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In the present paper, twelve Schiff bases derived from 3-amino-1H-1,2,4-triazole (ATz) and various benzaldehydes, and salicylaldehydes were synthesized. The 1H, 13C, and 15N NMR data are discussed in relation to the structure of ATz and its imine products. In addition, X-ray, ATR-FTIR, and UV–Vis analytical techniques are used for structure elucidation of ATz-based Schiff bases. It was found that the starting material, 3-amino-1H-1,2,4-triazole, exists as tautomeric mixture of three forms (Graphical Abstract) in solution, whereas in the solid state (13C and 15N CPMAS data) potentially tautomeric proton is located on nitrogen atom traditionally marked as N-2 (Graphical Abstract, 2N H structure). All investigated Schiff bases derived from salicylaldehydes exist in both phases as tautomeric equilibrium mixtures, where enol-imine forms are dominated structures. The positions of those equilibria only very slightly depend on substituents in phenol ring. Generally, the contributions of keto-amine forms in the solid state are higher comparing with DMSO solutions.

A new unexpected product of condensation reaction of 1,8-diaminonaphthalene (DAN) and carbonyl compound (here: dehydroacetic acid (dha)) was synthesized. Discussion about the molecular structure of possible products of this reaction was done on the base of NMR studies. The structure of the titled product in both DMSO solution and in the solid state was resolved by analysis of its spectral data (X-ray structure analysis, multinuclear NMR in solution and solid state spectra) and MS measurements. The presented studies provided clear evidence that the titled product exists in diluted DMSO solution as the mixture of two kinetic free ionic species whereas in concentrated DMSO solution as well as in the solid state this system forms associated ionic pairs bonded together by hydrogen bonds.

Former single-crystal and powder X-ray diffraction studies of 9,10-dimethyltriptycene (1) and its isotopomer-d12 selectively deuterated in the aromatic positions (1a) consistently delivered undistorted R3c structure of the material. On the other hand, 1H wide line NMR spectra of polycrystalline 1a reported by us previously were incompatible with the above structure. The presently reported 1H spectra of a single crystal of 1a shed new light onto these discrepancies. These spectra reveal two sharply defined environments of the methyl groups in the investigated crystal, of which only one is consistent with the R3c structure. In it, the methyl groups from neighboring molecules come as closely spaced pairs of D3d symmetry, coupled by intermolecular proton–proton dipole interactions. The other environment encompasses as much as about 20% of the methyl groups. They also appear to fit the R3c lattice but, at variance with those occurring in pairs, do not show dipole couplings to their neighbors. Despite these ...

Seven new oligomeric complexes of 4,4′-bipyridine; 3,3′-bipyridine; benzene-1,4-diamine; benzene-1,3-diamine; benzene-1,2-diamine; and benzidine with rhodium tetraacetate, as well as 4,4′-bipyridine with molybdenum tetraacetate, have been obtained and investigated by elemental analysis and solid-state nuclear magnetic resonance spectroscopy, 13C and 15N CPMAS NMR. The known complexes of pyrazine with rhodium tetrabenzoate, benzoquinone with rhodium tetrapivalate, 4,4′-bipyridine with molybdenum tetrakistrifluoroacetate and the 1 : 1 complex of 2,2′-bipyridine with rhodium tetraacetate exhibiting axial–equatorial ligation mode have been obtained as well for comparison purposes. Elemental analysis revealed 1 : 1 complex stoichiometry of all complexes. The 15N CPMAS NMR spectra of all new complexes consist of one narrow signal, indicating regular uniform structures. Benzidine forms a heterogeneous material, probably containing linear oligomers and products of further reactions. The complexes were characterized by the parameter complexation shift Δδ (Δδ = δcomplex − δligand). This parameter ranged from around −40 to −90 ppm in the case of heteroaromatic ligands, from around −12 to −22 ppm for diamines and from −16 to −31 ppm for the complexes of molybdenum tetracarboxylates with 4,4′-bipyridine. The experimental results have been supported by a density functional theory computation of 15N NMR chemical shifts and complexation shifts at the non-relativistic Becke, three-parameter, Perdew-Wang 91/[6-311++G(2d,p), Stuttgart] and GGA–PBE/QZ4P levels of theory and at the relativistic scalar and spin-orbit zeroth order regular approximation/GGA–PBE/QZ4P level of theory. Nucleus-independent chemical shifts have been calculated for the selected compounds. Copyright © 2015 John Wiley & Sons, Ltd.

The theory of nuclear spin-lattice relaxation in methyl groups in solids has been a recurring problem in nuclear magnetic resonance (NMR) spectroscopy. The current view is that, except for extreme cases of low torsional barriers where special quantum effects are at stake, the relaxation behaviour of the nuclear spins in methyl groups is controlled by thermally activated classical jumps of the methyl group between its three orientations. The temperature effects on the relaxation rates can be modelled by Arrhenius behaviour of the correlation time of the jump process. The entire variety of relaxation effects in protonated methyl groups have recently been given a consistent quantum mechanical explanation not invoking the jump model regardless of the temperature range. It exploits the damped quantum rotation (DQR) theory originally developed to describe NMR line shape effects for hindered methyl groups. In the DQR model, the incoherent dynamics of the methyl group include two quantum rate (i.e., coherence-damping) processes. For proton relaxation only one of these processes is relevant. In this paper, temperature-dependent proton spin-lattice relaxation data for the methyl groups in polycrystalline methyltriphenyl silane and methyltriphenyl germanium, both deuterated in aromatic positions, are reported and interpreted in terms of the DQR model. A comparison with the conventional approach exploiting the phenomenological Arrhenius equation is made. The present observations provide further indications that incoherent motions of molecular moieties in the condensed phase can retain quantum character over much broader temperature range than is commonly thought.

