A dinuclear triple-stranded helicate with a bis(benzene-o-dithiolato) ligand

The bis(benzene-o-dithiol) ligand H4-1 reacts with Ti4+ in a self-assembly reaction to give the dinuclear triple-stranded helicate [Ti2(1)3]4- which is the first helicate build exclusively from benzene-o-dithiolato donor groups.     

A novel mu(4)-oxo bridged copper tetrahedron derived by self-assembly: first example of double helical bis(tridentate) coordination of a hexadentate amine phenol ligand

In methanol, the reaction of Cu(ClO(4))(2).6H(2)O and the hexadentate amine phenol ligand (H(2)bahped) in the presence of triethylamine affords a tetranuclear copper(II) complex having the formula [Cu(4)(mu(4)-O)(bahped)(2)](ClO(4))(2). The X-ray structure of this complex shows a tetrahedral central [Cu(II)(4)(mu(4)-O)]unit coordinated to two hexadentate bridging (via the central ethylenediamine part) ligands. The compound is the first example of a mu(4)-oxo tetranuclear copper(II) complex without any bridging ligand along the six tetrahedral edges. Variable-temperature magnetic data clearly show an S(t) = 0 spin ground state for antiferromagnetic interactions between four (2)B(2) copper(II) ions in a dimer of dimers.     

Asymmetric transformation of a double-stranded, dicopper(I) helicate containing achiral bis(bidentate) Schiff bases

Reactions of the bis(bidentate) Schiff-bases N,N'-bis(6-alkyl-2-pyridylmethylene)ethane-1,2-diamine (where alkyl = H, Me, iPr) (L) with tetrakis(acetonitrile)copper(I) hexafluorophosphate and silver(I) hexafluorophosphate afforded, respectively, the double-stranded, dinuclear metal helicates [T-4-(R,R)]-(+/-)-[M2L2](PF6)2 (M = Cu, Ag). The helicates were characterized by 1H and 13C NMR spectroscopy, conductivity, microanalysis, and single-crystal X-ray structure determinations on selected compounds. Intermolecular ligand exchange and intramolecular inversion rates for the complexes were investigated by 1H NMR spectroscopy. Reversible intermolecular ligand exchange between two differently substituted helicates followed first-order kinetics. The rate constants (k) and corresponding half-lives (t(1/2)) for ligand exchange for the dicopper(I) helicates were k = (1.6-1.8) x 10(-6) s(-1) (t(1/2) = 110-120 h) in acetone-d6, k = 4.9 x 10(-6) s(-1) (t(1/2) = 40 h) in dichloromethane-d2, and k > 2 x 10(-3) s(-1) (t(1/2) < 5 min) in acetonitrile-d3. Ligand exchange for the disilver(I) helicates occurred with k > 2 x 10(-3) s(-1) (t(1/2) < 5 min). Racemization of the dicopper(I) helicate by an intramolecular mechanism was investigated by determination of the coalescence temperature for the diastereotopic isopropyl-Me groups in the appropriate complex, and DeltaG() > 76 kJ mol(-1) was calculated for the process in acetone-d6, nitromethane-d3, and dichloromethane-d2 with DeltaG() = 75 kJ mol(-1) in acetonitrile-d3. Complete anion exchange of the hexafluorophosphate salt of a dicopper(I) helicate with the enantiomerically pure Delta-(-)-tris(catecholato)arsenate(V) ([As(cat)3]-) in the presence of Dabco gave the two diastereomers (R,R)-[Cu2L2][Delta-(-)-[As(cat)3]]2 and (S,S)-[Cu2L2][Delta-(-)-[As(cat)3]]2 in up to 54% diastereomeric excess, as determined by (1)H NMR spectroscopy. The diastereomerically and enantiomerically pure salt (R,R)-[Cu(2)L2][Delta-(-)-[As(cat)3]]2 crystallized from the solution in a typical second-order asymmetric transformation. The asymmetric transformation of the dicopper(I) helicate is the first synthesis of a diastereomerically and enantiomerically pure dicopper(I) helicate containing achiral ligands.     

Synthesis and optical resolution of a Cu(I) double-stranded helicate with ketimine-bridged tris(bipyridine) ligands

A tetranuclear Cu(I) double-stranded helicate was synthesized from ketimine-bridged tris(bipyridine) ligands and Cu(I) ions, and the racemate was successfully resolved by diastereomeric salt formation using an optically pure phosphate anion followed by anion exchange with NaPF(6) without racemization.     

