Lipophilic Ga Complex with Broad-Spectrum Antimicrobial Activity and the Ability to Overcome Gallium Resistance in both Pseudomonas aeruginosa and Staphylococcus aureus.

Antibiotic resistance (AR) necessitates the discovery of new antimicrobials with alternative mechanisms of action to those employed by conventional antibiotics. One such strategy utilizes Ga3+ to target iron metabolism, a critical process for survival. Still, Ga-based therapies are generally ineffective against Gram-positive bacteria and promote Ga resistance. In response to these drawbacks, we report a lipophilic Ga complex, [Ga2L3(bpy)2] (L = 2,2'-bis(3-hydroxy-1,4-naphthoquinone; bpy = 2,2'-bipyridine)), effective against drug-resistant Pseudomonas aeruginosa (DRPA; minimum inhibitory concentration, MIC = 10 µM = 14.8 µg/mL) and methicillin-resistant Staphylococcus aureus (MRSA, MIC = 100 µM = 148 µg/mL) without iron-limited conditions. Importantly, [Ga2L3(bpy)2] shows noticeably delayed and decreased resistance in both MRSA and DRPA, with only 8× MIC in DRPA and none in MRSA after 30 passages. This is likely due to the dual mode of action afforded by Ga (disruption of iron metabolism) and the ligand (reactive oxygen species production). Overall, [Ga2L3(bpy)2] demonstrates the utility of lipophilic metal complexes with multiple modes of action in combatting AR in Gram-positive and Gram-negative bacteria.

One-Pot Self-Assembly of Dinuclear, Tetranuclear, and H-Bonding-Directed Polynuclear Cobalt(II), Cobalt(III), and Mixed-Valence Co(II)/Co(III) Complexes of Schiff Base Ligands with Incomplete Double Cubane Core.

The reaction of 2,6-diformyl-4-methylphenol (DFMF) with 1-amino-2-propanol (AP) and tris(hydroxymethyl)aminomethane (THMAM) was investigated in the presence of Cobalt(II) salts, (X = ClO4-, CH3CO2-, Cl-, NO3-), sodium azide (NaN3), and triethylamine (TEA). In one pot, the variation in Cobalt(II) salt results in the self-assembly of dinuclear, tetranuclear, and H-bonding-directed polynuclear coordination complexes of Cobalt(III), Cobalt(II), and mixed-valence CoIICoIII: [Co2III(H2L-1)2(AP-1)(N3)](ClO4)2 (1), [Co4(H2L-1)2(µ3-1,1,1-N3)2(µ-1,1-N3)2Cl2(CH3OH)2]·4CH3OH (2), [Co2IICo2III(HL-2)2(µ-CH3CO2)2(µ3-OH)2](NO3)2·2CH3CH2OH (3), and [Co2IICo2III (H2L12-)2(THMAM-1)2](NO3)4 (4). In 1, two cobalt(III) ions are connected via three single atom bridges; two from deprotonated ethanolic oxygen atoms in the side arms of the ligands and one from the1-amino-2-propanol moiety forming a dinuclear unit with a very short (2.5430(11) Å) Co-Co intermetallic separation with a coordination number of 7, a rare feature for cobalt(III). In 2, two cobalt(II) ions in a dinuclear unit are bridged through phenoxide O and µ3-1,1,1-N3 azido bridges, and the two dinuclear units are interconnected by two µ-1,1-N3 and two µ3-1,1,1-N3 azido bridges generating tetranuclear cationic [Co4(H2L-1)2(µ3-1,1,1-N3)2(µ-1,1-N3)2Cl2(CH3OH)2]2+ units with an incomplete double cubane core, which grow into polynuclear 1D-single chains along the a-axis through H-bonding. In 3, HL2- holds mixed-valent Co(II)/Co(III) ions in a dinuclear unit bridged via phenoxide O, µ-1,3-CH3CO2-, and µ3-OH- bridges, and the dinuclear units are interconnected through two deprotonated ethanolic O in the side arms of the ligands and two µ3-OH- bridges generating cationic tetranuclear [Co2IICo2III(HL-2)2(µ-CH3CO2)2(µ3-OH)2]2+ units with an incomplete double cubane core. In 4, H2L1-2 holds mixed-valent Co(II)/Co(III) ions in dinuclear units which dimerize through two ethanolic O (µ-RO-) in the side arms of the ligands and two ethanolic O (µ3-RO-) of THMAM bridges producing centrosymmetric cationic tetranuclear [Co2IICo2III (H2L1-2)2(THMAM-1)2]4+ units which grow into 2D-sheets along the bc-axis through a network of H-bonding. Bulk magnetization measurements on 2 demonstrate that the magnetic interactions are completely dominated by an overall ferromagnetic coupling occurring between Co(II) ions.

