Dinuclear Metallacycles with Single M-X-M Bridges (X = Cl, Br; M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II)): Strong Antiferromagnetic Superexchange Interactions.

A series of monochloride-bridged, dinuclear metallacycles of the general formula [M(μ-Cl)(μ-L)](ClO) have been prepared using the third-generation, ditopic bis(pyrazolyl)methane ligands L = m-bis[bis(1-pyrazolyl)methyl]benzene (L), M = Cu(II), Zn(II), and L = m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene (L*), M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II). These complexes were synthesized from the direct reactions of M(ClO)·6HO, MCl, and the ligand, L or L*, in the appropriate stoichiometric amounts. Three analogous complexes of the formula [M(μ-Cl)(μ-L)](BF), L = L, M = Cu(II), and L = L*, M = Co(II), Cu(II), were prepared from the reaction of [M(μ-F)(μ-L)](BF) and (CH)SiCl.

A cadmium(II) coordination polymer formed from a third generation tetratopic tris(pyrazolyl)methane ligand.

The reaction of a third generation tetratopic tris(pyrazolyl)methane ligand, namely 1,2,4,5-{[2,2,2-tris(1H-pyrazol-1-yl)ethoxy]methyl}benzene {1,2,4,5-CH[CHOCHC(pz)], L4}, and [Cd(thf)](BF) (thf is tetrahydrofuran) produces the coordination polymer catena-poly[[[bis[acetonitrilecadmium(II)]-μ-1,2,4,5-{[2,2,2-tris(1H-pyrazol-1-yl)ethoxy]methyl}benzene] tetrakis(tetrafluoroborate)]-diethyl ether-acetonitrile (1/2/2)], {[Cd(CHCN)(CHNO)](BF)·2CHO·2CHCN}. The Cd center is coordinated in a κ-fashion by one tris(pyrazolyl)methane group and in a κ-κ fashion by another, while the sixth coordination site on the Cd cation is occupied by an acetonitrile molecule. This bonding mode of the ligand generates an infinite one-dimensional structure built upon 32-atom metallomacrocycles connected by the CH spacer.

Silver(I) and rhenium(I) metal complexes of a 2,2'-bipyridine-functionalized third-generation tris(pyrazolyl)methane ligand.

Heterotopic ligands offer the possibility of preparing polynuclear bimetallic complexes. Recent studies of heteroditopic ligands and their metal complexes have focused on novel supramolecular systems, biological activity, and the development of MRI contrast agents. The heteroditopic ligand Bipy-CH-O-CH-C(pz) (Bipy-L; Bipy is 2,2'-bipyridine and pz is pyrazolyl) reacts with AgBF to produce the coordination polymer catena-poly[[silver(I)-(μ-5-{[tris(pyrazol-1-yl)methoxy]methyl-κN,N'}-2,2'-bipyridine-κN,N')] diethyl ether hemisolvate], {[Ag(CHNO)]BF·0.

Syntheses, structural, magnetic, and electron paramagnetic resonance studies of monobridged cyanide and azide dinuclear copper(II) complexes: antiferromagnetic superexchange interactions.

The reactions of Cu(ClO4)2 with NaCN and the ditopic ligands m-bis[bis(1-pyrazolyl)methyl]benzene (Lm) or m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene (Lm*) yield [Cu2(μ-CN)(μ-Lm)2](ClO4)3 (1) and [Cu2(μ-CN)(μ-Lm*)2](ClO4)3 (3). In both, the cyanide ligand is linearly bridged (μ-1,2) leading to a separation of the two copper(II) ions of ca. 5 Å.

Framework complexes of group 2 metals organized by homochiral rods and π···π stacking forces: a breathing supramolecular MOF.

The reactions of the potassium salts of the ligands (S)-2-(1,8-naphthalimido)propanoate (KL(ala)), (S)-2-(1,8-naphthalimido)-3-hydroxypropanoate (KL(ser)), and (R)-2-(1,8-naphthalimido)propanoate (KL(ala)*), enantiopure carboxylate ligands containing a 1,8-naphthalimide π···π stacking supramolecular tecton, and, in the case of L(ser)(-), an alcohol functional group with calcium or strontium nitrate under solvothermal conditions produce crystalline [Ca(L(ala))2(H2O)]·(H2O) (1); [Ca(L(ser))2]·(H2O)2 (2); [Sr(L(ala))2(H2O)]·(H2O)3 (3); [Sr(L(ala)*)2(H2O)]·(H2O)3 (3*); and [Sr(L(ser))2(H2O)] (5). Placing 3 under vacuum removes the interstitial waters to produce [Sr(L(ala))2(H2O)] (4) in a single-crystal to single-crystal transformation; introduction of water vapor to 4 leads to the reformation of crystalline 3. Each of these new complexes has a solid-state structure based on homochiral rod secondary building unit (SBUs) central cores.

