Search

A square [3x3] [Mn(II).sub.9] supramolecular grid complex with appended ligand SEt groups provides a focus for extended molecular organization through outer-sphere interactions with soft metal ions. Reactions with Ag(I) and Au(III) led to extended 3D arrays in complexes [[Mn.sub.9][(SEt2poap).sub.6]][Ag.sub.5.75][(C[F.sub.3]S[O.sub.3]).sub.2][(N[O.sub.3]).sub.9.75][([H.sub.2]O).sub.18] (4), [[Mn.sub.9](SEt2poapy[[Ag(CN).sub.2]].sub.2] [Ag3(CN)5](OH)2[([H.sub.2]O).sub.18] (5), and [[Mn.sub.9][(SEt2poap-3H).sub.4][(SEt2poap-2H).sub.2][(Au[Cl.sub.3]).sub.4]] [(Au[Cl.sub.4]).sub.3] 25[Cl.sub.1.75][([H.sub.2]O).sub.14] (6), involving [Mn.sub.9] [3x3] square grids with external Ag-S contacts, but with Au(III) extended organization resulting through Au-N ligand contacts only. Structural and magnetic properties are discussed. In the gold complex, magnetic and structural data revealed that Au(III) behaves as an oxidant, leading to oxidation of some corner Mn(II) sites in the grid to Mn(III). Intra-grid magnetic exchange is antiferromagnetic in all cases (J = -4.4 [cm.sup.-1] (4), J = -5.0 [cm.sup.-1] (5)), leading to noncompensation of spins because of the odd number of metal ions and low-spin ground states. Key words: self-assembly, manganese, grid, structure, magnetism. Un complexe carre [3x3] en grille supramoleculaire du [Mn(II).sub.9], auquel sont attaches des groupes ligands SEt, permet de cerner l'organisation moleculaire etendue par le biais des interactions de la sphere externe avec des ions de metal mou. Les reaction avec l'Ag(I) et l'Au(III) ont conduit a la formation de reseaux 3D etendus dans les complexes [[Mn.sub.9][(SEt2poap).sub.6]][Ag.sub.5.75][(C[F.sub.3]S[O.sub.3]).sub.2][(N[O.sub.3]).sub.9.75][([H.sub.2]O).sub.18] (4),Mng(SEt2poapU[Ag[(CN).sub.2]]2[Ag3(CN)5](OH)2(H2OW5)et[[Mn.sub.9][(SEt2poap-3H).sub.4][(SEt2poap- 2H).sub.2][(Au[Cl.sub.3]).sub.4]](AuCl4)3.25Cl1.75[([H.sub.2]O).sub.14](6), comportant des grilles carrees de [Mn.sub.9] [3x3] qui presentent des contacts externes Ag-S, mais dans lesquels l'organisation etendue d'Au(III) se traduisait par des contacts Au-N seulement. Les proprietes structurelles et magnetiques sont etudiees. Dans le cas du complexe d'or, les donnees magnetiques et structurelles ont revele que l'Au(III) se comportait comme un oxydant provoquant l'oxydation de certains Mn(II) angulaires de la grille en Mn(III). L'echange magnetique a l'interieur de la grille est dans tous les cas antiferromagnetique (J = -4,4 [cm.sup.-1] (4), J = -5 [cm.sup.-1] (5)) et entraine une non-compensation des spins en raison du nombre impair des ions metalliques et d'etats fondamentaux bas spin. [Traduit par la Redaction] Mots-cles : auto-assemblage, manganese, grille, structure, magnetisme., Introduction Transition-metal-based [M.sub.4] [2x2] square grid assemblies are well documented (M = Mn(II), Co(II), Ni(II), Cu(II), or [Zn(II)),.sup.1a-1d] with numerous examples involving picolinic-2-hydrazone ligands (e.g., poap and its analogues; Chart [...]

The preparation and structural characterization of two matched pairs of bisdithiazolyl and sulfur/selenium radicals ([R.sub.1] = Me, Et and [R.sub.2] = Ph) are described. The differences in conductivity within the isostructural series is interpreted in terms of their relative solid-state bandwidths, which is estimated from Extended Huckel band structure calculations.

The magnetic susceptibility and low-temperature magnetization curve of the [3 x 3] grid [Mn(III)4Mn(II)5(2poap-2H)6](ClO4)10.10H2O are analyzed within a spin Hamiltonian approach. The cluster exhibit a total spin S = 1/2 ground state.

