Self-assembly of neutral and cationic PdII organometallic molecular rectangles: synthesis, characterization and nitroaromatic sensing

Design and synthesis of three novel [2 + 2] self-assembled molecular rectangles 1-3via coordination driven self-assembly of predesigned Pd(ii) ligands is reported. 1,8-Diethynylanthracene was assembled with trans-Pd(PEt(3))(2)Cl(2) in the presence of CuCl catalyst to yield a neutral rectangle 1via Pd-C bond formation. Complex 1 represents the first example of a neutral molecular rectangle obtained via C-Pd coordination driven self-assembly. A new Pd(2)(II) organometallic building block with 180° bite-angle 1,4-bis[trans-(ethynyl)Pd(PEt(3))(2)(NO(3))]benzene (M(2)) containing ethynyl functionality was synthesized in reasonable yield by employing Sonagashira coupling reaction. Self-assembly of M(2) with two organic clip-type donors (L(2)-L(3)) afforded [2 + 2] self-assembled molecular rectangles 2 and 3, respectively [L(2) = 1,8-bis(4-pyridylethynyl)anthracene; L(3) = 1,3-bis(3-pyridyl)isophthalamide]. The macrocycles 1-3 were fully characterized by multinuclear NMR and ESI-MS spectroscopic techniques, and in case of 1 the structure was unambiguously determined by single crystal X-ray diffraction analysis. Incorporation of Pd-ethynyl bonds helped to make the assemblies π-electron rich and fluorescent in nature. Complexes 1-2 showed quenching of fluorescence intensity in solution in presence of nitroaromatics, which are the chemical signatures of many commercially available explosives.     

Self-assembly of rectangles and prisms via a molecular "clip"

Aromatic molecular "clips" bearing two symmetrically bound platinum moieties have been prepared. The molecular "clip" 4 readily self-assembled with linear linkers such as 4,4'-bipyridyl, 1,4-bis[2-(4-isocyano-3,5-diisopropylphenyl)ethynyl]benzene, and nicotinic acid to form molecular rectangles. The overall dimensions of the rectangle 7 were 7.3 Angstroms x 15.3 Angstroms. The molecular "clip" also self-assembled with tritopic pyridyl and isocyanide ligands to form trigonal prismatic frameworks. The characterization of the supramolecules by multinuclear NMR, electrospray mass spectrometry, and X-ray crystal structures is also reported.     

Flame AAS and UV-VIS determination of cobalt, nickel and palladium using the synergetic effect of 2-benzoylpyridine-2-pyridylhydrazone and thiocyanate ions

A quantitative synergetic extraction procedure for cobalt, nickel and palladium from thiocyanate aqueous solutions into methyl isobutyl ketone (MIBK), containing 2-benzoylpyridine-2-pyridylhydrazone (BPPH), was studied by flame atomic absorption spectrometry (FAAS) and molecular absorption spectrometry (UV-VIS). Using FAAS, linear calibration graphs were obtained from 0.0-0.5 mg l(-1) Co(II), 0.0-1.5 mg l(-1) Ni(II) and 0.0-2.0 mg l(-1) Pd(II). The reproducibilities were s(r,Co(II))=2.0%, s(r,Ni(II))=1.0% and s(r,Pd(II))=1.3% and the limits of detection were c(L,Co(II))=0.004 mg l(-1), c(L,Ni(II))=0.009 mg l(-1) and c(L,Pd(II))=0.012 mg l(-1). Using UV-VIS method the linear calibration graphs were 0.0-0.5 mg l(-1) for Co(II), 0.0-1.0 mg l(-1) for Ni(II) and 0.0-2.0 mg l(-1) for Pd(II). The reproducibilities were s(r,Co(II))=1.3%, s(r,Ni(II))=1.7% and s(r,Pd(II))=1.0% and the limits of detection were c(L,Co(II))=0.001 mg l(-1), c(L,Ni(II))=0.004 mg l(-1) and c(L,Pd(II))=0.002 mg l(-1). The extraction method is almost free from interferences and has been successfully applied to the determination of cobalt, nickel and palladium in dental alloys.     