Self-Assembly of Antiferromagnetically-Coupled Copper(II) Supramolecular Architectures with Diverse Structural Complexities.

The self-assembly of 2,6-diformyl-4-methylphenol (DFMP) and 1-amino-2-propanol (AP)/2-amino-1,3-propanediol (APD) in the presence of copper(II) ions results in the formation of six new supramolecular architectures containing two versatile double Schiff base ligands (H3L and H5L1) with one-, two-, or three-dimensional structures involving diverse nuclearities: tetranuclear [Cu4(HL2-)2(N3)4]·4CH3OH·56H2O (1) and [Cu4(L3-)2(OH)2(H2O)2] (2), dinuclear [Cu2(H3L12-)(N3)(H2O)(NO3)] (3), polynuclear {[Cu2(H3L12-)(H2O)(BF4)(N3)]·H2O}n (4), heptanuclear [Cu7(H3L12-)2(O)2(C6H5CO2)6]·6CH3OH·44H2O (5), and decanuclear [Cu10(H3L12-)4(O)2(OH)2(C6H5CO2)4] (C6H5CO2)2·20H2O (6). X-ray studies have revealed that the basic building block in 1, 3, and 4 is comprised of two copper centers bridged through one µ-phenolate oxygen atom from HL2- or H3L12-, and one µ-1,1-azido (N3-) ion and in 2, 5, and 6 by µ-phenoxide oxygen of L3- or H3L12- and µ-O2- or µ3-O2- ions. H-bonding involving coordinated/uncoordinated hydroxy groups of the ligands generates fascinating supramolecular architectures with 1D-single chains (1 and 6), 2D-sheets (3), and 3D-structures (4). In 5, benzoate ions display four different coordination modes, which, in our opinion, is unprecedented and constitutes a new discovery. In 1, 3, and 5, Cu(II) ions in [Cu2] units are antiferromagnetically coupled, with J ranging from -177 to -278 cm-1.

A Flexible Strategy for Modular Synthesis of Curcuminoid-BF2 /Curcuminoid Pairs and Their Comparative Antiproliferative Activity in Human Cancer Cell Lines.

A facile protocol that enables synthetic interconversion of CUR-BF2 and CUR compounds is described that significantly widens the preparative scope of curcuminoids, providing access to larger libraries of compounds, thus enabling comparative antiproliferative and apoptotic study of a larger library of synthetic analogs in cancer cell lines.

Deuterated Curcuminoids: Synthesis, Structures, Computational/Docking and Comparative Cell Viability Assays against Colorectal Cancer.

A series of deuterated curcuminoids (CUR) were synthesized, bearing two to six OCD3 groups, in some cases in combination with methoxy groups, and in others together with fluorine or chlorine atoms. A model ring-deuterated hexamethoxy-CUR-BF2 and its corresponding CUR compound were also synthesized from a 2,4,6-trimethoxybenzaldehyde-3,5-d2 precursor. As with their protio analogues, the deuterated compounds were found to remain exclusively in the enolic form. The antiproliferative activities of these compounds were studied by in vitro bioassays against a panel of 60 cancer cell lines, and more specifically in human colorectal cancer (CRC) cells (HCT116, HT29, DLD-1, RKO, SW837, and Caco2) and in normal colon cells (CCD841CoN). The deuterated CUR-BF2 adducts exhibited better overall growth inhibition by NCI-60 assay, while for other CUR-BF2 adducts the non-deuterated analogues were more cytotoxic. Results of the more focused comparative cell viability assays followed the same trend, but with some variation depending on cell lines. The CUR-BF2 adducts exhibited significantly higher cytotoxicity than CURs. Structural studies (X-ray and DFT) and computational molecular docking calculations comparing their inhibitory efficacy with those of known anticancer agents used in chemotherapy are also reported.

