Asymmetrically Substituted Phospholes as Ligands for Coinage Metal Complexes

A series of coinage metal complexes asymmetrically substituted 2,5-diaryl phosphole ligands is reported. Structure, identity, and purity of all obtained complexes were corroborated with state-of-the-art techniques (multinuclear NMR, mass spectrometry, elemental analysis, X-ray diffraction) in solution and solid state. All complexes obtained feature luminescence in solution as well as in the solid state. Additionally, DOSY-MW NMR estimation experiments were performed to achieve information about the aggregation behavior of the complexes in solution allowing a direct comparison with their structures observed in the solid state.     

Resorcinarene Bis‐Thiacrowns: Prospective Host Molecules for Silver Encapsulation

Mixed‐donor atom tetramethoxy resorcinarene bis‐thiacrown hosts, in which the crown unit contains both hard oxygen and soft sulfur donor atoms, were synthesized for soft metal cation binding. The binding properties were investigated both in solution and in the solid state by NMR spectroscopy and X‐ray crystallography. It was found that the resorcinarene bis‐thiacrowns were able to complex silver cations with remarkable affinity forming readily 1:2 host–guest complexes in solution. The solid state structures also revealed that the bis‐thiacrowns form silver complexes in an unanticipated endo‐ and exo‐cavity fashion within the same host molecule. Both the solution and solid state studies indicated the sulfur atoms to be the major contributing donor atoms in forming the binding interactions with silver cations.     

Catching gaseous SO2 in cone-type lanthanide complexes: an unexpected coordination mode for SO2 in f-element chemistry

Easy come, easy go: the first molecular SO(2) complexes of the lanthanides (Ln=Sm, Eu) have been prepared. The compounds can reversibly coordinate gaseous SO(2). Concomitant with the addition and removal of SO(2), the color of the complexes changes reversibly. The structures of the SO(2) compounds could be confirmed in solution and in the solid state.     

Chelating and bridging diphosphinoamine (PPh2)2N(iPr) complexes of copper(I)

The ligand bis(diphenylphosphino)isopropylamine (dppipa) has been shown to be a versatile ligand sporting different coordination modes and geometries dictated by copper(I). Most of the molecular structures were confirmed by X-ray crystallography. It is found in a chelating mode, in a monomeric complex when the ligand to copper ratio is 2:1. A tetrameric complex is formed when low ratios of ligand to metal (1:2) were used. But with increasing ratios of ligand to metal (1:1 and 2:1), a trimer or a dimer was obtained depending on the crystallization conditions. Variable temperature ³¹P{¹H} NMR spectra of these complexes in solution showed that the Cu–P bond was labile and the highly strained 4-membered structure chelate found in the solid state readily converted to a bridged structures. On the other hand, complexes with the ligand in a bridging mode in the solid state did not form chelated structures in solution. The effect of adding tetra-alkylammonium salts to solutions of various complexes of dppipa were probed by ³¹P{¹H} NMR and revealed the effect of counter ions on the stability of complexes in solution.     

Structural study of bis(triorganotin(IV)) esters of 4-ketopimelic acid

The set of six bis(triorganotin(IV)) esters of 4-ketopimelic acid was prepared. Their structures were studied using IR, NMR and X-ray crystallographic (cyclohexyl and ethyl derivatives) techniques both in solution and the solid state. Five of these compounds are polymeric in the solid state and depolymerise upon dissolving in non-coordinating and/or addition of coordinating solvent to monomeric species with four-coordinated tin atom or complexes with donor solvent with five-coordinated tin central atom. The tricyclohexyltin derivative is dimeric in the solid state and monomeric in solution.     