Structures of the main resonance and tautomeric forms of three Schiff bases of 2-hydroxy-1-naphthaldehyde (1OXA), 5-bromosalicylaldehyde (2OXA) and 5-nitrosalicylaldehyde (3OXA) with 1,8-diamine-3,6-dioxaoctane, before and after protonation and complexation of monovalent metal cations, have been studied by FTIR, 1H, 13C and 15N NMR methods. The spectroscopic investigations provided clear evidence that the Schiff bases exist in acetonitrile solution as three different tautomers: 1OXA in enamine-oxo, 2OXA in imine-hydroxy and 3OXA in a low-barrier O···H···N imine-oxo forms. It was found on the basis of multinuclear NMR studies, that in solid state, the enamine-oxo and imine-hydroxy tautomers are formed exclusively, but not the untypical imine-oxo tautomer, which requires strong stabilisation by solvent molecules in solution. MOG-PM6 calculations of the different tautomers allowed visualisation of their energetically the most favourable structures. Protonation of 1OXA–3OXA Schiff bases leads to formation of common forms, i.e. protonated imine-hydroxy structure, irrespectively of the structure of tautomer before protonation. In turn, coordination of monovalent metal cations implies common formation of zwitterionic forms within all studied ligands in solution. Application of FT-IR and NMR titrations in combination with ESI MS spectrometry revealed the nature and the structure of OXA complexes, whose formation is impeded by the intra- and intermolecular interactions. MOG-PM6 calculations allowed visualisation of Li+ and Na+ metal coordination sphere geometries within structure of all investigated complexes, stabilised by intermolecular interactions with solvent molecules.

The structure study of five Schiff bases derived from l -arginine ( l -Arg) and 2-hydroxy carbonyl compounds were performed in both solution and solid state using NMR and X-ray methods. Both analytical methods applied to the solid state sample of two Schiff bases showed a significant difference in molecular structures of unsubstituted and 7-CH3 substituted compounds. This effect was explained as a steric interaction of methyl group. Additionally the structure of two Cd2+ complexes with some Schiff bases were determined by NMR methods in DMSO solution and in the solid state. On the base of heteronuclear NMR measurement (13C, 15N and 113Cd) it was possible to define the complexation site on nitrogen atom. The large set of spectral parameters: chemical shifts, homo- and heteronuclear coupling constants, were used in structure study.

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.

13C, 15N CP/MAS, including 1H–13C and 1H–15N short contact time CP/MAS experiments, and FTIR methods were applied for detailed structural characterization of ansa-macrolides as 3-formylrifamycin SV (1) and its derivatives (2–6) in crystal and in powder forms. Although HPLC chromatograms for 2/CH3OH and 2/CH3CCl3 were the same for rifampicin crystals dissolved in respective solvents, the UV–vis data recorded for them were different in 300–375 nm region. Detailed solid state 13C and 15N CP/MAS NMR and FTIR studies revealed that rifampicin (2), in contrast to 3-formylrifamycin SV (1) and its amino derivatives (3–6), can occur in pure non-ionic or zwitterionic forms in crystal and in pure these forms or a mixture of them in a powder. Multinuclear CP/MAS and FTIR studies demonstrated also that 3–6 derivatives were present exclusively in pure zwitterionic forms, both in powder and in crystal. On the basis of the solid state NMR and FTIR studies, two conformers of 3-formylrifamycin SV were detected in powder form due to the different orientations of carbonyl group of amide moiety. The PM6 molecular modeling at the semi-empirical level of theory, allowed visualization the most energetically favorable non-ionic and zwitterionic forms of 1–6 antibiotics, strongly stabilized via intramolecular H-bonds. FTIR studies indicated that the originally adopted forms of these type antibiotics in crystal or in powder are stable in standard laboratory conditions in time. The results presented point to the fact that because of a possible presence of two forms of rifampicin (compound 2), quantification of the content of this antibiotic in relevant pharmaceuticals needs caution. Copyright © 2013 John Wiley & Sons, Ltd.

Complexation properties of dimeric rhodium(II) tetracarboxylates have been utilised in chemistry, spectroscopy and organic synthesis. Particularly, the combination of these rhodium salts with multifunctional ligands results in the formation of coordination polymers, and these are of interest because of their gas-occlusion properties. In the present work, the polymeric adducts of rhodium(II) tetraacetate with flexible ligands exhibiting conformational variety, ethane-1,2-diamine, propane-1,3-diamine and their N,N′-dimethyl- and N,N,N′,N′-tetramethyl derivatives, have been investigated by means of elemental analysis, 13C CPMAS NMR, 15N CPMAS NMR and density functional theory modelling. Elemental analysis and NMR spectra indicated the axial coordination mode and regular structures of (1 : 1)n oligomeric chains in the case of adducts of ethane-1,2-diamine, N,N′-dimethylethane-1,2-diamine N,N,N′,N′-tetramethylethane-1,2-diamine and N,N,N′,N′-tetramethylpropane-1,3-diamine. Propane-1,3-diamine and N,N′-dimethylpropane-1,3-diamine tended to form heterogeneous materials, composed of oligomeric (1 : 1)n chains and the additive of dirhodium units containing equatorially bonded ligands. Experimental findings have been supported by density functional theory modelling of some hypothetical structures and gauge-invariant atomic orbital calculations of NMR chemical shifts. Copyright © 2013 John Wiley & Sons, Ltd.

According to the damped quantum rotation (DQR) theory, hindered rotation of methyl groups, evidenced in nuclear magnetic resonance (NMR) line shapes, is a nonclassical process. It comprises a number of quantum-rate processes measured by two different quantum-rate constants. The classical jump model employing only one rate constant is reproduced if these quantum constants happen to be equal. The values of their ratio, or the nonclassicallity coefficient, determined hitherto from NMR spectra of single crystals and solutions range from about 1.20 to 1.30 in the latter case to above 5.0 in the former, with the value of 1 corresponding to the jump model. Presently, first systematic investigations of the DQR effects in wide-line NMR spectra of a powder sample are reported. For 1,1,1-triphenylethane deuterated in the aromatic positions, the relevant line-shape effects were monitored in the range 99-121 K. The values of the nonclassicality coefficient dropping from 2.7 to 1.7 were evaluated in line shape fits to the experimental powder spectra from the range 99-108 K. At these temperatures, the fits with the conventional line-shape model are visibly inferior to the DQR fits. Using a theoretical model reported earlier, a semiquantitative interpretation of the DQR parameters evaluated from the spectra is given. It is shown that the DQR effects as such can be detected in wide-line NMR spectra of powdered samples, which are relatively facile to measure. However, a fully quantitative picture of these effects can only be obtained from the much more demanding experiments on single crystals.

