Free Macrocycle Research Articles

Nanoscale Borromean links for real

Borohydride reduction of a Borromean Ring (BR) complex containing six zinc(II) ions and 12 imine bonds has resulted in its demetallation, producing a neutral BR compound and also its free macrocycle, following cleavage of at least one of the imine bonds in the ethanolic reaction mixture.

Binucleating Aza‐Sulfonate and Aza‐Sulfinate Macrocycles — Synthesis and Coordination Chemistry

AbstractThe preparation and ligating properties of S‐oxygenated derivatives of a macrobinucleating hexaazadithiophenolate macrocycle H2L1 of the Robson type towards nickel(II) and zinc(II) ions are reported. Nickel complexes of the hexaazadiphenylsulfonate ligand (L2)2− [(L2)NiII2(μ‐L)]+ (L = m‐Cl‐OBz− (3), Cl− (4) and OAc− (6)] are readily obtained in high yields by oxidation of the respective [(L1)NiII2(μ‐L)]+ parent complexes [L = m‐Cl‐OBz− (2), Cl− (1), OAc− (5)] with meta‐chloroperoxybenzoic acid or hydrogen peroxide. Decomposition of the sulfonate complexes gives the free macrocycle H2L2 which, upon treatment with Zn(OAc)2·2H2O, produces the diamagnetic zinc complex [(L2)ZnII2(OAc)]+ (8). A dinuclear CuII complex of the hexaazadisulfinate derivative (L3′)2−, [(L3)CuII2]2+ (9), is formed rather unexpectedly by air oxidation of (L1)2− in the presence of CuI. The crystal‐structure determinations of the perchlorate or tetraphenylborate salts of 2, 3, and 4 show that the new ligands support the formation of binuclear complexes with bowl‐shaped, calixarene‐like binding cavities. NMR spectroscopic studies of 8 show that the complexes retain their solid‐state structures in solution. A crystal‐structure determination of 9 reveals two five‐coordinate CuII ions bridged by the two sulfinate functions of (L3)2−. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Solution and Solid-State Properties of Mechanically Linked Polycarbonates

Solution and solid-state properties of novel mechanically linked polyearbonate copolymers are reported and compared to corresponding properties of a reference copolymer with identical chemical composition but no mechanical linkages. The unperturbed dimensions of the catenane copolymers in solution are smaller than for bisphenol A polycarbonate homopolymer, presumably reflecting favorable specific interactions between bisphenol A and catenane units. A difference is observed between the mechanically linked and unlinked analogues, pointing to a specific effect of the mechanical linkage. Crystallinity measurements suggest a segmented composition for the copolymers, consistent with the solid-state synthesis. The melting point of the catenane copolymers is lower than that of the bisphenol A polycarbonate homopolymer because of a copolymer effect. The melting point of a mechanically linked copolymer is higher than of the unlinked analogue, presumably because of the additional mobility in the melt introduced by free macrocycle chain ends vs interlocked catenane units.

Intramolecular sensitisation of europium(III) luminescence by 8-benzyloxyquinoline in aqueous solution

Two new tetraazamacrocylic ligands have been prepared, in which one of the four nitrogens bears an 8-benzyloxyquinoline group, bound either via a simple methylene unit (CH 2) (ligand 1), or through a longer, amide linker (CH 2C(O)N(Me)CH 2) (ligand 2), in both cases at the 2-position of the chromophore. The synthesis of ligand 1 involved a reductive amination reaction of the free macrocycle with 8-benzyloxyquinoline-2-carboxaldehyde, whilst ligand 2 was prepared by a more conventional alkylation pathway. The other three nitrogens of the macrocycle are functionalised with acetate donors, leading to a DO3A-type ligand suitable for complexation of lanthanide ions. The europium(III) complexes of the two ligands have been prepared. Both are luminescent in aqueous solution, displaying europium-based emission upon excitation into the UV absorption bands of the chromophore. From the luminescence lifetimes measured in H 2O and D 2O, it is concluded that, whilst [Eu 2] has the one expected water molecule in the inner-sphere of the metal ion, [Eu 1] has no metal-bound water molecules. This is attributed to the coordination of the quinoline nitrogen to the metal ion, forcing the benzyloxy group into the space normally occupied by the axial water molecule. However, further analysis shows that the greatly superior quantum yield of [Eu 1] over [Eu 2] is due to the much higher efficiency of energy transfer in the former, and not to a reduction in non-radiative decay of the excited state; in fact, overall non-radiative deactivation is greater in [Eu 1] than in [Eu 2].