Molecular geometry and optical activity of N-nitroso-2,2,6,6-tetramethylpiperidines generated by spontaneous crystallization and inclusion complexation with optically active diols

Three sterically strained N-nitrosamines and their inclusion complexes with optically active diols (TADDOLs) were obtained and their solid state crystal structures are described. Owing to the formation of N-nitroso-4-hydroxy-2,2,6,6-tetramethylpiperidine 2 as spontaneously resolvable conglomerate crystals (space group P3₂) its solid state CD was measured. The crystal structures of the inclusion complexes revealed that in all cases the guest nitrosamines assume chiral conformations as seen by their chiroptical spectra. The optically active nitrosamines are configurationally labile and rapidly racemize in solution. The solid state structures revealed that in order to avoid an allylic 1,3-strain [A^(1,3)], caused by an interaction of the nitrosamino group with the methyl substituents, the piperidine ring in 1 and 2 assumes a chair conformation significantly flattened at the amino nitrogen whereas in the 4-oxo derivative 3 the piperidine ring assumes a twist-boat conformation.     

Comprehensive chemical characterization of complexes involving lead-amino acid interactions

Complexes of lead with L-phenylalanine, L-isoleucine, L-valine, or L-arginine have been isolated from reaction mixtures containing lead nitrate and the respective amino acid in acidic aqueous solution. The compounds have been comprehensively characterized using X-ray crystallography, solid state NMR spectroscopy and solution state NMR spectroscopy, IR and Raman spectroscopies, and electrospray ionization mass-spectrometry. The solid state structures of lead-phenylalanine, lead-valine, and lead-valine-isoleucine complexes show a lead center coordinated by two amino acid ligands, while the lead-arginine complex is a cluster involving two lead centers and three arginine molecules. The structural, spectroscopic, and spectrometric characterization of the complexes provides a basis to establish a fundamental understanding of heavy metal-amino acid interactions.     

Synthesis and structural properties of lanthanide complexes formed with tropolonate ligands

We have previously reported the unique luminescence properties of ML4 complexes formed between tropolonate ligands and a series of lanthanide cations, several of them emitting in the near-infrared domain. The synthesis and composition of ML4 lanthanide tropolonate complexes have been previously described in the literature, but no structural information has been available so far. In this work, the crystal structures of several lanthanide tropolonate complexes (Ln3+ = Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+, Lu3+) have been isolated and systematically analyzed by X-ray diffraction and compared by using different criteria including the Kepert formalism. Such comparative work is rare in lanthanide coordination chemistry. The analysis of the structures in the solid state reveals that although the packing of the ML4 complexes depends on the nature of the metal ion, the coordination geometries around the different lanthanides is virtually similar for all the cations that have been analyzed; an indication that lanthanide-centered f orbitals play a role in controlling this coordination geometry. Analysis of the solution's behavior by stability constant determination reveals the formation of complexes with similar ML4 stoichiometries as those observed in the solid state. Nevertheless, analysis of the luminescence lifetimes indicates that the coordination environment around the lanthanide cations are different in the solid state and in solution, with the presence of one molecule of water bound to the lanthanide cation in solution. The presence of such a water molecule is a significant source of nonradiative deactivation of the excited states of the lanthanide cations, an unfavorable condition that leads to significant loss in fluorescence intensity of these lanthanide complexes. This exemplifies that such comparative analysis between the solid state and solution is important for the rationalization of the luminescence properties of the complexes. This analysis will aid us in optimizing ligand design for improved photophysical properties of the complex.     

all-Z-Tetrabenzo

Crystal structures of the silver complexes derived from tetrabenzo[16]annulene with AgOTf and AgClO(4) are different, although these two complexes show similar (1)H NMR spectra reflecting a similar clathrate structure in solution. The silver complex of pentabenzo[20]annulene with AgClO(4) adopts a clathrate structure both in the solid state and in solution.     

Synthesis,structure, chemistry,and applications of tetravalent nickel complexes

This review provides an overview of the synthetic pathways, structures, and reactivity of various nickel(IV) complexes. The complexes are classified according to the various ligand types including sulfur, oxygen, nitrogen, and phosphorus donors. The main emphasis is on different ligand systems which stabilize Ni in higher oxidation state in the solid state and solution. The structural aspects of the complexes are briefly discussed. The possible applications of these nickel(IV) complexes are reviewed and future prospects are also highlighted.     