The structural study of five Schiff bases derived from diaminomaleonitrile (DAMN) and 2-hydroxy carbonyl compounds was performed using 1H, 13C and 15N NMR methods in solution and in the solid state as well. ATR-FTIR and X-Ray spectroscopies were used for confirmation of the results obtained by NMR method. The imine obtained from DAMN and benzaldehyde was synthesized as a model compound which lacks intramolecular hydrogen bond. Deprotonation of all synthesized compounds was done by treating with tetramethylguanidine (TMG). NMR data revealed that salicylidene Schiff bases in DMSO solution exist as OH forms without intramolecular hydrogen bonds and independent on the substituents in aromatic ring. In the case of 2-hydroxy naphthyl derivative, the OH proton is engaged into weak intramolecular hydrogen bond. Two of imines (salDAMN and 5-BrsalDAMN) exist in DMSO solution as equilibrium mixtures of two isomers (A and B). The structures of equilibrium mixture in the solid state have been studied by NMR, ATR-FTIR and X-Ray methods. The deprotonation of three studied compounds (salDAMN, 5-BrsalDAMN, and 5-CH3salDAMN) proceeded in two different ways: deprotonation of oxygen atom (X form) or of nitrogen atom of free primary amine group of DAMN moiety (Y form). For 5-NO2salDAMN and naphDAMN only one form (X) was observed.

The five Schiff bases obtained by condensation of dehydroacetic acid, p-phenylenediamine and derivatives of salicylaldehyde were investigated by 13C and 15N CPMAS NMR methods to find the structure of intramolecular hydrogen bridges. Additionally the 15N NMR spectra in CDCl3 were done. The results obtained in the solid state and in solution were compared with the X-ray previously published for some of investigated compounds. The relatively small influence of substituent in salicylaldehyde unit on proton position was found as well as only small difference in the hydrogen bridges structure in both phases, solution and solid state, which is in contrast with results acquired for Schiff bases obtained from simple aliphatic amines.

The synthesis and structural properties of new mono- and bis-macrocyclic cyclidene complexes of copper(II) andnickel(II) are presented. The compounds with aliphatic ligands are flexible enough to stabilize metal centers in the three oxidation states +1, +2, and +3. All the electron-transfer processes in the 16-membered mono- and binuclear macrocyclic complexes of copper(II) and nickel(II) were fast and reversible. Two polymorphic forms of the 16-membered mononuclear complex of nickel(II) were isolated in the solid state and characterized. The 16-membered macrocyclic complexes show both U- and Z-shape conformations. The deviation of the macrocyclic ligand from planarity affects the electrochemical properties of the complexes and leads to stabilization of different oxidation states of the Cu and Ni metal centers. Substitution of the exocyclic nitrogen atoms with a second alkyl group increases the deviation from planarity and induces rotation of the functional groups at the meso position relative to the macrocyclic ring. In the bis-macrocyclic complexes, the electron-donating properties are improved and the formal potential of the metal(II)/metal(III) system is less positive with increasing linker length between the macrocyclic units. The acceptor properties of the metal(II) complexes are weaker, the formal potential of the metal(II)/metal(I) couple being shifted to more negative values.

Three model metal complexes: Ni(NCS)L, Zn2(NCS)2L2 and Cd2(NCS)2L2, consisting of the SCN− anion(s) and L = 2-[(2-dimethylaminoethylimino)-methyl]-phenolate, have been studied by X-ray diffraction and solid state NMR spectroscopy. The metal cations in these complexes have different coordination modes: Ni2+ is almost square-planar, the Zn2+ cation in Zn2(NCS)2L2 is pentacoordinated, whereas Cd2+ is penta- and hexacoordinated in [Cd2(NCS)2L2]. The different coordination of the metal cations influences the chemical shifts of the metal cations and also the nitrogen atoms. These chemical shifts can be correlated with the M–N and M–O bond lengths (M = Ni2+, Zn2+, Cd2+).

The complexation of five racemic N- and C-substituted aziridines with three rhodium(II) tetraacylates Rh 2 (CO 2 R) 4 [R = CH 3 , CF 3 or ( S )-C(OCH 3 )(CF 3 )Ph] in CDCl 3 solution has been investigated by 1 H, 13 C and 15 N NMR spectroscopy at various temperatures. Depending on the rhodium salt to ligand L molar ratio the 1:1 and 1:2 ([Rh 2 (CO 2 R) 4 ] L 2 ) axial adducts were formed. The enantiopure rhodium salt formed two 1:1 and three 1:2 distereoisomeric adducts in solution. In contrast to non-complexed aziridines, that exist as either a trans -conformer or as a cis- and trans -conformer mixture, an aziridine ring in the adducts adopted only the cis conformation. Under particular conditions the formation of 2:1 adducts ([Rh 2 (CO 2 R) 4 ] 2 L ) was observed. Nitrogen adduct formation shifts Δ δ = δ adduct − δ ligand from −17 to −30 ppm were used as a proof of complexation via the nitrogen atom in the aziridine ring. These experimental findings were validated by DFT calculations using 6-31g(2d), 6-311G++(2d,p) and LANL2DZ basis sets and two functionals, B3LYP and B3PW91.

