Chiral Coordination Compounds Research Articles

Synthesis, crystal structures and fluorescence recognition properties of two novel chiral coordination compounds based on alanine derivate

Two novel chiral coordination compounds {[Cd(D-pmala)(2,2′-bipy)(H2O)]⋅1·25H2O}n (1), {[Pb4(D-pmala)4(5,5′-DM-2,2′-bipy)4(H2O)2]⋅7H2O}n (2) (D-pmala = N-(4-carboxyl) benzoyl-d-alanine, 2,2′-bipy = 2,2′-Bipyridine, 5,5′-DM-2,2′-bipy = 5,5′-Dimethyl-2,2′- Bipyridine) have been successfully synthesized under hydrothermal conditions. Their structures were identified using single-crystal X-ray crystallography and characterized by infrared spectroscopy, elemental analysis, thermogravimetric analysis, powder X-ray diffraction and solid-state circular dichroism spectra. Crystallographic analysis indicate that compound 1 features a "Z"-shaped one-dimensional chain structure, which further extends into three-dimensional supramolecular architectures through hydrogen-bonding interactions. Compound 2 displays a two-dimensional layer structure, a two-dimensional double-layer network structures is further formed through the hydrogen-bonding interactions. Moreover, The fluorescence recognition properties of compound 1 indicate that it is highly selective in detecting Cu2+ ions and tyrosine (Tyr) enantiomers in aqueous solutions, which indicates that compound 1 can be expected to be a bifunctional fluorescent recognition sensor to detect metal ions and amino acid enantiomers.

A Bifunctional Coordination-Chain-Based Hydrogen-Bonded Framework for Quantitative Enantioselective Sensing.

Enantioselective sensing is highly crucial and challenging due to the highly similar physical/chemical properties of enantiomers which may have different chemical impact on organism. Luminescent coordination compounds have attracted great attention as sensing materials based on their controllable chemical and electric structures that can be highly matched with the targeted species. To achieve high-performance enantioselective sensing, the direct synthesis of chiral and luminescent bifunctional coordination compounds is a rational way but highly challenging due to the price and synthesis difficulty. Herein, an anionic coordination-chain-based hydrogen-bonded framework was applied as a host to accommodate chiral and luminescent centers via a facile cation exchange reaction, affording a bifunctional framework that possesses enantioselective sensing properties for the mixture of enantiomers. This study paves a pathway for constructing multifunctional coordination chain-based hydrogen-bonded frameworks for rapidly enantioselective sensing function.

Hydrogen-bonded metal-organic frameworks with multilevel chirality and strong circular dichroism response for circular polarization luminescence

In this work, a pair of chiral coordination compounds with formula as Cd[D-OH-bim]2(NO3)2 (1-D) and Cd[L-OH-bim]2(NO3)2 (1-L) (L-OH-bim = (L)-2-(1-Hydroxyethyl)benzimidazole; D-OH-bim = (D)- 2-(1-Hydroxyethyl)benzimidazole) are synthesized for circular polarization luminescence (CPL). Single crystal X-ray diffraction (SCXRD) results show that the 1-D and 1-L contain chiral Cd[OH-bim]2(NO3)2 units composed of Cd center and chiral OH-bim ligand (D- or L-OH-bim) as well as NO3–. The self-assembly of these chiral units by hydrogen bonding interaction generates a 3D hydrogen-bonded framework containing multiple chirality, such as chiral ligand, helical chain, chiral spatial arrangement and chiral framework (chiral space group and chiral topology). The bulk phase with multilevel chirality shows enhanced circular dichroism response and obvious CPL than that of the organic ligands as well as Cd[OH-bim]2(NO3)2 unit.

Circularly polarized luminescence in the one-dimensional assembly of binaphtyl-based Yb(iii) single-molecule magnets.

Lanthanide ions have attracted great interest owing to their optical and magnetic properties. Single-molecule magnet (SMM) behavior has been a fascinating science for thirty years. Moreover, chiral lanthanide complexes allow the observation of remarkable circularly polarized luminescence (CPL). However, the combination of both SMM and CPL behaviors in a single molecular system is very rare and deserves attention in the design of multifunctional materials. Four chiral one-dimensional coordination compounds involving 1,1'-Bi-2-naphtol (BINOL)-derived bisphosphate ligands and the Yb(iii) centre were synthesized and characterized by powder and single-crystal X-ray diffraction. All the Yb(iii)-based polymers displayed field-induced SMM behavior with magnetic relaxation occurring by applying Raman processes and near infrared CPL in the solid state.

