Structural properties of trans hydrido–hydroxo M(H)(OH)(NH2CMe2CMe2NH2)(PPh3)2 (M = Ru, Os) complexes and their proton exchange behaviour with water in solution

Topological Strain-Induced Regioselective Linker Elimination in a Chiral Zr(IV)-Based Metal-Organic Framework

The synthesis and behaviour of pyrazine mononuclear carbonyl complexes of Rh(I), Ir(I), Ru(II) and Os(II)

Polyamides : hydrogen bonding, the Brill transition, and superheated water

Solubilities and solid state properties of the sodium salts of drugs.

Open AccessCCS ChemistryRESEARCH ARTICLE18 Mar 2022Slow Phase Transition-Induced Scan Rate Dependence of Spin Crossover in a Two-Dimensional Supramolecular Fe(III) Complex Zhao-Yang Li, Ying-Ying Wu, Yao Li, Jin-Hua Wang, Arshia Sulaiman, Mohammad Khurram Javed, Ya-Chao Zhang, Wei Li and Xian-He Bu Zhao-Yang Li School of Materials Science and Engineering, Nankai University, Tianjin 300350 , Ying-Ying Wu School of Materials Science and Engineering, Nankai University, Tianjin 300350 , Yao Li School of Materials Science and Engineering, Nankai University, Tianjin 300350 , Jin-Hua Wang School of Materials Science and Engineering, Nankai University, Tianjin 300350 , Arshia Sulaiman School of Materials Science and Engineering, Nankai University, Tianjin 300350 , Mohammad Khurram Javed School of Materials Science and Engineering, Nankai University, Tianjin 300350 , Ya-Chao Zhang *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Guizhou Provincial Key Laboratory of Computational Nano-Material Science, Guizhou Education University, Guiyang 550018 , Wei Li School of Materials Science and Engineering, Nankai University, Tianjin 300350 and Xian-He Bu *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] School of Materials Science and Engineering, Nankai University, Tianjin 300350 College of Chemistry, Nankai University, Tianjin 300071 https://doi.org/10.31635/ccschem.022.202101721 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Spin crossover (SCO) is commonly accompanied by a synchronous phase transition. A few phase transition-coupled SCO compounds have been reported, yet the synergy between SCO and phase transition on different time scales has not been explored. Herein, we report an [Fe(H-5-Cl-thsa-Et)(5-Cl-thsa-Et)]·H2O ( 1·H2O; H2-5-Cl-thsa-Et = 5-chloro-salicylaldehyde ethylthiosemicarbazone) Fe(III) complex that displays a two-dimensional supramolecular structure and SCO behavior above room temperature. Its dehydrated form 1 exhibits a two-step spin transition with a plateau in the temperature-dependent magnetization (M−T) curve at room temperature and a 51 K thermal hysteresis loop (Tc↑↓ = 299/248 K) at a rate of 5 K/min. The improved SCO performance in 1 could be attributed to the stronger intralayer but weaker interlayer interactions, which is supported by single-crystal structural analysis and density functional theory calculations. Remarkably, complex 1 displays an unusual scan rate-dependent SCO behavior at rates of 0.5−30 K/min, in which M−T curve plateaus appear at lower scan rates (<10 K/min) but vanish at faster scan rates (≥10 K/min). Scan rate-dependent differential scanning calorimetry, powder X-ray diffractometry, time-dependent magnetic moment decays, and infrared spectroscopy consistently reveal that the slow structural relaxation is coupled with a slow crystallographic phase transition, which is the mechanism for the unusual scan rate-dependent SCO. Download figure Download PowerPoint Introduction Spin crossover (SCO) complexes have been among the most intensively studied switchable molecular materials over the past few decades. Reversible switching between high-spin (HS) and low-spin (LS) states is generally accompanied by changes in magnetic, optical, dielectric, and other material properties. This feature has prompted efforts to fundamentally understand the SCO process and develop potential applications for information storage, sensors, and visual displays, among others.1–5 Many such applications require materials that exhibit thermal hystereses in their spin transitions, ideally at room temperature and with 30–50 K hysteresis loops.6,7 Many SCO molecules and polymers have been discovered that are primarily based on Fe(II) and Fe(III) centers. However, only a few SCO compounds exhibit concurrent room temperature transitions with wide hysteresis loops,8 and many examples face problems associated with atmospheric oxidation of their Fe(II) forms and crystal degradation through solvent loss. Therefore, designing robust Fe(III) SCO complexes that exhibit strong cooperativity and understanding the origin of SCO at the molecular level remain challenging.9,10 Thermal hysteresis is a collective phenomenon driven by communication between spin centers. The physical origin of the process is complicated but can be speculated using physical models that involve elastic interactions, electrostatic contributions, coupling between spins, degrees of spin-lattice freedom, and electron-deformation interactions through phonon fields.9,11–14 Experiments have revealed that pronounced cooperative effects can be acquired by building covalent bridges between metal centers or by introducing H-bonding or π–π stacking moieties into the surrounding coordination environment.7,8,15–17 These interactions serve as propagators that transmit electronic and structural information between the building blocks. Owing to its collective nature, hysteresis is difficult to control; however, cooperativity can be enhanced by increasing the strengths of effective intermolecular interactions.18 We recently studied a family of mononuclear Fe(III) multistep, cooperative SCO compounds that exhibit the following characteristics19–21: (1) H2O-mediated hydrogen bonds and other classical H-bonds, such as N−H···O and O−H···N linkages, play critical roles in enhancing system cooperativity through strong intermolecular interactions. (2) Symmetry breaking accompanying three-, five-, and six-step transitions associated with H2O-formed hydrogen bonds. (3) Hysteresis loops, but at temperatures <15 K. We concluded that water molecules in the lattice are essential for multistability and cooperativity. The importance of solvent molecules in the lattice is also apparent