A series of sixteen Schiff bases (derivatives of salicylaldehydes and aryl amines) was studied to reveal the influence of substituents and the length of the linker on the properties of the H-bonding formed. In theory, two groups of compounds, derivatives of 2-(2-hydroxybenzylidenoamine)phenol) and 2-hydroxy-N-(2-hydroxybenzylideno)benzylamine, can form different types of H-bonds using one or two hydroxyl groups present in the molecules. Two other groups of compounds, derivatives of 4-(2-hydroxybenzylidenoamine)phenol and N-(2-hydroxybenzyideno)benzylamine, can form only one type of H-bond. It was confirmed by (15)N and (13)C NMR experiments, that in all cases only traditional, H-bonded six-membered chelate rings were formed. The positions of the hydrogen atom in the rings depend on the substituent and phase. Generally, the OH H-bond form dominates in solution, with exception of the nitro derivatives, where the NH tautomer is present. In the solid state the tautomeric equilibrium is strongly shifted to the NH form. Only for the 5-Br derivative of one compound was the reverse relationship found. According to the results of experimental charge density investigations, two intramolecular H-bonds in the 5-methoxy derivative of 2-hydroxy-N-(2'-hydroxybenzylideno)benzylamine) differ significantly in terms of charge density properties. The intra- and intermolecular H-bonds formed by the deprotonated oxygen atom from 2-OH group are strong, with significant charge density concentration at the bond critical point and a straight, well-defined bond path, whereas the second intramolecular H-bond formed by the oxygen atom from the 2'-OH group is quite weak, with ca. five times smaller charge density concentration than in the previous case and a bent bond path. In terms of energy densities, the latter H-bond appears to be a non-bonding interaction, with total energy density being slightly positive. In terms of source contributions to the density at the H-bond critical point from the atoms involved, the intermolecular, linear H-bond is very strong and charge-assisted in the source function classification, the N(1)-H(1N)···O(1) H-bond is medium-strength, while the third H-bond is extremely weak.

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.

A new hydrazone of 5-nitrosalicylaldehyde with indole-3-acetic hydrazide (NSIAH) has been obtained and its structure has been studied by X-ray, FT-IR and CPMAS in the solid as well as 1H, 13C and 15N NMR in the CH3CN-d3 and DMSO-d6 solutions. The hydrazone crystallises in the Pbca space group from the orthorhombic system with a = 9.5435(7) A, b = 11.0932(8) A and c = 29.672(2) A. According to Hirsfeld surface analysis, the whole structure is dominated by H···O interactions (ca. 32.2%) and by H···H interactions (ca. 30%). The other important contributions come from: H···C interactions 19.3%, C···C interactions (π...π electrons; ca. 6.6%) and H···N interactions (also ca. 5.9%). The crystal structure has provided clear evidence that the hydrazone exists in the imine (hydroxy) form in which one intramolecular O–H···N hydrogen bond exists. The existence of this tautomeric form is well reflected by the presence of characteristic bands in the FT-IR spectrum of NSIAH. In CH3CN-d3 solution the imine (hydroxy) form with the intramolecular O–H···N hydrogen bond is preserved, whereas in DMSO-d6 this bond is partially broken and stabilized by the intermolecular O–H···O ones with the solvent molecule. As follows from the PM5 calculations of the NSIAH structures solvated by three DMSO-d6 molecules, structure A including the intramolecular O-H···N hydrogen bond and structure B including only intermolecular hydrogen bonds, are energetically equivalent.

A series of aryl-substituted enaminoketones and their thio analogues in CDCl3 solution and in the solid state were studied by the use of high-resolution 1H and 13C as well as 13C cross polarization magic angle spinning (CP MAS) NMR spectra in combination with gauge including atomic orbitals-density functional theory (GIAO-DFT) calculations performed at the B3PW91/6–311 + + G(d,p) level of theory using the B3PW91/6-311 + + G(d,p)-optimized geometries. The analysis of the 13C NMR spectra in solution was done by using the Incredible Natural Abundance DoublE QUAntum Transfer Experiment (INADEQUATE) technique, whereas trends observed in the 13C shielding constants, calculated for the compounds studied, were a great help in assigning most of the signals in the 13C CP MAS NMR spectra. It was established on the basis of the experimental and theoretical NMR data that both groups of compounds exist in the form of Z-s-Z-s-E isomers in CDCl3 solution as well as in the solid state, with the NH hydrogen atom involved in intramolecular hydrogen bonding. This conclusion is in agreement with the fact that some of the compounds studied reveal liquid-crystalline properties. Three-bond H, H and C, H coupling constants measured in solution played a crucial role in the structure elucidation. Copyright © 2009 John Wiley & Sons, Ltd.

trans-[Co(py)4Cl2]Cl·6H2O, mer-[Co(py)3Cl3] and mer-[Co(py)3(CO3)Cl] were studied by UV-Vis, far-IR and 1H, 13C, 15N NMR. The formation of Co-N bonds lead to variable in sign and magnitude changes of 1H NMR chemical shifts, heavily dependent on proton position, coordination sphere geometry and character of auxiliary ligands. 13C nuclei were deshielded upon Co(III) coordination, while 15N NMR studies exhibited ca. 85–110 ppm shielding effects (ca. 15–25 ppm more expressed for nitrogens trans to N than trans to Cl or O). 13C and 15N CPMAS spectra revealed a slight inequivalency of formally identical Co-py bonds in trans-[Co(py)4Cl2]Cl·6H2O and mer-[Co(py)3Cl3], suggesting for the latter complex an existence of distortion isomers. In chloroform, a spontaneous trans-[Co(py)4Cl2]Cl → mer-[Co(py)3Cl3] + py reaction was monitored by 1H NMR and UV-Vis. This process of py → Cl substitution allowed the design of a more convenient and efficient method of mer-[Co(py)3Cl3] preparation.

The structure of some glucosamine Schiff bases has been studied by means of ab initio RHF and DFT calculation and CP/MAS 13C and 15N NMR measurements. The anomeric and tautomeric equilibria in a DMSO solution have been studied by 1H, 13C and 15N NMR spectroscopy. The anomeric composition of d -2-glucosamine Schiff bases in the solid state and in DMSO solution has been shown to depends on the tautomeric form of Schiff bases and electronic properties of substituents on the aromatic ring.

