Recurrence of carboxylic acid-pyridine supramolecular synthon in the crystal structures of some pyrazinecarboxylic acids.

X-ray crystal structures of pyrazinic acid 1 and isomeric methylpyrazine carboxylic acids 2-4 are analyzed to examine the occurrence of carboxylic acid-pyridine supramolecular synthon V in these heterocyclic acids. Synthon V, assembled by (carboxyl)O-H...N(pyridine) and (pyridine)C-H...O(carbonyl) hydrogen bonds, controls self-assembly in the crystal structures of pyridine and pyrazine monocarboxylic acids. The recurrence of acid-pyridine heterodimer V compared to the more common acid-acid homodimer I in the crystal structures of pyridine and pyrazine monocarboxylic acids is explained by energy computations in the RHF 6-31G* basis set. Both the O-H.N and the C-H...O hydrogen bonds in synthon V result from activated acidic donor and basic acceptor atoms in 1-4. Pyrazine 2,3- and 2,5-dicarboxylic acids 10 and 11 crystallize as dihydrates with a (carboxyl)O-H...O(water) hydrogen bond in synthon VII, a recurring pattern in the diacid structures. In summary, the carboxylic acid group forms an O-H...N hydrogen bond in pyrazine monocarboxylic acids and an O-H...O hydrogen bond in pyrazine dicarboxylic acids. This structural analysis correlates molecular features with supramolecular synthons in pyridine and pyrazine carboxylic acids for future crystal engineering strategies.     

Design of two series of 1:1 cocrystals involving 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine and carboxylic acids

Two series of a total of ten cocrystals involving 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine with various carboxylic acids have been prepared and characterized by single‐crystal X‐ray diffraction. The pyrimidine unit used for the cocrystals offers two ring N atoms (positions N1 and N3) as proton‐accepting sites. Depending upon the site of protonation, two types of cations are possible [Rajam et al. (2017). Acta Cryst. C 73 , 862–868]. In a parallel arrangement, two series of cocrystals are possible depending upon the hydrogen bonding of the carboxyl group with position N1 or N3. In one series of cocrystals, i.e. 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–3‐bromothiophene‐2‐carboxylic acid (1/1), 1 , 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–5‐chlorothiophene‐2‐carboxylic acid (1/1), 2 , 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–2,4‐dichlorobenzoic acid (1/1), 3 , and 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–2‐aminobenzoic acid (1/1), 4 , the carboxyl hydroxy group (–OH) is hydrogen bonded to position N1 (O—H…N1) of the corresponding pyrimidine unit (single point supramolecular synthon). The inversion‐related stacked pyrimidines are doubly bridged by the carboxyl groups via N—H…O and O—H…N hydrogen bonds to form a large cage‐like tetrameric unit with an R₄²(20) graph‐set ring motif. These tetrameric units are further connected via base pairing through a pair of N—H…N hydrogen bonds, generating R₂²(8) motifs (supramolecular homosynthon). In the other series of cocrystals, i.e. 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–5‐methylthiophene‐2‐carboxylic acid (1/1), 5 , 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–benzoic acid (1/1), 6 , 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–2‐methylbenzoic acid (1/1), 7 , 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–3‐methylbenzoic acid (1/1), 8 , 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–4‐methylbenzoic acid (1/1), 9 , and 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–4‐aminobenzoic acid (1/1), 10 , the carboxyl group interacts with position N3 and the adjacent 4‐amino group of the corresponding pyrimidine ring via O—H…N and N—H…O hydrogen bonds to generate the robust R₂²(8) supramolecular heterosynthon. These heterosynthons are further connected by N—H…N hydrogen‐bond interactions in a linear fashion to form a chain‐like arrangement. In cocrystal 1 , a Br…Br halogen bond is present, in cocrystals 2 and 3 , Cl…Cl halogen bonds are present, and in cocrystals 5 , 6 and 7 , Cl…O halogen bonds are present. In all of the ten cocrystals, π–π stacking interactions are observed.     

1,2,4,5‐Tetrazines vs. Carboxylic Acid Dimers: Molecular Chemistry vs. Supramolecular Chemistry

The structures of six new tetrazines have been determined and their molecular packing has been compared to the supermolecular architecture observed in related carboxylic acid dimers. In the tetrazines, covalent N? N bonds are considered to replace the intermolecular O? H???O hydrogen bonds of the carboxylic acids. In the systems investigated, it is apparent that, in the majority of cases, the covalent six‐membered ring of the tetrazine is an appropriate replacement for the carboxylic acid synthon. This apparent interplay between molecular and supramolecular units may have applications in the crystal engineering of new materials.     

