Synthesis and Applications of (ONO Pincer)Ruthenium‐Complex‐Bound Norvalines

Two (ONO pincer)ruthenium‐complex‐bound norvalines, Boc?[Ru(pydc)(terpy)]Nva?OMe ( 1 ; Boc=tert‐butyloxycarbonyl, terpy=terpyridyl, Nva=norvaline) and Boc?[Ru(pydc)(tBu‐terpy)]Nva?OMe ( 5 ), were successfully synthesized and their molecular structures and absolute configurations were unequivocally determined by single‐crystal X‐ray diffraction. The robustness of the pincer Ru complexes and norvaline scaffolds against acidic/basic, oxidizing, and high‐temperature conditions enabled us to perform selective transformations of the N‐Boc and C?OMe termini into various functional groups, such as alkyl amide, alkyl urea, and polyether groups, without the loss of the Ru center or enantiomeric purity. The resulting dialkylated Ru‐bound norvaline, n‐C₁₁H₂₃CO?l ‐[Ru(pydc)(terpy)]Nva?NH‐n‐C₁₁H₂₃ (l ‐ 4 ) was found to have excellent self‐assembly properties in organic solvents, thereby affording the corresponding supramolecular gels. Ru‐bound norvaline l ‐ 1 exhibited a higher catalytic activity for the oxidation of alcohols by H₂O₂ than parent complex [Ru(pydc)(terpy)] ( 11 a ).     

A pipecolic acid (Pip)‐containing dipeptide,Boc‐d‐Ala‐l‐Pip‐NHiPr

The title dipeptide, 1‐(tert‐butoxy­carbonyl‐d ‐alanyl)‐N‐iso­propyl‐l ‐pipecol­amide or Boc‐d ‐Ala‐l ‐Pip‐NHⁱPr (H‐Pip‐OH is pipecolic acid or piperidine‐2‐carboxylic acid), C₁₇H₃₁N₃­O₄, with a d –l heterochiral sequence, adopts a type II′β‐­turn conformation, with all‐trans amide functions, where the C‐terminal amide NH group interacts with the Boc carbonyl O atom to form a classical i+3 i intramolecular hydrogen bond. The C^α substituent takes an axial position [H^α (Pip) equatorial] and the trans pipecolamide function is nearly planar.     

Zinc (II), palladium (II) and cadmium (II) complexes containing 4‐methoxy‐N‐(pyridin‐2‐ylmethylene) aniline derivatives: Synthesis,characterization and methyl methacrylate polymerization

A series of Zn (II), Pd (II) and Cd (II) complexes, [(L) _n MX ₂ ] _m (L = L‐a–L‐c; M = Zn, Pd; X = Cl; M = Cd; X = Br; n, m = 1 or 2), containing 4‐methoxy‐N‐(pyridin‐2‐ylmethylene) aniline ( L‐a ), 4‐methoxy‐N‐(pyridin‐2‐ylmethyl) aniline ( L‐b ) and 4‐methoxy‐N‐methyl‐N‐(pyridin‐2‐ylmethyl) aniline ( L‐c ) have been synthesized and characterized. The X‐ray crystal structures of Pd (II) complexes [L ₁ PdCl ₂ ] (L = L‐b and L‐c) revealed distorted square planar geometries obtained via coordinative interaction of the nitrogen atoms of pyridine and amine moieties and two chloro ligands. The geometry around Zn (II) center in [(L‐a)ZnCl ₂ ] and [(L‐c)ZnCl ₂ ] can be best described as distorted tetrahedral, whereas [(L‐b) ₂ ZnCl ₂ ] and [(L‐b) ₂ CdBr ₂ ] achieved 6‐coordinated octahedral geometries around Zn and Cd centers through 2‐equivalent ligands, respectively. In addition, a dimeric [(L‐c)Cd(μ ‐ Br)Br] ₂ complex exhibited typical 5‐coordinated trigonal bipyramidal geometry around Cd center. The polymerization of methyl methacrylate in the presence of modified methylaluminoxane was evaluated by all the synthesized complexes at 60°C. Among these complexes, [(L‐b)PdCl ₂ ] showed the highest catalytic activity [3.80 × 10⁴ g poly (methyl methacrylate) (PMMA)/mol Pd hr^?1], yielding high molecular weight (9.12 × 10⁵ g mol^?1) PMMA. Syndio‐enriched PMMA (characterized using ¹H‐NMR spectroscopy) of about 0.68 was obtained with T_g in the range 120–128°C. Unlike imine and amine moieties, the introduction of N‐methyl moiety has an adverse effect on the catalytic activity, but the syndiotacticity remained unaffected.     