Synthesis and Crystal Structures of Palladium(II) Complexes of Macrobicyclic Azathiaether Ligands

AbstractThe macrobicyclic azathioether ligands L1 and L2 were investigated regarding their capability to form complexes with divalent palladium. L1 represents a cyclophane‐like ligand system comprising two 4‐tert‐butyl‐2, 6‐bis(aminomethyl)thiophenolate units, which are linked by an ethylene and two 3‐aza‐1, 5‐pentylene units to give two seventeen‐membered dithia‐triaza crowns fused at the common ArSCH2CH2SAr fragment. L2 is the hexa‐N‐methylated derivative of L1. Treatment of L1 and L2 with two equivalents of [PdCl2(CH3CN)2] gave the new complexes [(L1)Pd2Cl]+ (1) and [(L2)Pd2Cl2]2+ (2), respectively, which were isolated as perchlorate salts and characterized by elemental analysis, IR and NMR spectroscopy and by X‐ray crystallography. In 1, L1 acts as a septadentate ligand to give two distorted square‐planar PdN3S and PdN3Cl units, respectively. The structure of 2 shows L2 to be hexacoordinate, yielding two distorted square‐planar PdN2SCl units leaving two NMe groups dangling. NMR spectroscopic studies reveal that both complexes retain their solid‐state structures in solution. The reaction of L2 with one equivalent of [PdCl2(CH3CN)2] is accompanied by a bond cleavage reaction of one of the two aliphatic thioether bonds to afford the dinuclear complex [(L3)Pd2Cl2]Cl (3·Cl) of the ring‐opened 24‐membered hexaaza‐vinylthioether/thiophenolate derivative (L3)‐. The crystal structure determination of 3·Cl reveals two distorted‐square planar PdN2ClS units which are bridged by the thiophenolate sulfur atom of (L3)‐. The vinyl‐thioether moiety and the two remaining amine donors of (L3)‐ do not interact with the two palladium ions. The X‐ray structure analysis of the free macrocycle L2 demonstrates that the C‐S bond lengths become elongated upon coordination to the palladium(II) ions.

Silver complexes with unsaturated thiacrown ethers: inclusion behavior of conformationally restricted macrocycles.

The reactions of 18- and 21-membered unsaturated thiacrown ethers, 18-UT-6 and 21-UT-7, with CF(3)COOAg in acetone afforded novel silver(I) complexes Ag(I)(18-UT-6)(CF(3)COO) and Ag(I)(2)(21-UT-7)(CF(3)COO)(2), respectively. The crystal structure of Ag(I)(18-UT-6)(CF(3)COO) shows that the silver atom occupies the cavity of the 18-UT-6 and the geometry around the silver atom has a distorted five-coordinate square pyramidal arrangement. The crystal structure of Ag(I)(2)(21-UT-7)(CF(3)COO)(2) shows that the two silver atoms and all sulfur atoms are nearly coplanar and the two trifluoroacetate groups are located at the opposite sides of the plane. The stoichiometry for the complexation of 15-UT-5, 18-UT-6, and 21-UT-7 with CF(3)COOAg in solution was examined by (1)H NMR measurement. The titration plots of 15-UT-5 and 21-UT-7 show a distinct inflection point at 1:1 and 2:1 metal/macrocycle ratios, respectively, whereas the plot of 18-UT-6 gradually changes at the range of 1:1 to 2:1. From these results, 15-UT-5 and 21-UT-7 were found to show inclusion selectivity for number of silver ions, respectively, whereas 18-UT-6 showed low selectivity for the inclusion number of metals. Comparison of the oxidation and reduction potentials of the silver(I) complexes with those of free macrocycles and CF(3)COOAg revealed that unsaturated thiacrown ethers become difficult to be oxidized by complexation with CF(3)COOAg, and CF(3)COOAg becomes difficult to be reduced by complexation with unsaturated thiacrown ethers.

