Crystal structures and catalytic activities of Zn(II) compounds containing btp ligands

The structures of new compounds containing Zn(II) ions and btp (2,6-bis(N′-1,2,4-triazolyl)pyridine) ligands have been determined. With coordinating chloride and bromide anions, Zn(II) produces chains 2 and 3 containing C-H?X(Cl or Br) weak interactions to build crystal structures and they are face-to-face aligned. With non-coordinating anions, Zn(II) produces monomeric compounds 4 and 5 containing H-bonds between anions and water ligands and face-to-face π-π interactions to build crystal structures. The previously reported polymeric compound 1 containing [Zn(NO₃)(H₂O)₂(btp)₂]⁺ units bridged by btp ligands was found to carry out the catalytic transesterification of a range of esters with methanol at room temperature under mild conditions, whereas it did not catalyze the ring opening of epoxide (easier reaction) with methanol. These results indicate that the polymeric compound 1 shows selective reactivity. In addition, the catalyst 1 has shown even better catalytic activity than the corresponding Zn(NO₃)₂ salt.     

Zinc(II) complexes based on sterically hindered hydrotris(pyrazolyl)borate ligands: Synthesis, reactivity and solid-state structures

The coordination chemistry and reactivity of zinc(II) complexes supported by monoanionic hydrotris(pyrazolyl)borate ligands substituted by 3,3,3-mesityl groups (Tp^Ms) and 3,3,5-mesityl groups (Tp^Ms∗) have been investigated. Salt metathesis of ZnCl₂, ZnEt₂, and Zn(OAc)₂ with Tl[Tp^Ms] or Tl[Tp^Ms∗] cleanly afforded the corresponding compounds Tp^MsZnCl (1), Tp^MsZnEt (2), Tp^Ms∗ZnEt (3), and Tp^MsZnOAc (5). Compound 3 slowly disproportionates in benzene solution to afford the bis(ligand) complex (κ²-Tp^Ms∗)₂Zn (4). Acetate complex 5 as well as Tp^MsZnOCOPh (6) and [Tp^Ms∗ZnOAc]₂ (7) were alternatively prepared by acidolysis of the parent ethyl complexes (2, 3) with the corresponding carboxylic acid. No reaction was observed between 2 and 3 and alcohols (ROH; R = Et, iPr, Bn), while salt metathesis reactions of ZnEt(OR) with Tl[Tp^Ms] led to 2 instead of the desired zinc-alkoxide complex. Compounds 1-7 were characterized by elemental analysis, ¹H and ¹³C NMR spectroscopy, as well as by X-ray diffraction studies for 1, 2, 4, 5 and 7. The former compounds adopt a monomeric structure in the solid state while [Tp^Ms∗ZnOAc]₂ (7) exists as an anti-syn bridged acetate dimer. Complex 4 is four-coordinated, featuring a rare bidentate coordination mode of the Tp^Ms∗ ligands. The results are rationalized in terms of the variable steric constraint around the zinc atom provided by the Tp^Ms and Tp^Ms∗ ligands.     

Macrocyclic dinuclear gold(I) and silver(I) NHCs complexes

The ligands bis-(imidazolium) hexafluorophosphate (Himy = -C₃N₂H₃-, imidazolium; R = 1-naphthylmethylene, 1a; 9-anthracenylmethylene, 1b) with an oxoether chain were easily prepared by the reaction of substituted imidazole with the diglycol diiodide, followed by exchange of anions with . 1a and 1b reacted with Ag₂O in DMSO or CH₃CN to yield [2 + 2] dinuclear Ag(I) NHCs macrocyclic complexes 2a and 2b, which showed much different conformation in solid corresponding to the R- substituent. Carbene transmetalation reactions of 2a-b with Au(SMe₂)Cl give dinuclear Au(I) analogs 3a and 3b. The new NHCs complexes were characterized by elemental analyses, ¹H NMR, ¹³C NMR and the structures of 2a-b and 3a were confirmed by X-ray diffraction determination.     