(S)‐5‐Benzylimidazolidine‐2,4‐dione monohydrate

The crystal structure of the title compound, C₁₀H₁₀N₂O₂·H₂O, also known as l ‐5‐benzylhydantoin monohydrate, is described in terms of two‐dimensional supramolecular arrays built up from infinite chains assembled via N—H...O and O—H...O hydrogen bonds among the organic molecules and solvent water molecules, with graph‐set R³₃(10)C(5)C²₂(6). The hydrogen‐bond network is reinforced by stacking of the layers through C—H...π interactions.     

A triangular palladium(II) supramolecular coordination complex based on 1,4‐bis(1H‐imidazol‐1‐yl)benzene and (2,2′‐bipyridyl)palladium(II) nitrate: synthesis and crystal structure

The self‐assembly of ditopic bis(1H‐imidazol‐1‐yl)benzene ligands ( L ^H) and the complex (2,2′‐bipyridyl‐κ²N,N′)bis(nitrato‐κO)palladium(II) affords the supramolecular coordination complex tris[μ‐bis(1H‐imidazol‐1‐yl)benzene‐κ²N³:N^3′]‐triangulo‐tris[(2,2′‐bipyridyl‐κ²N,N′)palladium(II)] hexakis(hexafluoridophosphate) acetonitrile heptasolvate, [Pd₃(C₁₀H₈N₂)₃(C₁₂H₁₀N₄)₃](PF₆)₆·7CH₃CN, 2 . The structure of 2 was characterized in acetonitrile‐d₃ by ¹H/¹³C NMR spectroscopy and a DOSY experiment. The trimeric nature of supramolecular coordination complex 2 in solution was ascertained by cold spray ionization mass spectrometry (CSI–MS) and confirmed in the solid state by X‐ray structure analysis. The asymmetric unit of 2 comprises the trimetallic Pd complex, six PF₆^? counter‐ions and seven acetonitrile solvent molecules. Moreover, there is one cavity within the unit cell which could contain diethyl ether solvent molecules, as suggested by the crystallization process. The packing is stabilized by weak inter‐ and intramolecular C—H…N and C—H…F interactions. Interestingly, the crystal structure displays two distinct conformations for the L ^H ligand (i.e. syn and anti), with an all‐syn‐[Pd] coordination mode. This result is in contrast to the solution behaviour, where multiple structures with syn/anti‐ L ^H and syn/anti‐[Pd] are a priori possible and expected to be in rapid equilibrium.     

Diastereoselective Addition of Allyl Reagents to Variously N‐Monoprotected and N,N‐Diprotected L‐Alaninals

Diastereoselective C₃‐elongation processes of N‐Boc‐, N‐Z‐, N‐Bn‐N‐Boc‐, and N‐Bn‐N‐Z‐L ‐alaninals (Boc=^tBuOCO, Z=PhCH₂OCO, Bn=PhCH₂) using various allyl reagents, such as allyl bromide in the presence of Zn/aqueous NH₄Cl solution, of SnCl₂⋅2 H₂O/NaI or of Mg/CuCl₂⋅2 H₂O, as well as allyltrichlorosilane, are described. A substantially different influence of the N‐protecting groups replacing either one or two amino protons was observed, allowing the selective synthesis of either the syn‐ or anti‐diastereoisomer as a major product.     

Metal Derivatives of Thiosemicarbazones: Crystal and Mole­cular Structures of Mono‐ and Dinuclear Copper(II) Complexes with N1‐Subsitituted Salicylaldehyde Thiosemicarbazones

