Terpyridine isomerism as a tool for tuning red-to-NIR emissive properties in heteronuclear gold(I)-thallium(I) complexes

The polymeric linear chain [AuTl(C6Cl5)2]n reacts with three terpyridine-type ligands substituted with thiophene groups containing N-donor centres in different relative positions (L1, L2 and L3), leading to the Au(I)/Tl(I) complexes [AuTl(C6Cl5)2(L1)]n (1), [{AuTl(C6Cl5)2}2(L2)]n (2) and [AuTl(C6Cl5)2(L3)]n (3). X-Ray diffraction studies reveal that L1 acts as a chelate, while L2 and L3 act as bridging ligands, resulting in different coordination indexes for the thallium(I) centre. These structural differences strongly influence their optical properties, and while compounds 2 and 3 emit near the limit of the visible range, complex 1 emits in the infrared region. DFT calculations have also been carried out in order to determine the origin of the electronic transitions responsible for their optical properties.

From Mono- to Polynuclear 2-(Diphenylphosphino)pyridine-Based Cu(I) and Ag(I) Complexes: Synthesis, Structural Characterization, and DFT Calculations

A series of monometallic Ag(I) and Cu(I) halide complexes bearing 2-(diphenylphosphino)pyridine (PyrPhos, L) as a ligand were synthesized and spectroscopically characterized. The structure of most of the derivatives was unambiguously established by X-ray diffraction analysis, revealing the formation of mono-, di-, and tetranuclear complexes having general formulas MXL3 (M = Cu, X = Cl, Br; M = Ag, X = Cl, Br, I), Ag2X2L3 (X = Cl, Br), and Ag4X4L4 (X = Cl, Br, I). The Ag(I) species were compared to the corresponding Cu(I) analogues from a structural point of view. The formation of Cu(I)/Ag(I) heterobimetallic complexes MM'X2L3 (M/M' = Cu, Ag; X = Cl, Br, I) was also investigated. The X-ray structure of the bromo-derivatives revealed the formation of two possible MM'Br2L3 complexes with Cu/Ag ratios, respectively, of 7:1 and 1:7. The ratio between Cu and Ag was studied by scanning electron microscopy-energy-dispersive X-ray analysis (SEM-EDX) measurements. The structure of the binuclear homo- and heterometallic derivatives was investigated using density functional theory (DFT) calculations, revealing the tendency of the PyrPhos ligands not to maintain the bridging motif in the presence of Ag(I) as the metal center.

Near-white light emission from single crystals of cationic dinuclear gold(I) complexes with bridged diphosphine ligands

Three cationic dinuclear Au(I) complexes containing acetonitrile (AN) as an ancillary ligand were synthesized: [μ-L_Me(AuAN)₂]·2BF₄ (1), [μ-L_Et(AuAN)₂]·2BF₄ (2), and [μ-L_iPr(AuAN)₂]·2BF₄ (3) (L_Me = {1,2-bis[bis(2-methylphenyl)phosphino]benzene}, L_Et = {1,2-bis[bis(2-ethylphenyl)phosphino]benzene}, and L_iPr = {1,2-bis[bis(2-isopropylphenyl)phosphino]benzene}). The unique structures of complexes 1-3 with two P-Au(I)-AN rods bridged by rigid diphosphine ligands were determined through X-ray analysis. The Au(I)-Au(I) distances observed for complexes 1-3 were as short as 2.9804-3.0457 Å, indicating an aurophilic interaction between two Au(I) atoms. Unlike complexes 2 and 3, complex 1 incorporated CH₂Cl₂ into the crystals as crystalline solvent molecules. Luminescence studies in the crystalline state revealed that complexes 1 and 2 mainly exhibited bluish-purple phosphorescence (PH) at 293 K: the former had a PH peak wavelength at 415 nm with the photoluminescence quantum yield Φ_PL = 0.12, and the latter at 430 nm with Φ_PL = 0.13. Meanwhile, complex 3 displayed near-white PH, that is dual PH with two PH bands centered at 425 and 580 nm with Φ_PL = 0.44. The PH spectra and lifetimes of complexes 2 and 3 were measured in the temperature range of 77-293 K. The two PH bands observed for complex 3 were suggested to originate from the two emissive excited triplet states, which were in thermal equilibrium. From theoretical calculations, the dual PH observed for complex 3 is explained to occur from the two excited triplet states, T_1H and T_1L: the former exhibits a high-energy PH band (bluish-purple) and the latter exhibits a low-energy PH band (orange). The T_1H state is considered ³ILCT with a structure similar to that of the S₀-optimized structure. Conversely, the T_1L state is assumed to be a ³MLCT with a T₁-optimized structure, which has a short Au(I)-Au(I) bond and two bent rods (Au-AN). The thermal equilibrium between the two excited states is discussed based on computational calculations and photophysical data in the temperature range of 77-293 K. With regard to the crystal of complex 1, we were unable to precisely measure the temperature-dependent emission spectra and lifetimes, particularly at low temperatures, because the cooled crystals became irreversibly turbid over time.