Structural and magnetic characterization of one-dimensional oxalato-bridged metal(II) complexes with 4-amino-3,5-bis(2-pyridyl)-1,2,4-triazole ligand: A supramolecular open-framework

A new family of one-dimensional oxalato-bridged metal(II) complexes with formula {[M(ox)(abpt)]·4H₂O}_n [M^II = Mn (1), Fe (2), Co (3), Zn (4); ox = oxalate dianion; abpt = 4-amino-3,5-bis(2-pyridyl)-1,2,4-triazole] has been synthesized and chemically, structurally and magnetically characterized. The crystal structures of compounds 2-4 have been solved by single crystal X-ray diffraction, whereas complex 1 has been studied by means of X-ray powder diffraction methods. All of them are isomorphous and crystallize in the triclinic space group P. The metal atoms are bridged by bis-bidentate oxalate anions forming zig-zag chains in which bidentate chelating abpt ligands complete the octahedral O₄N₂ donor set. The crystal structures show an open-framework that contains rectangular channels in which easily removable hydrogen bonded ribbons of water molecules are located. The occurrence of antiferromagnetic intrachain interactions for compounds 1-3 was determined by cryomagnetic susceptibility measurements.     

Synthesis and structures of pyridinecarboxylate-containing zinc(II) complexes in dien and tren system

Four new zinc(II) complexes [Zn(dien)(μ-nic)]₂(BPh₄)₂·2CH₃OH (1), {[Zn(dien)(isonic)]BPh₄}_n (2), [Zn(tren)(nic)]BPh₄ (3) and [Zn(tren)(isonic)]BPh₄ (4) (dien/tren = diethylenetriamine/triethylenetriamine, nic/isonic = nicotinate/isonicotinate anion) were synthesized and structurally characterized by IR, ¹H NMR and single crystal X-ray diffraction. In the zinc(II) complexes of dien, both nicotinate and isonicotinate connect the zinc(II) ions via N,O-bis-monodentate mode. Complex 1 contains a centrosymmetric dinuclear unit bridged by two nicotinate anions in anti-parallel way. Complex 2 is characterized by an infinite one-dimensional zigzag chain bridged by isonicotinate anion in an end-to-end mode. The Zn···Zn distance is 6.782 for 1 and 8.805 Å for 2. While in the complexes of tren, both 3 and 4 are mononuclear complexes with nicotinate and isonicotinate coordinated to zinc(II) ion through only one oxygen atom of their carboxylate groups. The zinc(II) ions in all of the four complexes are in a distorted trigonal bipyramidal geometry. Complex 3 forms a dinuclear unit and complex 4 forms an infinite 2D sheet structure through intermolecular H-bonds. In all of the crystal lattices, the counterions act to balance the electronic charge at the same time to construct different 3D structures through noncovalent interactions such as C-H···π, N-H···π and van der Waals interactions.     

Manganese(II) and zinc(II) compounds via amino acid derivatives: Effects of temperature and solvents

To investigate the influence of temperature and the ratios of solvents on the design and synthesis of metal-organic frameworks (MOFs), we have synthesized and structurally characterized a series of supramolecular assemblies based on different amino acid derivatives and nitrogen-containing heterocyclic ligands, namely [Mn(phen)₂(phth)(H₂O)]·4H₂O (1), [Mn(phen)₂(HL1)₂]·3.5H₂O (2), [Zn(bpp)₂(L-Me)₂] (3), and [Zn(bpp)(L-Me)₂] (4) (H₂phth = phthalic acid, H₂L¹ = phthalyl-l-valine, H₂L = (+)-N-tosyl-l-glutamic acid, phen = 1,10-phenanthroline, bpp = 1,3-bis(4-pyridyl)propane, and L-Me = C₁₂H₁₃NO₆S-CH₃). Compounds 1 and 2, which are assembled through noncovalent interactions, were obtained by controlling the temperature. In 1, π-π stacking and hydrogen-bonding interactions lead to stacking in a 3D supramolecular network, while in 2, π-π stacking interactions form 1D chains that extend along the c-axis. Depending on the solvents employed, compounds 3 and 4 could be generated, with a 1D bpp-connected Zn-bpp-Zn double chain that is further hydrogen-bonded into a 2D network that extends parallel to the ac plane in 3, and a single chain in 4.     