Reactions of copper(II) acetate with N¹‐subsitituted salicylaldehyde thiosemicarbazones [R¹R²C²=N³–N²H–C¹(=S)–N¹HR³;R¹ = 2‐HO–C₆H₄–, R² = H : R³ = Me (H₂L¹), Et (H₂L²)] are described. Copper(II) acetate was reacted with H₂L¹ and H₂L² ligands in the presence of polypyridyl co‐ligands, and this led to the formation ofmononuclear complexes, [Cu(κ³‐O, N, S‐L¹)(κ²‐N, N‐bipy)] ( 1 ),[Cu(κ³‐O, N, S‐L)(κ²‐N, N‐phen)] [L = L¹ ( 3 ), L² ( 4 )], [Cu(κ³‐O, N, S‐L)(κ²‐N, N‐tmphen)] [L =L¹ ( 5 ), L² ( 6 )] and a dinuclear complex, [Cu₂L²₂(bipy)] ( 2 ) (bipy = 2, 2′‐bipyridine, phen = 1, 10‐phenanthroline, tmphen = 3, 4, 7, 8‐tetramethyl‐1, 10‐phenanthroline). In dinuclear complex 2 , one ligand is O, N³,S‐chelating, while second is O, N³,S‐chelation‐cum‐N²‐bridging; and in all others thio‐ligands are O, N³,S‐chelating. The μ_eff values for the complexes lie in the range of 1.79–1.83 BM. Complexes 1 , 3 – 6 have square pyramidal arrangement, whereas complex 2 has two independent molecules in the crystal lattice, and each molecule has trigonal bipyramidal square planar (5:4) coordination pair. Complexes 2 , 4 , and 6 showed fluorescence properties.     

Synthesis,structure and property of diorganotin N‐[(3‐methoxy‐2‐oxyphenyl)methylene]tyrosinates

Five new diorganotin N‐[(3‐methoxy‐2‐oxyphenyl)methylene] tyrosinates, R₂Sn[2‐O‐3‐MeOC₆H₃CH=NCH (CH₂C₆H₄OH‐4)COO] (R = Me, 1 ; Et, 2 ; Bu, 3 ; Cy, 4 ; Ph, 5 ), have been synthesized and characterized by elemental analysis, IR, NMR (¹H, ¹³C and ¹¹⁹Sn) spectra, and the X‐ray single crystal diffraction. In non‐coordinated solvent, complexes 1 – 5 have penta‐coordinated tin atom. In the solid state, 1 – 3 are centrosymmetric dimmers in which each tin atom is seven‐coordinated in a distorted pentagonal bipyramid, and 4 displays discrete molecular structure with distorted trigonal bipyramidal geometry, and the tin atom of 5 is hexa‐coordinated and possess the distorted octahedral geometry with a coordinational methanol molecule. The intermolecular O‐H???O hydrogen bonds in 1 – 4 link molecules into the different one‐dimensional supramolecular chain with R₂² (30) or R₂² (20) macrocycles, and the molecules of 5 are joined into a two‐dimensional supramolecular network containing R₄⁴ (24) and R₄⁴ (28) two macrocycles. Bioassay results against human tumour cell HeLa indicated that 3 ‐ 5 belonged to the efficient cytostatic agents and the activity decreased in the order 4 > 3 > 5 > 2 > 1. The fluorescence determinations show the complexes may be explored for potential luminescent materials.     

7‐Iodo‐5‐aza‐7‐deazaguanine: Syntheses of Anomeric D‐ and L‐Configured 2‐Deoxyribonucleosides

Iodination of N²‐isobutyryl‐5‐aza‐7‐deazaguanine ( 7 ) with N‐iodosuccinimide (NIS) gave 7‐iodo‐N²‐isobutyryl‐5‐aza‐7‐deazaguanine ( 8 ) in a regioselective reaction (Scheme 1). Nucleobase‐anion glycosylation of 8 with 2‐deoxy‐3,5‐di‐O‐toluoyl‐α‐D ‐ or α‐L ‐erythro‐pentofuranosyl chloride furnished anomeric mixtures of D ‐ and L ‐nucleosides. The anomeric D ‐nucleosides were separated by crystallization to give the α‐D ‐anomer and β‐D ‐anomer with excellent optical purity. Deprotection gave the 7‐iodo‐5‐aza‐7‐deazaguanine 2′‐deoxyribonucleosides 3 (β‐D ; ≥99% de) and 4 (α‐D ; ≥99% de). The reaction sequence performed with the D ‐series was also applied to L ‐nucleosides to furnish compounds 5 (β‐L ; ≥99% de) and 6 (α‐L ; ≥95% de).     