A series of model Schiff bases – 2,6-bis(alkylimino)phenol derivatives (Me, c-Pr, c-Bu, c-Pen and Ph) – has been studied by the solution and solid state (c-Pr and Ph derivatives) NMR methods. All compounds under investigations exhibit tautomeric equilibria in which proton is distributed between two imine sites. For the whole series, the strongest intramolecular H-bond is formed by the methyl derivative. The cycloaliphatic derivatives form weaker H-bonds. Their strength is proportional to the size of the aliphatic ring. The principal components of 15 N chemical shift anisotropy (CSA) tensor have been measured in the solid state for the cyclopropyl derivative. The first two principal components of the CSA tensor change in the same way with respects to hydrogen bond formation as the isotropic nitrogen chemical shift values. A relationship between the CSA principal components and structure of tautomers present in the system has been discussed. In chloroform solutions we also measured the coalescence temperatures to estimate the reaction rate and activation energy. For the c-Pr Schiff-base derivative, the X-ray structure has been established. This compound crystallizes in the monoclinic P 2 1 space group. There are two independent molecules in the crystal lattice. The geometry of the two moieties is very similar with the exception of some subtle changes in the intramolecular hydrogen bond and its vicinity. Although the molecules seem to be related by a glide plane, the symmetry is non-crystallographic and there is no indication of the existence of such a plane in the intensities of the reflections. We present details of the hydrogen bonds in both moieties.

Two hydrazones and one Schiff base of racemic gossypol have been studied by FT-IR, 13 C and 15 N CP-MAS spectroscopy. The spectroscopic methods have provided evidence that the hydrazones exist in the N -imine– N -imine tautomeric forms, whereas the Schiff base exists in the solid state as enamine–enamine tautomer. The spectral features characteristic of both tautomers and the hydrogen bonds within these structures are discussed.

Tautomerism in 6-mercaptopurine (6mpH), 2,6-dimercaptopurine (2,6dmp) and 6-mercaptopurine-9-riboside (6mp-9rb) was studied in the solution with 2D NMR methods-1H–13C HMBC and 1H–15N HMQC. The 15N NMR signals were assigned and the distribution of mobile protons proposed on the basis of δ13C, δ15N chemical shifts and JHC, JHN coupling constants, determined with HECADE. These heterocycles appear in DMSO-d6 as the thionic species with predominance of the following tautomers: N(1)H, N(7)H for 6mpH; N(1)H, N(3)H, N(7)H for 2,6dmp; N(1)H for 6mp-9rb. Quantum-chemical NMR calculations by GIAO method(RHF/6-31G**//B3LYP/6-31G**) allowed to evaluate the ratios of N(7)H, N(9): N(7), N(9)H tautomeric forms as ca. 3:1 for 6mpH and nearly 10:0 for 2,6dmp. The 13C and 15N CPMAS spectra were measured for solid 6mpH·H2O, anhydrous 6mpH, 2,6dmp and 6-mercaptopurinium chloride (6mpH2Cl), confirming the thionic character of all compounds. The 15N chemical shifts in the solid phase were calculated (B3LYP/6–31G**) for 6mpH·H2O and 6mpH2Cl, basing on the re-determined single crystal X-ray data (optimised with RHF/3-21G**).

The first salicylidenearylamines containing a proton sponge residue with 5′-bromo (6), 5′-nitro (7), and 3′,5′-dinitro (8) substituents have been synthesized. X-ray diffraction and 1H, 13C, and 15N NMR and infrared spectra revealed that 6 and 7 contain very strong OHN bridges typical of o-hydroxy Schiff bases. Additional π-electron coupling with the dimethylaminonaphthyl ring is manifested both in geometrical and infrared parameters. In the case of 7, proton transfer to the imine nitrogen atom occurs in the solid state, accompanied by a remarkable shortening of the OHN bridge (2.553 A). In dinitro derivative 8, the OH proton jumps to the dimethylamino groups, giving a new tautomeric form with the formation of a homoconjugated [NHN]+ cation. Protonation of 6 and 7, affecting the (dimethylamino)naphthyl moiety, disrupts the π-coupling and makes these molecules, unlike common aromatic Schiff bases, highly sensitive to hydrolysis, while 8, being already self-protonated, equilibrates in wet DMSO with the corresponding salicylaldehyde and arylamine in a ca. 1:1 ratio at room temperature.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The Schiff bases of racemic gossypol with l -arginine methyl ester (GSB1), 2-(aminomethyl)-18-crown-6 (GSB2) and 5-hydroxy-3-oxapentylamine (GSB3) were studied by FT–IR, 13 C and 15 N CP-MAS spectroscopy as well as by PM5 semiempirical calculations. The spectroscopic methods give clear evidence that all Schiff bases exist in the solid state as enamine–enamine tautomers. The structures of GSB1–GSB3 and the hydrogen bonds within these structures are discussed.

Eight Schiff bases (N-(R-salicylidene)–cycloalkilamines, R=H, 5-NO2 and 5-Br) obtained from cyclopropyl, cyclobutyl- and cyclopentylamine were investigated in terms of intramolecular hydrogen bond formation in chloroform solution and in the solid state. The relationship between cycloalkyl ring size and proton position was discussed. For the compounds which exist as OH form (salicylaldehyde and 5-bromosalicylaldehyde derivatives), no correlation between ring size and proton position in hydrogen bond was found. For 5-nitro derivatives, the structure of hydrogen bridge strongly depends on the cycloaliphatic ring size.

The 13C, 15N NMR of Schiff bases and their lithium salts, derivatives of amino acids (glycine, alanine, phenylalanine, valine and leucine) and 2-hydroxynaphthylaldehyde in solid state and in DMSO have been measured. The results have shown that the Schiff bases and their lithium salts exist mainly as the proton transferred NH form in solid state and DMSO. The nitrogen atom is protonated by hydrogen originating from the phenolic group.