Catalyst-free assembly of giant tris(heteroaryl)methanes: synthesis of novel pharmacophoric triads and model sterically crowded tris(heteroaryl/aryl)methyl cation salts.

A series of giant tris(heteroaryl)methanes are easily assembled by one-pot three-component synthesis by simple reflux in ethanol without catalyst or additives. Diversely substituted indoles (Ar1) react with quinoline aldehydes, quinolone aldehydes, chromone aldehydes, and fluorene aldehydes (Ar2CHO) and coumarins (Ar3) in 1:1:1 ratio to form the corresponding tris(heteroaryl)methanes (Ar1Ar2Ar3)CH along with (Ar1Ar1Ar2)CH triads. A series of new 2:1 triads were also synthesized by coupling substituted indoles with Ar2CHO. The coupling reactions could also be carried out in water (at circa 80 °C) but with chemoselectivity favoring (Ar1Ar1Ar2)CH over (Ar1Ar2Ar3)CH. The molecular structure of a representative (Ar1Ar2Ar3)CH triad was confirmed by X-ray analysis. Model tris(heteroaryl/aryl)methylium salts were generated by reaction with DDQ/HPF6 and studied by NMR and by DFT and GIAO-DFT.

Tuning charge carrier transport and optical birefringence in liquid-crystalline thin films: A new design space for organic light-emitting diodes.

Liquid-crystalline organic semiconductors exhibit unique properties that make them highly interesting for organic optoelectronic applications. Their optical and electrical anisotropies and the possibility to control the alignment of the liquid-crystalline semiconductor allow not only to optimize charge carrier transport, but to tune the optical property of organic thin-film devices as well. In this study, the molecular orientation in a liquid-crystalline semiconductor film is tuned by a novel blading process as well as by different annealing protocols. The altered alignment is verified by cross-polarized optical microscopy and spectroscopic ellipsometry. It is shown that a change in alignment of the liquid-crystalline semiconductor improves charge transport in single charge carrier devices profoundly. Comparing the current-voltage characteristics of single charge carrier devices with simulations shows an excellent agreement and from this an in-depth understanding of single charge carrier transport in two-terminal devices is obtained. Finally, p-i-n type organic light-emitting diodes (OLEDs) compatible with vacuum processing techniques used in state-of-the-art OLEDs are demonstrated employing liquid-crystalline host matrix in the emission layer.

Minority Currents in n-Doped Organic Transistors.

Doping allows us to control the majority and minority charge carrier concentration in organic field-effect transistors. However, the precise mechanism of minority charge carrier generation and transport in organic semiconductors is largely unknown. Here, the injection of minority charge carriers into n-doped organic field-effect transistors is studied. It is shown that holes can be efficiently injected into the transistor channel via Zener tunneling inside the intrinsic pentacene layer underneath the drain electrode. Moreover, it is shown that the onset of minority (hole) conduction is shifted by lightly n-doping the channel region of the transistor. This behavior can be explained by a large voltage that has to be applied to the gate in order to fully deplete the n-doped layer as well as an increase in hole trapping by inactive dopants.

Antiferromagnetically Coupled Dimeric Dodecacopper Supramolecular Architectures of Macrocyclic Ligands with a Symmetrical µ6-BO3(3-) Central Moiety.