Bidentate lactate binding in aqueous solution in a cationic,heptadentate lanthanide complex: an effective chiral derivatising agent

The X-ray crystal structures of cationic, heptadentate lanthanide complexes of holmium and ytterbium bound to lactate are reported and the observed bidentate chelation in the solid state is consistent with near-IR CD (Yb) and solution NMR measurements; the complexes are shown to act as aqueous chiral derivatising agents for alpha-hydroxy acids.     

Magnetic exchange coupling tunable by means of selective cation binding into poly(radical-armed) azacrowns

Host-guest complexes of tris(NN-CH2)-substituted 1,4,7-triazacyclononane and tetrakis(NN-CH2)-substituted 1,4,7,10-tetraazacyclododecane afforded the folded structures of the hosts where the NN radical oxygen atoms were coordinated to the guest metal ion, leading to enhanced antiferromagnetic couplings in the solid state and an ESR line broadening in the solution phase (NN = 4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide).     

Arylethynyl Groups That Modulate Anion-Binding and Assembling Modes of Rod- and Fan-Shaped π-Electronic Systems

The introduction of arylethynyl moieties at the pyrrole α- and β-positions of dipyrrolyldiketone BF₂ complexes as anion-responsive π-electronic molecules was investigated. The arylethynyl-substituted derivatives formed a variety of anion complexes with planar [1+1]- and interlocked [2+1]-type structures in solution and in the solid state. The derivatives with long alkyl chains in the introduced arylethynyl groups also formed mesophases in the form of ion pairs of the anion complexes and a counter cation. The geometries of the constituent anion complexes affected the packing modes of the dimension-controlled assemblies.     

Structural and electronic properties of phosphino(oligothiophene) gold(I) complexes

A series of gold(I) complexes containing phosphino(oligothiophene) ligands of varying conjugation length has been prepared. Solid state crystal structures of (PT3)AuCl (PT3 = 5-diphenylphosphino-2,2':5',2' '-terthiophene) and AuCl(PTP)AuCl (PTP = 2,5-diphenylphosphinothiophene) have been obtained. The complex AuCl(PTP)AuCl crystallizes as a dimer with two intermolecular Au-Au contacts. Variable temperature NMR spectroscopy is used to demonstrate the presence of aurophilic interactions in solution for AuI(PTP)AuI. Dual emission is observed for AuCl(PTP)AuCl in solution and is attributed to emission from both monomer and dimer. In the solid state, dimer emission is dominant. The iodo analogue, AuI(PTP)AuI, shows only low energy dimer emission in both solution and the solid state. Compounds in which the ligands contain longer bridges (either bithienyl or terthienyl) show absorption and emission bands due to the pi-pi* transition only, both in solution and the solid state.     

Manganese complexes of 1,3,5-triaza-7-phosphaadamantane (PTA): the first nitrogen-bound transition-metal complex of PTA

The structures of two manganese(II) complexes of 1,3,5-triaza-7-phosphaadamantane (PTA) reveal the first transition-metal complexes of PTA in which the metal preferentially coordinates to a nitrogen and not the phosphorus of PTA. The coordination environment about the manganese was probed using X-ray crystallography (solid state) and EXAFS spectroscopy (solution).     

Distinct M and P helical complexes of H2O and metal ions NiII, CuII, and ZnII with enantiomerically pure chiral bis(pyrrol-2-ylmethyleneamine)cyclohexane ligands: crystal structures and circular dichroism properties