Self-assembly in palladium(II) and platinum(II) chemistry: the biomimetic approach

The self-assembly of complex cationic structures by combination of cis-blocked square planar palladium(II) or platinum(II) units with bis(pyridyl) ligands having bridging amide units has been investigated. The reactions have yielded dimers, molecular triangles, and polymers depending primarily on the geometry of the bis(pyridyl) ligand. In many cases, the molecular units are further organized in the solid state through hydrogen bonding between amide units or between amide units and anions. The molecular triangle [Pt(3)(bu(2)bipy)(3)(mu-1)(3)](6+), M = Pd or Pt, bu(2)bipy = 4,4'-di-tert-butyl-2,2'-bipyridine, and 1 = N-(4-pyridinyl)isonicotinamide, stacks to give dimers by intertriangle NH.OC hydrogen bonding. The binuclear ring complexes [[Pd(LL)(mu-2)](2)](CF(3)SO(3))(4), LL = dppm = Ph(2)PCH(2)PPh(2) or dppp = Ph(2)P(CH(2))(3)PPh(2) and 2 = NC(5)H(4)-3-CH(2)NHCOCONHCH(2)-3-C(5)H(4)N, form transannular hydrogen bonds between the bridging ligands. The complexes [[Pd(LL)(mu-3)](2)](CF(3)SO(3))(4), LL = dppm or dppp, L = PPh(3), and 3 = N,N'-bis(pyridin-3-yl)-pyridine-2,6-dicarboxamide, and [[Pd(LL)(mu-4)](2)](CF(3)SO(3))(4), LL = dppm, dppp, or bu(2)bipy, L = PPh(3), and 4 = N,N'-bis(pyridin-4-yl)-pyridine-2,6-dicarboxamide, are suggested to exist as U-shaped or square dimers, respectively. The ligands N,N'-bis(pyridin-3-yl)isophthalamide, 5, or N,N'-bis(pyridin-4-yl)isophthalamide, 6, give the complexes [[Pd(LL)(mu-5)](2)](CF(3)SO(3))(4) or [[Pd(LL)(mu-6)](2)](CF(3)SO(3))(4), but when LL = dppm or dppp, the zigzag polymers [[Pd(LL)(mu-6)](x)](CF(3)SO(3))(2)(x) are formed. When LL = dppp, a structure determination shows formation of a laminated sheet structure by hydrogen bonding between amide NH groups and triflate anions of the type NH-OSO-HN.     

Self-assembled palladium(II) "click" cages: synthesis, structural modification and stability

Readily synthesised and functionalised di-1,2,3-triazole "click" ligands are shown to self-assemble into coordinatively saturated, quadruply stranded helical [Pd(2)L(4)](BF(4))(4) cages with Pd(II) ions. The cages have been fully characterised by elemental analysis, HR-ESMS, IR, (1)H, (13)C and DOSY NMR, DFT calculations, and in one case by X-ray crystallography. By exploiting the CuAAC "click" reaction we were able to rapidly generate a small family of di-1,2,3-triazole ligands with different core spacer units and peripheral substituents and examine how these structural modifications affected the formation of the [Pd(2)L(4)](BF(4))(4) cages. The use of both flexible (1,3-propyl) and rigid (1,3-phenyl) core spacer units led to the formation of discrete [Pd(2)L(4)](BF(4))(4) cage complexes. However, when the spacer unit of the di-1,2,3-triazole ligand was a 1,4-substituted-phenyl group steric interactions led to the formation of an oligomeric/polymeric species. By keeping the 1,3-phenyl core spacer constant the effect of altering the "click" ligands' peripheral substituents was also examined. It was shown that ligands with alkyl, phenyl, electron-rich and electron-poor benzyl substituents all quantitatively formed [Pd(2)L(4)](BF(4))(4) cage complexes. The results suggest that a wide range of functionalised palladium(II) "click" cages could be rapidly generated. These novel molecules may potentially find uses in catalysis, molecular recognition and drug delivery.     