Structure and properties of a new double-stranded tetranuclear [Cu(II)2]2 helicate

A novel double-stranded tetranuclear helicate composed of a pair of [Cu(II)(2)] dimers has been prepared and characterized by exploiting the flexibility, chelating ability and bridging potential of a hexadentate bis-oximate ligand.     

Controlled generation of acentric and homochiral coordination compounds from a versatile asymmetric ligand 4-(1H-1,2,4-triazol-3-yl)-4H-1,2,4-triazole

Luminescent acentric and homochiral coordination compounds, which possess new topological networks, multiple helical structures and NLO properties, have been generated through the control of a versatile asymmetric ligand as well as inorganic anions, and this suggests a new protocol for preparing acentric and chiral materials.     

Silver(I) coordination polymers based on a nano-sized bent bis(3-acetylenylphenyl-(4-cyanophenyl))oxadiazole ligand: the role of ligand isomerism and the templating effect of polyatomic anions and solvent intermediates

One nanosized oxadiazole bridging ligand, bis(3-acetylenylphenyl-(4-cyanophenyl))oxadiazole (L11), was designed and synthesized by the reaction of bis(3-iodophenyl)oxadiazole with 4-cyanophenylacetylene via a Sonogashira-Hagihara cross-coupling reaction. Eight Ag(I)-L11 coordination polymers with one-, two-, or three-dimensional structures have been successfully prepared by the reaction of L11 with various Ag(I) salts in solution. New coordination polymers were fully characterized by infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction. All new complexes contain silver heteroatom cluster-connecting nodes, and the L11 ligand is "doubling up" in the frameworks. In this Ag(I)-L11 system, the conformation of L11 is versatile because of the conformational rotation around the central oxadiazole moiety and depends greatly on the counterion and solvent system used in the formation of the complexes. In addition, the luminescence property and host-guest chemistry of some complexes were investigated primarily.     

Coordination chemistry of a new rigid, hexadentate bispidine-based bis(amine)tetrakis(pyridine) ligand

The hexadentate bispidine-based ligand 2,4-bis(2-pyridyl)-3,7-bis(2-methylenepyridine)-3,7-diazabicyclo[3.3.1]nonane-9-on-1,5-bis(carbonic acid methyl ester), L(6m), with four pyridine and two tertiary amine donors, based on a very rigid diazaadamantane-derived backbone, is coordinated to a range of metal ions. On the basis of experimental and computed structural data, the ligand is predicted to form very stable complexes. Force field calculations indicate that short metal-donor distances lead to a buildup of strain in the ligand; that is, the coordination of large metal ions is preferred. This is confirmed by experimentally determined stability constants, which indicate that, in general, stabilities comparable to those with macrocyclic ligands are obtained with the relative order Cu(2+) > Zn(2+) > Ni(2+) < Co(2+), which is not the typical Irving-Williams behavior. The preference for large M-N distances also emerges from relatively high redox potentials (the higher oxidation states, that is, the smaller metal ions, are destabilized) and from relatively weak ligand fields (dd-transition, high-spin electronic ground states). The potentiometric titrations confirm the efficient encapsulation of the metal ions since only 1:1 complexes are observed, and, over a large pH range, ML is generally the only species present in solution.     

Conformational supramolecular isomerism in one-dimensional silver(I) coordination polymer of a flexible bis(bidentate) N,N-donor ligand with p-xylyl spacer

The isolation and structural characterisation of three isomeric silver(I) complexes, 1a, 1b and 2 with the general formula {[AgL(1)]ClO(4)}(n) (where L(1) is a bis(bidentate) N,N-donor ligand derived from the Schiff-base condensation of α,α'-diamino-p-xylene and pyridine-2-carboxaldehyde) are discussed. Single-crystal X-ray structures reveal the polymeric nature for the complexes where all the silver ions are in pseudotetrahedral geometry with the AgN(4) coordination environment. Isomers 1a (Pc space group) and 1b (Cc space group) were crystallised from acetonitrile whereas 2 (C2/c space group) was crystallised during the synthesis from a solvent mixture of dicholormethane and methanol. The flexible ligand (L(1)) adopts only an anti conformation in 1b and the presence of two different anti conformations in the repeating unit results in the formation of a trapezoidal wave polymeric chain. However, both gauche and anti conformations of the ligand are found to be present in the polymeric chains of 1a. In the polymeric chain of 2, only one anti isomer of the ligand is present in the repeating unit resulting in a triangular wave chain. The structure of isomer 1a is solvent induced and solvent plays a major role in the crystal packing of this isomer. One-dimensional coordination polymers 1a, 1b and 2 are related to each other as conformational supramolecular isomers. Additionally, two independent polymeric chains parallel to each other: one triangular wave consisting of only an anti conformation and a trapezoidal wave chain consisting of alternate gauche and anti conformations of the ligand are observed in 1a. This is a rare example of two supramolecular isomers present in the same crystal. Six different conformers of the flexible ligand are observed in the crystals of coordination polymers.     