An economical synthesis of dibenzocyclamnickel(II) and a metal-free macrocycle with tetramethyl substituents

The cationic dibenzocyclamnickel(II) complex, [Ni(Me4Bzo2[14]aneN4)]2+, was obtained in good yield by Fe/HCl reduction of the corresponding tetraazaannulene complex [Ni(Me4taa)], (1) {Me4Bzo2[14]aneN4 = 5,7,12,14-tetramethyldibenzo[b,i]-1,4,8,11-tetraazacyclotetradecane; Me4taa = 5,7,12,14-tetramethyldibenzo[b,i]-1,4,8,11-tetraazaannulene(2-)}. The orange–red product was isolated as the chloride (2) and perchlorate (3) salts. Analogous reduction with Zn/HCl yielded a diprotonated silky-white product [Ni(Me4Bzo2[14]aneN4-H2)][ZnCl4]2, (4). In the dry state, complex (4) is stable only under an HCl atmosphere and readily dissociates to give a solution of (2) when dissolved in polar solvents. Complexes (2) and (3), upon treatment with an excess of aqueous NaCN, undergo facile demetallation yielding the metal free macrocycle Me4Bzo2[14]aneN4, (5). These compounds were characterized using a combination of i.r., u.v.–vis., 1H-n.m.r., mass spectroscopy and voltammetry techniques. Unlike the parent tetraazaannulene complex (1), the reduced macrocycle complex, [Ni(Me4Bzo2[14]aneN4)]2+ exhibits mild catalytic activity towards electro-reduction of CO2 in MeCN solution.

Template reaction of [Ni(ben) 3](ClO 4) 2 with acetone. Crystal structure of 1,11-bis-benzyl-5,7,7-trimethyl-1,4,8,11-tetra-aza-undeca-4-ene nickel(II) perchlorate

The template synthesis of a new open-chain tetra-aza ligand derived from N-benzylethylenediamine is reported. X-ray structural analysis of the title compound has been determined. 13C CP-MAS NMR for the [Ni(benacet)](ClO 4) 2 complex was made and assignment of the signals was carried out by the use of the open gate decoupling technique and by comparison with the Ni(II) and Zn(II) complexes of the trans-[14]diene ligand as well as with the perchlorate salt of the free macrocycle. Based on the type of isolated compound, a hypothesis of the possible mechanism of reaction that explains the formation of the mesityl moiety during the template reaction is discussed. This hypothesis could also be used to explain how in the original reaction made by Curtis, a mixture of cis- and trans-isomers are formed.

Conversion of some substituted phenols to the corresponding masked thiophenols, synthesis of a dinickel(II) dithiolate macrocyclic complex and isolation of some metal- and ligand-based oxidation products

A modified preparation of the masked thiolate head unit S-(2,6-diformyl-4-methylphenyl) dimethylthiocarbamate 6 is detailed and two new masked thiolate head units, S-(2,6-diformyl-4-tert-butylphenyl) dimethylthiocarbamate 7 and S-(2-formylphenyl) dimethylthiocarbamate 8, are prepared by this method. The synthesis, crystal structure, NMR spectra and electrochemical properties of the first macrocyclic complex to be derived from 7, [Ni2L1](ClO4)2, are discussed. Oxidation of [Ni2L2](CF3SO3)2 (L22− is derived from 6 and 1,3-diaminopropane) with cerium(IV) ammonium nitrate led to the precipitation of the black complex [Ni2L2][Ce(NO3)6], which is believed to contain a single nickel(III) centre. This complex decomposes in DMF over time (≈24 hours) to form the red dinickel(II) complex [Ni2L2](NO3)2·2DMF which has been structurally characterised. Oxidation of [Ni2L3](CF3SO3)2 (L32− is derived from 6 and 1,4-diaminobutane) with I2 results in ligand oxidation forming the metal free macrocycle (L3′)2+ which contains two five membered isothiazole rings. This is confirmed by the X-ray crystal structure determinations of (L3′)(I3)2 and (L3′)(I)2(I2)5.