Differentiation of Boc‐protected α,δ‐/δ,α‐ and β,δ‐/δ,β‐hybrid peptide positional isomers by electrospray ionization tandem mass spectrometry

Two new series of Boc‐N‐α,δ‐/δ,α‐ and β,δ‐/δ,β‐hybrid peptides containing repeats of L ‐Ala‐δ⁵‐Caa/δ⁵‐Caa‐L ‐Ala and β³‐Caa‐δ⁵‐Caa/δ⁵‐Caa‐β³‐Caa (L ‐Ala = L ‐alanine, Caa = C‐linked carbo amino acid derived from D ‐xylose) have been differentiated by both positive and negative ion electrospray ionization (ESI) ion trap tandem mass spectrometry (MS/MS). MSⁿ spectra of protonated isomeric peptides produce characteristic fragmentation involving the peptide backbone, the Boc‐group, and the side chain. The dipeptide positional isomers are differentiated by the collision‐induced dissociation (CID) of the protonated peptides. The loss of 2‐methylprop‐1‐ene is more pronounced for Boc‐NH‐L ‐Ala‐δ‐Caa‐OCH₃ (1), whereas it is totally absent for its positional isomer Boc‐NH‐δ‐Caa‐L ‐Ala‐OCH₃ (7), instead it shows significant loss of t‐butanol. On the other hand, second isomeric pair shows significant loss of t‐butanol and loss of acetone for Boc‐NH‐δ‐Caa‐β‐Caa‐OCH₃ (18), whereas these are insignificant for its positional isomer Boc‐NH‐β‐Caa‐δ‐Caa‐OCH₃ (13). The tetra‐ and hexapeptide positional isomers also show significant differences in MS² and MS³ CID spectra. It is observed that ‘b’ ions are abundant when oxazolone structures are formed through five‐membered cyclic transition state and cyclization process for larger ‘b’ ions led to its insignificant abundance. However, b₁⁺ ion is formed in case of δ,α‐dipeptide that may have a six‐membered substituted piperidone ion structure. Furthermore, ESI negative ion MS/MS has also been found to be useful for differentiating these isomeric peptide acids. Thus, the results of MS/MS of pairs of di‐, tetra‐, and hexapeptide positional isomers provide peptide sequencing information and distinguish the positional isomers. Copyright © 2010 John Wiley & Sons, Ltd.     

Dinuclear Palladium Complexes with Two Ligand‐Centered Radicals and a Single Bridging Ligand: Subtle Tuning of Magnetic Properties

The facile and tunable preparation of unique dinuclear [(L^?)Pd?X?Pd(L^?)] complexes (X=Cl or N₃), bearing a ligand radical on each Pd, is disclosed, as well as their magnetochemistry in solution and solid state is reported. Chloride abstraction from [PdCl( NNO^ISQ )] ( NNO^ISQ =iminosemiquinonato) with TlPF₆ results in an unusual monochlorido‐bridged dinuclear open‐shell diradical species, [{Pd( NNO ^ISQ)}₂(μ‐Cl)]⁺, with an unusually small Pd‐Cl‐Pd angle (ca. 93°, determined by X‐ray). This suggests an intramolecular d⁸–d⁸ interaction, which is supported by DFT calculations. SQUID measurements indicate moderate antiferromagnetic spin exchange between the two ligand radicals and an overall singlet ground state in the solid state. VT EPR spectroscopy shows a transient signal corresponding to a triplet state between 20 and 60 K. Complex 2 reacts with PPh₃ to generate [Pd(NNO^ISQ)(PPh₃)]⁺ and one equivalent of [PdCl( NNO^ISQ )]. Reacting an 1:1 mixture of [PdCl( NNO^ISQ )] and [Pd(N₃)( NNO^{I SQ})] furnishes the 1,1‐azido‐bridged dinuclear diradical [{Pd( NNO ^ISQ)}₂(κ¹‐N;μ‐N₃]⁺, with a Pd‐N‐Pd angle close to 127° (X‐ray). Magnetic and EPR measurements indicate two independent S=1/2 spin carriers and no magnetic interaction in the solid state. The two diradical species both show no spin exchange in solution, likely because of unhindered rotation around the Pd?X?Pd core. This work demonstrates that a single bridging atom can induce subtle and tunable changes in structural and magnetic properties of novel dinuclear Pd complexes featuring two ligand‐based radicals.     