Eight Schiff bases, derived from tris(2-aminoethyl)amine and some aromatic aldehydes have been investigated by heteronuclear NMR methods in solution and in the solid state. Six of those compounds can form intramolecular hydrogen bonds and two remaining imines which do not have hydroxyl substituent in position 2 cannot form such bonds and were chosen as a model compounds for nonbonded structure. The tautomeric equilibrium position of investigated compounds were estimated on the base of nitrogen chemical shifts and nitrogen-proton one bond coupling constants when available. In solution for each compound in all temperatures applied, single symmetrical dynamic averaged structures were found but in the solid state in a few cases mixtures of several nonequivalent or nonsymmetrical structures were observed. Generally at low temperature the –NH– form is more abundant then at room temperature. Similarly in the solid state the proton transfer from oxygen to nitrogen site is more effective in comparison with the solution, except for the 9-formyl-8-hydroxyjulolidine derivative for which different behavior was found.

In present work set of eight Schiff bases derived from substituted salicylaldehydes and aliphatic and aromatic amines has been studied in the solid state by 15 N and 13 C CPMAS NMR methods. 15 N CPMAS NMR measurement is especially useful for investigation of the tautomerism in the compounds considered, owing to the large difference in the nitrogen chemical shifts of OH and NH tautomers. In the solid state, four of the compounds examined were shown by 15 N CPMAS NMR to exist as OH tautomeric forms, and the remaining four as the corresponding NH forms with different stage of proton transfer process, from oxygen to nitrogen site. This was confirmed by 13 C CPMAS. The results reported were compared with those obtained for only two compounds in CDCl 3 solutions (solubility problems).

The 13C, 15N CP MAS NMR and FT-IR spectra of dioxomolybdenum (VI) complexes of trans-N,N′-bis-(R-salicylidene)-1,2-cyclohexanediamine (R=H, R=3,5-diCl, R=3,5-diBr, R=4,6-diOCH3), trans-N,N′-bis-(2-OH-naphthylidene)-1,2-cyclohexanediamine and trans-N-(salicylidene)-N′-(2-OH-naphthylidene)-1,2-cyclohexanediamine have been measured. Comparative analysis of the NMR and IR spectra of the complexes with those of the corresponding ligands has shown that the complexation of the di-Schiff bases leads to changes in the conformation of the ligands and the charge redistribution. The asymmetric structure and non-planar structure of the complexes have been suggested.

The zinc triad metal chloride complexes with pyridazine of [M(pyridazine)Cl2]n type, M=Zn(II) (1), Cd(II) (2), Hg(II) (3), were synthesized. The crystal and molecular structures of 2 and 3 were studied by single crystal X-ray diffraction. They are isostructural polymers of formulae catena[bis(μ2-chloro)-(μ2-pyridazine-N,N′)]cadmium(II) and catena[bis(μ2-chloro)-(μ2-pyridazine-N,N′)]mercury(II). They crystallize in the orthorhombic Imma space group (2: a=7.056(1), b=7.447(1), c=13.113(1) A; 3: a=7.129(1), b=7.398(1), c=13.073(2) A). The central atoms have the geometry of square bipyramid and are bridged by axial pyridazines and equatorial chlorides. The Cd–N and Hg–N bonds are 2.371(3) and 2.407(5) A, the Cd–Cl and Hg–Cl being 2.6279(7) and 2.6626(12) A, respectively. The X-ray powder diffractograms suggest 1 has a similar structure, being different from the monomeric species Zn(pyridazine)2Cl2 (4), already described by several authors as the sole product of ZnCl2+pyridazine reaction. The 15N CPMAS-NMR measurements of 1–3 reveal significant shielding (65–90 ppm) of nitrogen nuclei upon the formation of coordination bondings, the observed low-frequency shifts decreasing with the atomic mass of the metal.

Five Schiff bases derivatives of 2,2′-dihydroxybiphenyl-3-carboxaldehyde and various para substituted anilines have been synthesised and studied by FT-IR, 1 H, 13 C, 15 N NMR and CPMAS spectroscopy. The structure of the Schiff base includes two intramolecular OH⋯O and OH⋯N hydrogen bonds forming a hydrogen-bonded chain. All Schiff bases studied exist in imine form in chloroform and acetonitrile solution. On the basis of the CPMAS and FT-IR spectra in solid state the SCH5 base has been proved to exist in the enamine form.

The 1 H{ 15 N} heteronuclear correlation and 15 N cross-polarized magic angle spinning NMR spectra of purine ( 1 ) were measured. The Zn(II) chloride complexes with 1 , 7-methylpurine ( 2 ) and 9-methylpurine ( 3 ) were synthesised and studied by analytical methods, far-IR and 15 N NMR. The formulae of ZnL 2 Cl 2 (L= 1 ) and [ZnLCl 2 ] n (L= 2 , 3 ) were found. The formation of Zn(II)N coordination bonds resulted in 3–15 ppm low-frequency shifts of the respective 15 N NMR signals: N-7 for 1 ; N-1, N-9 for 2 ; N-1, N-7 for 3 .

14 N, 15 N and 17 O NMR and data are reported for some mesoionic 1,3-diazoles, 1,3-oxazoles and 1,3-thiadiazoles. Additionally, 15 N CP/MAS NMR data are also given for five mesoionic 1,3-diazoles. The relation between compound structures and NMR parameters has been discussed. 15 N chemical shift values for diazoles, taken from CP/MAS NMR measurements, are very similar to the values observed for compounds in the solution. These imply the structure similarity of compounds in both phases, and allow excluding the chain–ring equilibrium in the solution. The cyclic, ‘mesoionic’ structure of 1,3-diazole have been confirmed by X-ray diffraction study.

The proton transfer equilibrium in a series of double Schiff base derivatives of trans-1,2-diaminocyclohexane in solution and the solid state was studied by means of 15N NMR spectroscopy and analysis of the deuterium isotope effect on the chemical shifts Δ15N(D). The presence of a proton transfer equilibrium in the N-2-hydroxynaphthylidene moieties of the Schiff bases studied in the solid state at room temperature was evidenced. The results confirmed the interrelation of the two hydrogen bonds in double Schiff base derivatives of trans-1,2-diaminocyclohexane. Copyright © 2003 John Wiley & Sons, Ltd.