N,N-Didansyl-4,13-diaza-18-Crown-6: A Fluorescence-sensitive, Weakly Complexing Macrocycle Used to Probe the Phospholipid Vesicle Environment

N, N-Didansyl-4, 13-diaza-18-crownh-a6s been prepared and characterized by standard chemical techniques. The fluorescence emission of the dansyl sidearms are sensitive to the environment and the macrocycle has been used to probe the interior of a phospholipid bilayer. An experiment to probe the environment experienced by metal cation complexes of this macrocycle failed, apparently due to its extremely low cation binding strength. This macrocycle was also ineffective in transporting Na+ through a bulk CHC13 membrane. A solid state structure of the free macrocycle suggests why binding is so poor for this compound.

Structures and cationic complexes of 18[(2,6)pyridino-6-corand-6] (‘sexipyridine’)

The conformers of the title compound and its (gas phase) complexes with alkali metal cations and some molecular cations have been structurally optimized at HF/3-21G and HF/6-31G* levels of theory, with extended basis set single-point DFT calculations to include some of the effects of electron correlation. The only stable conformer found for the free macrocycle has D3 symmetry, and stable complexes of the same symmetry are demonstrated for Na+ and K+. Stable complexes of lower (C3) symmetry are also found for the possible template cations H3O+ and NH4+. Binding energies for the alkali metal cations ions are significantly larger than those found in comparable computational studies on structurally-related macrocycles. Finally, the complex with another potential template cation, C(NH2)3+, is also explored.

Zinc and cadmium complexes of an 18-membered N4O2 oxaaza-Schiff base macrocycle and the corresponding reduced form †

The metal templated (Cd and Zn) cyclocondensation of 2,6-pyridinedicarbaldehyde and 1,5-bis(2-aminophenoxy)-3-azapentane is reported together with the crystal structures of two mononuclear cadmium macrocyclic Schiff base complexes, [CdL1(NO3)2] 1 and [CdL1(H2O)2][ClO4]2 2 and a dinuclear, µ-hydroxy-bridged zinc macrocyclic Schiff base complex [Zn2L12(OH)][ClO4]3·CH3CN 3·CH3CN. The corresponding reduced macrocycle, L2, has been synthesised by using the MnII-templated cyclocondensation of 2,6-pyridinedicarbaldehyde and 1,5-bis(2-aminophenoxy)-3-azapentane in methanol followed by an in situ reductive demetallation of the Schiff base macrocyclic manganese(II) complex using excess sodium borohydride. The crystal structures of the free macrocycle L2, [CdL2(NO3)2] 4 and [CdL2(CH3CN)2][ClO4]2 5 are reported.

A molecular orbital study on a tetra-aza macrocycle containing 2,2′-bipyridines and its lithium complex

Singlet transition energies and oscillator strengths of two configurational isomers of a dicyano dibutyl tetra-aza macrocycle containing four pyridine rings and their lithium complexes were calculated using the CNDO/S CI method at ab initio RHF/3-21G optimized geometries. The results were in good agreement with those derived from the UV-Visible absorption spectra. The drastic spectral changes observed upon complexation in the trans-isomer were found to be due to the significant conformational change in the bipyridine moiety and the resulting energy separation of the frontier π orbitals. The close proximity between the triplet states and the singlet excited state suggested that the intersystem crossing might occur in the trans form of the lithium free macrocycle. This is one of the possible explanations of the large discrepancy in fluorescence intensities between the trans-isomer of the macrocycle and its lithium complex.