Molecular interactions of zinc(II) cyclams with polycarboxylato ligands

Four new zinc(II) cyclams of the composition {Zn(L)(tp²⁻) · H₂O}_n (1), {Zn(L)(H₂bta²⁻) · 2H₂O}_n (2), [Zn₂(L)₂(ox²⁻)] 2ClO₄ · 2DMF (3), and Zn(L)(H₂btc⁻)₂ · 2DMF (4), where L = cyclam, tp²⁻ = 1,4-benzenedicarboxylate ion, H₂bta²⁻ = 1,2,4,5-benzenetetracarboxylate ion, ox²⁻ = oxalate ion, DMF = N,N-dimethylformamide, and H₂btc⁻ = 1,3,5-benzenetricarboxylate ion, have been synthesized and structurally characterized by a combination of analytical, spectroscopic and crystallographic methods. The carboxylato ligands in the complexes 1-4 show strong coordination tendencies toward zinc(II) cyclams with hydrogen bonding interactions between the pre-organized N-H groups of the macrocycle and oxygen atoms of the carboxylato ligands. The macrocycles in 1, 2, and 4 adopt trans-III configurations with the appropriate R,R,S,S arrangement of the four chiral nitrogen centers, respectively. However, the complex 3 shows an unusual cis V conformation with the R,R,R,R nitrogen configuration. The finding of strong interactions between the carboxylato ligands and the zinc(II) ions may provide additional knowledge for the improved design of receptor-targeted zinc(II) cyclams in anti-HIV agents.     

Zinc(II) complexes with 1,8-naphthyridine-based ligand: Crystal structures and luminescent properties

The reactions of 2,4-dimethyl-7-(2-pyridylamino)-1,8-naphthyridine (L1) with Zn(ClO₄)₂ · 6H₂O, and bis(5,7-dimethyl-1,8-naphthyrid-2-yl)amine ligand (L2) with Zn(OAc)₂ · 2H₂O, ZnCl₂ or Zn(ClO₄)₂ · 6H₂O afforded four blue luminescent zinc(II) complexes, [Zn(L1)₂](ClO₄)₂ · 2CH₂Cl₂ (1), [Zn(L2)(OAc)₂] · CH₂Cl₂ (2), [Zn(L2)₂][ZnCl₄] · 3.5CH₂Cl₂ (3) and [Zn(L2)₂](ClO₄)₂ (4), respectively. Crystal structures of complexes 1-3 have been determined by X-ray structural analyses as mononuclear complexes with pseudo-tetrahedral geometry. The crystal packing of 1 reveals the coordination cation which is self-assembled to stair chains through aromatic π-π interactions. The intermolecular N-H?O hydrogen bond in 2 generates a centrosymmetric H-bonded dimer. However, the crystal lattice of 3 shows that the molecules are linked by extensive intermolecular hydrogen bonds between the amino groups and the anions, resulting in a one-dimensional zigzag chain. Furthermore, these molecular pairs or chains were self-assembled to two-dimensional sheets or three-dimensional networks through aromatic π-π interactions. All the zinc(II) complexes display intense intraligand ¹(π-π^∗) fluorescence with λ_max at 380 and 393 nm for 1, 385 and 404 nm for 2-4 in methanol at room temperature, respectively. Emission quantum yields of these complexes are in the range from 0.41 to 0.57. The broad emission bands in their solid-state emission spectra are attributed to intraligand ¹(π-π^∗) transition and aromatic π-π interactions as well.     

Anion effects on construction of Zn compounds with a chelating ligand bis(2-pyridylmethyl)amine and their catalytic activities

Three Zn^II complexes containing bispicam ligands (bispicam = bis(2-pyridylmethyl)amine), [Zn(bispicam)₂](NO₃)₂·2CH₃OH 4A, [Zn(bispicam)(NO₃)₂] 4B, and [Zn(bispicam)₂](OTf)₂6, were obtained, and their structures were determined by X-ray crystallography. Complexes of the general formulation [Zn(bispicam)₂]X₂ (X = Cl⁻ (1), Br⁻ (2), I⁻ (3), NO₃⁻ (4A), ClO₄⁻ (5), and OTf⁻ (6)) show fac geometric isomers (a) or enantiomers (c) and (d) according to anions. Moreover, complexes 4-6 could carry out the catalytic transesterification of a range of esters with methanol under the mild conditions. Importantly, the catalyst 4B with an unsaturated structure has shown better efficiency than the catalysts, 4A, 5, and 6, having saturated structures. To explain this reactivity difference, two different reaction mechanisms have been proposed (metal-based vs. amide N-H-based).     

