Carboxylate Chemistry Research Articles

Iodine(I) pnictogenate complexes as Iodination reagents

Halogen(I) complexes are widely used as halogenation reagents and traditionally feature homoleptic stabilising Lewis bases, though the recent revitalisation of iodine(I) carboxylate chemistry has provided isolable examples of heteroleptic iodine(I) complexes. This work reports iodine(I) pnictogenate complexes stabilised by a Lewis base (L), Ph2P(O)O─I─L, synthesised via cation exchange from the silver(I) precursor, (Ph2P(O)OAg)n. The complexes were characterised in both solution (1H, 1H-15N HMBC, 31P) and the solid state, and supplemented computationally by DFT studies. Interestingly, these iodine(I) pnictogenates demonstrate a range of stabilities, and have been found to excel as iodination reagents in comparison to carbonyl hypoiodites, with comparable reactivity to the eponymous Barluenga’s reagent in the iodination of antipyrine.

Reversible Chemical Protein Modification to Endogenous Glutathione and Its Utilities in the Manufacture of Transcellular Pro-Enzymes

Proteins have been perceived as being an intriguing modality of therapeutics for the treatment of intractable diseases in view of their superlative precision and versatility. Nonetheless, proteins' intrinsic characters, particularly their being hydrophilic macromolecules with unmethodical charges, have imposed the exceeding challenge of seeking transcellular trafficking into cells' interiors. To circumvent this drawback, we have attempted to employ triple-functional amine-reactive 4-(2-((2-(((4-nitrophenoxy)carbonyl)oxy)ethyl)disulfaneyl)ethoxy)-4-oxobutanoic acid for the efficient incorporation of the anionic carboxyl moiety into amine-enriched enzymes, resulting in overall negatively charged pro-enzymes. The resulting pro-enzymes could be readily electrostatically assembled with cationic species [for instance: block copolymers of poly(ethylene glycol)-polylysine] into core-shell architectural delivery nanoparticles for their facilitated endocytosis into cells. Noteworthy is the aforementioned carboxylation chemistry designed to allow facile reversal of the pro-enzymes to the original amine groups due to the thiolysis of intermediate disulfide linkage for subsequent cascade reactions in response to the cytosol-enriched glutathione. Therefore, cytosol-selective structural disassembly for the liberation and activation of the pro-enzymes was accomplished. Our subsequent investigations utilizing ribonuclease A and catalase as the model enzymes demonstrated appreciable transcellular transportation of the active enzymes to the cell interiors, exerting overwhelming cytotoxic potencies and H2O2 scavenging capacities, respectively. Hence, we reported an unprecedented redox-stimulated charge reversal strategy in engineering cytosol-activatable pro-enzymes, manifesting a simple and efficient approach in the manufacture of transcellular proteinic therapeutics, which should be highlighted to promote their wide availability for use with diverse functional proteins as molecular biological tools and precision therapeutics.

Electrochemically induced grafting of ferrocenyl polymers for ultrasensitive cleavage-based interrogation of matrix metalloproteinase activity

Being closely associated with a variety of physiological and pathological processes, matrix metalloproteinases (MMPs) are useful as potential targets for drug therapy and informative markers for disease diagnosis. On the basis of the electrochemically induced grafting of ferrocenyl polymers and the proteolytic cleavage of recognition peptide, a novel electrochemical sensor is presented in this work for the highly specific interrogation of MMP activities at ultralow levels. The recognition peptide, to be immobilized via the N-terminus, is free of carboxyl group. The presence of the target MMP would cleave the end-tethered recognition peptide, generating a free carboxyl group at the C-terminus of the rest fragment. To be used as the reversible addition−fragmentation chain-transfer (RAFT) agent, the dithiobenzoate, 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid (CPAD), can therefore be tethered via the carboxylate-Zr(IV)-carboxylate chemistry. Subsequently, the grafting of ferrocenyl polymers through electrochemically induced RAFT (eRAFT) polymerization of ferrocenylmethyl methacrylate (FcMMA) would recruit a large quantity of Fc redox reporters on electrode surface. With benefits from the excellent specificity of the enzyme-substrate recognition, the presented cleavage-based sensor is highly selective. Under optimal conditions, the detection limit in the presence of MMP-2 as the model target can be as low as 0.27 pg mL−1, with a linear range from 1 pg mL−1 to 1 ng mL−1. Furthermore, its applicability in the interrogation of MMP activity in complex serum samples and the screening of MMP inhibitors is satisfactory. The presented cleavage-based electrochemical MMP sensor is easy to fabricate and low-cost, thus showing great promise in drug discovery and disease diagnosis.