The synthesis and crystal structures of the amide NS3 macrocycle L1, and the silver complexes [Ag(L1)]n[CF3SO3]n and of [Ag(L2)]2[CF3SO3]2(where L1=9-oxo-1,4,7-trithia-10-azacyclododecane andL2=7-oxo-2,5,11-trithia-8-azatetradecane-12-orthobenzenophane).

he free macrocycle, L 1 was prepared by caesium carbonate promoted ring closure of the free NS 3 dithiol with dibromoethane and crystallised from CDCl 3. The X-ray structure shows exodentate orientation of the sulfur and nitrogen atoms. Reaction of silver triflate with 1 molar equivalent of L 1 in chloroform⧸methanol affords the homoleptic polynuclear species [ Ag( L 1)] + n that shows (3+1) thioether coordination to each of the silver centres, with one sulphur donor of each macrocycle bridging between metal centres. The macrocycle is coordinated as a neutral ligand, with ligation occurring only through the sulphur atoms and the amide nitrogen remaining protonated and uncoordinated. Reaction between silver triflate and L 2 affords the dimeric species [ Ag L 2] 2 2 with coordination by the three sulphur donor atoms to the silver centre. Tetrahedral coordination is completed by an unexpected Ag–C interaction with the aromatic backbone. In both metal complexes, no interaction is observed between the silver atom and the amide nitrogen.

Methylation of Tethered Thiolates in [(bme-daco)Zn](2) and [(bme-daco)Cd](2) as a Model of Zinc Sulfur-Methylation Proteins.

The dimeric dithiolate complex [1,5-bis(mercaptoethyl)-1,5-diazacyclooctanato]zinc(II), [(bme-daco)Zn](2) or Zn-1, and its cadmium analogue, Cd-1, were investigated as models for the active site of zinc-dependent methylation proteins. The key issue addressed was whether alkylation of a thiolate in a relatively rigid tetradentate ligand would result in coordination of the thioether product to the metal. On the basis of (1)H and (13)C NMR spectroscopy and similar reactivity toward alkylating agents, the newly synthesized cadmium complex, Cd-1, is proposed to be isostructural with the previously reported Zn-1 complex, which is known from X-ray crystallography to be dimeric in the solid state (Tuntulani, T.; Reibenspies, J. H.; Farmer, P. J.; Darensbourg, M. Y. Inorg. Chem.1992, 31, 3497). Iodomethane reacts with Zn-1 in hot CH(3)OH/CH(3)CN to produce a thioether which dissociates, replaced by coordination of iodide in the pseudotetrahedral complex, (Me(2)bme-daco)ZnI(2) or Zn-2. Complex Zn-2 crystallizes in the triclinic P&onemacr; space group with a = 7.911(2) Å, b = 10.675(2) Å, c = 12.394(2) Å, alpha = 75.270(10) degrees, beta = 75.270(10) degrees, gamma = 82.12(2) degrees, V = 998.270 Å(3), and Z = 2. An analogous reaction was observed for the cadmium derivative, Cd-1, which displays a (1)H NMR spectrum identical to that of Zn-2. In attempts to promote thioether binding, the iodide was displaced by addition of AgBF(4) to solutions of Zn-2 or the BF(4)(-) analogue was synthesized directly from Zn(BF(4))(2) and methylated ligand, Me(2)bme-daco, to yield Zn-3. Similar reactions with the cadmium analogue yielded a product identified as Cd-3 that was indistinguishable from Zn-3 by (1)H NMR. The (113)Cd NMR spectra of Cd-3 displayed a single resonance at 88 ppm consistent with a hard donor environment and inconsistent with sulfur binding. As a further attempt to induce thioether binding to zinc, the macrocyclization reagent 1,3-dibromopropane was added to Zn-1. The resulting product, [BrZn(macrocycle)](+), was only slightly soluble in pyridine and identified by +FAB/MS as the desired macrocyclic product with a large amount of free macrocycle ligand. Recrystallization from pyridine/ether resulted in loss of the zinc as Zn(py)(2)Br(2), which was obtained as colorless crystals and characterized by X-ray crystallography. Complex Zn(py)(2)Br(2) crystallizes in the monoclinic P2(1)/c space group with a = 8.534(2) Å, b = 18.316(4) Å, c = 8.461(2) Å, beta = 101.07(3) degrees, V = 1297.9(5) Å(3), and Z = 4.