Novel long bipyridine-type linking ligands containing an intervening naphthalene fragment: [Zn(L)(NO3)2], [Zn(L)(NO3)2], and [Cd(L)1.5(NO3)2] (L = (4-py)-CHN-C10H6-NCH-(4-py); L = (3-py)-CHN-C10H6-NCH-(3-py))

Novel bipyridine-type linking ligands L¹ ((4-py)-CHN-C₁₀H₆-NCH-(4-py)) and L² ((3-py)-CHN-C₁₀H₆-NCH-(3-py)), a pair of isomers due to possessing different pairs of terminal pyridyl groups, were prepared by the Schiff-base condensation. In ligand L¹, the N?N separation between the terminal pyridyl groups is 16.0 Å, with their nitrogen donor atoms at the para positions (4,4′). The corresponding N?N separation in ligand L² is 14.2 Å, with the nitrogen donor atoms at the meta positions (3,3′). 1-D zigzag-chain coordination polymers [Zn(L¹)(NO₃)₂] (1) and [Zn(L²)(NO₃)₂] (2) were prepared by reactions of Zn(NO₃)₂ · 6H₂O with ligands L¹ and L², respectively, by solution diffusion. Polymer 3, [Cd(L¹)_1.5(NO₃)₂], prepared from Cd(NO₃)₂ · 4H₂O and L¹, exhibits a 1-D ladder structure, whose repeating ladder unit consists of four Cd metals and four L¹ ligands to create a large 76-membered ring with dimensions of 20.8 × 20.8 Å. All products were structurally characterized by X-ray diffraction.     

Two three-dimensional cyano-bridged bimetallic cadmium(II) and copper(II)-copper(I) mixed-valence polymer compounds: Crystal structures and thermal stability analysis and magnetic properties

Two cyano-bridged cadmium(II) and copper(II)-copper(I) mixed-valence polymer compounds 1 and [Cu^II(en)₂]_0.5[CdCu^I(CN)₃] · Cl · H₂O 2 (en = 1,2-ethanediamine) through systematically varying the solution environment have been synthesized and structurally characterized by single crystal X-ray diffraction analysis. The cyano anions connected the copper and cadmium centres with bidentate or tridentate bridging modes resulting in two complicated 3D networks for 1 and 2. Compound 1 has a rare 5,6-connected network, while compound 2 can be reduced to a 6-connected α-Po net. The magnetic and thermal properties of 1 and 2 are also studied.     

Zinc(II) complexes of 2-acetyl pyridine 1-(4-fluorophenyl)-piperazinyl thiosemicarbazone: Synthesis, spectroscopic study and crystal structures - Potential anticancer drugs

2-Acetyl pyridine thiosemicarbazone containing an 1-(4-fluorophenyl)-piperazinyl ring incorporated at N(4)-position, HAcPipPheF (1) and the zinc(II) complexes [Zn(AcPipPheF)₂] (2) and [Zn(OAc)(AcPipPheF)]₂ (3) have been prepared and structurally characterized by means of vibrational and NMR (¹H and ¹³C) spectroscopy. The crystal structures of the compounds 1-3 have been determined by X-ray crystallography. The metal coordination geometry of [Zn(AcPipPheF)₂] is described as distorted octahedral configuration in a trans-N-cis-N-cis-S configuration. In [Zn(OAc)(AcPipPheF)]₂ one of the acetato group exhibits monoatomic bridge and the other bridges in a bidentate manner. The zinc(1) metal ion is coordinated in a distorted octahedral configuration while the metal coordination of Zn(2) is described as distorted square pyramidal. Biomedical studies revealed that, compounds 1-3 displayed potent anticancer activity. The antiproliferative activity of 1-3 was found to be considerably stronger than that of cis-platin. The IC₅₀ values range from 26 to 90 nM, against all cell lines tested, while for cis-platin the IC₅₀ values range from 2 to 17 μM and for the zinc salt, ZnCl₂, the IC₅₀ values range from 81 to 93 μM. The complex 3 shows the highest activity against all four cancer cell lines and the highest selectivity against K562 and MDA-MB-453 cancer cell lines. The compounds inhibited tumor cell proliferation by arresting the cell cycle progression at the S phase.     