Chiral coordination compounds with exceptional enantioselectivity

The new homochiral Zn-based coordination compounds reveal excellent enantioselective sensing behavior toward d- and l-histidine attributed to the host–guest interactions through the rigid chiral backbones.

A pair of stable Zn(II) enantiomeric coordination compounds: synthesis, crystal structures and luminescent recognition properties

A pair of stable chiral coordination compounds {[Zn (D-hpg) (bpe)]⋅(NO3)⋅(C2H6O)}n1-D, {[Zn (L-hpg) (bpe)]⋅(NO3)⋅(C2H6O)}n1-L (D-Hhpg = D-(−)-4-Hydroxyphenylglycine, L-Hhpg = L-(+)-4-Hydroxyphenylglycine, bpe = 1,2-bis(4-pyridyl)ethane) have been successfully synthesized. Their structures were determined by single-crystal X-ray diffraction analysis and characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis and powder X-ray diffraction. Interestingly, they are 2D layer structures that consist of left- or right-handed helical chains, respectively. Circular dichroism and luminescent properties of compounds 1-D and 1-L were investigated at room temperature. Moreover, 1-D and 1-L show similar selectivity toward Cu2+ ions through luminescent quenching in aqueous solution. In addition, 1-D also displays an excellent recognition ability on detecting CH3OH.

Symmetry-Dependent Vibrational Circular Dichroism Enhancement in Co(II) Salicylaldiminato Complexes.

Chiral coordination compounds of Co(II) and other open-shell metal complexes display enhanced vibrational circular dichroism (VCD) spectra associated with the existence of low-lying excited states (LLESs). In addition to the enhancement, a series of Co(II) salicylaldiminato complexes exhibits an almost monosignate pattern of VCD bands, a unique feature if compared with the usual alternation of positive and negative signals. Frequency and excited-state calculations reveal that VCD enhancement and sign reversal selectively affect the normal modes of B symmetry of the C2-symmetric pseudotetrahedral species thanks to their combination with one or more LLES having the same B symmetry. This proves the strict relation between VCD enhancement and monosignate appearance and demonstrates an unprecedented symmetry dependence of the two phenomena.

Structural and photoluminescent properties of six chiral coordination compounds based on N-acetyl-L-tyrosine

Six novel chiral coordination compounds, namely [Cd(acty)(phen)2](ClO4)·3H2O 1, {[Cd(acty)(bpp)2(H2O)2](NO3)·2H2O}n2, {[Cd(acty)(bpp)2(H2O)2](ClO4)·2H2O}n3, {[Zn2(acty)2(bpp)2(O)]·3.5H2O}n4, {[Ag4(acty)2(bpp)4](NO3)2·8H2O}n5, {[Ag(acty)(4,4’-bipy)]·2H2O}n6 have been synthesized in the presence of N-donor ligands (Hacty = N-acetyl-L-tyrosine, phen = 1,10-phenanthroline, bpp = 1,3-di(4-pyridyl)propane, 4,4’-bipy = 4,4’-bipyridine). Compound 1 shows a 0D structure in the presence of phen. Compounds 2 and 3 are isostructural 1D right-hand helical chains via flexible bpp ligand. Compound 4 features a 1D double-chain structure and 5 displays a 2D (6,6)-connected grid network also by bpp ligand. Compound 6 displays a 1D single-chain structure by rigid 4,4’-bipy ligand. Compound 1, 2 and 5 are further extended into 3D supramolecular architectures through hydrogen-bonding interactions. Compounds 4 and 6 are further linked by hydrogen-bonding interactions into a 2D supramolecular layer. Circular dichroism and luminescent properties of compounds 1−6 were investigated at room temperature. Our results highlight the frameworks and luminescent properties can be controlled via adjusting ancillary N-donor ligands and metal centers.

Water-Soluble Ruthenium (II) Chiral Heteroleptic Complexes with Amoebicidal in Vitro and in Vivo Activity.