Polynuclear coordination complexes result from the interplay between the arrangement of the binding sites of a ligand, and their donor content, and the coordination preferences of the metal ion involved. Rational control of the ligand properties, such as denticity, geometry, and size, can lead to large, and sometimes predictable, polynuclear assemblies. This Alcan Award Lecture highlights our "adventures" with polynucleating ligands over the last 25 years, with examples ranging from simple dinucleating to more exotic high-denticity ligands. Complexes with nuclearities ranging from 2 to 36 have been produced, many of which have novel magnetic, electrochemical, and spectroscopic properties. Self-assembly strategies using relatively simple "polytopic" ligands have been very successful in producing high-nuclearity clusters in high yield. For example, linear "tritopic" ligands produce [M.sub.9] (M = Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II)) [3 x 3], flat grid-like molecules, which have quantum dot-like arrays of nine closely spaced metal centers in electronic communication. Some of these grids are discussed in terms of their novel magnetic and electrochemical properties, and also as multistable nanometer-scale platforms for potential molecular device behaviour. Bigger ligands with extended arrays of coordination pockets, and the capacity to self-assemble into much larger grids, are highlighted to illustrate our current and longer term goals of generating polymetallic molecular two-dimensional layers on surfaces. Key words: Alcan Award Lecture, transition metal, polynuclear, structure, magnetism, electrochemistry, surface studies, molecular device.

Mn(II)9 self-assembled [3X 3] grid complexes were successfully oxidized chemically and electrochemically. Structures were reported for [Mn9(2poap-2H)6](NO3)6(super .)14H2O (1), [Mn9(2poap-2H)6](CIO4)10(super .)10H2O (3), and [Mn9-(Cl2poap-2H)6](ClO4)9.14H2O.3CH3CN (10).

A series of [3*3] Mn (II)(sub 9), antiferromagneticaly coupled, alkoxided-bridged, square grid complexes, derived from a group of tritopic dihydraizde ligands, is described. With the appropriate coordination information encoded into the ligand itself, self-assembly was shown to be successful in generating novel polynuclear assemblies with ordered, and to some extent predictable, arrays of metal ions in close proximity.

Research has been conducted on Mn(II) systems, a similar magnetically coupled Fe(III) (sub)9 complex and Zn(II) (sub)9, (Pb(II) (sub)3) (sub)2 and Fe(III) (sub)5 derivatives with the ligands. The structures, magnetic properties amd Mossbauer data of these structures are reported.

Reduction of [[(CNSNS).sub.2]][As [[F.sub.6]].sub.2] with triphenylantimony and tetrabutylammonium chloride produced the diradical 5,5'-bis(1,3,2,4-dithiadiazolyl) [SNSNC-CNSNS] in high yield as a black solid with widely ranging magnetic susceptibilities (e.g., 0.6 to 2.6 [micro][sub.B]), which on oxidation with As[F.sub.5] regenerated [[(CNSNS).sub.2]][As[[F.sub.6]].sub.2]. The identity of [SNSNC-CNSNS] was established from EPR, vibrational, and mass spectra. Ab initio molecular orbital [MPW1PW91/6-311G(2df)] calculations show the lowest energy structure to consist of two coplanar rings separated by a C--C single bond (1.444 [Angstrom]), reflected in the comparison of the vibrational spectra of the diradical with that of [[(CNSNS).sub.2]][As[[F.sub.6]].sub.2] and the calculated spectra. Confidence in the calculated [MPW1PW91/6-311G(2df)] structure of the diradical is supported by the excellent agreement between the calculated and X-ray single crystal structure geometries of [[CNSSN].sub.2] and [[[(CNSNS).sub.2].sup.2+]] in [[(CNSNS).sub.2]][[As[F.sub.6]].sub.2]. The molecular orbitals indicate the diradical is essentially disjoint, confirmed by a very small (0.07 kJ [mol.sup.1]) GVB-PP(TC-SCF)/6-311G* calculated singlet-triplet energy gap. Accordingly, the EPR spectrum of the diradical (in tetrahydrofuran, 293 K) shows a simple 3-line pattern (g = 2.0043, a([14.sup]N) = 1.11 mT) with no observable exchange coupling between the two radical centers. Mechanical grinding of the diradical results in a large increase in paramagnetism (e.g., from 1.03 to 2.55 [micro][sub.B]) that is unprecedented in main group chemistry. The X-ray diffraction data of the ground and unground powder are consistent with a second order phase change on grinding. Attempts to obtain crystals of the diradical by sublimation led instead to numerous decomposition and rearrangement products, including 4-cyano-l,2,3,5-dithiadiazolyl [NC-CNSSN], monoclinic space group C2/c, a = 9.46(2) [Angstrom], b = 7.625(5) [Angstrom], c = 13.17(2) [Angstrom], [beta] = 107.94(4)[degrees], Z = 8. The structure consists of axially symmetric, co-facial, cis dimers linked to form strands through two sets of C[equivalent to][N.sup.[delta]] ... [S.sup.[delta]] contacts. More efficient and larger scale preparations of [SNS][As[F.sub.6] and [[(CNSNS).sub.2]][Asp[[F.sub.6].sub.2]] are reported. Key words: 5,5'-bis(1,3,2,4-dithiadiazolyl), diradical, paramagnetism, mechanical grinding, second order phase change, 4-cyano- 1,2,3,5-dithiadiazolyl.