Syntheses and Crystal Structures of Four New Complexes [Mn(4,4''-bip)2(OH2)4](DBA)·4H2O and [M(OH2)(HDPA)2]·3H2O (M = Mn, Co, Ni)

Four new transition metal complexes, [Mn(4,4'-bip)2(OH2)4](DBA)·4H2O 1(4,4'-bip = 4,4'-bipyridine, H2DBA = benzene-1,3-dicarboxylic acid) and [M(OH2)(HDPA)2]·3H2O (M = Mn 2, M = Co 3, M = Ni 4,H2DPA = 2,6-pyridine-dicarboxylic acid), have been prepared from the reaction of transition metals and carboxylic acids, and characterized by X-ray and elemental analyses. For compound 1, the packing diagram shows that a three-dimensional network is formed via hydrogen bonds and strong π-π interactions. For compounds 2, 3 and 4,a double-helical chain is formed through hydrogen bonds. Moreover, a three-dimensional network is constructed from chains via complicated hydrogen bonds between crystal water molecules and oxygen atoms of HDPA-.     

Conformational analysis of N-methylglycine and N,N-dimethylglycine by ab initio calculations

Eight of the most stable conformers of N-methylglycine (NMG) and five of N,N-dimethylglycine (DMG) were analyzed by high level ab initio calculations. Since NMG has only one amino hydrogen and a carboxylic acid hydrogen, it is capable of the formation of various types of hydrogen-bonded conformers and as a result is ideally suited to studying the importance of hydrogen-bonding on the relative stabilities of the various types of conformers of glycine and N-alkylated glycines. Comparisons of the relative energies of the various NMG and DMG conformers that have different types and number of hydrogen bonds (H-bonds) reveal the importance of hydrogen bonds to the stability of the different types of conformers. For NMG, conformer Ib which has two types of H-bonds and a dipole moment of 1.2 debyes is the most stable. Conformer Ib is similar to that of the most stable conformer of glycine. For DMG, on the other hand, IIc is the most stable conformer. IIc has a dipole moment of 5.6 debyes (compared to a value of 1.1 debyes for another of its conformers, Ic) and only one H-bond which involves the carboxylic acid and amino functionalities. The stability of IIc is attributed to the relative strength of the type H-bond formed — a similar type H-bond of glycine and NMG is predicted to be weaker. Thus, for a particular conformer, the relative strength and number of possible H-bonds that can be formed, and not necessarily the magnitude of the dipole moment, play key roles in the relative stability of amino acid conformers in the gas phase.     

Crystal structure of 1:1 Complexes between urea and two crown ether derivatives of phthalic acid, 2,3,5,6,8,9,11,12,14,15-decahydrobenzo[1,4,7,10,13,16]hexaoxacyclo-octadecin-18,19-dicarboxylic acid (i) and 2,3,5,6,8,9,11,12-octahydro-benzo[1,4,7,10,13]pentaoxacyclopentadecin-15,16-dicarboxylic acid (II)

The crystal structures of the titlke compounds have been determined by X-ray diffraction. Urea, I crystallizes in the triclinic PI space group with cell dimensions a = 8.336(2), b = 11.009(2), c = 13.313(2) Å, α = 105.55(3), β = 103.62(3), γ = 104.63(3)° and Z = 2 final R value 0.072 for 2105 observations. Urea, II crystallizes in the orthorhombic P2₁2₁2₁ space group with cell dimensions a = 8.750(2), b = 10.844(3) and c = 21.215(3) Å and Z = 4, final R value 0.083 for 599 observations. All the hydrogen atoms were located in the complex urea, I ; urea molecules form hydrogen bonded dimers about centers of symmetry, these dimers are sandwiched between macrocyclic rings forming one simple and one bifurcated hydrogen bond from the “endo” hydrogen atoms to the ether oxygen atoms. These units are held by hydrogen bonding between the urea molecules and carboxylic acids in two other units; these hydrogen bonds are cyclic involving eight atoms -(N-H(exo)…O(keto)-C-O-H…O(urea)-C)-. Only one carboxylic acid group per molecule takes part in these hydrogen bonds, the other forms a short, 2.490(7) Å, internal bond to the acceptor keto oxygen atom. N(H)…O bonds range from 2.930(7) to 3.206(7) Å, O(H)…O is 2.475(6) Å. In the complex urea, II each urea is hydrogen bonded to three different host molecules and vice versa; the urea “endo” hydrogen atoms bond to the ether oxygen atoms, while both “exo” hydrogen atoms take part in cyclic hydrogen bonds to carboxylic acids. There is not internal hydrogen bond. N(H)…O bonds range from 2.83 to 3.26(2) A and the O-…O bonds are 2.55 and 2.56(2) Å.     