in Hofmann-type Fe(II) SCO systems.22–24 Guest molecules intercalated between layers or located in pores play vital roles via host–host and host–guest interactions that determine the strength of the cooperativity.25–29 To the best of our knowledge, solvent molecules are crucial for intermolecular interaction regulation and hence affect the entire SCO behavior. In addition to pursuing high-performance SCO compounds, that is, those exhibiting a large hysteresis loop, abrupt spin transition, and room temperature Tc, researchers have more recently focused on rare examples that exhibit scan rate dependence.30–33 The cooling branch of a hysteresis loop is commonly believed to depend more on the scan rate than the heating branch, as one generally starts with an HS lattice, and an LS center occupies less volume than an HS center. This causes a change in the width of the hysteresis loop but barely affects its shape. Herein, we report an unusual temperature-scan rate-dependent SCO complex 1 that exhibits significant shape and positional M−T curve changes at various scan rates. 1 was obtained by the in situ dehydration of [Fe(H-5-Cl-thsa-Et)(5-Cl-thsa-Et)]·H2O (H2-5-Cl-thsa-Et = 5-chlorosalicylaldehyde ethylthiosemicarbazone) ( 1·H2O). 1·H2O undergoes SCO above room temperature, whereas 1 exhibits room temperature SCO (Tc↑↓ = 299/248 K) and a fixed hysteresis loop of 51 K at a scan rate of 5 K/min. Single-crystal structure analyses reveal that both 1·H2O and 1 have clear two-dimensional (2D) layer structures. Dehydration expands the interlayer distances and strengthens intermolecular interactions within 2D layers. Density functional theory (DFT) calculations support a molecular mechanism in which dehydration relieves the internal chemical pressure of the lattice by destroying water-mediated hydrogen bonds. Both experimental and theoretical results consistently indicate that (1) scan rate-dependent SCO involves a slow crystallographic phase transition and (2) dehydration results in intensifying the intralayer intermolecular interactions, which effectively enhances SCO cooperativity. To the best of our knowledge, 1 is the first example of Fe(III) SCO compounds that exhibit scan rate dependence. Experimental Methods Measurements Magnetic susceptibility data were collected using a Quantum Design MPMS3 superconducting quantum interference device (SQUID) magnetometer with an applied magnetic field of 0.1 T in sweep mode. Data were first collected for 1·H2O between 5 and 300 K and then in situ collected between 5 and 400 K at a scan rate of 5 K/min for four continuous cycles for 1. The scan rate-dependent behavior of 1 was then studied at 0.5, 1, 2, 5, 10, 20, and 30 K/min. The data were corrected for contributions from the sample holder and intrinsic diamagnetism. Mössbauer experiments were performed using a 57Co/Rh (925 MBq) source in a constant-acceleration transmission spectrometer (Ulvac Cryogenics Inc., Japan) equipped with a closed-cycle helium refrigerator (Ulvac Cryogenics Inc.). The spectrometer was calibrated using standard Fe foil. The driving speed of the radiation source was ±6.0 mm/s. A fresh sample of 1·H2O was analyzed at 5 K. The sample was cooled to 80 K after being heated in situ to 400 K (identical process to SQUID) and then examined at 320 K. The data collected at 320 K correspond to complex 1. High-resolution powder X-ray diffractometry (PXRD) profiles were obtained using a Rigaku SmartLab instrument that features a PhotonMax high-flux 9 kW rotating anode X-ray source coupled with a D/tex Ultra 250 detector and attached to an Anton Paar TTK 600 Low Temperature Chamber. The detailed conditions were a reflection geometry between 100 and 400 K at 2, 5, and 10 K/min (2θ scan range: 5−35°; increment: 0.02°; 2θ scan rate: 10°/min; sample atmosphere: vacuum). Thermogravimetric analysis (TGA) was conducted on a Rigaku standard thermogravimetric-differential thermal analysis (TG-DTA) analyzer from room temperature to 800 °C at 10 K/min in a flowing argon atmosphere. 1·H2O was subjected to differential scanning calorimetry (DSC) between 170 and 410 K on a TA (United States) DSC-25 instrument in a helium atmosphere in an aluminum crucible at 15 K/min for the first cycle (in situ dehydration); 1 was then subjected to multicycle DSC between 170 and 370 K at 2, 5, 10, 15, 20, 25, and 30 K/min. Scanning electron microscopy (SEM) images were acquired using a JSM-7800F instrument. X-ray photoelectron spectroscopy (XPS) was performed using a Thermo Scientific ESCALAB 250Xi instrument. Time- and temperature-dependent infrared (IR) reflectivity spectra for 1 were acquired using a Bruker Tensor 27 instrument with an in situ cell (OPERANDO-DRCRO-R). 1·H2O was cooled to 100 K after being heated to 440 K and then heated to 320 K at 20 K/min. Single-crystal X-ray diffractometry (SC-XRD) data for 1·H2O were collected on an ADSC Quantum-210 detector with synchrotron radiation (λ = 0.700 Å) at the two-dimensional supramolecular crystallography (2D-SMC) beamline of the Pohang Accelerator Laboratory, South Korea. The structures were solved using direct methods (SHELXS-97/SHELXS-2014) and refined using full-matrix least-squares calculations on F2 (SHELXL-97) included in the SHELX-TL program package.34 SC-XRD data for 1 were collected on a Rigaku XtaLAB MM007 CCD diffractometer with Cu Kα radiation (λ = 1.5418 Å). Diffraction profiles were integrated using the CrystalAlice PRO program. Structures were solved and refined by full-matrix least-square methods using Olex2 software35 within the SHELXT and SHELXL programs, respectively. All nonhydrogen atoms were refined with anisotropic displacement parameters. X-ray crystallographic data have been deposited at the Cambridge Crystallographic Data Centre (CCDC): CCDC number 2035662 for 1·H2O (100 K), 2145471 for 1·H2O (300 K), 2035660 for 1 (100 K), and 2035661 for 1 (310 K). These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif Synthesis of H2-5-Cl-thsa-Et H2-5-Cl-thsa-Et was synthesized in a similar manner to that reported.36,37 5-Chloro-2-hydroxybenzaldehyde (156.0 mg, 1.0 mmol) and 4-ethyl-3-thiosemicarbazide (119.0 mg, 1.0 mmol) were refluxed in dried ethanol (10.0 mL) for 3 h. Colorless crystals of H2-5-Cl-thsa-Et