Research has been conducted on the properties of the transition-metal complexes with coordinated radicals. The design and synthesis of the molecular-based magnetic materials have been explored via the metal-radical assemblies and the results are discussed.

Research has been conducted on the binuclear metal-radical complexes. The synthesis of these complexes formed by the reaction of M(hfac) (sub)2 .2H (sub)2 O where M=Mn or Ni and hfac= hexafluoroacetylacetonate) with the 1,5-dimethyl-3-(4,6-dimethylpyrimidin-2-yl)-6-oxoverdazyl radical is described.

Research describes the synthesis of unique, homoleptic, trigonal bipyramidal cluster complexes by a strict self-assembly process involving the ligands poap and p3oap and the proper metal perchlorate salt.

Research has been undertaken into the x-ray crystal structure and magnetic characteristics of a molecular crystal made up of 1,5-dimethyl-3-(2-pyridyl)-6-oxoverdazyl radical and hydroquinone. It was found that the magnetic properties of this material are extremelyu unusual in that strong magnetic exchange interactions dominate despite the lack of close intermolecular contacts involving only atoms bearing substantial spin density.

The synthesis and x-ray structural characterization of Mn, Co, Cu, Ni, and Zn compounds with monosubstituted diphenylaminosquarate ligand are described. All are polymeric except for the nickel compound, which exists as a simple salt.

Research has been conducted on the tetranuclear copper(II) and nickel(II) complexes. A self-assembly process that involves a single ligand and metal salt is described.

4,7-dithiadecane-2,9-dione dioxime formed nickel complexes with unusual structural properties. In contrast with trimethylene-dithioeher chelates, decreasing the oligomethylene linkage between the two thioether sulfur donors had a marked impact on the outcome of the connected equilibria for complex deprotonation, self-association and reaction with nitrile. Antiferromagnetic exchange interactions were firmly identified among possible Ni-Ni interactions.

Five complexes belonging to the class of tetradente N4 diazine ligand were characterized. Analyses showed that the complexes had the same spiral structure, with three canted ligands wrapped around the dinuclear metallic core and three diazine N2 groups acting as bridges among the manganese, iron, cobalt and nickel centers. The magnetic properties of the Mn(II) derivative implied the presence of weak ferromagnetic coupling. The Fe(II) and Co(III) complexes were low-spin, while the Mn(II) and Ni(II) complexes were high-spin.

Variable magnetic exchange coupling is observed in dinuclear copper(II) complexes with single diazine bridges, depending on the rotation angle of the magnetic planes around the N-N bond. This is consistent with a previous model which states a relationship between magnetic exchange and the rotation of the copper magnetic planes about the N-N bond as well as the alignment of the diazine nitrogen p orbitals. Two of the complexes also involve tetradentate ligand coordination with an N-N bridge between the metal centers.

Tetraaminodiphenols macrocyclic ligand was used in the synthesis of a series of heterobimetallic complexes. The magnetic parameters of these complexes are studied. Results indicate that the complexes behave ferromagnetically with the exception of the manganese-based complex. The copper-based complex had the highest ferromagnetic interaction. The exchange coupling constant is well correlated with the angle formed by the metal planes in this complex.