Copper(II) and zinc(II) chemistry of a new hexadentate cyclam-based bis-di-2-pyridylmethanamine ligand

In the endo-conformation of the substituted cyclam derivative L, with two trans-disposed di-2-pyridylmethanamine (dipa) coordination sites (endo: both dipa subunits on the same face of cyclam), the bis-dipa-substituted cyclam platform may form hexacoordinate mononuclear complexes with the two dipa subunits coordinated to one metal ion or dinuclear complexes, when the two dipa subunits are coordinated to two metal ions (oligonuclear linear chain complexes with exo-configured ligands L and metal ions coordinated to the cyclam unit have not been observed so far). Here, the structures, relative stabilities and spectroscopic properties of the mononuclear complexes of Cu^II and Zn^II, which are formed in preference to other structural possibilities, are discussed, and the preference for their formation is also evaluated.     

Silver(I) coordination polymers containing heteroditopic ureidopyridine ligands: the role of ligand isomerism, hydrogen bonding, and stacking interactions

New silver (I) coordination polymers has been successfully designed and synthesized using heteroditopic ureidopyridine ligands 1 and 2 via a combination of coordinations bonds, hydrogen bonding, and pi-pi stacking interactions. This study shows an example of the orientation of the pyridine nitrogen relative to the urea moiety (4-substituted, 1, or 3-substituted, 2), used to control the packing of resulting crystalline coordination polymers. The ureidopyridine ligands present some flexibility because of the conformational rotation around the central urea moiety. The co-complexation of the silver(I) cation by two pyridine moieties and of the PF(6)(-) counteranion by the urea moiety results in the formation of discrete [1(2)Ag](+)PF(6)(-), (3) and [2(2)Ag](+)PF(6)(-), (4) complexes presenting restricted rotation around the central urea functionality. The geometrical information contained in the structures of ligands 1 and 2 and the heteroditopic complexation of silver hexafluorophosphate are fully exploited in an independent manner resulting in the emergence of quasi-rigidly preorganized linear and angular building blocks of 3 and 4, respectively. Additional pi-pi stacking contacts involving interactions between the pi-donor benzene and the pi-acceptor pyridine systems reinforce and direct the self-assembly of the above-described combined structural motifs in the solid state. Accordingly, linear and tubular arrays of pi-pi stacked architectures are generated in the solid state by synergistic and sequential metal ion complexation, hydrogen bonding, and pi-pi stacking interactions.     

Network diversity and supramolecular isomerism in copper(II)/1,2-bis(4-pyridyl)ethane coordination polymers

Reactions of copper(II) sources with 1,2-bis(4-pyridyl)ethane (bpe) yielded metal-organic networks with diverse topologies and dimensionalities. Compounds [Cu(bpe)₂(dmf)₂]_n(ClO₄)_2n·2ndmf (1·2ndmf), [Cu(bpe)₂(dmf)₂]_n(ClO₄)_2n·3.5ndmf (2·3.5ndmf), [Cu(bpe)₂(NO₃)₂]_n·2nH₂O (4·2nH₂O) and [Cu₂(bpe)(O₂CMe)₄]_n·0.7nH₂O (5·0.7nH₂O) have been isolated by altering the copper(II) source, the reaction solvent and the crystallization process. Compounds 1·2ndmf and 2·3.5ndmf consist of cationic [Cu(bpe)₂(dmf)₂]²⁺ repeating units assembled to 1D and 2D (4,4) networks, respectively, and represent supramolecular isomers due to the conformational isomerism of the bridging bpe molecules. Compound 4·2nH₂O consists of neutral mononuclear [Cu(dpe)₂(NO₃)₂] repeating units assembled to inclined interpenetrating (4,4) sheets describing an overall entanglement that is 3D in nature, and compound 5·0.7nH₂O consists of neutral dinuclear repeating units assembled to cross-linked 1D chains.     