The enantiomerically pure bis-bidentate ligands of bis(pyrrol-2-ylmethyleneamine)cyclohexane [H2(LR,S)] are easily synthesized from condensation of the pure R,R and S,S enantiomers of the 1,2-diaminecyclohexane spacer with 2 equiv of pyrrole-2-carbaldehyde. The coordination of [H2(LR,S)] with a H2O molecule and metal ions NiII, CuII, and ZnII gives rise to distinct helical structures and crystal packing motifs: homochiral and enantiopure infinite single-helical polymeric chains of [(H2(LR,S).H2O)n] via hydrogen bonds, mononuclear single helices of [NiII(LR,S)] and [CuII(LR,S)], and a double-stranded dinuclear helicate of [ZnII2(LR,S)2], respectively. The helical structures for all metal complexes in the solid state still remain in the solution. Remarkably, chiral ligands of [H2(LR)] and [H2(LS)] predetermine the chirality of the helices and helicates, i.e., P left-handedness and M right-handedness, respectively. The structural changes of these complexes induced by different coordinators are also characterized by circular dichroism (CD) and absorption spectra in both the solid state and solution. Analysis of CD spectra, with aids of absolute determination of single-crystal X-ray diffraction structures, reveals both intraligand and interligand chromophore couplings. For the potential applications of these complexes, other experiments such as magnetism, photoluminescence, and nonlinear optical properties have also been investigated.     

Trinuclear rhodium hydride complexes

Three novel trinuclear rhodium hydride complexes of the type {[Rh(PP*)H](3)(μ(2)-H)(3)(μ(3)-H)}[BF(4)](2) containing diphosphines Tangphos, t-Bu-BisP* and Me-DuPHOS have been synthesised. The new compounds are very stable. Their structures have been characterized by X-ray analysis in the solid state and by NMR-spectroscopic investigations in solution.     

Preparation and structural studies on dibutyltin(IV) complexes with pyridine mono- and dicarboxylic acids

A number of organotin(IV) complexes with pyridine mono- and dicarboxylic acids (containing ligating -COOH group(s) and aromatic {N} atoms) were prepared in the solid state. The bonding sites of the ligands were determined by means of FT-IR spectroscopic measurements. It was found that in most cases the -COO⁻ groups form bridges between two central {Sn} atoms, thereby leading to polymeric (oligomeric) complexes. On this basis, the experimental ¹¹⁹Sn Mössbauer spectroscopic data were treated with partial quadrupole splitting approximations. The calculations predicted the existence of complexes with octahedral (oh) and trigonal-bipyramidal (tbp) structures, but the formation of complexes with pentagonal-bipyramidal (pbp) structures could not be ruled out. Single-crystals of 2-picolinic and pyridine-2,6-dicarboxylic acid Bu₂Sn(IV)²⁺ complexes were obtained. The X-ray diffraction studies revealed that the central {Sn} atoms are in a pbp environment with bond distances characteristic of organotin(IV) compounds. The two butyl groups are located in axial positions. ¹¹⁹Sn NMR measurements in dmso solution and in the solid state indicated that the polymeric structures of the complexes are not retained in solution. The results of the solid-state ¹¹⁹Sn NMR measurements for compounds 1a, 2a and 6a are in agreement with the structures predicted by Mössbauer spectroscopy and revealed by X-ray diffraction.     

The synthesis and structural study of five-coordinate triorganotin(IV) tropolonates and dibenzoylmethanates

The complexes [1,3-diphenyl-1,3-propanedionato]tricyclohexyltin(IV), (tropolonato)triphenyltin(IV), and (tropolonato)tricyclohexyltin(IV) have been prepared for the first time and have been found to be five-coordinate in the solid state. These and related five-coordinate complexes prepared previously have been studied by a variety of physical methods; ¹³C NMR, UV, IR, Raman, dipole moments and the Kerr effect. While all structures are demonstrably five-coordinate, and all chelates bidentate in the solid state, the geometries of two of the complexes in solution appear to vary somewhat from the expected fac or mer. There is evidence from the solution Kerr effect and ¹³C NMR that cyclohexyl derivatives may disproportionate.     

Sandwich-shaped silver(I) metallomacrocycles encapsulating a XF6(2-) (X = Si, Ge and Sn) anion

A series of sandwich-shaped complexes based on two square tetranuclear Ag(I) metallomacrocycles, [[Ag4(pprd)4]2(XF6)]-(BF4)6.8MeNO2 (pprd = 4-(2-pyridyl)pyrimidine; X = Si, Ge and Sn), in which a XF6(2-) anion is encapsulated, were prepared and their structures were characterized both in the solid state and solution.