were obtained in 78% yield upon slow evaporation of the filtrate. Synthesis of 1·H2O A 14.0-mg quantity (0.4 mmol) of dimethylamine was added to a solution of H2-5-Cl-thsa-Et (51.6 mg, 0.2 mmol) in MeOH (8.0 mL), and the resulting mixture was stirred for 20 min at room temperature. A 1.0-mL portion of an aqueous solution containing 0.1 mmol (40.4 mg) [Fe(NO3)3]·9H2O was added to the mixture, which was heated at 80 °C for 8 h. Black microcrystals of 1·H2O were obtained in 79% yield (based on [Fe(NO3)3]·9H2O) after cooling to room temperature and washing with cold methanol/water. Single crystals of 1·H2O suitable for XRD were obtained by recrystallization from 1:1 MeOH:CH3CN. Elemental analysis results for 1·H2O (C20H23Cl2FeN6O3S2): calculated, H, 3.95; C, 40.97; N, 14.33%. Found: H, 4.052; C, 40.827; N, 14.385%. Acquisition of 1 Dehydrated single crystals of 1 were collected after the in situ dehydration of 1·H2O at 380 K for 2 h in the SQUID instrument (pressure: 3–8 Torr; state: purged). Single crystals of 1 suitable for SC-XRD were carefully picked out from the vacuum grease. Finding high-quality single crystals of 1 after annealing is extremely difficult, as reported for most cases. After dozens of trials, we determined the structure of 1 at 100 K, which corresponds to the LS state. Single-crystal experiments did not provide a reasonable structure for the HS state. As an alternative, we used DFT calculations to optimize the HS state structure based on the experimental structure of the LS state (see Computational section). Elemental analysis for 1 (C20H21Cl2FeN6O2S2): calculated, H, 3.72; C, 42.27; N, 14.79%. Found: H, 4.079; C, 42.180; N, 14.780%. Computational Section DFT calculations were performed with the SIESTA package.38 Full structure relaxations, including the unit cell and atomic positions, were performed based on the conjugate gradient algorithm. The X-ray crystal structure determined at 100 K was chosen as the starting geometry. We set the parameter controlling the forced convergence of the geometry optimization to 0.04 eV/Å. Our calculations used the Perdew–Burke–Ernzerhof (PBE)39 exchange-correlation functional based on the generalized gradient approximation. We applied a Hubbard-U correction40 at the Fe site to account for the strong correlation effects of the 3d electrons. The Ueff parameter was set to 1.55 eV, which is optimal for PBE in studying spin-crossover properties.41 The DFT-D2 correction developed by Grimme42 was included to consider noncovalent interactions involved in the secondary coordination environment in the molecular crystals. We employed Troullier–Martins norm-conserving pseudopotentials,43 and nonlinear core correction was included for the magnetic Fe atom. We used a triple-ζ plus polarization numerical atomic basis for the basis sets. The finite range of the atomic orbitals was controlled using an energy shift of 50 meV. The fineness of the real-space grids for the numerical integrals was controlled with a mesh cutoff of 200 Ry. Only the Γ point was used for Brillouin zone sampling. We simulated the smearing of electron occupations based on the Methfessel–Paxton function at an electronic temperature of 1000 K. The electronic energies in different spin states were obtained by standard spin-polarized DFT calculations under a fixed spin-moment scheme. Results and Discussion Design and synthesis Complex 1·H2O was prepared by refluxing H2-5-Cl-thsa-Et, Fe(NO3)3·9H2O, and diethylamine in methanol/water (8:1 v/v). The single-crystal structure of 1·H2O confirms that it is a neutral complex (see "Single-crystal structures" section). While 1·H2O was prepared in a manner similar to our previously reported compounds, we emphasize that the use of diethylamine as a mild base is crucial in preparing this charge-neutral Fe(III) complex. The addition of an excess quantity of strong base leads to complete deprotonation and an anionic ferric compound, whereas the addition of one equivalent of a mild base leads to mono-deprotonation and a cationic ferric product. The use of a mild organic base in controlled amounts (1.5−2.0 equiv) is required to obtain the neutral ferric compound that displays SCO behavior (see "Magnetic properties" section). This crucial synthetic strategy is illustrated in Supporting Information Scheme S1. Basic characterizations The microcrystalline product was collected by filtration, washed with cold methanol/water and used for physical characterization studies (see Experimental Section). Single crystals of 1·H2O suitable for X-ray diffractometry were obtained by recrystallization from MeOH/CH3CN (1:1 v/v). The single-crystal structure of 1·H2O is shown in Supporting Information Figure S1 (also see the "Single-crystal structures" section). PXRD at room temperature confirmed the phase purity and crystallinity of 1·H2O ( Supporting Information Figure S2). TGA revealed that the water molecule in 1·H2O is gradually lost at T ≥ 340 K with a plateau appearing at 430 K, indicating the complete transformation of 1·H2O into 1 ( Supporting Information Figure S3a); 1 stabilizes at ∼500 K ( Supporting Information Figure S3b). Based on the TGA data, complex 1 can be obtained by in situ heating in a SQUID magnetometer. Single crystals of 1·H2O and 1 were subjected to SEM, which revealed that the crystal surface of 1 had slightly degraded, but its morphology was well retained upon thermal treatment, as shown in Supporting Information Figure S4, indicating that 1 is thermally robust, which is important for a utility material. XPS confirmed the exclusive presence of Fe(III) and the absence of Fe(II) following dehydration ( Supporting Information Figure S5). Magnetic properties and Mössbauer spectra The magnetic properties of 1·H2O were examined by temperature-dependent magnetic susceptibility (M−T) studies at 5−300 K using a SQUID magnetometer with a 0.1 T DC field. As shown in Supporting Information Figure S6, χMT at 5 K is 0.47 cm3 K mol−1, which is consistent with the expected value for LS Fe(III) ions (S = 1/2). χMT is ∼1.16 cm3 K mol−1 at 300 K, which indicates that an incomplete spin transition may occur above room temperature. Magnetic experiments were next performed at 5−400 K with a 5 K/min scan rate. Supporting