Role of ligand conformation in the structural diversity of copper(II) and silver(I) coordination polymers containing the angular dipyridyl ligand bearing amide spacer

The new dipyridyl ligands N,N′-(methylenedi-p-phenylene)bis(pyridine-4-carboxamide), L1, and N,N′-(methylenedi-p-phenylene)bis(pyridine-3-carboxamide), L2, incorporating amide spacers have been synthesized and reacted with metal salts to give complexes of the types [Cu(L1)₂X₂]_∞ (X = Cl, 1 and X = Br, 2), {[Cu(L1)₂(DMF)](NO₃)₂}_∞, 3, {[Ag₂(L1)₂](SO₄)}_∞, 4, and {[Cu(L2)(DMSO)₂(NO₃)](NO₃)}_∞, 5. All compounds have been characterized by spectroscopic methods and their structures determined by X-ray crystallography.Complexes 1, 2 and 3 form 1-D double-stranded polymeric chains showing rhombic molecular squares with approximate dimensions of 16.95 × 19.13 Å² for 1, 17.03 × 19.06 Å² for 2 and 16.66 × 19.94 Å² for 3. Complex 4 forms infinite 1-D zigzag polymeric chains, which are interlinked through a series of Ag–O interactions to form wavy 1-D ladder like chains, and complex 5 forms 1-D sinusoidal chains. While the L1 ligands in complexes 1, 2 and 3 adopt the cis conformation and that in complex 4 adopts trans conformation, the L2 ligand in complex 5 adopts the trans-anti conformation. The ligand conformations also differ in the dihedral angles between the pyridyl and phenyl rings. All complexes exhibit emissions which may be tentatively assigned as intraligand (IL) π → π* transition.     

Structural diversity for three Zn(II) coordination polymers from 4-nitrobenzene-1,2-dicarboxylate and bispyridyl ligand

Three Zn(II) complexes, [Zn₂(bpp)₂(FNA)₂]·H₂O (1), [Zn(bpp)(FNA)]·H₂O (2), and Zn₂(bpp)₂(FNA)₂ (3) (bpp = 1,3-bi(4-pyridyl)propane, H₂FNA = 4-nitrobenzene-1,2-dicarboxylic acid), were synthesized and characterized by single-crystal and powder X-ray diffraction methods, IR spectroscopy, TG analyses, elemental analyses, and fluorescent analysis. In 1, the Zn(II) ions are linked by FNA anions and bpp into 2-D layers. The Zn(II) ions in 2 are bridged by FNA anions into chiral chains, which are interlinked by bpp into 3-D metal–organic framework with (6⁵·8) CdS topology. Complex 3 features 1-D zigzag chains, which are interconnected by bpp ligands to give a 3-D framework with (6·7⁴·8)(6⁴·7·8) topology. Complexes 2 and 3 exhibit significant ferroelectric behavior (for 2 remnant polarization Pr = 0.050 μC cm^?2, coercive field Ec = 1.13 kV cm^?1, saturation of the spontaneous polarization Ps = 0.239 μC cm^?2; for 3 Pr = 0.192 μC cm^?2, Ec = 4.64 kV cm^?1, Ps = 0.298 μC cm^?2).     

Synthesis and coordination chemistry of a photoswitchable bis(phosphine) ligand

A 1,2-dithienylethene compound bearing bis(phosphine) groups (1o) represents a new class of photoresponsive ligands where there are steric and electronic differences between two photogenerated isomers. The coordination chemistry of this ligand class is demonstrated by preparing a gold(I) complex (2o) and a phosphine selenide (3o).     

Novel Zn（Ⅱ） ladder-like coordination polymer constructed from designed ferrocenyl ligand

Reaction of Zn（NO3）2·6H2O with 3-（4-carboxylphenylamino）-l-ferrocenyl-2-butylen-l-one （HL） and 4,4′-bipyfidine （4,4′- bipy） in methanol solution resulted in a novel ladder-like coordination polymer {[Zn2L2（μ2-L）2（4,4′-bipy）2]·MeOH}n （1）. Its crystal structure, thermal and electrochemical properties are presented.     

Synthesis of (S)-N-(diphenylphosphinyl)-S-methyl-S-phenyl sulfoximide: a new ligand for asymmetric catalysis

The synthesis of (S)-N-(diphenylphosphinyl)-S-methyl-S-phenyl sulfoximide is reported. Preliminary investigations into the use of this novel sulfoximide as a ligand for asymmetric conjugate addition reactions are also described.