MgZnO Dual Gate Thin Film Transistor for the Sensitive Determination of Modified Folic Acid

Folate receptor (FR) is a typical tumor-associated antigen that has been widely used as a biomarker for the determination of cancer. A biosensing platform functionalized with folic acid (FA) is essential to FR detection because FA specifically binds FR. We demonstrate an MgZnO dual-gate thin-film transistor (MZO DGTFT) based biosensor for the sensitive determination of FA derivative, hexadecyl alkynated folic acid (HAFA). The receptor is an MZO nanostructure (MZO $_{\mathrm {nano}}$ ) modified sensing pad which electrically connects to the top gate of DGTFT. The bottom gate of DGTFT is used to bias the device to its optimum operation point, enabling high sensitivity. First, 11-azidoundecanoic acid (AA) was bond onto the MZO $_{\mathrm {nano}}$ surface as the linker layer, resulting in negative charges to MZO $_{\mathrm {nano}}$ due to carboxylic acid binding chemistry. HAFA was then immobilized on MZO $_{\mathrm {nano}}$ via click reaction with AA. HAFA is a polar molecule with the positive end adjacent to AA/MZO $_{\mathrm {nano}}$ , and therefore, the electrostatic condition of MZO $_{\mathrm {nano}}$ is impacted again. Such changes were detected by DGTFT that displayed significant drain current variations. Fourier-transform infrared spectroscopy (FTIR) imaging confirms such successful chemical processes. This MZO DGTFT biosensor with HAFA is promising for potential applications in the detection of FR overexpressed cancer cells.

Highly sensitive lung cancer DNA detection via GO enhancing eATRP signal amplification

Atom transfer radical polymerization (ATRP) is an effective polymerization technology, and low ppm ATRP attracts unceasing interest in biological field. In this work, a fast and effective electrochemical biosensor based on graphene oxide (GO) via electrochemically mediated ATRP (eATRP) realized the ultrasensitive detection of lung cancer DNA. Peptide nucleic acid (PNA) was used as capture probes to specifically recognize target DNA, GO was connected to PNA/DNA heteroduplexes via phosphate-Zr4+-carboxylate chemistry to introduce eATRP initiators. Under a potentiostatic condition, eATRP was initiated with the help of reducibility of electrons, and numerous monomers labeled with ferrocene moieties were grafted onto GO. GO was synthesized by modified Hummer’s method and was characterized by Fourier transform infra-red spectra (FT-IR) and X-ray diffraction (XRD). The analytical performance of this biosensor was evaluated by square wave voltammetry (SWV) under optimal conditions, its limit of detection (LOD) was 0.213 aM (R2 = 0.994) with a linear range from 1.0 aM to 100 fM. High selectivity of this biosensor indicated a good application potential of genotyping of single nucleotide polymorphisms (SNPs), and simple operation and highly sensitive analytical performance endowed this biosensor a superior application prospect. More importantly, a novel thinking for material application in biological detection was provided in this work.

Redox-Neutral Photocatalytic C−H Carboxylation of Arenes and Styrenes with CO2

Summary Carbon dioxide (CO2) is an attractive one-carbon (C1) building block in terms of sustainability and abundance. However, its low reactivity limits applications in organic synthesis as typically high-energy reagents are required to drive transformations. Here, we present a redox-neutral C─H carboxylation of arenes and styrenes using a photocatalytic approach. Upon blue-light excitation, the anthrolate anion photocatalyst is able to reduce many aromatic compounds to their corresponding radical anions, which react with CO2 to afford carboxylic acids. High-throughput screening and computational analysis suggest that a correct balance between electron affinity and nucleophilicity of substrates is essential. This novel methodology enables the carboxylation of numerous aromatic compounds, including many that are not tolerated in classical carboxylation chemistry. Over 50 examples of C─H functionalizations using CO2 or ketones illustrate a broad applicability. The method opens new opportunities for the valorization of common arenes and may find application in late-stage C─H carboxylation.