Selective coordination of coinage metals using orthogonal ligand scaffolds

Group 11 metal complexes with their ability to form metallophilic interations are widely pursued to develop multifunctional luminescent materials. Heteronuclear coinage metal complexes are promising candidates to tune electronic and optical properties which are not readily accessed by their homometallic congeners. In this review, we present the concept of orthogonal ligands which are rationally designed to access heteronuclear coinage metal complexes and studied in terms of their photophysical properties. Bifunctional ligands containing soft and hard donor atoms have the potential of providing different coordination modes to selectively synthesise heterobimetallic complexes in a predictable manner. This review deals with ligand sets composed of pyridine, bipyridine- or iminopyridine-substituted NHCs featuring C-N coordination modes, phosphine-based N-heterocycles and amidinate ligand scaffolds comprising of P-N functionalities and mixed phosphine-phosphine oxide with P-O donor sites. Therefore, the scope of this perspective is the discussion of heteronuclear coinage metal complexes supported by recently developed bifunctional ligands in terms of their synthesis, coordination geometries and tunability of optical properties when compared to their homometallic analogues.

Platinum Indolylphosphine Fluorido and Polyfluorido Complexes: An Interplay between Cyclometallation, Fluoride Migration, and Hydrogen Bonding

The reaction of [PtCl2 (COD)] (COD=1,5-cyclooctadiene) with diisopropyl-2-(3-methyl)indolylphosphine (iPr2 P(C9 H8 N)) led to the formation of the platinum(ii) chlorido complexes, cis-[PtCl2 {iPr2 P(C9 H8 N)}2 ] (1) and trans-[PtCl2 {iPr2 P(C9 H8 N)}2 ] (2). The cis-complex 1 reacted with NEt3 yielding the complex cis-[PtCl{κ2 -(P,N)-iPr2 P(C9 H7 N)}{iPr2 P(C9 H8 N)}] (3) bearing a cyclometalated κ2 -(P,N)-phosphine ligand, while the isomer 2 with a trans-configuration did not show any reactivity towards NEt3 . Treatment of 1 or 3 with (CH3 )4 NF (TMAF) resulted in the formation of the twofold cyclometalated complex cis-[Pt{κ2 -(P,N)-iPr2 P(C9 H7 N)}2 ] (4). The molecular structures of the complexes 1-4 were determined by single-crystal X-ray diffraction. The fluorido complex cis-[PtF{κ2 -(P,N)-iPr2 P(C9 H7 N)}{iPr2 P(C9 H8 N)}] ⋅ (HF)4 (5 ⋅ (HF)4 ) was formed when complex 4 was treated with different hydrogen fluoride sources. The Pt(ii) fluorido complex 5 ⋅ (HF)4 exhibits intramolecular hydrogen bonding in its outer coordination sphere between the fluorido ligand and the NH group of the 3-methylindolyl moiety. In contrast to its chlorido analogue 3, complex 5 ⋅ (HF)4 reacted with CO or the ynamide 1-(2-phenylethynyl)-2-pyrrolidinone to yield the complexes trans-[Pt(CO){κ2 -(P,C)-iPr2 P(C9 H7 NCO)}{iPr2 P(C9 H8 N)}][F(HF)4 ] (7) and a complex, which we suggest to be cis-[Pt{C=C(Ph)OCN(C3 H6 )}{κ2 -(P,N)-iPr2 P(C9 H7 N)}{iPr2 P(C9 H8 N)}][F(HF)4 ] (9), respectively. The structure of 9 was assigned on the basis of DFT calculations as well as NMR and IR data. Hydrogen bonding of HF and NH to fluoride was proven to be crucial for the existence of 7 and 9.

Instrument-model refinement in normalized reciprocal-vector space for X-ray Laue diffraction

A simple yet efficient instrument-model refinement method for X-ray diffraction data is presented and discussed. The method is based on least-squares minimization of differences between respective normalized (i.e. unit length) reciprocal vectors computed for adjacent frames. The approach was primarily designed to work with synchrotron X-ray Laue diffraction data collected for small-molecule single-crystal samples. The method has been shown to work well on both simulated and experimental data. Tests performed on simulated data sets for small-molecule and protein crystals confirmed the validity of the proposed instrument-model refinement approach. Finally, examination of data sets collected at both BioCARS 14-ID-B (Advanced Photon Source) and ID09 (European Synchrotron Radiation Facility) beamlines indicated that the approach is capable of retrieving goniometer parameters (e.g. detector distance or primary X-ray beam centre) reliably, even when their initial estimates are rather inaccurate.