Influence of the phosphine arrangement on the reactivity of palladium(II) and platinum(II) polyphosphine complexes with copper(I) chloride

The distorted square-planar complexes [Pd(PNHP)Cl]Cl (1) (PNHP = bis[2-(diphenylphosphino)ethyl]amine), [M(P₃)Cl]Cl [P₃ = bis[2-(diphenylphosphino)ethyl]phenylphosphine; M = Pd (2), Pt (3)] and [Pt(NP₃)Cl]Cl (5) (NP₃ = tris[2-(diphenylphosphino)ethyl]amine), coexisting in the later case with a square-pyramidal arrangement, react with one equivalent of CuCl to give the mononuclear heteroionic systems [M(L)Cl](CuCl₂) [L = PNHP, M = Pd (1a); L = P₃, M = Pd (2a), Pt (3a); L = NP₃, M = Pt (5a)]. The crystal structure of 3a confirms that Pt(II) retains the distorted square-planar geometry of 3 in the cation with P₃ acting as tridentate chelating ligand, the central P atom being trans to one chloride. The counter anion is a nearly linear dichlorocuprate(I) ion. However, the five-coordinate complexes [Pd(NP₃)Cl]Cl (4), [M(PP₃)Cl]Cl (M = Pd (6), Pt (7); PP₃ = tris[2-(diphenylphosphino)ethyl] phosphine) containing three fused five-membered chelate rings undergo a ring-opening by interaction with one (4, 6, 7) and two (6, 7) equivalents of CuCl with formation of neutral MCu(L)Cl₃ [L = NP₃, M = Pd (4a); L = PP₃, M = Pd (6a), Pt (7a)] and ionic [MCu(PP₃)Cl₂](CuCl₂) [M = Pd (6b), Pt (7b)] compounds, respectively. The heteronuclear systems were shown by ³¹P NMR to have structures where the phosphines are acting as tridentate chelating ligands to M(II) and monodentate bridging to Cu(I). Further additions of CuCl to the neutral species 6a and 7a in a 1:1 ratio resulted in the achievement of the ionic complexes 6b and 7b with ions as counter anions. It was demonstrated that the formation of heterobimetallic or just mononuclear mixed salt complexes was clearly influenced by the polyphosphine arrangement with the tripodal ligands giving the former compounds. However, complexes [M(NP₃)Cl]Cl constitute one exception and the type of reaction undergone versus CuCl is a function of the d⁸ metal centre.     

Chromium(III) complexes with 2-(2′-pyridyl)imidazole: Synthesis, crystal structure and magnetic properties

The preparation, crystal structure and variable temperature-magnetic investigation of three 2-(2′-pyridyl)imidazole-containing chromium(III) complexes of formula PPh₄[Cr(pyim)(C₂O₄)₂]·H₂O (1), AsPh₄[Cr(pyim)(C₂O₄)₂]·H₂O (2) and [Cr₂(pyim)₂(C₂O₄)₂(OH₂)₂]·2pyim · 6H₂O (3) [pyim = 2-(2′-pyridyl)imidazole, , and ] are reported herein. The isomorphous compounds are made up of discrete [Cr(pyim)(C₂O₄)₂]⁻ anions, cations [X = P (1) and As (2)] and uncoordinated water molecules. The chromium environment in 1 and 2 is distorted octahedral with Cr-N and Cr-O bond distances varying in the ranges 2.040(3)-2.101(3) and 1.941(3)-1.959(3) Å, respectively. The angle subtended by the chromium(III) ion by the two didentate oxalate ligands cover the range 82.49(12)-82.95(12)°, values which are somewhat greater than those concerning the chelating pyim molecule [77.94(13) (1) and 78.50(13)° (2)]. Complex 3 contains discrete centrosymmetric [Cr₂(pyim)₂(C₂O₄)₂(OH)₂] neutral units where the two chromium(III) ions are joined by a di-μ-hydroxo bridge, the oxalate and pyim groups acting as peripheral didentate ligands. Uncoordinated water and pyim molecules are also present in 3 and they contribute to the stabilization of its structure by extensive hydrogen bonding and π-π type interactions. The values of the intramolecular chromium-chromium separation and angle at the hydroxo bridge in 3 are 2.9908(12) Å and 99.60(16)°, respectively. Magnetic susceptibility measurements of 1-3 in the temperature range 1.9-300 K show the occurrence of weak inter- (1 and 2) and intramolecular (3) antiferromagnetic couplings. The magnetic properties of 3 have been interpreted in terms of a temperature-dependent exchange integral, small changes of the angle at the hydroxo bridge upon cooling being most likely responsible for this peculiar magnetic behavior.     

