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Thirteen ternary complexes of optically pure chiral rhodium(II) tetracarboxylates with chiral ligands and triphenylphosphine, formed in situ in CDCl3 solution, were examined by nuclear magnetic resonance spectroscopy. As chiral substrates, two dimeric rhodium tetracarboxylates, derivatives of Mosher's acid and N-phthaloyl tert-leucine, were used. Two chiral amines, N,N-dimethyl-butan-2-amine and N,N-dimethyl-1-phenylethanamine, and some derivatives of methionine, selenomethionine, S-methylcysteine, leucine and proline, were applied as chiral ligands, both optically pure and racemic. An achiral component of ternary complexes, triphenylphosphine, acted as a 31P NMR probe. Ternary complexes containing optically pure ligands revealed 31P NMR signals (233 K, CDCl3) within the range from ca. −24 to −36 ppm, appearing as doublets due to 1J(103Rh,31P) coupling constants of ca. 90 Hz. For some combinations of racemic ligand and dirhodium tetracarboxylate, the signals appeared as quartets due to the presence of two diastereomeric ternary complexes. In these cases, diastereomeric dispersion varied from 14 to 88 Hz. Such signal splitting was not observed for the corresponding complexes of optically pure ligands. The presence of bulky substituents in rhodium tetracarboxylate increases diastereomeric dispersion. These results suggested that ternary complexes in question, in combination with 31P NMR technique, can serve, in some cases, as a means of the optical purity analysis of chiral ligands.

The development of a method capable of distinguishing a single atom in a single molecule is important in many fields. The results reported herein demonstrate sub-nanometer resolution for angularly resolved X-ray photoelectron spectroscopy (ARXPS). This is made possible by the incorporation of a Maximum Entropy Method (MEM) model, which utilize density corrected electronic emission factors to the X-ray photoelectron spectroscopy (XPS) experimental results. In this paper we report on the comparison between experimental ARXPS results and reconstructed for both inorganic and organic thin film samples. Unexpected deviations between experimental data and calculated points are explained by the inaccuracy of the constants and standards used for the calculation, e.g. emission factors, scattering intensity and atomic density through the studied thickness. The positions of iron, nitrogen and fluorine atoms were determined in the molecules of the studied self-assembled monolayers. It has been shown that reconstruction of real spectroscopic data with 0.2 nm resolution is possible.

Complexation of three dimeric rhodium(II) tetracarboxylates: tetraacetylate, tetrakistrifluoroacetylate and optically pure rhodium(II) Mosher's acid derivative, with selenomethionine, the methyl ester of selenomethionine and its N-phthaloyl and N-formyl derivatives, have been investigated by 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. Studies were performed using the NMR titration procedure, in D2O or CDCl3 solution depending on the solubility of substrates and ligands. In the presence of rhodium substrate, ligands formed subsequently 1:1 and 1:2 complexes, consisting of one dirhodium moiety and one or two ligand molecules, respectively. The parameter complexation shift Δδ, defined as a difference between the chemical shift of a nucleus in a complex and corresponding chemical shift in the free ligand, varied from −0.3 to +0.6 ppm (1H) and from −3.3 to +5.4 ppm (13C). Complexation shift pattern indicated the complexation via the selenium atom. For chiral substrate and racemic ligands, diastereomeric dispersions Δν(1H) reached the value up to 140 Hz.