Architectural formation of a conjugated bimetallic Pd(II) complex via oxidative complexation and a tetracyclic Pd(II) complex via self-assembling complexation

The conjugated homobimetallic palladium(II) complex [(L1)Pd(qd)Pd(L1)] (qd = quinonediimine) was obtained in a one-pot reaction by the in-situ oxidative complexation of 1,4-phenylenediamine with the palladium(II) complex [(L1)Pd(MeCN)] (H2L1 = N,N'-bis(2-phenylethyl)-2,6-pyridinedicarboxamide) while in the absence of an additional ligand [(L1)Pd(MeCN)] was converted to the amide-bridged macrocyclic tetramer [Pd(L1)]4.     

Isostructural M2L4 molecular capsules with anthracene shells: synthesis, crystal structures, and fluorescent properties

An isostructural series of M(2)L(4) molecular capsules quantitatively self-assembled from two M(II) ions (M=Zn, Cu, Pt, Pd, Ni, Co, and Mn) and four bent ligands with embedded anthracene fluorophores. X-ray crystallographic analysis (for M=Zn, Cu, Ni, and Pd) confirmed the formation of closed-shell structures in which the large interior cavities inside the molecular capsules (about 1 nm) were shielded by eight anthracene panels. Analysis of the Zn(II) and Cu(II) structures showed the inclusion of an unusual triad guest cluster; four MeCN molecules, one water molecule, and one CF(3)SO(3)(-) ion were located inside the cavities. Full characterization by NMR spectroscopy and MS (ESI-TOF) demonstrated that the molecular capsules were quite stable and persist in solution. The fluorescence properties of the isostructural capsules were strongly dependent on the identity of the metal species: the Zn(II) capsule emitted strong blue fluorescence with a high quantum yield (Φ=0.8), in sharp contrast to the weakly emissive Ni(II) and Mn(II) capsules and the completely non-emissive Pd(II), Pt(II), and Co(II) capsules. On the other hand, the Cu(II) capsule exhibited solvatochromism and solvent-dependent emission behavior; blue emission of the capsule was "on" in DMSO but "off" in MeCN.     

Interplay of terminal amino group and coordinating side chains in directing regioselective cleavage of natural peptides and proteins with palladium(II) complexes

Palladium(II) ions anchored to side chains of histidine and methionine residues in peptides and proteins in weakly acidic aqueous solutions promote hydrolytic cleavage of proximate amide bonds in the backbone. In this study, we determine how attachment of Pd(II) ions to histidine and methionine anchors and also to the terminal amino group in six natural peptides (chains A and B of insulin, segment 11-14 of angiotensinogen, pentagastrin, angiotensin II, and segment 3-8 of angiotensin II) and two proteins (ubiquitin and cytochrome c) affects regioselectivity and rate of backbone cleavage. These Pd(II)-promoted reactions follow a clear pattern of regioselectivity, directed by the anchoring side chains. When the Pd(II) reagent is nonspecifically anchored to the terminal amino group, the ligating site that is present in almost all proteins, the cleavage is fortunately absent. When the reagent is anchored to a residue in positions 1, 2, or 3, cleavage is absent, because the terminal amino group and deprotonated amide nitrogen atom(s) interposed between it and the anchor "lock" the Pd(II) ion in hydrolytically inactive chelate complexes. When the reagent is anchored to residues in positions beyond 3, the second amide bond upstream from the anchor is regioselectively cleaved in all cases when the anchor was "isolated," that is, flanked by noncoordinating side chains. Segment 3-8 of angiotensin II undergoes additional cleavage, which we explain by determining the rate constants for the cleavage, identifying the rate-limiting displacement of ethylenediamine ligand from the Pd(II) ion, and detecting several intermediates. Experiments with cytochrome c demonstrate that the number of cleavage sites can be controlled by adjusting the mole ratio of the Pd(II) reagent to the substrate. Our inorganic peptidases are useful for biochemical applications because their regioselectivity and reactivity set them apart from proteolytic enzymes and organic chemical reagents.     