Information Figure S7 shows the presence of a two-step SCO for the first cycle. Based on the sample environment (3−8 Torr, Tmax = 400 K) in the SQUID magnetometer and the TGA data, dehydration must have occurred during heating in the SQUID experiments, which indicates that 1· x H2O (x = 1–0) is present during the first heating process (5–400 K) and that 1 is present during the first cooling process (400–5 K). Thus, the SCO behavior is and not of the magnetic properties of 1 at 5−400 K over continuous cycles at 5 K/min the and SCO behavior shown in Figure 1. The two-step transitions during heating and cooling unusual that are on the HS and more abrupt on the LS room temperature. The transition temperatures are = K and = K, hysteresis of 51 K on the LS and K on the HS We that a plateau between 300 and 320 K only during heating and is to an state based on the χMT Figure 1 M−T curve for 1 acquired during continuous cycles at a scan rate of 5 K/min. The are Download figure Download PowerPoint Mössbauer spectra were acquired at 5 K for 1·H2O and at 320 K for 1 ( Supporting Information Figure and The data collected at 5 K a single shift = = LS = whereas the data collected at 320 K a of for the HS and for the LS The results are consistent with the magnetic susceptibility data and the presence of a state at 320 K that exhibits two-step spin transition behavior. The of molecular water from 1·H2O its SCO behavior and results in a two-step spin transition state a room temperature Tc, and an K hysteresis loop for 1. change in SCO behavior is to from structural we examined in the single-crystal structures of 1·H2O and 1 with the of the molecular the structural change within and between 2D layers. Single-crystal structures 1·H2O was subjected to SC-XRD at 100 and 300 K, whereas 1 was at 100 and K ( Supporting Information S2). 1·H2O in the 1 in the at 100 K but into at K, with parameter of and which confirms that the structure of 1 is molecules are present in the unit cell of 1 at K of which the HS and LS Fe(III) centers to be based on the ( Supporting Information Figure This is consistent with the magnetic quantity χMT = cm3 which corresponds to the of the magnetic of HS and LS A single-crystal of 1·H2O was used to determine changes in the of unit cell upon in situ The in Supporting Information shows that solvent as the crystal is the and the cell volume expands = consistent with the of SCO. In we that the crystal volume of 1 = is the as that of 1·H2O = which is to the interlayer consistent with the PXRD The unit an Fe(III) and an water The metal center is with a 1·H2O exhibits distances of at 100 K and at 300 K, which are of LS Fe(III) and the distances in 1 are at 100 K, also of LS Fe(III) centers ( Supporting Information The structure for the HS state of 1 was not obtained many we performed DFT calculations to optimize the HS structures of 1·H2O and 1, as shown in Supporting Information Figure The of the HS state structures of 1·H2O and 1 are in Supporting Information and S6, respectively. The apparent between 1·H2O and 1 are from their different intermolecular interactions and structures. As shown in Supporting Information Figure of classical hydrogen bonds are in the structure of 1·H2O ( Supporting Information involves intermolecular hydrogen to water molecules with distances of and The involves Å) and Å) hydrogen to H2O and results in the of a The involves intermolecular and hydrogen bonds with distances of and respectively. However, for 1, only one of effective hydrogen ( Supporting Information as hydrogen bonds H2O are The intermolecular hydrogen bonds form a structure with distances of as shown in Supporting Information Figure The 2D layer structure involves a of The distances in the 2D layer are in 1, which are than the of for as shown in and These indicate that the of molecular water room within the 2D which the Fe(III) centers to more of distances in Figure 2 2D supramolecular structures of 1·H2O and 1, the hydrogen Download figure Download PowerPoint apparent between 1·H2O and 1 is the between the 2D which is in 1·H2O than in 1. As shown in and the between the layers is in 1·H2O but in 1. The interlayer is in but in 1, it is by as shown in Supporting Information Figure are effective interlayer interactions in 1·H2O or 1, for the and ( Supporting Information Figure which indicates that the most effective intermolecular interactions in 1 from the 2D Supporting Information Scheme the structural by can be into account in the correlation of the 2D supramolecular structure and the improved SCO (1) the are the interactions between layers in both 1·H2O and 1, which it to change the between layers with the covalent (2) hydrogen is the interaction in the 2D supramolecular which can be or to the cooperativity with Hofmann-type SCO coordination Therefore, we that between the interlayer and intralayer hydrogen interactions a crucial in enhancing SCO cooperativity in supramolecular compound 1. Figure 3 structures of 1·H2O and 1, distances between 2D layers by the Fe atoms in Download figure Download PowerPoint DFT calculations We the electronic properties of molecular crystals of 1·H2O and 1 using DFT calculations to understand the physical origin of the change in SCO behavior. The results that the distances between magnetic centers in the of spin states (S = 2, and 10, Supporting Information Figure are by in the absence of molecular water ( Supporting Information Figure This is consistent with experimental X-ray structures. We first the changes in electronic energies accompanying the spin transitions, which revealed energy for the and centers in 1 that are less than those in 1·H2O to the of molecular water ( Supporting Information Figure In the energy of 1·H2O is to be which well with the change In in the by intermolecular interactions are a in results in a lower Tc, which is consistent with the experimental we changes in the coordination environment upon water by the density of states of the and In the HS the 3d the and which the orbitals This essential feature the to be from the energy between the centers of the and 3d is for 1·H2O than for 1 ( Supporting Information Figure which is of a more pronounced electron by intermolecular interactions in the with the