Linear Copper Complex Arrays as Versatile Molecular Strings: Syntheses, Structures, Luminescence, and Magnetism

The defined linear arrangement of metal atoms in discrete coordination complexes or polymers is still one of the most intriguing challenges in synthetic chemistry. These chain arrangements are of fundamental importance, because of their potential applications as molecular wires and single molecule magnets (SMM) in microelectronic devices on a molecular scale. Oligonuclear Group 11 metal complexes with suitable bridging ligands, specifically those that are based on copper as the first choice of a cheap precursor coinage metal, are of particular interest in this regard. This is due to the superior luminescence properties of these linear clusters that often show d¹⁰ ⋅⋅⋅d¹⁰ interactions in their molecular structures. The combination of Cu^I with heavier coinage metal ions results in tunable emissive arrays that are also stimuli-responsive. Thus, both linear multinuclear Cu^I and linear heteropolymetallic Cu^I /Ag^I as well as Cu^I /Au^I clusters are excellent candidates for applications in molecular/organic light-emitting devices (OLEDs). Alternatively, paramagnetic multinuclear cupric arrays are prominent as potential molecular wires with enhanced magnetic properties through multiple coupled d⁹ centers. This Review covers the whole range of linear multinuclear assemblies of cuprous and cupric ions in complexes and coordination polymers, their syntheses, photophysical behavior, and magnetic properties. Moreover, recent advances in the rapidly progressing field of hetero-Cu^I /Ag^I and Cu^I /Au^I molecular strings are also discussed.

Impact of High Pressure on Metallophilic Interactions and Its Consequences for Spectroscopic Properties of a Model Tetranuclear Silver(I)-Copper(I) Complex in the Solid State

Structure-property relationships were investigated via combined high-pressure spectroscopic and X-ray diffraction techniques for a model luminescent Ag₂Cu₂L₄ (L = 2-diphenylphosphino-3-methylindole) complex in the crystalline state. The experimental results were contributed by theoretical calculations, compared with the previously evaluated light-induced geometrical changes, and discussed in the context of available literature to date. To the best of our knowledge, this is the first study of this kind devoted to a coinage-metal complex for which the argentophilic interactions are crucial. High-pressure X-ray diffraction and optical spectroscopy experiments showed close correspondence between structural changes and optical properties. The unit-cell angles, absorption edges, emission maxima, decay lifetimes and silver-copper bond trends, all change around 2-3 GPa. A blue-shift to red-shift switch when increasing the pressure was observed for both absorption and emission spectra. This is unique behavior when compared to the literature-reported coinage metal systems. It also occurred that the pressure-induced structural changes differ notably from the geometrical distortions observed for the excited state. Interestingly, shortening of the Ag-Ag bond itself does not ensure the red shift of the absorption and emission spectra. All the optical spectroscopy data are suggestive of an important role of defects, likely related to the lack of a hydrostatic pressure transmitting medium, for pressures higher than 3 GPa.

New Au(i)–Cu(i) heterometallic complexes: the role of bridging pyridazine ligands in the presence of unsupported metallophilic interactions

The use of N-donor pyridazine ligands in different amounts in the reaction with a Au(i)/Cu(i) precursor allows the control of metallophilic interactions in the solid state.

Adjustable coordination of a hybrid phosphine–phosphine oxide ligand in luminescent Cu, Ag and Au complexes

The mixed-donor ligand shows variable binding ability with respect to d¹⁰ metal ions to afford a series of mono- and dinuclear complexes with tunable photophysical characteristics.

TiCl4-promoted condensation of methyl acetoacetate, isobutyraldehyde, and indole: a theoretical and experimental study

A combined DFT and experimental study of the title reaction points to a three-step mechanism: (1) titanium enolate formation, (2) Knoevenagel condensation of enolate and aldehyde, and (3) Michael addition of indole.

Gold(i) complexes of bisphosphines with bis(azol-1-yl)methane backbone: structure of a rare dinuclear gold(i) complex [(Au2Cl){CH2(1,2-C3H2N2PPh2)2}3Cl]

This paper describes the synthesis of gold(i) complexes of bisphosphines based on bis(azol-1-yl)methane viz. bis(imidazol-1-yl)methane, bis(pyrazol-1-yl)methane and bis(1,2,4-triazol-1-yl)methane.

Shedding light on the photochemistry of coinage-metal phosphorescent materials: a time-resolved Laue diffraction study of an Ag(I)-Cu(I) tetranuclear complex

The triplet excited state of a new crystalline form of a tetranuclear coordination d(10)-d(10)-type complex, Ag2Cu2L4 (L = 2-diphenylphosphino-3-methylindole ligand), containing Ag(I) and Cu(I) metal centers has been explored using the Laue pump-probe technique with ≈80 ps time resolution. The relatively short lifetime of 1 μs is accompanied by significant photoinduced structural changes, as large as the Ag1···Cu2 distance shortening by 0.59(3) Å. The results show a pronounced strengthening of the argentophilic interactions and formation of new Ag···Cu bonds on excitation. Theoretical calculations indicate that the structural changes are due to a ligand-to-metal charge transfer (LMCT) strengthening the Ag···Ag interaction, mainly occurring from the methylindole ligands to the silver metal centers. QM/MM optimizations of the ground and excited states of the complex support the experimental results. Comparison with isolated molecule optimizations demonstrates the restricting effect of the crystalline matrix on photoinduced distortions. The work represents the first time-resolved Laue diffraction study of a heteronuclear coordination complex and provides new information on the nature of photoresponse of coinage metal complexes, which have been the subject of extensive studies.