Pillar height dependent formation of unprecedented Pd8 molecular swing and Pd6 molecular boat via multicomponent self-assembly

Three-component self-assembly of a cis-blocked 90° Pd(II) acceptor with a mixture of a tetraimidazole and a linear dipyridyl donor self-discriminated into unusual Pd(8) molecular swing (1) and Pd(6) molecular boat (2), which are characterized by single-crystal X-ray diffraction analysis; their ability to bind C(60) in solution is established by fluorescence titration.     

Tetradentate bis(o-iminobenzosemiquinonate(1-)) pi radical ligands and their o-aminophenolate(1-) derivatives in complexes of nickel(II), palladium(II), and copper(II)

The coordination chemistries of the potential tetradentate ligands N,N'-bis(3,5-di-tert-butyl-2-hydroxyphenyl)ethylenediamine, H4[L1], the unsaturated analogue glyoxal-bis(2-hydroxy-3,5-di-tert-butylanil), H2[L2], and N,N'-bis(2-hydroxy-3,5-di-tert-butylphenyl)-2,2-dimethylpropylenediamine, H4[L3], have been investigated with nickel(II), palladium(II), and copper(II). The complexes prepared and characterized are [Ni(II)(H3L1)2] (1), [Ni(II)(HL2)2].5/8CH2Cl2 (2), [Ni(II)(L3**)] (3), [Pd(II)(L3**)][Pd(II)(H2L3) (4), and [Cu(II)(H2O)(L4)] (5), where (L4)2- is the oxidized diimine form of (L3)4- and (L3**)2- is the bis(o-iminosemiquinonate) diradical form of (L3)4-. The structures of compounds 1-5 have been determined by single crystal X-ray crystallography. In complexes 1 and 2, the ligands (H3L1)- and (HL2)- are tridentate and the nickel ions are in an octahedral ligand environment. The oxidation level of the ligands is that of an aromatic o-aminophenol. 1 and 2 are paramagnetic (mu(eff) approximately 3.2 mu(B) at 300 K), indicating an S = 1 ground state. The diamagnetic, square planar, four-coordinate complexes 3 and [Pd(II)(L3**)] in 4 each contain two antiferromagnetically coupled o-iminobenzosemiquinonate(1-) pi radicals. Diamagnetic [Pd(II)(H2L3)] in 4 forms an eclipsed dimer via four N-H.O hydrogen bonding contacts which yields a nonbonding Pd.Pd contact of 3.0846(4) A. Complex 5 contains a five-coordinate Cu(II) ion and two o-aminophenolate(1-) halves in (L4)2-. The electrochemistries of complexes 3 and 4a ([Pd(II)(L3**)] of 4) have been investigated, and the EPR spectra of the monocations and -anions are reported.     

Combined C-H functionalization/C-N bond formation route to carbazoles

A new method in which a series of substituted carbazoles is efficiently produced by the combination of an amide and an arene is described. The key feature of this method is the palladium-catalyzed tandem directed C-H functionalization and amide arylation. The method tolerates substitution on either ring of the biaryl amide substrates, and the products can be assembled in a simple two-step protocol from readily available reagents. The Pd(0) species generated are reoxidized to Pd(II) in the presence of Cu(OAc)2 and an atmosphere of oxygen.     

Pd(II) Binding Strength of a Novel Ambidentate Dipeptide-Hydroxypyridinonate Ligand: A Solution Equilibrium Study

A novel ambidentate dipeptide conjugate (H(L1)) containing N-donor atoms of the peptide part and an (O,O) chelate at the hydroxypyridinone (HP) ring is synthesized and characterized. It is hoped that this chelating ligand can be useful to obtain multitargeted Co(III)/Pt(II) dinuclear complexes with anticancer potential. The Pd(II) (as a Pt(II) model but with faster ligand exchange reactions) binding strength of the ligand was studied in an aqueous solution with the combined use of pH-potentiometry and NMR. In an equimolar solution, (L1)⁻ was found to bind Pd(II) via the terminal amino and increasing number of peptide nitrogens of the peptide backbone over a wide pH range. At a 2:1 Pd(II) to ligand ratio, the presence of [Pd₂H_–x(L1)] (x = 1–4) species, with high stability and with the coordination of the (O,O) chelating set of the ligand, was detected. The reaction of H(L1) with [Co(tren)]³⁺ (tren = tris(2-aminoethyl)amine) indicated the exclusive binding of (L1)⁻ via its (O,O) donor atoms to the metal unit, while treatment of the resulting Co-complex with Pd(II) afforded the formation of a Co/Pd heterobimetallic complex in solution with an (NH₂, N_amide) coordination of Pd(II). Shortening the peptide backbone in H(L1) by one peptide unit compared to the structurally similar ambidentate chelator consisting of three peptide bonds resulted in the slightly more favorable formation of the N-coordinated Pd(II) species, allowing the tailoring of the coordination properties.     