Synthesis and characterisation of thioether crown hydrazones, and palladium(II) and platinum(II) complexes of 6-(2,4-dinitrophenylhydrazono)-1,4,8,11-tetrathiacyclotetradecane

Reaction of the functionalised thioether crowns [14]aneS4-6-one (1,4,8,11-tetrathiacyclotetradecan-6-one, L1) and [10]aneS3-9-one (1,4,7-trithiacyclodecan-9-one, L2) with 2,4-dinitrophenylhydrazine in a protic solvent under acidic catalysis afforded the corresponding hydrazones L3 and L4, respectively, in high yield. Reaction of [14]aneS4-6-one with p-nitrophenylhydrazine under similar conditions affords the hydrazone L5. Reaction of L3 with [Pd(MeCN)4][BF4]2 in MeCN yielded the complex [Pd(L3)][BF4]2, while reaction of this ligand with [Pt(EtCN)4][CF3SO3]2 in MeCN afforded [Pt(L3)][CF3SO3]2. The single-crystal structures of L3–L5 and of [Pd(L3)][BF4]2 have been determined. In all cases, π–π stacking is observed, the free macrocycles crystallising as polymeric arrays of face-sharing hydrazone moieties. In [Pd(L3)]2+, π–π interactions alternate with face sharing between planar [PdS4]2+ units constructing a one-dimensional polymeric array. The hydrazone function forces distortions of the respective macrocyclic rings and imparts chirality to the [Pd(L3)]2+ cation. The potential of these molecules as building blocks for macrocyclic liquid crystals and extended supramolecular arrays is discussed, as is the need to consider steric factors in rationalising the reactivity of keto-functionalised thioether crowns.

Conformational analysis of 14- and 16-membered unsaturated oxa, thia, and selena macrocyclic ligands

Crystallographic results retrieved from the Cambridge Structural Database (CSD) have been used to perform systematic conformational analyses of the free and metal-coordinated ligands 1,4,8,11-tetraoxa/thia/selenacyclotetradecane, 1,5,9,13-tetraoxa/thia/selenacyclohexadecane, and their derivatives. Conformational classifications established using symmetry-modified Jarvis-Patrick cluster analysis have been displayed in torsional space by principal component analysis (PCA) plots. Relative molecular mechanics energies of free macrocycles in the observed conformations are compared with the cluster populations and the effect of metal coordination investigated. While the conformations of the free macrocycles in the solid state are those with low molecular mechanics energies, substantial reorganization is required to produce tetradentate chelating conformers, particularly with S donors. With the latter, several such conformers occur, while one predominates with O donors for both macrocycles, in agreement with molecular mechanics predictions. Factors influencing the conformations adopted are discussed.

Vibrational study and semiempirical calculation for the hexaazacyclophane copper(II) complex

Abstract The FTIR and Raman spectra of the hexaazacyclophane Cu(II) complex were recorded, and analyzed from a normal coordinate treatment by using an extended number of internal coordinates. The CuN force constant equal to 1.0 mdyn A −1 represents satisfactorily the CuN bonding. Bond orders and total charge density for the metal free macrocycle and the complex were calculated within the molecular orbital theory framework at the INDO/1 level. Semiempirical results suggest a high electronic density on the coordination site.