Synthesis, structures and DNA binding of ternary transition metal complexes M(II)L with the 2,2-bipyridylamine (L = p-HB, M = Co, Ni, Cu and Zn)

New ternary transition metal complexes of formulations [Co(bpa)(p-HB)₂](bpa = 2,2′-bipyridylamine, p-HB = p-hydroxybenzenecarboxylic acid) (1), [Ni(bpa)(p-HB)(H₂O)₂]⁺(NO₃)⁻ · H₂O (2), , [Cu(bpa)(p-HB)Cl] (4) and [Zn(bpa)(p-HB)₂]₂ · 0.5H₂O (5) are prepared, their structural features are characterized by crystal structural studies, and their DNA binding propensity has been evaluated by fluorescence method. The molecular structure of complex 1 shows the six coordinate octahedral geometry with one bpa and two p-HB ligands, complex 2 is the cationic complex and has the six coordinate octahedral structure with one bpa, one p-HB and two aqua ligands, complex 3 is also the cationic complex of octahedral coordination with two bpa and one p-HB ligands, complex 4 is five coordinate distorted square pyramidal with one bpa, one p-HB and chloride ligands and complex 5 has the distorted octahedral coordination with two p-HB and one bpa ligands. In all of the complexes, both bpa and p-HB act as the bidentate N and O-donor ligands, respectively. The intermolecular H-bond networks, together with π-π interaction in their solid state are also described. The complexes show the competitive inhibition of ethidium binding to DNA, and the DNA binding propensity can be reflected as the relative order: 3 > 2 > 1 > 5 > 4, in which the cationic charged Ni(II) complexes 2 and 3 show the most effective inhibition ability.     

Silver coordination complexes of 2-(diphenylphosphinomethyl)pyridine and their bipyridine derivatives

Reaction of 2-(diphenylphosphinomethyl)pyridine (PMP-21) with the silver(I) salts of tetrafluoroborate , triflate (Otf⁻), and trifluoroacetate (tfa⁻) affords dinuclear complexes (2-4), where the ligand bridges the two silver centers, and the anions interact with the metal centers to varying degrees. Further reaction of AgBF₄ and AgOtf with reaction solutions containing PMP-21 and either the bidentate 5,5′-dimethyl-2,2′-bipyridine or 4,4′-bipyridine ligands produce dimeric and bridged structural motifs. The ability of 5,5′-dimethyl-2,2′-bipyridine to chelate and the 4,4′-bipyridine to serve as a connector between metal centers, allows the construction of coordinative structures where the effect of ligand ratio and either interacting or non interacting anions influence the silver coordination environment, allowing it to take on several geometries including trigonal bipyramidal, 5, both T-shaped and tetrahedral in a single structure, 6 and 8, trigonal pyramidal, 7, and trigonal planar, 9. Structures 2, 3, and 4 display comparable Ag-Ag contacts ranging from 2.7979(10) to 3.0538(4) Å, with a corresponding weakening of the metallophilic interaction when a bipyridine ligand is coordinated. Low-temperature luminescence spectra were collected for all compounds and are compared.     