Reactions between 2,6-diformyl-4-alkyl(R)-phenol (R = CH3 or C(CH3)3) and 1,3-diamino-2-hydroxypropane (1,3-DAP) in the presence of copper(II) salts (Cu(BF4)2·6H2O, Cu(ClO4)2·6H2O/H3BO3/Ar) and triethylamine (TEA) in a single pot result in self-assembly of dimeric dodecacopper supramolecular architectures of 30-membered hexatopic macrocyclic ligands (H6L4 and H6L5) with unique and fascinating structures having the BO3(3-) anion as the central species bonded to all six copper centers in a symmetrical fashion (µ6-BO3(3-)). A number of closely related macrocyclic hexacopper complexes are reported: {[Cu6(L4)(µ6-BO3)(µ-H2O)(C3H7NO)2(BF4)][BF4]2·3C3H7NO}2 (1) (DMF = C3H7NO), {[Cu6(L4)(µ6-BO3)(µ-C3H7NO)3][ClO4]3·3C3H7NO}2 (2), {[Cu6(L5)(µ6-BO3)(µ-OH)(H2O)3(C3H7NO)][BF4]2·6C3H7NO·4C2H5OH·2H2O}2 (3), {[Cu6(L5)(µ6-BO3)(µ-CH3OH)(CH3OH)2][ClO4]3·10H2O}2 (4), and {[Cu6(L5)(µ6-BO3)(µ-CH3CO2)(µ-CH3O)(CH3OH)][BF4]·13CH3OH·8H2O}2 (5). A polymeric side product {[Cu2(H2L2)(CH3OH)(BF4)][BF4]}n (6), involving a 2 + 2 macrocyclic ligand, was also isolated and structurally characterized. Complex 6 involves dinuclear copper(II) units linked through BF4(-) anions to form a novel 1D single-chain polymeric coordination compound. This appears to be the first report in which a central BO3(3-) species is linked to six copper(II) ions held together by a single macrocyclic ligand through three µ1,1-O(BO3(3-)) and three µ1,3-O(BO3(3-)) bridges. In complexes 1-5 the BO3(3-) is present in the center of the macrocyclic cavity and is bonded to all six metal centers arranged in a benzene-like hexagonal array. In the hexagonal array there are alternate double (µ-alkoxide and µ1,3-O(BO3(3-))) and (µ-phenoxide and µ1,1-O(BO3(3-))) bridges between the Cu(II) centers. The symmetrical hexa-bridging nature of µ6-BO3(3-) is unprecedented in transition metal complex chemistry, and along with alkoxide and phenoxide bridges in the equatorial plane provides effective pathways for an overall antiferromagnetic exchange interaction between six copper(II) centers. In 1, 3, and 5 the BO3(3-) moiety is produced in one step (synthetic) by an unusual copper(II)-macrocycle complex catalyzed hydrolysis of BF4(-) ion in methanol. In 2 and 4 the central species (BO3(3-)) comes from boric acid (H3BO3) which is added to reaction mixture of Cu(ClO4)2/H6L4/H6L5 under inert conditions to confirm the identity of the central species.

Oligonuclear Fe complexes (Fe, Fe4, Fe6, Fe9) derived from tritopic pyridine bis-hydrazone ligands-structural, magnetic, and Mössbauer studies.

Tri-topic pyridine bis-hydrazone ligands produce polynuclear complexes with Fe(II) and Fe(III) salts with varying nuclearity and metal ion oxidation states. Mononuclear, tetranuclear, hexanuclear, and nonanuclear examples are discussed using structural, magnetic and Mössbauer data. In one case, although X-ray data suggest a [3 × 3] Fe9 grid (space group P42/n), careful examination of the structure, in conjunction with magnetic and Mössbauer data, indicates an unusual situation where the corner and center sites are present at unit occupancy, whereas side site occupancy is ∼0.6.

Synthesis of a potential intermediate for TMC-95A via an organocatalyzed aldol reaction.

N-Prolinylanthranilamide-based pseudopeptide organocatalyst 14 was shown to promote enantioselective direct aldol reaction of 7-iodoisatin and 2,2-dimethyl-1,3-dioxan-5-one with 90% conversion (75% isolated yield), 90% enantioselectivity, and 23:1 diastereoselectivity. To demonstrate the synthetic utility of this chemistry, the racemic aldol reaction product was converted in five steps to a potential intermediate for construction of the natural product TMC-95A.