CH stretching vibration of N-methylformamide as a sensitive probe of its complexation: infrared matrix isolation and computational study

The complexes between trans-N-methylformamide (t-NMF) and Ar, N(2), CO, H(2)O have been studied by infrared matrix isolation spectroscopy and/or ab initio calculations. The infrared spectra of NMF/Ne, NMF/Ar and NMF/N(2)(CO,H(2)O)/Ar matrices have been measured and the effect of the complexation on the perturbation of t-NMF frequencies was analyzed. The geometries of the complexes formed between t-NMF and Ar, N(2), CO and H(2)O were optimized in two steps at the MP2/6-311++G(2d,2p) level of theory. The four structures, found for every system at this level, were reoptimized on the CP-corrected potential energy surface; both normal and CP corrected harmonic frequencies and intensities were calculated. For every optimized structure the interaction energy was partitioned according to the SAPT scheme and the topological distribution of the charge density (AIM theory) was performed. The analysis of the experimental and theoretical results indicates that the t-NMF-N(2) and CO complexes present in the matrices are stabilized by very weak N-H···N and N-H···C hydrogen bonds in which the N-H group of t-NMF serves as a proton donor. In turn, the t-NMF-H(2)O complex present in the matrix is stabilized by O-H···O(C) hydrogen bonding in which the carbonyl group of t-NMF acts as a proton acceptor. Both, the theoretical and experimental results indicate that involvement of the NH group of t-NMF in formation of very weak hydrogen bonds with the N(2) or CO molecules leads to a clearly noticeable red shift of the CH stretching wavenumber whereas engagement of the CO group as a proton acceptor triggers a blue shift of this wavenumber.     

Comparison of the hydrogen‐bond patterns in 2‐amino‐1,3,4‐thiadiazolium hydrogen oxalate, 2‐amino‐1,3,4‐thiadiazole–succinic acid (1/2), 2‐amino‐1,3,4‐thiadiazole–glutaric acid (1/1) and 2‐amino‐1,3,4‐thiadiazole–adipic acid (1/1)

The X‐ray single‐crystal structure determinations of the chemically related compounds 2‐amino‐1,3,4‐thiadiazolium hydrogen oxalate, C₂H₄N₃S⁺·C₂HO₄⁻, (I), 2‐amino‐1,3,4‐thiadiazole–succinic acid (1/2), C₂H₃N₃S·2C₄H₆O₄, (II), 2‐amino‐1,3,4‐thiadiazole–glutaric acid (1/1), C₂H₃N₃S·C₅H₈O₄, (III), and 2‐amino‐1,3,4‐thiadiazole–adipic acid (1/1), C₂H₃N₃S·C₆H₁₀O₄, (IV), are reported and their hydrogen‐bonding patterns are compared. The hydrogen bonds are of the types N—H...O or O—H...N and are of moderate strength. In some cases, weak C—H...O interactions are also present. Compound (II) differs from the others not only in the molar ratio of base and acid (1:2), but also in its hydrogen‐bonding pattern, which is based on chain motifs. In (I), (III) and (IV), the most prominent feature is the presence of an R₂²(8) graph‐set motif formed by N—H...O and O—H...N hydrogen bonds, which are present in all structures except for (I), where only a pair of N—H...O hydrogen bonds is present, in agreement with the greater acidity of oxalic acid. There are nonbonding S...O interactions present in all four structures. The difference electron‐density maps show a lack of electron density about the S atom along the S...O vector. In all four structures, the carboxylic acid H atoms are present in a rare configuration with a C—C—O—H torsion angle of ∼0°. In the structures of (II)–(IV), the C—C—O—H torsion angle of the second carboxylic acid group has the more common value of ∼|180|°. The dicarboxylic acid molecules are situated on crystallographic inversion centres in (II). The Raman and IR spectra of the title compounds are presented and analysed.     