Synthesis and study of the light absorbing, redox and photophysical properties of Ru(II) and Os(II) complexes of 4,7-diphenyl-1,10-phenanthroline containing the polyazine bridging ligand 2,3-bis(2-pyridyl)pyrazine

Metal-ligand cooperativity (MLC) relies on chemically reactive ligands to assist metals with small-molecule binding and activation, and it has facilitated unprecedented examples of catalysis with metal complexes. Despite growing interest in combining ligand-centered chemical and redox reactions for chemical transformations, there are few studies demonstrating how chemically engaging redox active ligands in MLC affects their electrochemical properties when bound to metals. Here we report stepwise changes in the redox activity of model Ru complexes as zero, one, and two BH3 molecules undergo MLC binding with a triaryl noninnocent N2S2 ligand derived from o-phenylenediamine (L1). A similar series of Ru complexes with a diaryl N2S2 ligand with ethylene substituted in place of phenylene (L2) is also described to evaluate the influence of the o-phenylenediamine subunit on redox activity and MLC. Cyclic voltammetry (CV) studies and density functional theory (DFT) calculations show that MLC attenuates ligand-centered redox activity in both series of complexes, but electron transfer is still achieved when only one of the two redox-active sites on the ligands is chemically engaged. The results demonstrate how incorporating more than one multifunctional reactive site could be an effective strategy for maintaining redox noninnocence in ligands that are also chemically reactive and competent for MLC.