Polynuclear lanthanide (Ln) complexes of a tri-functional hydrazone ligand--mononuclear (Dy), dinuclear (Yb, Tm), tetranuclear (Gd), and hexanuclear (Gd, Dy, Tb) examples.

The lanthanide coordination chemistry of a tri-functional vanillin-hydrazone-oxime ligand reveals a variety of different products, depending on reaction conditions, with mono-nuclear (Dy), dinuclear (Yb, Tm), tetranuclear (Gd) and hexanuclear (Gd, Tb, Dy) examples. The Ln6 (Ln = Gd, Dy, Tb) complexes form in the presence of both triethylamine and acetic acid, and have unique, flat hexanuclear structures built on a µ3-O bridged triangular core, with the six lanthanide ions bridged further through µ-acetate and µ-Ohydrazone connections in an expanded fused triangular array. Similar reaction conditions with Yb(III) and Tm(III) lead preferentially to dinuclear systems, while in the presence of a competitive benzoate ligand a rectangular Gd4 complex results. Variable temperature DC magnetic data for the Gd(III) complexes reveal weak antiferromagnetic exchange. AC magnetic data on the other polynuclear complexes down to 2 K, both in the absence and presence of external bias fields, revealed no significant out of phase signals normally indicative of SMM behavior. However, the mononuclear Dy(III) complex shows frequency dependent AC signals and maxima in the temperature range 2-20 K in the presence of an external bias field, indicative of SMM behaviour, with Ueff = 36(1) K, and τ0 = 4.4(2) × 10(-6) s.

Tetranaphthyleno[5,6-bcd:11,12-b'c'd':17,18-b''c''d'':23,24-b'''c'''d''']tetrafuran.

The title compound, C(40)H(16)O(4) or [C(10)H(4)O](4), is a planar tetrameric cyclooligomer which crystallizes in the monoclinic space group P2(1)/n. The compound is located on an inversion center with the asymmetric unit consisting of half of the molecule. The compound displays an interesting packing structure, where the cyclooligomer displays both layered packing with respect to nearest neighbors and a rotation of adjacent planar rings that results in additional interactions. The geometric parameters of the compound agree well with those of comparable cyclooligomers, while the packing reveals some similarities and differences.

Structures and magnetic properties of an antiferromagnetically coupled polymeric copper(II) complex and ferromagnetically coupled hexanuclear nickel(II) clusters.