Synthesis and helical conformation of poly(N‐propargylamides) carrying L‐aspartic acid in the side chain

Aspartic acid‐based novel poly(N‐propargylamides), i.e., poly[N‐(α‐tert‐butoxycarbonyl)‐L ‐aspartic acid β‐benzyl ester N′‐propargylamide] [poly( 1 )] and poly[N‐(α‐tert‐butoxycarbonyl)‐L ‐aspartic acid α‐benzyl ester N′‐propargylamide] [poly( 2 )] with moderate molecular weights were synthesized by the polymerization of the corresponding monomers 1 and 2 catalyzed with (nbd)Rh⁺[η⁶‐C₆H₅B^?(C₆H₅)₃] in CHCl₃ at 30 °C for 2 h in high yields. The chiroptical studies revealed that poly( 1 ) took a helical structure in DMF, while poly( 2 ) did not in DMF but did in CH₂Cl₂, CHCl₃, and toluene. The helicity of poly( 1 ) and poly( 2 ) could be tuned by temperature and solvents. Poly( 2 ) underwent solvent‐driven switch of helical sense, accompanying the change of the tightness. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5168–5176, 2005     

Two cobalt(II) supramolecular isomers based on N,N′‐bis(pyridin‐3‐yl)oxalamide induced by the molecular orientation of lattice DMF molecules

Supramolecular isomerism for coordination networks refers to the existence of different architectures having the same building blocks and identical stoichiometries. For a given building block, different arrangements can lead to the formation of a series of supramolecular isomers. Two one‐dimensional Co^II coordination polymers based on N,N′‐bis(pyridin‐3‐yl)oxalamide (BPO), both catena‐poly[[[dichloridocobalt(II)]‐bis[μ‐N,N′‐bis(pyridin‐3‐yl)oxalamide‐κ²N:N′]] dimethylformamide disolvate], {[CoCl₂(C₁₂H₁₀N₄O₂)₂]·2C₃H₇NO}_n, have been assembled by the solvothermal method. Single‐crystal X‐ray diffraction analyses reveal that the two compounds are supramolecular isomers, the isomerism being induced by the orientation of the dimethylformamide (DMF) molecules in the crystal lattice.     

Temperature‐induced solid‐to‐solid transformation in helical homochiral coordination polymers

The reactions of (R)‐ and (S)‐4‐(1‐carboxyethoxy)benzoic acid (H₂CBA) with 1,3‐bis(2‐methyl‐1H‐imidazol‐1‐yl)benzene (1,3‐BMIB) ligands afforded a pair of homochiral coordination polymers (CPs), namely, poly[[[μ‐1,3‐bis(2‐methyl‐1H‐imidazol‐1‐yl)benzene][μ‐(S)‐4‐(1‐carboxylatoethoxy)benzoato]zinc(II)] monohydrate], {[Zn(C₁₀H₈O₅)(C₁₄H₁₄N₄)]·H₂O}_n or {[Zn{(S)‐CBA}(1,3‐BMIB)]·H₂O}_n ( 1‐L ), and poly[[[μ‐1,3‐bis(2‐methyl‐1H‐imidazol‐1‐yl)benzene][μ‐(R)‐4‐(1‐carboxylatoethoxy)benzoato]zinc(II)] monohydrate] ( 1‐D ). Three kinds of helical chains exist in compounds 1‐D and 1‐L , which are constructed from Zn^II atoms, 1,3‐BMIB ligands and/or CBA^2? ligands. When the as‐synthesized crystals of 1‐L and 1‐D were further heated in the mother liquor or air, poly[[μ‐1,3‐bis(2‐methyl‐1H‐imidazol‐1‐yl)benzene][μ‐(S)‐4‐(1‐carboxylatoethoxy)benzoato]zinc(II)], [Zn(C₁₀H₈O₅)(C₁₄H₁₄N₄)]_n or [Zn{(S)‐CBA}(1,3‐BMIB)]_n ( 2‐L ), and poly[[μ‐1,3‐bis(2‐methyl‐1H‐imidazol‐1‐yl)benzene][μ‐(R)‐4‐(1‐carboxylatoethoxy)benzoato]zinc(II)] ( 2‐D ) were obtained, respectively. The single‐crystal structure analysis revealed that 2‐L and 2‐D only contained one type of helical chain formed by Zn^II atoms and 1,3‐BMIB and CBA^2? ligands, which indicated that the helical chains were reconstructed though solid‐to‐solid transformation. This result not only means the realization of helical transformation, but also gives a feasible strategy to build homochiral CPs.     