Metal-ligand cooperativity (MLC), a phenomenon that leverages reactive ligands to promote synergistic reactions with metals, has proven to be a powerful approach to achieving new and unprecedented chemical transformations with metal complexes. While many examples of MLC are known with a wide range of substrates, experimentally quantifying how ligand modifications affect MLC binding strength remains a challenge. Here we describe how cyclic voltammetry (CV) was used to quantify differences in MLC binding strength in a series of square-pyramidal Ru complexes. This method relies on using multifunctional ligands (those capable of both MLC and ligand-centered redox activity) as electrochemical reporters of MLC binding strength. The synthesis and characterization of Ru complexes with three different redox-active tetradentate ligands and two different ancillary phosphines (PPh3 and PCy3) are described. Titration CV studies conducted using BH3·THF with BH3 as a model MLC substrate allowed ΔGMLC to be quantified for each complex. Compared to our base triaryl ligand, increasing π conjugation in the backbone of the redox-active ligand enhanced MLC binding, whereas increasing π conjugation in the flanking groups decreased the MLC binding strength. Structures and spectroscopic data collected for the isolated MLC complexes are also described along with supporting DFT calculations that were used to illuminate electronic factors that likely account for the observed differences in the MLC binding strength. These results demonstrate how redox-active ligands and CV can be used to quantify subtle differences in the MLC binding strength across a series of structurally related complexes with different ligand modifications.