One macrocyclic and two macrobicyclic Schiff bases have been synthesized and investigated by 1 H, 13 C and 15 N NMR spectroscopy in solid state and CDCl3 solution at different temperatures. The results obtained have shown that all studied Schiff bases in CDCl3 solution at ambient temperature exist in a fast dynamical equilibrium that leads to the averaged symmetrical structure. The presence of flexible aliphatic chains and possibility of formation of different intramolecular hydrogen bonds in II and III leads to several different conformations in CDCl3 solution at low temperatures. An asymmetry of the Schiff bases molecules in solid state has been established. q 2002 Elsevier Science B.V. All rights reserved.

Three Schiff bases: 1-( N -methyl-iminomethyl)-2-naphthol ( I ), 1-( N -isopropyl-iminomethyl)-2-naphthol ( II ) and 1-( N -isopropyl-α-iminoethyl)-2-naphthol ( III ) have been investigated by 15 N and 13 C NMR spectroscopy in order to study the tautomeric equilibrium in both the solid and liquid phases. For two derivatives of 2-hydroxy-1-naphthaldehyde ( I and II ), the NH tautomers have been found to be dominant in both the phases. The Schiff base derived from 2-hydroxy-1-acetonaphthone ( III ) exists in the CDCl 3 solution mainly in the NH form but in the solid state only the OH tautomer has been detected. The steric effect of the methyl group at the imine carbon atom seems to be responsible for such exceptional behaviour of the Schiff base investigated. Additionally, the principal components of 15 N chemical shift (CS) tensor of the compound III and two model compounds (5-methoxy-salicylidenmethylamine ( IV ) and 4-methoxy-salicylidenemethylamine ( V )) have been measured to confirm the electronic structure of III .

The pure polymorphic forms I, II, and III of finasteride were prepared and their purity was confirmed by FTIR, differential scanning calorimetry, and X-ray powder diffraction measurements. The preparation experiments demonstrated that the desolvation process of some finasteride solvates does result not only in the formation of polymorphic forms I and II, but also in obtaining the pure form III. The 13 C cross-polarization magic angle spinning (CP-MAS) and the 15 N CP-MAS spectra can distinguish all three polymorphic forms of finasteride. Additionally, the data point to the presence of only one molecule in crystallographic asymmetric unit of polymorphic forms I and III and two molecules in the form II. The application of electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) spectroscopy for finasteride polymorphic forms shows that the three polymorphs could be distinguished by the characteristic shapes of their VCD spectra in the spectral range 1520–1440 cm − 1 . The ECD spectral patterns of all these forms, however, are almost indistinguishable because of their close similarity. Comparison of the 13 C CP-MAS spectra of forms I, II, and III with those reported in the literature indicates that the so-called finasteride “form X” is identical to the previously known finasteride form III. On this basis, the existence of form X was excluded.

Seven new oligomeric complexes of 4,4'-bipyridine; 3,3'-bipyridine; benzene-1,4-diamine; benzene-1,3-diamine; benzene-1,2-diamine; and benzidine with rhodium tetraacetate, as well as 4,4'-bipyridine with molybdenum tetraacetate, have been obtained and investigated by elemental analysis and solid-state nuclear magnetic resonance spectroscopy, (13)C and (15)N CPMAS NMR. The known complexes of pyrazine with rhodium tetrabenzoate, benzoquinone with rhodium tetrapivalate, 4,4'-bipyridine with molybdenum tetrakistrifluoroacetate and the 1 : 1 complex of 2,2'-bipyridine with rhodium tetraacetate exhibiting axial-equatorial ligation mode have been obtained as well for comparison purposes. Elemental analysis revealed 1 : 1 complex stoichiometry of all complexes. The (15)N CPMAS NMR spectra of all new complexes consist of one narrow signal, indicating regular uniform structures. Benzidine forms a heterogeneous material, probably containing linear oligomers and products of further reactions. The complexes were characterized by the parameter complexation shift Δδ (Δδ = δcomplex - δligand). This parameter ranged from around -40 to -90 ppm in the case of heteroaromatic ligands, from around -12 to -22 ppm for diamines and from -16 to -31 ppm for the complexes of molybdenum tetracarboxylates with 4,4'-bipyridine. The experimental results have been supported by a density functional theory computation of (15)N NMR chemical shifts and complexation shifts at the non-relativistic Becke, three-parameter, Perdew-Wang 91/[6-311++G(2d,p), Stuttgart] and GGA-PBE/QZ4P levels of theory and at the relativistic scalar and spin-orbit zeroth order regular approximation/GGA-PBE/QZ4P level of theory. Nucleus-independent chemical shifts have been calculated for the selected compounds.

The 1 H, 13 C and 15 N NMR spectra of 4-bromo-6-diethylaminomethyl-2-R-iminomethyl-phenol have been recorded in CDCl 3 , in temperatures of 230–300 K. The presence of equilibrium between the two competitive OH⋯NCH 2 and OH⋯NC intramolecular hydrogen bonds has been found. The rotation of the OH group slows down at 230 K (in the NMR-time scale). Compound 1 (RNC 2 H 5 ) exists mainly with the OH group engaged in the intramolecular hydrogen bond to the imine-N atom (85%). The weakening the hydrogen bond by substitution of the N -alkyl by the N -aniline group (compound 2 ) increases the population of the Mannich type form (to 40%).

The 1H, 13C, 15N and 77Se NMR data of various annelated 1,3-selenazoles and -1,3-selenazolines are discussed in terms of tautomerism, configurational and conformational preference as well as HOMO–LUMO transition energies. The interpretations are corroborated by semi-empirical calculations. Divergencies in solution- and solid-state 77Se NMR data are discussed. Copyright © 2001 John Wiley & Sons, Ltd.