Ultrasensitive detection of CYFRA 21-1 DNA via SI-RAFT based in-situ metallization signal amplification

Cytokeratin fragment antigen 21-1 (CYFRA 21-1) DNA is a significant biomarker with relation to non-small cell lung cancer. Here, we described an ultrasensitive electrochemical biosensor for detection of CYFRA 21-1 DNA (target DNA, tDNA) via surface-initiated reversible addition fragmentation chain transfer (SI-RAFT) polymerization-based DNA metallization signal amplification strategy. Specifically, 5′terminal modified thiol peptide nucleic acid (PNA) probes are immobilized on the gold electrode surface (by Au-S selfassembly) for the identification of specific tDNA sequences. After hybridization, the 4-cyano-4-(phenylcarbonothioylthio) pentanoic acid (CPAD) is tethered to the PNA/DNA duplexes by means of the recognized phosphate-Zr4+-carboxylate chemistry. Subsequently, in the situation of C3H4O as the monomer, SI-RAFT polymerization can bring numerous aldehyde groups sites for the subsequent silver mirror reaction. The acrolein-polymers act as reductant to reduce Ag+ into Ag0, and then the silver particles are deposited on the polymer skeleton, which significantly amplifies the electrochemical signal. Under optimal conditions, the designed sensor for tDNA detection show a wide linear range from 100 aM to 1 nM, and the detection limit is as low as 0.89 aM. Moreover, the proposed biosensor exhibits prominent applicability for analysis of tDNA in serum samples and high selectivity for different mismatched oligonucleotide fragments. Given the proposed biosensor without extra natural enzyme or bio-labels, this method has enormous potential in bioanalysis.

Electrochemical CYFRA21-1 DNA sensor with PCR-like sensitivity based on AgNPs and cascade polymerization.

In this work, a new method of CYFRA21-1 DNA (tDNA) detection based on electrochemically mediated atom transfer radical polymerization (e-ATRP) and surface-initiated reversible addition-fragmentation chain transfer polymerization (SI-RAFT) cascade polymerization and AgNP deposition is proposed. Firstly, the peptide nucleic acid (PNA) probe is captured on a gold electrode by Au-S bonds for specific recognition of tDNA. After hybridization, PNA/DNA strands provide high-density phosphate groups for the subsequent ATRP initiator by the identified carboxylate-Zr4+-phosphate chemistry. Then, a large number of monomers are successfully grafted from the DNA through the e-ATRP reaction. After that, the chain transfer agent of SI-RAFT and methacrylic acid (MAA) are connected by recognized carboxylate-Zr4+-carboxylate chemistry. Subsequently, through SI-RAFT, the resulting polymer introduces numerous aldehyde groups, which could deposit many AgNPs on tDNA through silver mirror reaction, causing significant amplification of the electrochemical signal. Under optimal conditions, this designed method exhibits a low detection limit of 0.487aM. Moreover, the method enables us to detect DNA at the level of PCR-like and shows high selectivity and strong anti-interference ability in the presence of serum. It suggests that this new sensing signal amplification technology exhibits excellent potential of application in the early diagnosis of non-small cell lung cancer (NSCLC). Graphical abstract Electrochemical detection principle for CYFRA21-1 DNA based on e-ATRP and SI-RAFT signal amplification technology.

Across the Board: Arjan W. Kleij on Electrosynthesis for Regioselective Carboxylation of Aromatic Alkenes.

In this series of articles, the board members of ChemSusChem discuss recent research articles that they consider of exceptional quality and importance for sustainability. This entry features Prof. A. W. Kleij, who discusses the use of electrosynthesis to advance the regioselective hydrocarboxylation of low-value olefins to afford high-value carboxylic acids using carbon dioxide as reagent. In particular, in a recent breakthrough contribution a general β-carboxylation of aromatic olefins is displayed and as such significantly expands state-of-the-art carboxylation chemistry.

CuBr2/EDTA-mediated ATRP for ultrasensitive fluorescence detection of lung cancer DNA

In this paper, we reported a system for the ultrasensitive fluorescence detection of cytokeratin fragment antigen 21–1 DNA (CYFRA21-1 DNA) for the early diagnosis of lung cancer. The approach used electron transfer atom transfer radical polymerization (ARGET-ATRP) with ethylenediaminetetraacetic acid (EDTA) as the metal ligand. Firstly, thiolated peptide nucleic acid (PNA) was linked to aminated magnetic beads solutions (MBs) by a cross-linking agent and then hybridized with CYFRA21-1 DNA (tDNA). Subsequently, Zr4+ was introduced into the MBs by conjugating with the phosphate group of tDNA, and the initiator of ARGET-ATRP was introduced into via phosphate-Zr4+-carboxylate chemistry. Next, Cu(II)Br/EDTA was reduced to Cu(I)/EDTA by ascorbic acid (AA) to trigger ARGET-ATRP and then a large amount of fluorescein-o-acrylate (FA) molecules were grafted from the surface of the MBs, which amplified significantly the fluorescent signal. Under optimal conditions, a strong linear relationship of tDNA over the range from 0.1 fM to 1 nM (R2 = 0.9988). The limit of detection was as low as 23.8 aM (~143 molecules). The fluorescence detection based on the ARGET-ATRP strategy yielded excellent sensitivity, selectivity, outstanding anti-interference properties, and cost-effectiveness. These results indicated that this strategy has considerable potential for biological detection and early clinical diagnosis.