Syntheses and Structures of Two Isomorphous Metal-organic Coordination Complexes Based on 4-Pyrimidin-5-ylbenzoic Acid

The reactions of 4-pyrimidin-5-ylbenzoic acid （HL） with Co（NO3）2·6H2O and Ni（NO3）2·6H2O gave rise to two isomorphous mononuclear coordination complexes, namely, [CoL2（H2O）4] （1） and [NiL2（H2O）4] （2）. Both compounds were characterized by IR spectroscopy and single-crystal X-ray diffraction. X-ray crystallographic analyses reveal that they crystallize in monoclinic, space group P21/n. In the crystal structures of these two complexes, only one nitrogen atom of L coordinates to the metal center, and neither carboxylate group nor another nitrogen atom of L links to Co（Ⅱ） or Ni（Ⅱ）. 2D Layers with significant hydrogen bonds can be observed, and they are further linked by L to form a 3D supramolecular network. Nitrogen atoms are not involved in forming hydrogen bonds, but carboxylic groups of the ligands play an important role in the configuration of this hydrogen-bond layer.     

Phonon-driven proton transfer in 3,5-pyridine dicarboxylic acid studied by 2H, 14N, and 17O nuclear quadrupole resonance

Hydrogen bonding in crystalline 3,5-pyridine dicarboxylic acid has been studied by (2)H, (14)N, and (17)O nuclear quadrupole resonance. The (2)H and (17)O data show the presence of two distinct hydrogen bonds, a "normal" O-H···O bond and a short, strong N···H···O bond, with significantly different NQR parameters. In the latter, the temperature variation of the (14)N nuclear quadrupole resonance (NQR) parameters is related to the phonon-driven proton transfer in the N···H···O hydrogen bond. The temperature dependence of the N···H and H···O distances in the N···H···O hydrogen bond is extracted from the (14)N NQR data.     

Structure, energetics, and infrared spectra of weakly bound HC(2n+1)N···HCl complexes. A theoretical study

Three model systems, HCN···HCl, HC(3)N···HCl, and HC(5)N···HCl, have been investigated computationally with the use of the second-order M?ller-Plesset (MP2) and the coupled cluster (with single and double excitations and noniterative inclusion of triples) methods. The global minima are linear hydrogen-bonded structures with HCl as a proton donor. Bent structures are proton-side complexes with HCl as an electron donor, while the bifurcated hydrogen bonds are predicted for t-shape complexes. One of the most important findings in this paper is that, according to symmetry-adapted perturbation analysis, the induction-to-dispersion ratios are the biggest for linear complexes, and it is the most noticeable difference between linear, bent, and t-shape structures.     

Unusual electron charge density in carboxylic acid. 17O quadrupole coupling in cis-cyclobutane-1,2-dicarboxylic acid

The (17)O NQR frequencies have been measured in cis-cyclobutane-1,2-dicarboxylic acid and the quadrupole coupling tensors have been determined at various temperatures. Two O···H oxygen positions and two O-H oxygen positions are observed, showing the presence of two different types of O-H···O hydrogen bonds in the unit cell. The quadrupole coupling constants at the O-H oxygen positions are approximately 30% lower than the lowest quadrupole coupling constants experimentally observed at the C-O-H positions in other carboxylic acids with either ordered or disordered hydrogen bonds. The O-H distances have been calculated from the (17)O-(1)H dipole-dipole interaction at the O-H oxygen positions. The obtained values are longer than the O-H distances usually found in O-H···O hydrogen bonds with comparable O···O distance, in agreement with the proposed proton exchange O-H···O ? O···H-O, which partially averages the dipole-dipole interaction. The energy difference of the two proton configurations, O-H···O and O···H-O, is calculated from the O-H distances determined by NQR. The temperature dependence of the (17)O quadrupole coupling tensors at the (17)O···H-O oxygen positions is analyzed in the model of proton exchange and the energy differences of the two proton configurations obtained by this analysis agree with the values obtained from the O-H distances. The quadrupole coupling tensors are analyzed in a model based on the Townes and Dailey model. The model shows that the population of an oxygen lone pair orbital is at this oxygen position reduced from 2 to approximately 1.3. The electron electric charge is most probably transferred to the oxygen σ and π electron orbitals. This may be associated with the structure of the cyclobutane ring, where the X-ray data show the presence of two unusually short C-C bonds.     