Complexation of rhodium(II) tetraacetate and rhodium(II) tetrakistrifluoroacetate with a set of heteroaromatic N-oxides containing additional functional groups was investigated by means of density functional theory (DFT) calculations, and 1 H, 13 C and 15 N nuclear magnetic resonance (NMR) spectroscopy in CDCl 3 solutions. Chemical shifts for five N-oxides and their 1:1 adducts with rhodium tetraacetate were computed at the B3PW91/[6-311++G(2d,p), Stuttgart ECP)//B3LYP/[6-31G(2d), LANL2DZ] theory level applying IEF PCM (CHCl 3 ) solvation model and taking into account various complexation modes and conformational variety. Calculated values were used for the estimation of complexation shifts Δ δ (Δ δ = δ adduct − δ ligand ). The largest negative complexation shift were estimated for heteroatoms bonded to Rh, from −37 to −70 ppm (N), from −100 to −160 ppm (O in NO group), from −13 to −23 ppm (O in OCH 3 group), and from −12 to −22 ppm (Cl). For the remaining heteroatoms in adducts, the corresponding Δ δ values ranged from −22 to +8.2 ppm (N), from +3 to +58 ppm (O) and from +6 to +51 ppm (Cl). The Δ δ ( 1 H) usually did not exceed 1 ppm, whereas Δ δ ( 13 C) varied from ca. −1 to +7 ppm. Some trends useful for the determination of the complexation site were extracted from calculated data sets. Theoretical findings were applied to analyse experimental NMR data.

Complexation of tetrakis(μ2-N,N'-diphenylformamidinato-N,N')-di-rhodium(II) with ligands containing nitrile, isonitrile, amine, hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups has been studied in liquid and solid phases using 1H, 13C and 15N NMR, 13C and 15N cross polarisation–magic angle spinning NMR, and absorption spectroscopy in the visible range. The complexation was monitored using various NMR physicochemical parameters, such as chemical shifts, longitudinal relaxation times T1, and NOE enhancements. Rhodium(II) tetraformamidinate selectively bonded only unbranched amine (propan-1-amine), pentanenitrile, and (1-isocyanoethyl)benzene. No complexation occurred in the case of ligands having hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups, and more expanded amine molecules such as butan-2-amine and 1-azabicyclo[2.2.2]octane. Such features were opposite to those observed in rhodium(II) tetracarboxylates, forming adducts with all kind of ligands. Special attention was focused on the analysis of Δδ parameters, defined as a chemical shift difference between signal in adduct and corresponding signal in free ligand. In the case of 1H NMR, Δδ values were either negative in adducts of rhodium(II) tetraformamidinate or positive in adducts of rhodium(II) tetracarboxylates. Experimental findings were supported by density functional theory molecular modelling and gauge independent atomic orbitals chemical shift calculations. The calculation of chemical shifts combined with scaling procedure allowed to reproduce qualitatively Δδ parameters. Copyright © 2013 John Wiley & Sons, Ltd.

The complexation of dimeric rhodium(II) tetrakistrifluoroacetylate with 25 ligands containing oxygen atoms: alcohols, ethers, ketones, aldehydes, carboxylic acids and esters in chloroform solution have been investigated by 1 H and 13 C NMR spectroscopy and Density Functional Theory (DFT) methods. Investigated ligands form 1:1 adducts in our experimental conditions, with stability constants in the order of several hundred mol −1 . The exchange of ligands in solution is fast on the NMR spectroscopic timescale. The decrease of longitudinal relaxation times T 1 in ligands in the presence of rhodium salt has been tested as the means of determination of the complexation site in ligands. The influence of complexation on chemical shifts in ligands was evaluated by a parameter complexation shift Δ δ (Δ δ = δ add − δ lig ). These parameters were positive (>0 ppm) and did not exceed 1 ppm for 1 H NMR; and varied from ca. −5 to +15 ppm in the case of 13 C NMR. The calculation by DFT methods using the B3LYP functional (structure optimization, electronic energy) and B3PW91 functional (shielding), and combinations of the (6-31G(2d), 6-311G++(2d,p), and LANL2DZ basis sets, followed by scaling procedures reproduced satisfactorily 1 H and 13 C chemical shifts and, with some limitations, allowed to estimate Δ δ parameters.