Electrochemical DNA Biosensing via Electrochemically Controlled Reversible Addition-Fragmentation Chain Transfer Polymerization.

Sensitive and selective sensing of biological molecules is fundamental to disease diagnosis and infectious disease surveillance. Herein, an ultrasensitive and highly selective electrochemical DNA biosensor is described by exploiting the electrochemically controlled reversible addition-fragmentation chain-transfer (eRAFT) polymerization as a signal amplification strategy and the peptide nucleic acid (PNA) probes as the recognition elements. Specifically, the PNA probes with a thiol at their 5'-terminals are anchored to a gold electrode surface (via gold-sulfur self-assembly) for sequence-specific recognition of target DNA (tDNA) fragments, of which the phosphate sites serve as the anchorages for the targeted labeling (via the well-established phosphate-Zr4+-carboxylate chemistry) of the carboxyl-group-containing chain-transfer agents (CTAs) for the succedent eRAFT polymerization, wherein the initiating radicals are generated through electrochemical reduction of aryl diazonium salts under a potentiostatic condition. In the presence of ferrocenylmethyl methacrylate (FcCH═CH2) as the monomer, the grafting of polymer chains from the CTA-anchored sites as a result of the eRAFT polymerization brings numerous electroactive Fc tags to the electrode surface, outputting a high electrochemical sensing signal even in the presence of trace amounts of tDNA fragments. Under the optimized conditions, the linear range of the described electrochemical DNA biosensor spans from 10 aM to 10 pM ( R2 = 0.998), with an attomolar detection limit (4.1 aM) being achieved. Moreover, the described electrochemical DNA biosensor is highly selective and applicable to the sensing of tDNA fragments in complex serum samples. Given its high efficiency, easy operation, and low cost, this biosensor shows great promise in real applications.

Nanoroughness, Surface Chemistry, and Drug Delivery Control by Atmospheric Plasma Jet on Implantable Devices.

Implantable devices need specific tailored surface morphologies and chemistries to interact with the living systems or to actively induce a biological response also by the release of drugs or proteins. These customized requirements foster technologies that can be implemented in additive manufacturing systems. Here, we present a novel approach based on spraying processes that allow to control separately topographic features in the submicron range (∼60 nm to 2 μm), ammine or carboxylic chemistry, and fluorophore release even on temperature-sensitive biodegradable polymers such as polycaprolactone (PCL). We developed a two-steps process with a first deposition of 220 nm silica and poly(lactic- co-glycolide) (PLGA) fluorescent nanoparticles by aerosol followed by the deposition of a fixing layer by an atmospheric pressure plasma jet (APPJ). The nanoparticles can be used to create the nanoroughness and to include active molecule release, while the capping layer ensures stability and the chemical functionalities. The process is enabled by a novel APPJ which allows deposition rates of 10-20 nm·s-1 at temperatures lower than 50 °C using argon as the process gas. This approach was assessed on titanium alloys for dental implants and on PCL films. The surfaces were characterized by Fourier transform infrared, atomic force microscopy, and scanning electron microscopy (SEM). Titanium alloys were tested with the preosteoblast murine cells line, while the PCL film was tested with fibroblasts. Cell behavior was evaluated by viability and adhesion assays, protein adsorption, cell proliferation, focal adhesion formation, and SEM. The release of a fluorophore molecule was assessed in the cell growing media, simulating a drug release. Osteoblast adhesion on the plasma-treated materials increased by 20% with respect to commercial titanium alloy implants. Fibroblast adhesion increased by a 100% compared to smooth PCL substrates. The release of the fluorophore by the dissolution of the PLGA nanoparticles was verified, and the integrity of the encapsulated drug model was confirmed.