Three water-soluble Ru(II) chiral heteroleptic coordination compounds [Ru(en)(pdto)]Cl2 (1), [Ru(gly)(pdto)]Cl (2), and [Ru(acac)(pdto)]Cl (3), where pdto = 2,2'-[1,2-ethanediylbis-(sulfanediyl-2,1-ethanediyl)]dipyridine, en = ethylendiamine, gly = glycinate, and acac = acetylacetonate, have been synthezised and fully characterized. The crystal structures of compounds 1-3 are described. The IC50 values for compounds 1-3 are within nanomolar range (14, 12, and 6 nM, respectively). The cytotoxicity for human peripheral blood lymphocytes is extremely low (>100 μM). Selectivity indexes for Ru(II) compounds are in the range 700-1300. Trophozoites exposed to Ru(II) compounds die through an apoptotic pathway triggered by ROS production. The orally administration to infected mice induces a total elimination of the parasite charge in mice faeces 1-2-fold faster than metronidazole. Besides, all compounds inhibit the trophozoite proliferation in amoebic liver abscess induced in hamster. All our results lead us to propose these compounds as promising candidates as antiparasitic agents.

L- and D-[LnZn(IN)3(C2H4O2)]n (Ln = Eu, Sm, and Gd): Chiral Enantiomerically 3D 3d-4f Coordination Polymers Constructed by Interesting Butterfly-like Building Units and -[Ln-O-Zn]n- Helices.

A total of six three-dimensional chiral coordination compounds L- and D-[LnZn(IN)3(C2H4O2)]n (Ln = Eu, Sm, and Gd; HIN = isonicotinic acid) have been successfully synthesized under hydrothermal conditions without any chiral auxiliary and characterized by IR, TG, elemental analyses, and solid-state circular dichroism spectra. The structures of 1-6 were determined by single-crystal X-ray structural analysis, which shows that L-[LnZn(IN)3(C2H4O2)]n (Ln = Eu (1), Sm (2), and Gd (3)) crystallize in space group P6522 and are levogyrate. The chiral frameworks of L-[LnZn(IN)3(C2H4O2)]n are constructed from L-helical Ln-O-Zn cluster chains, while adjacent L-type helical -[Ln-O-Zn]n- chains are connected through IN(-) ligands. D-[LnZn(IN)3(C2H4O2)]n (Ln = Eu (4), Sm (5), and Gd (6)) crystallize in space group P6122, and their chiral frameworks consist of D-helical Ln-O-Zn cluster chains. The observed second-harmonic generation efficiencies of [EuZn(IN)3(C2H4O2)]n, [SmZn(IN)3(C2H4O2)]n, and [GdZn(IN)3(C2H4O2)]n are 0.4, 0.3, and 0.3 times that of urea, respectively. We also studied luminescence spectra and luminescence lifetimes of 1 and 2. The luminescence lifetimes of 1 and 2 are 1.18 ms, and 29.6 μs, respectively.

3D chiral and 2D achiral cobalt(ii) compounds constructed from a 4-(benzimidazole-1-yl)benzoic ligand exhibiting field-induced single-ion-magnet-type slow magnetic relaxation.

Organizing magnetically isolated 3d transition metal ions, which behave as single-ion magnet (SIM) units, in a coordination network is a promising approach to design novel single-molecule magnets (SMMs). Herein 3D chiral and 2D achiral cobalt(ii) coordination compounds based on single metal nodes with a 4-(benzimidazole-1-yl)benzoic acid (Hbmzbc) ligand, namely, [Co(bmzbc)2(1,2-etdio)]n () (1,2-etdio = 1,2-ethanediol) and [Co(bmzbc)2(Hbmzbc)]n (), have been synthesized and structurally characterized. The 3D chiral structure with 2-fold interpenetrating qtz topological nets consisting of totally achiral components was obtained via spontaneous resolution, while the achiral structure is a 2D (4,4) net. In both structures, individual cobalt(ii) ions are spatially well separated by the long organic ligands in the well-defined networks. Magnetic measurements on and showed field-induced slow magnetic relaxation resulting from single-ion anisotropy of the individual Co(ii) ions. Analysis of the dynamic ac susceptibilities with the Arrhenius law afforded an anisotropy energy barrier of 16.8(3) and 31.3(2) K under a 2 kOe static magnetic field for and , respectively. The distinct coordination environments of the Co(ii) ions in and lead to the different anisotropic energy barriers.