Protonation of free 2,9-bis(p-biphenylyl)-1,10-phenanthrolinesites in a 56-membered macrocycle and in its ReIand CuIcomplexes Absorption spectra, luminescence properties, and excited state interactions

We have investigated the absorption and luminescence properties, and the 1H NMR spectra of (i) a macrocycle (L–L) made of a 56-membered ring incorporating two 2,9-bis(p-biphenylyl)-1,10-phenanthroline units and (ii) its metal complexes (L–L)Re(CO)3Cl and [(L–L)Cu(A)]+, where the latter is a catenate species (A is a 33-membered macrocycle containing a 2,9-p-biphenylyl-1,10-phenanthroline unit). The free macrocycle and its complexes contain, respectively, two and one free phenanthroline sites which can be protonated. Addition of trifluoroacetic acid to CH2Cl2 solutions of L–L, (L–L)Re(CO)3Cl, and [(L–L)Cu(A)]+ causes strong changes in the absorption spectra, with maintenance of the same family of isosbestic points in all cases. The 1H NMR spectrum of L–L is identical to that of the uncomplexed phenanthroline site of [(L–L)Cu(A)]+ and (L–L)Re(CO)3Cl. Such absorption and NMR data show that the two phenanthroline units of L–L do not interact in the ground state. For this macrocycle, the changes in the absorption spectrum upon protonation are accompanied by the disappearance of the very strong (emission quantum yield Φem = 0.89), short lived (τ = 1.7 ns) fluorescence band (λmax = 419 nm) of the 2,9-bis(p-biphenylyl)-1,10-phenanthroline units, with the appearance of a weak (Φem = 0.019), short lived (τ = 1.9 ns), strongly red-shifted (λmax = 572 nm) band. The results obtained show that the two equivalent basic sites of L–L are independently protonated. In the monoprotonated L · H+–L species, energy transfer from the unprotonated to the protonated site occurs. The phosphorescence band of L–L (λmax = 538 nm, τ = 0.8 s), which can be observed on cooling the solution to 77 K, moves slightly to the red (λmax = 571 nm, τ = 1.1 s) upon protonation. In the [(L–L)Cu(A)]+ and (L–L)Re(CO)3Cl complexes, protonation occurs at the free coordination site, as shown by the changes observed in the absorption and emission spectra. In the [(L · H+–L)Cu(A)]+ complex, the lowest triplet metal-to-ligand charge-transfer (3MLCT) level of the metal-based moiety lies below the lowest singlet excited state and the lowest triplet excited state of the protonated moiety. Therefore, both the fluorescence and (at 77 K) the phosphorescence of the protonated moiety are, at least in part, quenched. In Re(L · H+–L)(CO)3Cl, the lowest 3MLCT of the Re-based moiety is very close in energy to the fluorescent and phosphorescent levels of the protonated moiety with a consequent more complex luminescence behaviour.

Preorganization of tetrathiamacrocyclic ligands: implications from computed and experimentally determined structures

The tetrathiamacrocycles trans-6,13-dihydroxy-1,4,8,11-tetrathiacyclotetradecane (L 1 ) and its benzo- (L 2 ), syn- and anti-dibenzo-substituted derivatives (L 3 and L 3′ , respectively) have been prepared by conventional methods, and a benzo-substituted-1,4,7,10-tetrathiacyclotridecane (L 4 ) was obtained by substitution of o-dichlorobenzene after activation with an organometallic fragment. The structures of L 1 –L 4 and of the four palladium(II) complexes [PdL 1 ]Cl 2 ·2H 2 O, [PdL 2 ][PF 6 ] 2 , [PdL 3′ ][PF 6 ]Cl and [PdL 4 ][PF 6 ] 2 were determined by X-ray crystallography. All the experimentally determined structures were accurately reproduced by molecular mechanics calculations, using a constant-parametrization scheme. Two parameters for the evaluation of the extent of preorganization of free macrocycle molecules, based on structural and strain-energy differences of the free macrocycles and their corresponding metal complexes, are introduced and discussed on the basis of the experimentally determined and computed structural data for L 1 –L 4 , their metal complexes and other similar ligand and metal complex systems. The implications for the design of new compounds leading to high stability and high metal-ion selectivity are outlined.