The metamagnetic behavior of an azide-bridged copper(II) ferromagnetic chain compound was described through analytical studies of variable-temperature diamagnetic data of the crystal compound. Data have shown that the presence of the carboxylate bridges between the copper(II) centers decreased the influence of the antiferromagnetic bridge. The metamagnetic behavior was secondary to the interlayer antiferromagnetic coupling.

The first structural characterizations are achieved for the mononuclear and dinuclear copper(II) complexes and a vanadyl complex of diaminomaleonitrile-derived Schiff-base ligands. The complexes are colored and have strong visible absorptions at low energy, which is related to pi-conjugation. An unusual reaction between a dinuclear macrocyclic complex and acetone yields a half-saturated diacetonyl macrocyclic ligand with the addition of two acetone molecules to the macrocyclic ligand. The complex is antiferromagnetically coupled.

The phenoxide bridge angle in macrocyclic bis(mu(sub 2)-phenoxide)-bridged copper complexes is linearly correlated to the exchange integral in the range 98.8-104.7 degrees. This type of straight-line correlation is limited to structures with flat dinuclear centers and no electronic perturbations. The presence of electron-withdrawing substituents on the boundary of the macrocyclic ligand significantly reduces the antiferromagnetic exchange coupling.

A series of polynucleating, poly(aminophthalazine) ligands with two, three, and four connected phthalazine groups has been synthesized. The reaction of these ligands with copper salts yields tetranuclear, hexanuclear, and octanuclear derivatives. The study indicates that the (pyridylamino)-phthalazine groups consists of a nanometer sized tetranuclear and octanuclear arrays of antiferromagnetically coupled, hydroxo-bridged, dinuclear copper(II) centers.

Novel hexacopper(II) and hexanickel(II) complexes were produced through template condensation of 2,6-diformyl-4-(R)phenol, where R is methyl or tert-butyl, with diamines in the presence of copper(II) and nickel(II) salts and bases. Infrared spectra were examined to obtain magnetic data, while a planar hexanuclear six-spin model and a model involving 12 spins were used to examine the magnetic properties of the complexes.

Novel dinuclear(II) complexes which combine mu2-1,2 diazine and mu2-1,1-azide bridges are net antiferromagnetic with a -2J value of about 112 to 932 cm-1. In these compounds, the azide becomes an antiferromagnetic bridge and contributes to the overall spin exchange in complexes where the bridge angles are greater than 180 degrees. The synthesis, crystallographic and magnetic properties of these compounds are presented.

Experimental studies use 2, 6-bis((dimethylamino)methyl)-4-methylphenolato ligand to prepare various polynuclear Cu(II)-lanthanide(III) complexes with aminoalcohol ligands. Single-crystal X-ray diffraction experiments help determine the structures of a mononuclear Cu complex, two heteronuclear complex and a tetranuclear Cu complex. Variable-temperature magnetic susceptibility studies indicate that paramagnetism of the Pr(III) ion dominates the magnetism of a heteronuclear complex, while antiferromagnetic exchanges of the Cu(II) ion are dominant in the magnetism of tetranuclear complex. Spectroscopic and extended Huckel molecular orbital methods help characterize the mononuclear Cu complex.

Cyclic voltammetric studies of a series of synthesized phenoxy- and carboxylate-bridged macrocyclic dinickel(II) complexes reveal that reversible one-electron oxidation occurs in all complexes. X-ray studies enable the determination of the structure of an acetate complex. Weak Ni...Ni exchange interactions in the compounds are revealed by variable-temperature magnetic susceptibility studies. Substitution for carboxylate RCO(Sub 2)(super -) anion leads to weak ferromagnetic or weak antiferromagnetic behavior. Spectroscopic studies indicate different exchange coupling constants for different complexes.

Magnetochemical, single-crystal X-ray diffraction and spectroscopic studies of mu2-1,1-azide-bridged dicopper(II) complexes of seven tetradentate (N4) diazine ligands facilitate the determination of the azide bridge angles. Ferromagnetic exchange is significant in complexes with azide bridge angles less than 106 degrees, while antiferromagnetism is significant for complexes with larger angles. Dimensions of the dinuclear center are regulated by diazine ring size and ligand bite.