Gas-phase investigation of Pd(II)-alanine complexes with small native and derivatized peptides containing histidine

We report here the generation of gas-phase complexes containing Pd(II), a ligand (deprotonated alanine, A-), and/or N-terminus derivatized peptides containing histidine as one of the amino acids. The species were produced by electrospray ionization, and their gas-phase reactions were investigated using ion-trap tandem mass spectrometry. Pd(II) forms a stable diaqua complex in the gas phase of the formula, [Pd(A-) (H(2)O)(2)]+, (where A- = deprotonated alanine) along with ternary complexes containing A- and peptide. The collision-induced dissociation (CID) patterns of the binary and ternary complexes were investigated, and the dissociation patterns for the ternary complexes suggest that: (a) the imidazole ring of the histidine side group may be the intrinsic binding site of the metal ion, and (b) the peptides fragment primarily by cleavage of the amide bond to the C-terminal side of the histidine residues. These observations are in accord with previous solution-state studies in which Pd(II) was shown to cause hydrolysis of an amide bond of a peptide at the same position.     

Metalla-supramolecular rectangles as electron reservoirs for multielectron reduction and oxidation

The electron-transfer capacity of molecular rectangle ions [Pt(II)(4)(PEt(3))(8)(mu-anth(2-))(2)(mu-L)(2)](4+) with anth = anthracene-1,8-diyl and L = 4,4'-bipyridine (bp) or 1,2-bis(4-pyridyl)ethene (bpe) was investigated in acetonitrile and dichloromethane using cyclic voltammetry, EPR, and UV-vis-near-IR spectroelectrochemistry. The compounds can be reversibly reduced, first in a two-electron process and then via two closely separated one-electron steps. Oxidation was also possible at rather low potentials in a reversible two-electron step, followed by an electrochemically irreversible process. The spectroscopic results indicate reduction at the neutral acceptor ligands L and oxidation at the formally dianionic anthracene "clips". In contrast, the prototypical molecular square ([Pt(triphos)(mu-bp)](4))(8+) undergoes only irreversible reduction.     

Structural characterization of four members of the electron-transfer series [PdII(L)2)2]n (L = o-Iminophenolate derivative; n = 2-, 1-, 0, 1+, 2+). ligand mixed valency in the monocation and monoanion with S = (1)/(2) ground states

