic radioisotopes in used nuclear fuel owing to its combined features of high fission yield, long half-life, and high environmental mobility. There are only a handful of functional materials that can remove TcO₄^- anion from aqueous solution and identifying for new, stable materials with high anion-exchange capacities, fast kinetics, and good selectivity remains a challenge. We report here an 8-fold interpenetrated three-dimensional cationic metal-organic framework material, SCU-100, which is assembled from a tetradentate neutral nitrogen-donor ligand and two-coordinate Ag⁺ cations as potential open metal sites. The structure also contains a series of 1D channels filled with unbound nitrate anions. SCU-100 maintains its crystallinity in aqueous solution over a wide pH range from 1 to 13 and exhibits excellent β and γ radiation-resistance. Initial anion exchange studies show that SCU-100 is able to both quantitatively and rapidly remove TcO₄^- from water within 30 min. The exchange capacity for the surrogate ReO₄^- reaches up to 541 mg/g and the distribution coefficient K_d is up to 1.9 × 10⁵ mL/g, which are significantly higher than all previously tested inorganic anion sorbent materials. More importantly, SCU-100 can selectively capture TcO₄^- in the presence of large excess of competitive anions (NO₃^-, SO₄^2-, CO₃^2-, and PO₄^3-) and remove as much as 87% of TcO₄^- from the Hanford low-level waste melter off-gas scrubber simulant stream within 2 h. The sorption mechanism is well elucidated by single crystal X-ray diffraction, showing that the sorbed ReO₄^- anion is able to selectively coordinate to the open Ag⁺ sites forming Ag-O-Re bonds and a series of hydrogen bonds. This further leads to a single-crystal-to-single-crystal transformation from an 8-fold interpenetrated framework with disordered nitrate anions to a 4-fold interpenetrated framework with fully ordered ReO₄^- anions. This work represents a practical case of TcO₄^- removal by a MOF material and demonstrates the promise of using this type of material as a scavenger for treating anionic radioactive contaminants during the nuclear waste partitioning and remediation processes.

Coordination change, lability and hemilability in metal–organic frameworks

Deformation or cleavage/reformation of metal–ligand bonds in MOFs lies at the heart of chemical/thermal stability and dynamic/flexible behaviour, provides avenues for post-synthetic modification, and can enable novel or improved performance for a variety of applications.

Solvent-mediated preparation of a heterometallic [2 × 2] grid via a 1D metal–organic template with extraordinary acid/base-resistance

Here, we have demonstrated that a metal–organic chain can serve as a template to prepare a heterometallic [2 × 2] grid through a solvent-mediated strategy.

Reversible, Selective Trapping of Perchlorate from Water in Record Capacity by a Cationic Metal-Organic Framework

We report the capture of ppm-level aqueous perchlorate in record capacity and kinetics via the complete anion exchange of a cationic metal-organic framework. Ambient conditions were used for both the synthesis of silver 4,4'-bipyridine nitrate (SBN) and the exchange, forming silver 4,4'-bipyridine perchlorate (SBP). The exchange was complete within 90 min, and the capacity was 354 mg/g, representing 99% removal. These values are greater than current anion exchangers such as the resins Amberlite IRA-400 (249 mg/g), Purolite A530E (104 mg/g), and layered double hydroxides (28 mg/g). Moreover, unlike resins and layered double hydroxides, SBN is fully reusable and displays 96% regeneration to SBN in nitrate solution, with new crystal formation allowing the indefinite cycling for perchlorate. We show seven cycles as proof of concept. Perchlorate contamination of water represents a serious health threat because it is a thyroid endocrine disruptor. This noncomplexing anionic pollutant is significantly mobile and environmentally persistent. Removal of other anionic pollutants from water such as chromate, pertechnetate, or arsenate may be possible by this methodology.

Spin-crossover complex encapsulation within a magnetic metal–organic framework

We report the solid-state incorporation of a mononuclear iron(iii) spin-crossover (SCO) complex within the pores of a magnetic metal–organic framework (MOF).

Mechanism of Formation of Copper(II) Chloro Complexes Revealed by Transient Absorption Spectroscopy and DFT/TDDFT Calculations

Copper(II) complexes are extremely labile with typical ligand exchange rate constants on the order of 10(6)-10(9) M(-1) s(-1). As a result, it is often difficult to identify the actual formation mechanism of these complexes. In this work, using UV-vis transient absorption when probing in a broad time range (20 ps to 8 μs) in conjunction with DFT/TDDFT calculations, we studied the dynamics and underlying reaction mechanisms of the formation of extremely labile copper(II) CuCl4(2-) chloro complexes from copper(II) CuCl3(-) trichloro complexes and chloride ions. These two species, produced via photochemical dissociation of CuCl4(2-) upon 420 nm excitation into the ligand-to-metal-charge-transfer electronic state, are found to recombine into parent complexes with bimolecular rate constants of (9.0 ± 0.1) × 10(7) and (5.3 ± 0.4) × 10(8) M(-1) s(-1) in acetonitrile and dichloromethane, respectively. In dichloromethane, recombination occurs via a simple one-step addition. In acetonitrile, where [CuCl3](-) reacts with the solvent to form a [CuCl3CH3CN](-) complex in less than 20 ps, recombination takes place via ligand exchange described by the associative interchange mechanism that involves a [CuCl4CH3CN](2-) intermediate. In both solvents, the recombination reaction is potential energy controlled.