Providing Support in Favor of the Existence of a PdII/PdIV Catalytic Cycle in a Heck‐Type Reaction

The complex [Pd(O,N,C‐L)(OAc)], in which L is a monoanionic pincer ligand derived from 2,6‐diacetylpyridine, reacts with 2‐iodobenzoic acid at room temperature to afford the very stable pair of Pd^IV complexes (OC‐6‐54)‐ and (OC‐6‐26)‐[Pd(O,N,C‐L)(O,C‐C₆H₄CO₂‐2)I] (1.5:1 molar ratio, at ?55 °C). These complexes and the Pd^II species [Pd(O,N,C‐L)(OX)] and [Pd(O,N,C‐L′)(NCMe)]ClO₄, (X=MeC(O) or ClO₃, L′=another monoanionic pincer ligand derived from 2,6‐diacetylpyridine), are precatalysts for the arylation of CH₂?CHR (R?CO₂Me, CO₂Et, Ph) using IC₆H₄CO₂H‐2 and AgClO₄. These catalytic reactions have been studied and a tentative mechanism is proposed. The presence of two Pd^IV complexes was detected by ESI(+)‐MS during the catalytic process. All the data obtained strongly support a Pd^II/Pd^IV catalytic cycle.     

Synthesis of β‐Peptides with β‐Helices from New C‐Linked Carbo‐β‐Amino Acids: Study on the Impact of Carbohydrate Side Chains

The design and synthesis of β‐peptides from new C‐linked carbo‐β‐amino acids (β‐Caa) presented here, provides an opportunity to understand the impact of carbohydrate side chains on the formation and stability of helical structures. The β‐amino acids, Boc‐(S)‐β‐Caa_(g)‐OMe 1 and Boc‐(R)‐β‐Caa_(g)‐OMe 2 , having a D ‐galactopyranoside side chain were prepared from D ‐galactose. Similarly, the homo C‐linked carbo‐β‐amino acids (β‐hCaa); Boc‐(S)‐β‐hCaa_(x)‐OMe 3 and Boc‐(R)‐β‐hCaa_(x)‐OMe 4 , were prepared from D ‐glucose. The peptides derived from the above monomers were investigated by NMR, CD, and MD studies. The β‐peptides, especially the shorter ones obtained from the epimeric (at the amine stereocenter C_β) 1 and 2 by the concept of alternating chirality, showed a much smaller propensity to form 10/12‐helices. This substantial destabilization of the helix could be attributed to the bulkier D ‐galactopyranoside side chain. Our efforts to prepare peptides with alternating 3 and 4 were unsuccessful. However, the β‐peptides derived from alternating geometrically heterochiral (at C_β) 4 and Boc‐(R)‐β‐Caa_(x)‐OMe 5 (D ‐xylose side chain) display robust right‐handed 10/12‐helices, while the mixed peptides with alternating 4 and Boc‐β‐hGly‐OMe 6 (β‐homoglycine), resulted in left‐handed β‐helices. These observations show a distinct influence of the side chains on helix formation as well as their stability.     

7‐Iodo‐8‐aza‐7‐deaza‐2′‐deoxy­adenosine and 7‐bromo‐8‐aza‐7‐deaza‐2′‐deoxyadenosine

The isomorphous structures of the title molecules, 4‐amino‐1‐(2‐deoxy‐β‐d ‐erythro‐pento­furan­osyl)‐3‐iodo‐1H‐pyrazolo‐[3,4‐d]pyrimidine, (I), C₁₀H₁₂IN₅O₃, and 4‐amino‐3‐bromo‐1‐(2‐deoxy‐β‐d ‐erythro‐pento­furan­osyl)‐1H‐pyrazolo[3,4‐d]­pyrimidine, (II), C₁₀H₁₂BrN₅O₃, have been determined. The sugar puckering of both compounds is C1′‐endo (^1′E). The N‐­glycosidic bond torsion angle χ¹ is in the high‐anti range [?73.2 (4)° for (I) and ?74.1 (4)° for (II)] and the crystal structure is stabilized by hydrogen bonds.     