The reaction of the ligand 2-(2-trifluoromethyl)anilino-4,6-di-tert-butylphenol, H(2)((1)L(IP)), and PdCl(2) (2:1) in the presence of air and excess NEt(3) in CH(2)Cl(2) produced blue-green crystals of diamagnetic [Pd(II)((1)L(ISQ))(2)] (1), where ((1)L(ISQ))(*)(-) represents the o-iminobenzosemiquinonate(1-) pi radical anion of the aromatic ((1)L(IP))(2-) dianion. The diamagnetic complex 1 was chemically oxidized with 1 equiv of Ag(BF(4)), affording red-brown crystals of paramagnetic (S = (1)/(2)) [Pd(II)((1)L(ISQ))((1)L(IBQ))](BF(4)) (2), and one-electron reduction with cobaltocene yielded paramagnetic (S = (1)/(2)) green crystals of [Cp(2)Co][Pd(II)((1)L(ISQ))((1)L(IP))] (3); ((1)L(IBQ))(0) represents the neutral, diamagnetic quinone form. Complex 1 was oxidized with 2 equiv of [NO]BF(4), affording green crystals of diamagnetic [Pd(II)((1)L(IBQ))(2)](3)(BF(4))(4){(BF(4))(2)H}(2).4CH(2)Cl(2) (5). Oxidation of [Ni(II)((1)L(ISQ))(2)] (S = 0) in CH(2)Cl(2) solution with 2 equiv of Ag(ClO(4)) generated crystals of [Ni(II)((1)L(IBQ))(2)(ClO(4))(2)].2CH(2)Cl(2) (6) with an S = 1 ground state. Complexes 1-5 constitute a five-membered complete electron-transfer series, [Pd((1)L)(2)](n) (n = 2-, 1-, 0, 1+, 2+), where only species 4, namely, diamagnetic [Pd(II)((1)L(IP))(2)](2-), has not been isolated; they are interrelated by four reversible one-electron-transfer waves in the cyclic voltammogram. Complexes 1, 2, 3, 5, and 6 have been characterized by X-ray crystallography at 100 K, which establishes that the redox processes are ligand centered. Species 2 and 3 exhibit ligand mixed valency: [Pd(II)((1)L(ISQ))((1)L(IBQ))](+) has localized ((1)L(IBQ))(0) and ((1)L(ISQ))(*)(-) ligands in the solid state, whereas in [Pd(II)((1)L(ISQ))((1)L(IP))](-) the excess electron is delocalized over both ligands in the solid-state structure of 3. Electronic and electron spin resonance spectra are reported, and the electronic structures of all members of this electron-transfer series are established.     

Investigating the effect of hydrogen bonding environments in amide cleavage reactions at zinc(II) complexes with intramolecular amide oxygen co-ordination

Amide oxygen co-ordination to a zinc(II) ion around a hydrogen bonding microenvironment is a common structural/functional feature of metalloproteases. We report two strategies to position hydrogen bonding groups in the proximity of a zinc(II)-bound amide oxygen, and we investigate their effect on the stability of the amide group. Polydentate tripodal ligands (6-R1-2-pyridylmethyl)-R2 (R1= NHCOtBu, R2= N(CH2-py-6-X)2 X = H L1, X = NH2, H L2, X = NH2 L3) form [(L)Zn]2+ cations (L =L1, 1; L2, 2; L3, 3) with intramolecular amide oxygen co-ordination (1-3), and intramolecular N-H...O=C(amide) hydrogen bonding (2, 3) rigidly fixed by the ligand framework. 1-3 undergo cleavage of the tert-butyl amide upon addition of Me4NOH.5H2O (1 equiv.) in methanol at 50(1) degrees C. Under these conditions the half-life, t(1/2), of the amide bond is 0.4 h for 1, 9 h for 2 and 320 h for 3. Mononuclear zinc(II) complexes of (6-NHCOtBu-2-pyridylmethyl)-R2(R2= N(CH2CH2)2S) L4 and chelating N2 ligands without hydrogen bonding groups (1,10-phenanthroline L5, 2-(aminomethyl)pyridine L6) as control compounds, and with an amino hydrogen bonding group (6-amino-2-(aminomethyl)pyridine L7) have been synthesised. Amide cleavage is in this case faster at the zinc(II) complex with the amino hydrogen bonding group. Thus, hydrogen bonding environments can both accelerate and slow down amide bond cleavage reactions at zinc(II) sites. Importantly, the magnitude of the effect exerted by the hydrogen bonding environments was found to be significant; 800-fold rate difference. This result highlights the importance of hydrogen bonding environments around metal centres in amide cleavage reactions, which may be relevant to the chemistry of natural metalloproteases and applicable to the design of more efficient artificial protein cleaving agents.     