Binuclear nickel(II) complexes exhibit an antiferromagnetic behavior with extensive variation of exchange parameter (J) over the -1 to -67 per centimeter range as revealed by variable-temperature susceptibility measurements. Increased tetragonal distortion around metal centers leads to a decrease in J value from -17 per centimeter to -29 per centimeter. J decreases from -50 per centimeter to -67 per centimeter when the stereochemistry of Ni(II) changes to the square pyramidal configuration.

X-ray crystallographic studies on two dinuclear Cu(II) complexes of the tetradentate thiadiazole ligands BPMTD and BPTD reveal the presence of standard dinuclear ones containing mu(1, 2)-thiadiazole-N,N' bridges. A third one dimensional polymeric chain complex does not involve thiadiazole bridging. Cyclic voltammograms for the first two complexes are consistent with one-step, two-electron, quasi-reversible redox reaction.

Spectroscopic and X-ray crystallographic studies yield the structures of the Cu(II) and Co(II) complexes of 1,2,4, 5-tetrakis(benzimidazol-2-yl)benzene (BTBI). (Cu2(BTBI)2Cl2)(Cu2(BTBI)-Cl2(DMF)4)Cl4.12DMF is a metallacyclic BTBI complex containing a nine-fragment asymmetric unit. (Co2(BTBI)Br4).4DMF is a nonmetallacyclic Co(II)-BTBI complex which is symmetric near its center. Two nitrogen atoms bind each Co center, and the ligand has two Br atoms on each side.

A binuclear copper(II) complex of the 17-membered macrocyclic ligand HM3 is formed by template condensation of 2,6-diformyl-4-methylphenol with PTA in the presence of copper(II) nitrate and trifluoromethanesulfonate. Cu2(M3)(mu2-OMe)(NO3)2 produces tetranuclear Cu(II) derivatives on treatment with chloride, azide, thiocyanate and bromide. Cu(II) complexes have phenoxide and methoxide bridges between the two Cu centers, and exhibit antiferromagnetic coupling properties.

A cyclophane ring exhibits lack of flexibility when a 1, 4-aromatic fragment is added to it. Endo-dentate coordination is augmented by ortho- and meta-aromatic spacers. Rare, elongated polymeric derivatives are formed and endo-dentate coordination is favored for minute 1.1, due to lack of flexibility. Solid state characteristics such as conductance necessitate these experiments. A wide variety of magnetic characteristics require the participation of paramagnetic metal cores when geometric resemblances are observed.

The reaction of the N4 diazine ligand 1, 4-bis(2-pyridylthio)phthalazine (PTPH) affords the formation of the dinuclear copper(II) complexes (Cu2(PTPH)Cl4).2CH3OH and (Cu2(PTPH)Br4).1.5H20, where the two copper centers are antiferromagnetically coupled. In reaction with copper(II) nitrate, PTPH forms a tetranuclear complex (Cu2(PTPH)(micro3-OH)(NO3)(H2O))2 and a dinuclear nitrate complex (Cu2(PTPH)-(micro2-OH)(NO3)2(H2O)2)(NO3). Magnetic measurements show that the complexes exhibit strong antiferromagnetic coupling with -2J in the range 124-313 cm-1. The crytal structures of the complexes are also discussed.

The reaction of 2,6-diformyl-4-(R)-phenol with 3,6-bis(aminoethyl thio)pyridazine in the presence of copper(II) salts with BF4 and ClO4 anions formed dinuclear copper(II) complexes. Structural analyses revealed that the resulting complexesexhibited Cu2N4O2 dinuclear units with phenoxide bridges and imine nitrogen coordination taking a different molecular twist which increased the axial donoraccessibility of pyridazine nitrogens. In addition, magnetic and electrochemical tests showed the strong antiferromagnetic coupling nature and reactivity of the compounds.

A series of 20-membered-copper octadentate complexes were synthesized from template condensation of 2,6-diformyl-4-tert-butylphenol or 2,6-diformyl-4-methylphenol with 1,3-diamino-2-hydroxypropane in ethanol or methanol in the presence of copper(II) salts. The polymeric complexes were formed when copper(II) acetate and excess azide was used while a dinuclear, chlorobridged structure was obtained with the template condensation with CuCl. The results of single-crystal x-ray analyses and the electrochemical, magnetic and spectral characteristics of the complexes were discussed.