Two Pairs of Homochiral Coordination Polymers with Helices Based on Semi‐rigid Lactic Acid Ligands

Utilizing semirigid lactic acid derivatives (R)‐H₂CBA and (S)‐H₂CBA as chiral ligands, two pair of homochiral coordination polymers formulated as [Zn((R)‐CBA)(1,4‐DIB)] · H₂O ( 1 ‐ D ), [Zn((S)‐CBA)(1,4‐DIB)] · H₂O ( 1 ‐ L ), [Co((R)‐CBA)(1,4‐DIB)] · H₂O ( 2 ‐ D ) and [Co((S)‐CBA)(1,4‐DIB)] · H₂O ( 2 ‐ L ) were prepared under solvothermal reaction condition. Single X‐ray diffraction study reveals that all the complexes are comprised of three kinds of helical chains, which are constructed by corresponding metal ions, CBA^2– ligands, and/or 1,4‐DIB ligands. Moreover, some physical characteristics, such as PXRD, thermal stabilities, solid‐state circular dichroism (CD), luminescent and magnetic properties are also investigated.     

Two new CoII coordination polymers with multifunctional 5‐amino‐2,4,6‐tribromoisophthalic acid and flexible isomeric bis(imidazole) ligands: preparation,crystal structure and characterization

Two new Co^II coordination polymers (CPs), namely, catena‐poly[[[(5‐amino‐2,4,6‐tribromobenzene‐1,3‐dicarboxylato‐κO)aquacobalt(II)]‐bis[μ‐1,3‐bis(imidazol‐1‐ylmethyl)benzene‐κ²N:N′]] 4.75‐hydrate], {[Co(C₈H₂Br₃NO₄)(C₁₄H₁₄N₄)₂(H₂O)]·4.75H₂O}_n, (1), and poly[(μ‐5‐amino‐2,4,6‐tribromobenzene‐1,3‐dicarboxylato‐κ²O¹:O³)[μ‐1,2‐bis(imidazol‐1‐ylmethyl)benzene‐κ²N:N′]cobalt(II)], [Co(C₈H₂Br₃NO₄)(C₁₄H₁₄N₄)]_n, (2), have been synthesized successfully by the assembly of multifunctional 5‐amino‐2,4,6‐tribromoisophthalic acid (H₂ATBIP) and Co^II ions in the presence of the flexible isomeric bis(imidazole) ligands 1,3‐bis(imidazol‐1‐ylmethyl)benzene (mbix) and 1,2‐bis(imidazol‐1‐ylmethyl)benzene (obix). The isomeric mbix and obix ligands have a big influence on the structures of CPs (1) and (2). CP (1) is composed of chains of nanometre‐sized elliptical rings, in which the Co^II atom exhibits a distorted octahedral coordination geometry and ATBIP²⁻ acts as a monodentate ligand. Two adjacent chains are interlinked by π–π stacking interactions and hydrogen bonds, resulting in a supramolecular double chain. Hydrogen‐bonded R₈⁶(16) rings extend adjacent supramolecular double chains into a two‐dimensional supramolecular layer. Halogen bonding and a hydrogen‐bonded R₄²(8) ring further link the two‐dimensional supramolecular layers, leading to the formation of a three‐dimensional supramolecular network. The Co^II ion in CP (2) is tetracoordinated, exhibiting a distorted tetrahedral configuration. The ATBIP²⁻ ligand exhibits a bis(monodentate) coordination bridging mode, linking adjacent Co^II ions into zigzag chains, which are further bridged by the auxiliary bridging obix ligand, resulting in a two‐dimensional (4,4) topological network. Interlayer hydrogen and halogen–halogen bonding further extend the two‐dimensional layers into a three‐dimensional supramolecular network. A detailed analysis of the solid‐state UV–Vis–NIR diffuse‐reflectance spectra of (1) and (2) indicates that a wide optical band gap exists in both (1) and (2). CP (1) exhibits an irreversible dehydration–rehydration behaviour.     

Racemic dipeptide glycyl‐dl‐leucine at 120 K

The structure of glycyl‐dl ‐leucine, C₈H₁₆N₂O₃, has been determined at 120 K by single‐crystal X‐ray diffraction. In addition to three N—H?O‐type hydrogen bonds of the positively charged RNH₃⁺ group of the zwitterionic mol­ecule, an intermolecular N—H?O contact exists between the peptide bond and the carboxyl­ate group. Four hydrogen‐bond cycles were identified, giving a complex pattern.