Ytterbium amides of linked bis(amidinate): synthesis, molecular structures, and reactivity for the polymerization of L-lactide

The steric effect of an amide group on the synthesis, molecular structures and reactivity of ytterbium amides supported by linked bis(amidinate) L (L = [Me3SiNC(Ph)N(CH2)3NC(Ph)NSiMe3]) is reported. Reaction of LYbCl(THF)2 with equimolar NaNHAr' and NaNHAr (Ar' = 2,6-Me2C6H3; Ar = 2,6-iPr2C6H3), respectively, gave the corresponding monometallic amide complexes LYb(NHAr')(DME) 1 and LYb(NHAr)(DME) 2, in which the linked bis(amidinate) is coordinated to the metal center as a chelating ligand. The similar reaction with NaN(SiMe3)2 afforded a bimetallic amide complex (TMS)2NYb(L)2YbN(TMS)2 3 formed through the rearrangement reaction of L induced by the bulky N(SiMe3)2 group. In complex 3 the two linked bis(amidinate)s act as bridging ancillary ligands to link two YbN(TMS)2 species in one molecule. The definite molecular structures of 1-3 were provided by single-crystal X-ray analysis. Complexes 1-3 are efficient initiators for the polymerization of L-lactide, and their catalytic performance is highly dependent on the amido groups and molecular structures. The polymerizations initiated by complexes 1 and 2 proceeded in a living fashion as evidenced by the narrow polydispersities of the resulting polymers, together with the linear natures of the number average molecular weight versus conversion plots, while the polymerization system with complex 3 provided polymers with rather broad molecular weight distributions.     

Assembly of a heterobinuclear 2-D network: a rare example of endo- and exocyclic coordination of Pd(II)/Ag(I) in a single macrocycle

The S3O2 macrocycle L1 was synthesized by a dithiol-dihalide coupling reaction under high-dilution conditions. The reaction of L1 with K2PdCl4 afforded an exocoordinated complex 1, [cis-Cl2Pd(L1)], which can then be manipulated to provide a heterobinuclear complex 3, {[Pd(L1)Ag(NO3)(2.5)](NO3)(0.5)}n, utilizing endocyclic Pd(II) and exocyclic Ag(I) in a single macrocycle through a successive reaction with AgNO3. The network of 3 contains a unique honeycomb-like 2-D sheet made up of the repeating unit [Ag6(NO3)6].     

Self-assembly and molecular recognition of a luminescent gold rectangle

A luminescent molecular rectangle [Au(4)(micro-PAnP)(2)(micro-bipy)(2)](OTf)(4) (1.(OTf)(4)) (PAnP = 9,10-bis(diphenylphosphino)anthracene, bipy = 4,4'-bipyridine, X = NO(3)(-) or OTf(-)), synthesized from the self-assembly of the molecular "clip" Au(2)(micro-PAnP)(OTf)(2) and bipy, shows a large rectangular cavity of 7.921(3) x 16.76(3) A. The electronic absorption and emission spectroscopy, and electrochemistry of the metallacyclophane, have been studied. The 1(4+) ions are self-assembled into 2D mosaic in the solid state via complementary edge-to-face interactions between the Ph groups. (1)H NMR titrations ratify the 1:1 complexation between 1(4+) and various aromatic molecules. Comparing the structures of the inclusion complexes indicates an induced-fit mechanism operating in the binding. The emission of 1(4+) is quenched upon the guest binding. The binding constants are determined by both (1)H NMR and fluorescence titrations. Solvophobic and ion-dipole effects are shown to be important in stabilizing the inclusion complexes.     

Versatility and reactivity of salicylaldehyde <Emphasis Type="Italic">S</Emphasis>-methylisothiosemicarbazone in palladium(II) complexes

New palladium(II) complexes, [Pd(HL)Cl] · H₂O (I) and {K[Pd(L¹)(NO₂)] · H₂O}₂, with S-methylisothiosemicarbazone of salicylaldehyde (H₂L) and its derivative (H₂L¹) were synthesized. X-ray diffraction analysis demonstrated the ambident nature of S-alkylated thiosemicarbazone, which is attached to palladium(II) through O, N, and S donor atoms in I and through O, N, and N atoms in II. This is the first known case of metal coordination of the alkylated sulfur atom of a thiosemicarbazide moiety of the ligand. A mechanism of nitrosation of the terminal amide nitrogen atom of the H₂L¹ ligand during complexation was proposed.