Squarato-bridged polymeric networks of iron(II) with N-donor coligands: Syntheses, crystal structures and magnetic properties

Two new squarato-bridged Fe(II) polymeric networks of molecular formula [Fe(squarate)(bpp)₂(H₂O)₂] (1) and [Fe(squarate)(bpee)(H₂O)₂] (2) [bpp = 1,3-bis(4-pyridyl)propane; bpee = 1,2-bis(4-pyridyl)ethylene; ] have been synthesized and characterized by single-crystal X-ray diffraction studies and low temperature (300-2 K) magnetic measurements. Complex 1 is a 1D coordination chain of Fe(H₂O)₂ units connected by μ-O,O″ squarate dianions with monocoordinated bpp ligands dangling from the polymer. These 1D chains ultimately transform to a thick 2D layer through π-π interaction of pyridyl rings as well as through hydrogen bonds. Whereas structural determination of complex 2 reveals an inclined interpenetrated 3D architecture. Magnetic data for both the complexes 1 and 2 have been fitted using the Fisher formula for S = 2 system and show antiferromagnetic coupling for both the complexes. The best fit parameters are J = −0.40 cm⁻¹, g = 2.30 and R = 0.01 for complex 1 and J = −0.49 cm⁻¹, g = 2.08 and R = 1.9 × 10⁻³ for complex 2.     

One-dimensional Zn(II) oligo(phenyleneethynylene)dicarboxylate coordination polymers: Synthesis, crystal structures, thermal and photoluminescent properties

The rigid, π-conjugated dicarboxylic acid 1,4-bis-[2-(4-carboxyphenyl)ethynyl]-2,5-dihexylbenzene {HO₂C[PEP(hexyl)₂EP]CO₂H} has been used to synthesise the new crystalline coordination polymers {Zn(O₂C[PEP(hexyl)₂EP]CO₂)(DMF)₂} (1) and {Zn(O₂C[PEP(hexyl)₂EP]CO₂)(DEF)₂} (2) in N,N-dimethylformamide (DMF) and N,N-diethylformamide (DEF), respectively, under mild conditions. Single-crystal X-ray crystallography revealed that 1 and 2 are isostructural and consist of uncharged zigzag coordination chains in which [Zn(formamide)₂]²⁺ fragments are bridged by (O₂C[PEP(hexyl)₂EP]CO₂)²⁻ ligands. The zigzag chains possess different intra-chain Zn?Zn?Zn angles due to the different volumes of the coordinating formamide molecules and subtle differences in the hydrophobic inter-chain interactions. Upon heating 1 and 2 to 200 °C, removal of the coordinating formamide molecules occurs, yielding the formamide-free compounds 1-DMF and 2-DEF of composition {Zn(O₂C[PEP(hexyl)₂EP]CO₂)}. According to powder X-ray diffraction and FT-IR spectroscopy studies, these materials are not crystalline but still possess partial ordering of intact, yet modified coordination chains in a structural arrangement which appears to be related to the respective parent compounds. Compounds 1, 2, 1-DMF and 2-DEF exhibit blue photoluminescence. The emission maxima of 1-DMF and 2-DEF are red-shifted by ca. 25 nm with respect to λ_max of 1 and 2, respectively.     

Unusual kinetic and thermodynamic control in the formation of Pt(II)-complexes of a new C1-symmetric phosphine-phosphite

Versatile synthetic routes have been applied to prepare the new asymmetric phosphine-phosphite ligands 8 and 12. The chiral ligands have been designed so that the corresponding ligating groups have similar electronic properties and steric bulk, but 8 forms 6-, while 12 forms 7-membered chelate rings in their coordination compounds. The chelate size variation results in a markedly different coordination behavior towards Pt(II). In their reactions with Pt(PhCN)₂Cl₂ at 1:1 stoichiometry 12 forms the expected Pt(12)Cl₂ complex, while 8 gives the cation quantitatively. In the kinetically controlled reaction is the major product even at a 8:Pt(PhCN)₂Cl₂ = 1:2 ratio. Most interestingly, at 1:1 ligand to precursor ratio, cation rearranges to Pt(8)Cl₂ within one day, indicating that the neutral complex is thermodynamically more favorable.