Reactions between 2,6-diformyl-4-methylphenol (DFMF) and tris(hydroxymethyl) aminomethane (THMAM = H(3)L2) in the presence of copper(II) salts, CuX(2) (X = CH(3)CO(2)(-), BF(4)(-), ClO(4)(-), Cl(-), NO(3)(-)) and Ni(CH(3)CO(2))(2) or Ni(ClO(4))(2)/NaC(6)H(5)CO(2), sodium azide (NaN(3)), and triethylamine (TEA), in one pot self-assemble giving a coordination polymer consisting of repeating pentanuclear copper(II) clusters {[Cu(2)(H(5)L(2-))(µ-N(3))](2)[Cu(N(3))(4)]·2CH(3)OH}(n) (1) and hexanuclear Ni(II) complexes [Ni(6)(H(3)L1(-))(2)(HL2(2-))(2)(µ-N(3))(4)(CH(3)CO(2))(2)]·6C(3)H(7)NO·C(2)H(5)OH (2) and [Ni(6)(H(3)L1(-))(2)(HL2(2-))(2)(µ-N(3))(4)(C(6)H(5)CO(2))(2)]·3C(3)H(7)NO·3H(2)O·CH(3)OH (3). In 1, H(5)L(2-) and in 2 and 3 H(3)L1(-) and HL2(2-) represent doubly deprotonated, singly deprotonated, and doubly deprotonated Schiff-base ligands H(7)L and H(4)L1 and a tripodal ligand H(3)L2, respectively. 1 has a novel double-stranded ladder-like structure in which [Cu(N(3))(4)](2-) anions link single chains comprised of dinuclear cationic subunits [Cu(2)(H(5)L(2-))(µ-N(3))](+), forming a 3D structure of interconnected ladders through H bonding. Nickel(II) clusters 2 and 3 have very similar neutral hexanuclear cores in which six nickel(II) ions are bonded to two H(4)L1, two H(3)L2, four µ-azido, and two µ-CH(3)CO(2)(-)/µ-C(6)H(5)CO(2)(-) ligands. In each structure two terminal dinickel (Ni(2)) units are connected to the central dinickel unit through four doubly bridging end-on (EO) µ-azido and four triply bridging µ(3)-methoxy bridges organizing into hexanuclear units. In each terminal dinuclear unit two nickel centers are bridged through one µ-phenolate oxygen from H(3)L1(-), one µ(3)-methoxy oxygen from HL2(2-), and one µ-CH(3)CO(2)(-) (2)/µ-C(6)H(5)CO(2)(-) (3) ion. Bulk magnetization measurements on 1 show moderately strong antiferromagnetic coupling within the [Cu(2)] building block (J(1) = -113.5 cm(-1)). Bulk magnetization measurements on 2 and 3 demonstrate that the magnetic interactions are completely dominated by ferromagnetic coupling occurring between Ni(II) ions for all bridges with coupling constants (J(1), J(2), and J(3)) ranging from 2.10 to 14.56 cm(-1) (in the H = -J(1)(S(1)S(2)) - J(1)(S(2)S(3)) - J(2)(S(3)S(4)) - J(1)(S(4)S(5)) - J(1)(S(5)S(6)) - J(2)(S(1)S(6)) - J(3)(S(2)S(6)) - J(3)(S(2)S(5)) - J(3)(S(3)S(5)) convention).

Stability and ring-shift tautomerization of cyclic anhydrides of benzenehexasulfonic acid.

Upon heating in a dry atmosphere, benzenehexasulfonic acid forms three cyclic anhydrides. Mono- and dianhydride do not hydrolyze readily due their flatter structures compared to the hydrolysis products. The trianhydride appears more to be reactive toward hydrolysis. In solutions, the mono- and dianhydride undergo ring-shift tautomerization, which is in the latter case shifted toward the para isomer.

1,1,3,3-Tetramethylguanidine solvated lanthanide aryloxides: pre-catalysts for intramolecular hydroalkoxylation.

The synthesis and structural characterization of six 1,1,3,3-tetramethylguanidine (H-TMG) solvated lanthanide aryloxide complexes are reported. Ln[N{Si(CH3)3}2]3 (Ln = Nd, La) was reacted with two equivalents of both H-TMG and HOAr {HOAr = HOC6H2(CMe3)2-2,6 (H-DBP) or HOC6H2(CMe3)2-2,6-CH3-4 (H-4MeDBP)} and one equivelent of ethanol (HOEt) to yield the corresponding [Nd(H-TMG)2(4MeDBP)2(OEt)] (1) and [La(H-TMG)2(DBP)2(OEt)] (2). Compounds 1 and 2 were further reacted with 4-pentyn-1-ol {HO(CH2)3C[triple bond]CH} to isolate [Nd(H-TMG)2(4MeDBP)2{O(CH2)3C[triple bond]CH}] (3) and [La(H-TMG)2(DBP)2{O(CH2)3C[triple bond]CH}] (4), respectively. Three equivalents of HOAr and one equivalent of H-TMG were additionally reacted with Ln[N{Si(CH3)3}2]3 to generate [Nd(4MeDBP)3(H-TMG)] (5) and [La(DBP)3(H-TMG)] (6). In order to examine the formation of 1-6, the interaction of H-TMG and HOAr was further examined in solution and the hydrogen bonded complexes (H-TMG:HOAr), 7 and 8, were isolated. Upon successful isolation of 1-6, the utility of 1, 2, 4 and 5 as pre-catalysts for the intramolecular hydroalkoxylation of 4-pentyn-1-ol was investigated. The bulk powders for all complexes were found to be in agreement with the crystal structures based on elemental analyses, FT-IR spectroscopy, and 1H and 13C NMR investigations.