Cobalt(II) complexes with bis-2,4-[N-(S)-phenylalanyl]-6-chlorotriazine: synthesis, structure, and application for separation of enantiomers of butan-2-ol

The chiral coordination compounds [Co(L)(H2O)2(MeOH)] n (1) and Co2(L)2(H2O)(MeOH)4 (2) were synthesized by the reaction of bis-2,4-[N-(S)-phenylalanyl]6-chlorotriazine (LH2) with cobalt(II) pivalate or acetate. In molecules 2, the CoII ions are linked by a bridging water molecule and two carboxy groups of the L2– anion. By passing the racemate of butan-2-ol through a chromatographic column containing complex 1 as the stationary phase, a mixture enriched with the (S)-isomer of this alcohol can be obtained.

Enantioselective synthesis of a chiral coordination polymer with circularly polarized visible laser.

Circular dichroism is known to be the feature of a chiral agent which has inspired scientist to study the interesting phenomena of circularly polarized light (CPL) modulated molecular chirality. Although several organic molecules or assemblies have been found to be CPL-responsive, the influence of CPL on the assembly of chiral coordination compounds remains unknown. Herein, a chiral coordination polymer, which is constructed from achiral agents, was used to study the CPL-induced enantioselective synthesis. By irradiation with either left-handed or right-handed CPL during the reaction and crystallization, enantiomeric excesses of the crystalline product were obtained. Left-handed CPL resulted in crystals with a left-handed helical structure, and right-handed CPL led to crystals with a right-handed helical structure. It is exciting that the absolute asymmetric synthesis of a chiral coordination polymer could be enantioselective when using CPL, and provides a strategy for the control of the chirality of chiral coordination polymers.

Reactions of Pyridyl‐Functionalized, Chelating λ3‐Phosphinines in the Coordination Environment of RhIII and IrIII

Rh(III) and Ir(III) complexes based on the λ(3)-P,N hybrid ligand 2-(2'-pyridyl)-4,6-diphenylphosphinine (1) react selectively at the P=C double bond to chiral coordination compounds of the type [(1H⋅OH)Cp*MCl]Cl (2,3), which can be deprotonated with triethylamine to eliminate HCl. By using different bases, the pKa value of the P-OH group could be estimated. Whereas [(1H⋅O)Cp*IrCl] (4) is formed quantitatively upon treatment with NEt3, the corresponding rhodium compound [(1H⋅O)Cp*RhCl] (5) undergoes tautomerization upon formation of the λ(5)σ(4)-phosphinine rhodium(III) complex [(1⋅OH)Cp*RhCl] (6) as confirmed by single-crystal X-ray diffraction. Blocking the acidic P-OH functionality in 3 by introducing a P-OCH3 substituent leads directly to the λ(5)σ(4)-phosphinine iridium(III) complex (8) upon elimination of HCl. These new transformations in the coordination environment of Rh(III) and Ir(III) provide an easy and general access to new transition-metal complexes containing λ(5)σ(4)-phosphinine ligands.

Syntheses and properties of two chiral multidentate carboxylate copper coordination compounds

A chiral ligand, (R)-2-(4-(carboxymethoxy)phenoxy)propanoic acid, is employed as building block to construct two chiral coordination compounds, [Cu(L)(bipy)(H2O)] (1) and [Cu2(L)2(phen)4(H2O)13] (2), by the solvent-thermal method and the volatilization method, respectively. The compounds are characterized by single-crystal X-ray diffraction (XRD), IR spectra, XRD, TGA, and circular dichroism spectra. Compound 1 is comprised of right-handed helical chains and 2 shows a separated structure, both of which extend to 3-D supramolecular framework by hydrogen bonds and π ··· π interactions. CD indicates both compounds retain original stereo character with strong fluorescence at room temperature.