Seven compounds, forming intramolecular hydrogen bonds, mostly non-symmetric derivatives of [2,2′-bipyridyl]-3,3′-diol (BP(OH)2) were synthesised. Six of them were chosen for the further analysis. It was proved that the electron-donating (CH3) or electron withdrawing (COOH, COOCH3) substituent introduced next to the reactive proton transfer site (N-atom) may change the parameters of hydrogen bridge in a predictable way. The ab initio (GIAO-CHF/DZP//6-31 G∗∗) and semiempirical (PM3) calculations of the ground state were performed. The molecular geometries, Mulliken net charges, NMR shielding constants were compared with some experimental data. In particular, the 15N nuclear magnetic resonance was used to compare the strength of two internal H-bonds of the molecule.

15 N NMR spectra of a series of N -(R-salicylidene)-alkylamines in CDCl 3 solution were measured. Proton transfer equilibrium has been established on the basis of the temperature dependence of the 15 N chemical shift and 1 J NH coupling constants.

1,2,4-Triazolo-[1,5α]-pyrimidine (tp) was studied by gradient heteronuclear multiple-quantum correlation 15N–1H NMR and by cross-polarized magic angle spinning 13C, 15N NMR. The 15N signals were unambiguously assigned. The assignments of some IR absorption bands were proposed by comparison to purine and adenine spectra. The obtained results were used for the investigation of Zn(tp)2X2-type complexes (X=Cl, Br, I, NCS), suggesting a pseudo-tetrahedral configuration around the Zn(II) ion with unidentately N(3) bonded heterocycles and halides or thiocyanates (N bonded) in terminal positions. A slight shielding effect on the N(3) nucleus upon the formation of Zn(II)–N coordination bonding was observed.

Palladium(II) complexes of formula [Pd(tp)2Cl2] 1, [Pd(dmtp)2Cl2]·H2O 2, [Pd(dptp)2Cl2]·H2O 3, [Pd(dbtp)2Cl2] 4a, 4b, where tp = 1,2,4-triazolo[1,5-a]pyrimidine, dmtp = 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine, dptp = 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine, dbtp = 5,7-di-tert-butyl-1,2,4-triazolo[1,5-a]pyrimidine, were prepared. The crystal structure of [Pd(dbtp)2Cl2]·0.5 C2H5OH 4c was resolved by X-ray diffraction analysis, exhibiting monomeric, nearly square-planar cis geometry and N(3) co-ordination. A small tetrahedral distortion from the co-ordination plane was observed. The Pd–Cl distances are 2.276(1) and 2.283(1) A, and Pd–N 2.042(3) and 2.040(3) A. Spectroscopic measurements (UV-VIS, IR, NMR) suggested analogous structures for 1, 2 and 3. Compounds 4a and 4b are most likely rotational isomers in solution and distortional isomers in the solid state. 15N–1H heteronuclear correlation NMR was measured for 2, 4a and 4b whereas 1 and 3 were characterized with 13C and 15N CP MAS. Significant shielding of the co-ordinated N(3) and adjacent C(2) or C(3a) nuclei was observed.

(13)C, (15)N CP/MAS, including (1)H-(13)C and (1)H-(15)N short contact time CP/MAS experiments, and FTIR methods were applied for detailed structural characterization of ansa-macrolides as 3-formylrifamycin SV (1) and its derivatives (2-6) in crystal and in powder forms. Although HPLC chromatograms for 2/CH3 OH and 2/CH3 CCl3 were the same for rifampicin crystals dissolved in respective solvents, the UV-vis data recorded for them were different in 300-375 nm region. Detailed solid state (13)C and (15)N CP/MAS NMR and FTIR studies revealed that rifampicin (2), in contrast to 3-formylrifamycin SV (1) and its amino derivatives (3-6), can occur in pure non-ionic or zwitterionic forms in crystal and in pure these forms or a mixture of them in a powder. Multinuclear CP/MAS and FTIR studies demonstrated also that 3-6 derivatives were present exclusively in pure zwitterionic forms, both in powder and in crystal. On the basis of the solid state NMR and FTIR studies, two conformers of 3-formylrifamycin SV were detected in powder form due to the different orientations of carbonyl group of amide moiety. The PM6 molecular modeling at the semi-empirical level of theory, allowed visualization the most energetically favorable non-ionic and zwitterionic forms of 1-6 antibiotics, strongly stabilized via intramolecular H-bonds. FTIR studies indicated that the originally adopted forms of these type antibiotics in crystal or in powder are stable in standard laboratory conditions in time. The results presented point to the fact that because of a possible presence of two forms of rifampicin (compound 2), quantification of the content of this antibiotic in relevant pharmaceuticals needs caution.

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.

Complexation properties of dimeric rhodium(II) tetracarboxylates have been utilised in chemistry, spectroscopy and organic synthesis. Particularly, the combination of these rhodium salts with multifunctional ligands results in the formation of coordination polymers, and these are of interest because of their gas-occlusion properties. In the present work, the polymeric adducts of rhodium(II) tetraacetate with flexible ligands exhibiting conformational variety, ethane-1,2-diamine, propane-1,3-diamine and their N,N'-dimethyl- and N,N,N',N'-tetramethyl derivatives, have been investigated by means of elemental analysis, (13)C CPMAS NMR, (15)N CPMAS NMR and density functional theory modelling. Elemental analysis and NMR spectra indicated the axial coordination mode and regular structures of (1 : 1)n oligomeric chains in the case of adducts of ethane-1,2-diamine, N,N'-dimethylethane-1,2-diamine N,N,N',N'-tetramethylethane-1,2-diamine and N,N,N',N'-tetramethylpropane-1,3-diamine. Propane-1,3-diamine and N,N'-dimethylpropane-1,3-diamine tended to form heterogeneous materials, composed of oligomeric (1 : 1)n chains and the additive of dirhodium units containing equatorially bonded ligands. Experimental findings have been supported by density functional theory modelling of some hypothetical structures and gauge-invariant atomic orbital calculations of NMR chemical shifts.