Synthesis and characterization of gold(III) complexes possessing 2,9-dialkylphenanthroline ligands: to bind or not to bind?

In an effort to discover potential alternatives to the anti-cancer drug cisplatin, the synthesis of gold(III) polypyridyl coordination complexes was pursued. Specifically, this report describes the synthesis and characterization of a series of 2,9-dialkyl-1,10-phenanthroline (Rphen) gold(III) coordination complexes (R = n-butyl, sec-butyl, and tert-butyl). Due to the steric hindrance imparted by the alkyl substituents, these ligands do not react with HAuCl4 to form square-planar gold(III) dichloride complex ions, as is the case with 1,10-phenanthroline, but instead form salts comprised of [AuCl(4)](-) anions and protonated 2,9-dialkylphenanthroline cations (compounds 1 and 2). In an effort to facilitate direct binding between the substituted phenanthroline and the gold(iii) metal center, reactions were carried out between the ligand and NaAuCl4 in the presence of a Ag(I) salt. The precipitation of one equivalent of AgCl afforded the formation of neutral, distorted square-pyramidal gold(iii) trichloride complexes (compounds 3 and 4). Primary or secondary substitutions at the alpha carbon of the alkyl substituent allow direct metal-ligand coordination, whereas a tertiary substituent inhibits chelation and results only in the formation of a salt comprised of a protonated phenanthroline cation and a [AuCl2]- anion (compound 5). Compounds 1-4 have been characterized by 1H NMR, UV/vis, IR spectroscopy, and X-ray crystallography.

Self-assembly of mixed-valence Co(II/III) and Ni(II) clusters: azide-bridged 1D single chain coordination polymers comprised of tetranuclear units, tetranuclear Co(II/III) complexes, ferromagnetically coupled azide-bridged tetranuclear, and hexanuclear Ni(II) complexes: synthesis, structural, and magnetic properties.

One-pot reactions between 2,6-diformyl-4-methylphenol (DFMP) and 2-aminoethanol (AE) in the presence of cobalt(II) salts [Co(ClO4)2, CoCl2, Co(CH3CO2)2, Co(NO3)2] and sodium azide result in the self-assembly of novel one-dimensional single chain mixed-valence cobalt coordination polymers {[Co2(II)Co2(III) (HL)2(OCH3)2(N3)3]ClO(4).5H2O.CH3OH}n (1), {[Co2(II)Co2(III) (HL)2(OCH3)2(N3)3]Cl.H2O}n (2) in which tetra-cobalt cationic units are bridged by symmetrical 1,3-azides, forming single chains; mixed valence neutral tetranuclear clusters [Co2(II)Co2(III) (HL)2(OCH3)2(N3)4]CH3OH.2H2O (3), [Co2(II)Co2(III)(HL)2(OCH3)2(N3)2(CH3CO2)2].2CH3OH.2H2O (4), and the cationic cluster [Co2(II) Co2(III) (HL)2(OCH3)2(CH3OH)2(N3)2](NO3)2 (5). In all these reactions, H3L, the potentially pentadentate (N2O3), trianionic double Schiff base ligand 2,6-bis[(2-hydroxy-ethylimino)-methyl]-4-methylphenol is formed. The reaction between DFMP and AE in the presence of nickel(ii) salts and sodium azide in methanol-water mixture results in the self-assembly of ferromagnetically coupled hexanuclear complexes [Ni6(H2L)2(HL-1)2(H2O)2(N3)6](ClO4)(2).2CH3OH (6), and [Ni6(H2L)2(HL-1)2(CH3OH)2(N3)6](BF4)2 (7), involving double (H3L) and single (H2L-1) Schiff base ligands, and a neutral tetranuclear complex [Ni4(H2L)2(OCH3)2(CH3CO2)2(N3)2] (8) with only double Schiff-base (H3L). In these complexes, the nature of the anion and the reaction conditions seem to play an important role in directing the formation of tetranuclear, hexanuclear or polymeric clusters. All complexes involve divacant double cubane-type cores containing three to four different types of bridging ligands (phenoxy, azido, methoxy/alkoxy, and acetate). Variable temperature magnetic properties of these spin coupled clusters have been investigated and magneto-structural correlations have been established.