Electrochemically mediated in situ growth of electroactive polymers for highly sensitive detection of double-stranded DNA without sequence-preference

The ability to directly detect double-stranded DNA (dsDNA) without sequence-preference continues to be a major challenge. Herein, we report an electrochemical method for the direct, highly sensitive detection of dsDNA based on the strand replacement of dsDNA by peptide nucleic acid (PNA) and the in situ growth of electroactive polymers through the surface-initiated electrochemically mediated atom transfer radical polymerization (SI-eATRP). Thiolated PNA molecules are firstly self-assembled onto gold electrode surface for the specific recognition of target dsDNA (dsDNA-T), which in turn leads to the formation of a high density of PNA/DNA heteroduplexes on the electrode surface for the subsequent attachment of ATRP initiators via the phosphate-Zr4+-carboxylate chemistry. By applying a negative potential to the electrode, the air-stable CuII deactivators can be reduced into the CuI activators so as to trigger the surface-initiated polymerization for the in situ growth of electroactive polymers. Due to the strand replacement of dsDNA by PNA, dsDNA can be directly detected without sequence-preference. Besides, the growth of polymers enables the modification of numerous electroactive probes, thereby greatly improving the electrochemical signal. Under optimal conditions, a good linearity between the electrochemical signal and the logarithm of dsDNA-T concentration over the range from 1.0 fM to 1.0nM, with a detection limit of 0.47 fM, can be obtained. Results indicate that it is highly selective, and holds high anti-interference capability in the presence of human serum samples. Therefore, this method offers great promises in providing a universal and efficient solution for the direct detection of dsDNA.

Electrochemically Mediated Surface-Initiated de Novo Growth of Polymers for Amplified Electrochemical Detection of DNA.

The development of convenient and efficient strategies without involving any complex nanomaterials or enzymes for signal amplification is of great importance in bioanalytical applications. In this work, we report the use of electrochemically mediated surface-initiated atom transfer radical polymerization (SI-eATRP) as a novel amplification strategy based on the de novo growth of polymers (dnGOPs) for the electrochemical detection of DNA. Specifically, the capture of target DNA (tDNA) by the immobilized peptide nucleic acid (PNA) probes provides a high density of phosphate groups for the subsequent attachment of ATRP initiators onto the electrode surface by means of the phosphate-Zr4+-carboxylate chemistry, followed by the de novo growth of electroactive polymer via the SI-eATRP. De novo growth of long polymeric chains enables the labeling of numerous electroactive probes, which in turn greatly improves the electrochemical response. Moreover, it circumvents the slow kinetics and poor coupling efficiency encountered when nanomaterials or preformed polymers are used and features sufficient flexibility and simplicity in controlling the degree of signal amplification. Under optimal conditions, it allows a highly sensitive and selective detection of tDNA within a broad linear range from 0.1 fM to 0.1 nM (R2 = 0.996), with the detection limit down to 0.072 fM. Compared with the unamplified method, more than 1.2 × 106-fold sensitivity improvement in DNA detection can be achieved. By virtue of its simplicity, high efficiency, and cost-effectiveness, the proposed dnGOPs-based signal amplification strategy holds great potential in bioanalytical applications for the sensitive detection of biological molecules.

Structural aesthetics in molecular nanoscience: a unique Ni26 cluster with a 'rabbit-face' topology and a discrete Ni18 'molecular chain'.

The use of a previously unexplored Schiff-base ligand in Ni(II) carboxylate chemistry has afforded a Ni26 cluster with a record nuclearity that crystallizes with a unique 'rabbit-face'-like topology, and a Ni18 compound that adopts an unusual 'molecular chain' structure.

The acid test: the chemistry of carboxylic acid functionalised {Cr7Ni} rings

The synthesis, structures and magnetism of a new nano-scale constructs using carboxylic acid functionalised {Cr7Ni} rings are reported. Well-established carboxylate chemistry is used to synthesise of spectacular assemblies including a {Zn4O} tetrahedron surrounded by an octahedron of {Cr7Ni} rings.