L- and d-[Ln(HCO2)(SO4)(H2O)]n (Ln = La, Ce, Pr, Nd, and Eu): Chiral Enantiomerically 3D Architectures Constructed by Double −[Ln–O]n– Helices

A total of 10 three-dimensional chiral coordination compounds L- and D-[Ln(HCO(2))(SO(4))(H(2)O)](n) (Ln = La, Ce, Pr, Nd, and Eu) have been synthesized without any chiral auxiliary and characterized by IR, thermogravimetric, and elemental analyses. Their structures were determined by single-crystal X-ray structural analysis, which shows that L-[Ln(HCO(2))(SO(4))(H(2)O)](n) (Ln = La, Ce, Pr, Nd, and Eu) crystallize in space group P4(3) and are laevogyrate and isostructural. The chiral frameworks of L-[Ln(HCO(2))(SO(4))(H(2)O)](n) are constructed from L-helical Ln-O cluster chains, while adjacent L-type helical -[Ln-O](n)- chains are connected through O-Ln-O linkages to form chiral intertwined Ln-O double helices of left-handedness. D-[Ln(HCO(2))(SO(4))(H(2)O)](n) crystallize in space group P4(1), and their chiral frameworks consist of D-helical Ln-O cluster chains. The observed second-harmonic-generation efficiencies of [La(HCO(2))(SO(4))(H(2)O)](n), Ce(HCO(2))(SO(4))(H(2)O)](n), [Pr(HCO(2))(SO(4))(H(2)O)](n), [Nd(HCO(2))(SO(4))(H(2)O)](n), and [Eu(HCO(2))(SO(4))(H(2)O)](n) are 0.7, 0.8, 0.7, 0.5, and 0.7 times that of urea, respectively. It is particularly interesting that [Pr(HCO(2))(SO(4))(H(2)O)](n) shows good two-photon absorption.

In search of conformationally chiral square-planar complexes: dichloridobis(2-methoxypyridine-κN)copper(II)

The title compound, [CuCl2(C6H7NO)2], was synthesized during a study of conformationally chiral square-planar coordination compounds. The coordination geometry deviates from the square-planar geometry generally adopted by copper(II) chloride complexes with pyridine ligands towards a tetrahedral arrangement of ligands. The complex is conformationally chiral but crystallizes in a centrosymmetric space group with both enantiomers present in the unit cell.

Natural Circular Dichroism in X-ray Spectroscopy

The measurement of natural circular dichroism has been extended to the X-ray region. XNCD spectra have been measured for uniaxial single crystals of the chiral coordination compounds Na3[Nd(digly)3]·2NaBF4·6H2O (digly = 2,2‘-oxydiacetate) and {[Co(en)3]Cl3}2·NaCl·6H2O (en = ethane-1,2-diamine) and for ionic crystals such as LiIO3. The XANES part of the XNCD shows circular dichroism corresponding to chiral multiple scattering paths of the photoelectron. In addition, both the Nd(III) and Co(III) compounds show quadrupole allowed pre-edge features (2p → 4f for Nd and 1s → 3d for Co) which have exceptionally large Kuhn dissymmetry factors. The theory of XNCD is discussed and the circular dichroism is shown to be due to the interference between allowed electric dipole and electric quadrupole transition moments (E1−E2 mechanism). This new spectroscopy represents a useful extension to techniques for the study of both molecular and crystal structural enantiomorphism.

Charge-transfer excited state properties of chiral transition metal coordination compounds studied by chiroptical spectroscopy

Chiroptical properties of chiral coordination compounds can be used to assign absolute configuration of ground and excited states. We discuss examples of transition metal complexes where MLCT, LMCT, MMCT and exciton LCT transitions have been observed. Such models are dimolybdenum complexes, cyclometallated Pt and Pd complexes, helicates, and complexes with Schiff-bases, conjugated diimines, catecholates and hydroxamates as ligands. The theoretical methods to assign configurations, i.e. comparison methods, exciton theory or quantum mechanical calculations, are reviewed and shown for selected examples.

ChemInform Abstract: Structural Chemistry of Cobalt(III) Complexes of Thioacylhydrazide and Thioacylhydrazonate Ligands. Crystal Structures of (‐)D‐fac‐Tris(thioacethydrazide)cobalt(III) Chloride, (‐)D‐fac‐Tris(formaldehydethioacethydrazidato)cobalt(III) Hydrate, and fac‐Tris(thiosemicarbazide)cobalt(III) Chloride.

AbstractThe three title complexes are investigated by X‐ray diffraction in order to clarify the degree of delocalization in the three ligand systems and to establish the absolute configuration (Δ) of the two chiral coordination compounds.