4,4'-, 5,5'-, and 6,6'-dimethyl-2,2'-bipyridyls: the structures, phase transitions, vibrations, and methyl group tunneling of their complexes with chloranilic acid

The crystal and molecular structures of 4,4(')- and 6,6(')-dimethyl-2,2(')-bipyridyl complexes with 2,5-dichloro-3,6-dihydroxy-p-benzoquinone (chloranilic acid, CLA) have been determined and compared with those of the complex with the 5,5(')-derivative, which is known to possess interesting antiferroelectric properties. In the crystalline state, all three compounds form hydrogen bonded chains with N(+)-H···O(-) and O-H···N bridges on both sides of the bipyridyl constituent. The comparison of three derivatives indicates that the N(+)-H···O(-) hydrogen bonds are shortest for the 5,5(')-dimethyl complex. The 4,4(')- and 6,6(')-derivatives do not show any ferroelectric feature. The 6,6(')-one is, however, characterized by a continuous phase transition, revealed in the differential scanning calorimetry, dilatometric, and dielectric characteristics. The tunneling splitting measured by neutron backscattering in the energy range ±30 μeV for the neat dimethyl bipyridyls and their complexes with CLA indicates that the different splittings are primarily due to the crystal packing effect and that charge transfer between interacting compounds plays only a minor role.     

Amino-Induced 2D Cu-Based Metal–Organic Framework as an Efficient Heterogeneous Catalyst for Aerobic Oxidation of Olefins

With the assistance of hydrogen bonds of the o-amino group, we have successfully tuned a coordination structure from a metal–organic polyhedron (MOP) to a two-dimensional (2D) metal–organic framework (MOF). The amino group forms hydrogen bonds with the two vicinal carboxylic groups, and induces the ligand to coordinate with copper ions to form the 2D structure. The obtained 2D Cu-based MOF (Cu-AIA) has been applied as an efficient heterogeneous catalyst in the aerobic epoxidation of olefins by using air as oxygen source. Without the aggregation problem of active sites in MOPs, Cu-AIA possesses much higher reactivity than MOP-1. Furthermore, the amino group of the framework has been used as a modifiable site through post-synthetic metalation (PSMet) to prepare a 2D MOF-supported Pd single-site heterogeneous catalyst, which shows excellent catalytic performance for the Suzuki reaction. It indicates that Cu-AIA can also work as a good 2D MOF carrier for the derivation of other heterogeneous catalysts.     

Ab initio study of ternary complexes X:(HCNH)(+):Z with X, Z = NCH, CNH, FH, ClH, and FCl: diminutive cooperative effects on structures, binding energies, and spin-spin coupling constants across hydrogen bonds

Ab initio calculations have been performed on a series of complexes in which (HCNH)(+) is the proton donor and CNH, NCH, FH, ClH, and FCl (molecules X and Z) are the proton acceptors in binary complexes X:HCNH(+) and HCNH(+):Z, and ternary complexes X:HCNH(+):Z. These complexes are stabilized by C-H(+)···A and N-H(+)···A hydrogen bonds, where A is the electron-pair donor atom of molecules X and Z. Binding energies of the ternary complexes are less than the sum of the binding energies of the corresponding binary complexes. In general, as the binding energy of the binary complex increases, the diminutive cooperative effect increases. The structures of these complexes, data from the AIM analyses, and coupling constants (1)J(N-H), (1h)J(H-A), and (2h)J(N-A) for the N-H(+)···A hydrogen bonds, and (1)J(C-H), (1h)J(H-A), and (2h)J(C-A) for the C-H(+)···A hydrogen bonds provide convincing evidence of diminutive cooperative effects in these ternary complexes. In particular, the symmetric N···H(+)···N hydrogen bond in HCNH(+):NCH looses proton-shared character in the ternary complexes X:HCNH(+):NCH, while the proton-shared character of the C···H(+)···C hydrogen bond in HNC:HCNH(+) decreases in the ternary complexes HNC:HCNH(+):Z and eventually becomes a traditional hydrogen bond as the strength of the HCNH(+)···Z interaction increases.     

Tartaric acid and its O-acyl derivatives. 7. Crystal structure of O-p-anisoyl-D-tartaric acid and its dimethylammonium salt trihydrate

Monoacylated derivatives O-p-anisoyl-d-tartaric acid and its N,N-dimethylammonium salt are synthesized by the partial hydrolysis of O,O′-di-p-anisoyl-d-tartaric acid. Crystal and molecular structures of both compounds have been determined and analyzed. In both of them, some strong and moderate strength [O-H…O] hydrogen bonds exist between the carboxylic units. The intermolecular hydrogen bonds link the adjacent fragments forming infinite one-dimensional chains parallel to the X-axis.     