Complexation of rhodium(II) dimeric tetraacylates: tetraacetate Rh 2 AcO 4 , tetratrifluoroacetate Rh 2 TFA 4 , and ( S )-Mosher’s acid salt Rh 2 MTPA 4 with both enantiomerically pure and racemic methionine and its derivatives: hydrochloric salt of methionine, hydrochloric salt of methionine methyl ester, N -formyl methionine, N -phthaloyl methionine, N -phthaloyl methyl ester of methionine, and methyl ester of N , N -dimethylmethionine has been investigated by means of 1 H and 13 C nuclear magnetic resonance ( 1 H and 13 C NMR) and absorption electronic spectroscopy in the visible range. Complexation processes were investigated in D 2 O or CDCl 3 solutions, depending on the ligands’ and rhodium salts’ solubilities. Some supporting measurements were performed in the solid phase, using 13 C and 15 N CPMAS NMR techniques. All ligands investigated form 1:1 and 1:2 adducts in the solution, depending on the rhodium salt to ligand molar ratios. The complexation site in the ligands (S atom) was deduced on the basis of the NMR parameter adduct formation shift (Δ δ = δ adduct − δ ligand ) and calculated chemical shifts (DFT, NMR GIAO). In the cases of the Rh 2 TFA 4 and Rh 2 MTPA 4 adducts, decreasing the temperature within the range 220–254 K slowed down the ligand exchange and allowed us to observe the signals of all diastereoisomers in the 1 H and 13 C NMR spectra.

The complexation of N-phthaloyl, N-formyl, and N,N-dimethyl derivatives of S-methylcysteine methyl ester (both racemic and optically pure) with three dimeric rhodium(II) salts, acetate Rh2AcO4, trifluoroacetate Rh2TFA4, and (R)-(+)-α-methoxy-α-trifluoromethylphenylacetate Rh2Mosh4 was investigated by nuclear magnetic resonance spectroscopy (NMR) at room and lower temperatures. The complexation was carried out in situ, in CDCl3 solution using titration procedure; the results were examined by the analysis of 1H and 13C NMR chemical shift change (Δδ). The complexation of free S-methyl cysteine and hydrochloride salt of its methyl ester was performed in D2O solution. For comparison, complexation of some derivatives of leucine, phenylalanine, and proline was examined. N-phthaloyl and N-formyl derivatives of cysteine formed 1 : 1 and 1 : 2 axial complexes with all dirhodium salts. Rhodium substrates were bonded via sulfur. In one case, the complexation of Rh2TFA4 by both sulfur and N-formyl oxygen was noted. Similar complexation of Rh2TFA4, via CHO group, was found for N-formyl derivatives of leucine, phenylalanine, and proline. For N,N-dimethyl derivative of cysteine, both N and S atoms were involved in bonding. At room temperature, in all cases, ligand exchange was fast on the NMR timescale.

Complexation of tetrakis(μ2-N,N'-diphenylformamidinato-N,N')-di-rhodium(II) with ligands containing nitrile, isonitrile, amine, hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups has been studied in liquid and solid phases using (1)H, (13)C and (15)N NMR, (13)C and (15)N cross polarisation-magic angle spinning NMR, and absorption spectroscopy in the visible range. The complexation was monitored using various NMR physicochemical parameters, such as chemical shifts, longitudinal relaxation times T1 , and NOE enhancements. Rhodium(II) tetraformamidinate selectively bonded only unbranched amine (propan-1-amine), pentanenitrile, and (1-isocyanoethyl)benzene. No complexation occurred in the case of ligands having hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups, and more expanded amine molecules such as butan-2-amine and 1-azabicyclo[2.2.2]octane. Such features were opposite to those observed in rhodium(II) tetracarboxylates, forming adducts with all kind of ligands. Special attention was focused on the analysis of Δδ parameters, defined as a chemical shift difference between signal in adduct and corresponding signal in free ligand. In the case of (1)H NMR, Δδ values were either negative in adducts of rhodium(II) tetraformamidinate or positive in adducts of rhodium(II) tetracarboxylates. Experimental findings were supported by density functional theory molecular modelling and gauge independent atomic orbitals chemical shift calculations. The calculation of chemical shifts combined with scaling procedure allowed to reproduce qualitatively Δδ parameters.