Synthesis, structure, and reactivity of low-coordinate 1,1,3,3-tetraethylguanidinate complexes.

Diethylcyanamide is added to a hexanes solution of lithium diethylamide [LiN(CH(2)CH(3))(2)] resulting in the formation of lithium 1,1,3,3-tetraethylguanidinate, [Li(mu-TEG)](6) (1). Upon successful isolation of 1, the metathesis reaction of MX(2) (MX(2) = MnBr(2), FeBr(2), CoBr(2), and ZnCl(2)) with [Li(mu-TEG)](6) and lithium bistrimethylsilylamide, LiN(SiMe(3))(2), was performed to generate dinuclear tetraethylguanidinate (TEG) complexes with the general formula [M(mu-TEG){N(SiMe(3))(2)}](2) {M = Mn (2), Fe (3), Co (4), Zn (5)}. Further reaction of 2 with 2 equiv of ethanol (EtOH) and 2 equiv of 2,6-ditert-butylphenol (H-DBP) results in the formation of the manganese alkoxide, [Mn(mu-OEt)(DBP)(H-TEG)](2) (6). Elemental analysis, FT-IR spectroscopy, UV-vis spectroscopy, and single crystal X-ray diffraction were utilized to characterize the six compounds.

Copper coordination polymers based on single-chain or sheet structures involving dinuclear and tetranuclear copper(II) units: synthesis, structures, and magnetostructural correlations.

Reactions between the potentially pentadentate (N(2)O(3)), trianionic double Schiff-base ligand 2,6-bis[[(2-hydroxyethyl)imino]methyl]-4-methylphenol (H(3)L) and Cu(CH(3)CO(2))(2) or Cu(ClO(4))(2), in the presence of NaN(3), give novel coordination polymers with chain {[Cu(2)(H(2)L)(N(3))(3)](2).H(2)O}(n) (1) or sheet [Cu(2)(H(2)L)(N(3))(3)](n) (2) and [Cu(2)(HL)(N(3))](n)[ClO(4)](n) (3) structures, respectively. These clusters are comprised of repeating dinuclear units (1) or their dimers (2 and 3). In these compounds, H(3)L acts as a tridentate (N(2)O) monoanionic (1), tetradentate (ON(2)O) monoanionic (2), or pentadentate (O(3)N(2)) dianionic (3) ligand. Compound [Cu(2)(HL)(N(3))(2)(H(2)O)].0.5CH(3)OH (4) formed from the reaction of Cu(CH(3)CO(2))(2) with H(3)L under reflux, which did not afford crystals suitable for X-ray studies. X-ray structure determinations have revealed that the basic building block in 1-3 comprises two copper centers bridged through one mu-phenolate O atom from H(2)L(-) or HL(2-) and one mu-azido(N1,N1) ion. Compounds 1-3 unveil three different ways in which this Cu(2) basic unit may be organized in the crystalline phase at the supramolecular level through a variety of bridging interactions involving additional azide ligands or alkoxide groups from the side arms of the ligand H(3)L. Bulk magnetization measurements have served to demonstrate that the magnetic interactions are completely dominated by the strong antiferromagnetic coupling occurring within the Cu(2) building block, with coupling constants ranging from 330 to 560 cm(-1) (in the H = -JS(1)S(2) convention). These results together have been incorporated with data from the few related copper dimers reported exhibiting the same bridging pattern into a study aimed at extracting possible magnetostructural correlations within this Cu(2) unit. An earlier predicted correlation between J and the angle formed by the phenoxide bridge and the Cu(2) core has been identified for the first time.