Communication: spectroscopic measurement of the binding energy of a carboxylic acid-water dimer

Infrared-ultraviolet two color pump-probe spectroscopy is used to measure the binding energy, D(0,) of a carboxylic acid-water dimer where the acid is 9-hydroxy-9-fluorenecarboxylic acid. The acid-water configuration presents a standard structure for the general acid-water interaction where the water bonds to the carboxylic acid group through two intermolecular hydrogen bonds. Photodissociation studies with product vibrational state resolution have enabled an accurate determination of the binding energy for this acid-water system to be D(0) = 2975 ± 30 cm(-1). Quantum chemical calculations are performed to compare with the experimental observations and a recent measurement on the water dimer (D(0) = 1105 ± 10 cm(-1)).     

Creation of Ternary Multicomponent Crystals by Exploitation of Charge‐Transfer Interactions

Four new ternary crystalline molecular complexes have been synthesised from a common 3,5‐dinitrobenzoic acid (3,5‐dnda) and 4,4′‐bipyridine (bipy) pairing with a series of amino‐substituted aromatic compounds (4‐aminobenzoic acid (4‐aba), 4‐(N,N‐dimethylamino)benzoic acid (4‐dmaba), 4‐aminosalicylic acid (4‐asa) and sulfanilamide (saa)). The ternary crystals were created through the application of complementary charge transfer and hydrogen‐bonding interactions. For these systems a dimer was created through a charge‐transfer interaction between two of the components, while hydrogen bonding between the third molecule and this dimer completed the construction of the ternary co‐crystal. All resulting structures display the same acid ??? pyridine interaction between 3,5‐dnba and bipy. However, changing the third component causes the proton of this bond to shift from neutral OH ??? N to a salt form, O^? ??? HN⁺, as the nature of the group hydrogen bonding to the carboxylic acid was changed. This highlights the role of the crystal environment on the level of proton transfer and the utility of ternary systems for the study of this process.     

Elucidation of Metal‐Ion Accumulation Induced by Hydrogen Bonds on Protein Surfaces by Using Porous Lysozyme Crystals Containing RhIII Ions as the Model Surfaces

Metal‐ion accumulation on protein surfaces is a crucial step in the initiation of small‐metal clusters and the formation of inorganic materials in nature. This event is expected to control the nucleation, growth, and position of the materials. There remain many unknowns, as to how proteins affect the initial process at the atomic level, although multistep assembly processes of the materials formation by both native and model systems have been clarified at the macroscopic level. Herein the cooperative effects of amino acids and hydrogen bonds promoting metal accumulation reactions are clarified by using porous hen egg white lysozyme (HEWL) crystals containing Rh^III ions, as model protein surfaces for the reactions. The experimental results reveal noteworthy implications for initiation of metal accumulation, which involve highly cooperative dynamics of amino acids and hydrogen bonds: i) Disruption of hydrogen bonds can induce conformational changes of amino‐acid residues to capture Rh^III ions. ii) Water molecules pre‐organized by hydrogen bonds can stabilize Rh^III coordination as aqua ligands. iii) Water molecules participating in hydrogen bonds with amino‐acid residues can be replaced by Rh^III ions to form polynuclear structures with the residues. iv) Rh^III aqua complexes are retained on amino‐acid residues through stabilizing hydrogen bonds even at low pH (≈2). These metal–protein interactions including hydrogen bonds may promote native metal accumulation reactions and also may be useful in the preparation of new inorganic materials that incorporate proteins.     

基于吡啶酰胺类配体一维带状配位聚合物的合成、结构及荧光性质

通过吡啶酰胺类配体3,5-二(4-吡啶酰胺基)吡啶(4-DPBA)与相应金属盐反应,合成了3个配位聚合物{[Zn(4-DPBA)2(NO3)2].4DMF}n(1),{[Cd(4-DPBA)2(NO3)2].4DMF}n(2)和{[Cu(4-DPBA)2(DMF)2](ClO4)2.7DMF.2H2O}n(3),并用红外光谱、元素分析、粉末及单晶X-射线衍射等方法对其进行了表征。结果表明配合物1和2是同构的,由平行的一维带状链通过氢键连接而成二维层状结构,而配合物3是由3种不同取向的一维带状链构成二维多层结构。这3个配合物最终均通过氢键连接形成三维超分子结构。研究了配合物1和2的荧光性质。