A MnII6MnIII6 Single-Strand Molecular Wheel with a Reuleaux Triangular Topology: Synthesis, Structure, Magnetism, and DFT Studies

The use of the anion of 3-methyl-1,3,5-pentanetriol (mpt(3-)) in manganese carboxylate chemistry has afforded the new Mn(II/III)12 cluster [Mn(II)6Mn(III)6(mpt)6(CH3CO2)12(py)6]·3CH3CN (1·3CH3CN). Complex 1 was isolated in moderate yield by the reaction of Mn(CH3CO2)2·4H2O and H3mpt in a 2.6:1 molar ratio in a solvent mixture of acetonitrile and pyridine. The structure of 1 consists of alternating [Mn(II)2(CH3CO2)3(py)](+) and [Mn(III)2(μ-OR)2(CH3CO2)(py)](3+) dimeric units (three of each dimer), linked at each end by two alkoxo and one acetate bridges; the mpt(3-) ligands adopt the η(2):η(2):η(2):μ4 coordination mode. The overall metal topology of this new Mn12 wheel resembles a guitar plectrum, or a Reuleaux triangle. Complex 1 displays an unprecedented structural topology, being the first example of a Mn(II)6Mn(III)6 wheel constructed from alternating homovalent dimers and the only known Mn12 loop with the trigonal symmetry of a Reuleaux triangle (all other reported loops were ellipsoids). Variable-temperature, solid-state direct- and alternating-current magnetization studies were carried out on complex 1, revealing the presence of antiferromagnetic exchange interactions between the metal ions in the molecule, which lead to a spin ground-state value S = 0; the exchange coupling parameters J were calculated using density functional theory employing a hybrid B3LYP functional.

Hexanuclear zinc(II) carboxylate complexes from the use of pyridine-2,6-dimethanol: Synthetic, structural and photoluminescence studies

The employment of pyridine-2,6-dimethanol (pdmH2) in zinc(II) carboxylate chemistry is reported. The syntheses, crystal structures, and spectroscopic characterization are described for the structurally similar cluster compounds [Zn6(OH)2(O2CR)8(pdmH)2] (R=Ph (1); But (2)), obtained in very good yields by the reactions between Zn(O2CR)2·2H2O (R=Ph, But) and pdmH2 in a 3:1molar ratio in MeOH or MeCN solvent media, respectively. The [Zn6(μ3-OH)2(μ3-OR)2]8+ core of both clusters can be conveniently described as four edge-sharing triangles (RO−=pdmH−). The three crystallographically unique metal ions in both 1 and 2 are found in three different coordination environments (4-, 5- and 6-coordinate), within the same molecule, a very rare case in hexanuclear Zn(II) cluster chemistry. The benzoate-analogue ZnII6 (1) displays photoluminescence with a maximum at 404nm, upon maximum excitation at 337nm, whereas the pivalate-analogue ZnII6 (2) shows a non-emissive character; the origin of the photoluminescence is discussed.

Synthesis and characterization of CoIII3 inverse metallacrowns via use of 6-methyl-2-pyridylaldoxime

Abstract The use of 6-methyl-2-pyridylaldoxime (6-mepaoH) in cobalt carboxylate chemistry has yielded metallacrowns with general formula [CoIII3(μ3-O)(O2CMe)3(6-mepao)3]2[CoII(L)4] (1⋅ 2MeOH ⋅ 1.5H2O, L = AcO− and 2⋅ 2.5H2O, L = NCS−). Compounds 1 and 2 display an unusual structural motif in cobalt-oximate chemistry, consisting of CoIII triangles centered by one μ3-oxo ligand. Crystal structure and EPR characterization of CoII anions are reported.

Use of 6-methylpyridine-2-carbaldehydeoxime in nickel(ii) carboxylate chemistry: synthetic, structural and magnetic properties of penta and hexanuclear complexes

The use of 6-methylpyridine-2-carbaldehydeoxime ligand (6-mepaoH), in nickel(II) chemistry has been investigated and three new clusters isolated in mild conditions. Depending on the nature of the metal starting salts and the reaction conditions, the Ni(II)/6-mepaoH system has provided access to the complexes [Ni(6)(O(2)CPh)(6)(6-mepao)(6)] (1), [Ni(6)(O(2)CMe)(6)(6-mepao)(6)] (2) and [Ni(5)(3-Cl-BzO)(4)(6-mepao)(4)(6-mepaoH)(2)(N(3))(2)] (3), where 3-Cl-BzO(-) is the 3-chlorobenzoate anion. Compounds 1 and 2 are two new members of the [Ni(6)(O(2)C-R)(oximato)(6)] family of hexanuclear complexes whereas 3 exhibits an unusual irregular bowtie topology including end-on azido bridges. The structures of the three compounds have been determined by single-crystal X-ray crystallography. Variable-temperature dc magnetic susceptibility studies were carried out for 1-3. The data indicate antiferromagnetic exchange for complexes 1 and 2 and ferrimagnetic interaction for complex 3.