Influence of the third monomer component on the X-ray-analyzed crystal structure of ethylene–tetrafluoroethylene copolymer

Double Free: A Promising Route toward Moisture-Stable Hypotoxic Hybrid Perovskites

We synthesized two 4Me-PNP ligands which block metal-ligand cooperation (MLC) with the Ru center and compared their Ru complex chemistry to their two traditional analogues used in acceptorless alcohol dehydrogenation catalysis. The corresponding 4Me-PNP complexes, which do not undergo dearomatization upon addition of base, allowed us to obtain rare, albeit unstable, 16 electron mono-CO Ru(0) complexes. Reactivity with CO and H2 allows for stabilization and extensive characterization of bis-CO Ru(0) 18 electron and Ru(II) cis and trans dihydride species that were also shown to be capable of C(sp2 ) -H activation. Reactivity and catalysis are contrasted to non-methylated Ru(II) species, showing that an MLC pathway is not necessary, with dramatic differences in outcomes during catalysis between i Pr and t Bu PNP complexes within each of the 4Me and non-methylated backbone PNP series being observed. Unusual intermediates are characterized in one of the new and one of the traditional complexes, and a common catalysis deactivation pathway was identified.

We synthesized two 4Me-PNP ligands which block metal-ligand cooperation (MLC) with the Ru center and compared their Ru complex chemistry to their two traditional analogues used in acceptorless alcohol dehydrogenation catalysis. The corresponding 4Me-PNP complexes, which do not undergo dearomatization upon addition of base, allowed us to obtain rare, albeit unstable, 16 electron mono CO Ru(0) complexes. Reactivity with CO and H2 allows for stabilization and extensive characterization of bis CO Ru(0) 18 electron and Ru(II) cis and trans dihydride species that were also shown to be capable of C(sp2)-H activation. Reactivity and catalysis are contrasted to non-methylated Ru(II) species, showing that an MLC pathway is not necessary, with dramatic differences in outcomes during catalysis between iPr and tBu PNP complexes within each of the 4Me and non-methylated backbone PNP series being observed. Unusual intermediates are characterized in one of the new and one of the traditional complexes, and a common catalysis deactivation pathway was identified.

A new class of triarylpyridinio-derivatized [4'-(p-phenyl)(n)]terpyridyl ligands, R(1)(2)R(2)TP(+)-(p)(n)tpy, was designed as a novel category of electron-acceptor (A)-substituted proto-photosensitizing molecules. The first elements of this versatile family of ligands (i.e., n = 0, 1 and R(1) = R(2) = H), H(3)TP(+)-tpy and H(3)TP(+)-ptpy, were synthesized as well as their Ru(II) and Os(II) complexes to form the related acceptor-functionalized M(tpy)(2)(2+) and M(ptpy)(2)(2+) photosensitizer components denoted P0 and P1, respectively. Within the P1 series of compounds, an electron-donor (D)-substituted ligand, Me(2)N-ptpy, was also involved and associated with H(3)TP(+)-ptpy, giving rise to various combinations (up to 10 polyad systems). The two resulting series of nanometer-scale rigid rod-like photosensitized supramolecular architectures are of potential interest for long-range photoinduced electron transfer purposes. The main structural features of such supermolecules were determined by comparing the results obtained from (i) single-crystal X-ray analysis of the two free ligands together with that of the P0A/Ru and P1A(2)/Ru complexes and (ii) a detailed solution (1)H NMR study of the P0 series and, more specifically, of the P0A/Ru dyad (ROESY experiment). It is shown that the pseudoperpendicular conformation of the covalently linked A and P subunits found in the solid state is persistent in fluid medium; i.e., A is not conjugated with P (P0 and P1). The first insights regarding the consequences upon intercomponent couplings of combined substituent effects and conjugation (case of D-based polyads)-or absence of conjugation-are discussed in the light of ground-state electronic properties of the compounds.

Cluster chemistry: XC. Some complexes obtained from reactions between M3(CO)12 (M = Ru or Os) or Ru3(μ-dppm)(CO)10 and 2-substituted triphenylphosphines and related keto-phosphine ligands

Gas-Induced Phase Transition of Dipeptide Supramolecular Assembly