Hydroxide-bridged cubane complexes of nickel(II) and cadmium(II): magnetic, EPR, and unusual dynamic properties.

The reactions of M(ClO4)2·xH2O (M = Ni(II) or Cd(II)) and m-bis[bis(1-pyrazolyl)methyl]benzene (Lm) in the presence of triethylamine lead to the formation of hydroxide-bridged cubane compounds of the formula [M4(μ3-OH)4(μ-Lm)2(solvent)4](ClO4)4, where solvent = dimethylformamide, water, acetone. In the solid state the metal centers are in an octahedral coordination environment, two sites are occupied by pyrazolyl nitrogens from Lm, three sites are occupied by bridging hydroxides, and one site contains a weakly coordinated solvent molecule. A series of multinuclear, two-dimensional and variable-temperature NMR experiments showed that the cadmium(II) compound in acetonitrile-d3 has C2 symmetry and undergoes an unusual dynamic process at higher temperatures (ΔGLm‡ = 15.

Dinuclear metallacycles with single M-O(H)-M bridges [M = Fe(II), Co(II), Ni(II), Cu(II)]: effects of large bridging angles on structure and antiferromagnetic superexchange interactions.

The reactions of M(ClO4)2·xH2O and the ditopic ligands m-bis[bis(1-pyrazolyl)methyl]benzene (Lm) or m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene (Lm*) in the presence of triethylamine lead to the formation of monohydroxide-bridged, dinuclear metallacycles of the formula [M2(μ-OH)(μ-Lm)2](ClO4)3 (M = Fe(II), Co(II), Cu(II)) or [M2(μ-OH)(μ-Lm*)2](ClO4)3 (M = Co(II), Ni(II), Cu(II)). With the exception of the complexes where the ligand is Lm and the metal is copper(II), all of these complexes have distorted trigonal bipyramidal geometry around the metal centers and unusual linear (Lm*) or nearly linear (Lm) M-O-M angles. For the two solvates of [Cu2(μ-OH)(μ-Lm)2](ClO4)3, the Cu-O-Cu angles are significantly bent and the geometry about the metal is distorted square pyramidal.

NMR investigations of dinuclear, single-anion bridged copper(II) metallacycles: structure and antiferromagnetic behavior in solution.

The nuclear magnetic resonance (NMR) spectra of single-anion bridged, dinuclear copper(II) metallacycles [Cu2(μ-X)(μ-L)2](A)3 (L(m) = m-bis[bis(1-pyrazolyl)methyl]benzene: X = F(-), A = BF4(-); X = Cl(-), OH(-), A = ClO4(-); L(m)* = m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene: X = CN(-), F(-), Cl(-), OH(-), Br(-), A = ClO4(-)) have relatively sharp (1)H and (13)C NMR resonances with small hyperfine shifts due to the strong antiferromagnetic superexchange interactions between the two S = 1/2 metal centers. The complete assignments of these spectra, except X = CN(-), have been made through a series of NMR experiments: (1)H-(1)H COSY, (1)H-(13)C HSQC, (1)H-(13)C HMBC, T1 measurements and variable-temperature (1)H NMR. The T1 measurements accurately determine the Cu···H distances in these molecules.

Zinc(II) and cadmium(II) monohydroxide bridged, dinuclear metallacycles: a unique case of concerted double Berry pseudorotation.

The reactions of M(ClO4)2·6H2O [M = Zn(II), Cd(II)] and the ligands m-bis[bis(1-pyrazolyl)methyl]benzene, L(m), or m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene, L(m)*, in the presence of a base yield the hydroxide bridged dinuclear metallacycles [M2(μ-OH)(μ-L)2](ClO4)3, L = L(m), M = Zn(II) (1); L = L(m)*, M = Zn(II) (2), Cd(II) (3). In the solid state, the coordination environment of the metals is distorted trigonal bipyramidal with the bridging hydroxide in an equatorial position and M-O-M angles greater than 161°. The observation of two equal intensity resonances for each type of pyrazolyl-ring hydrogen in the (1)H NMR for all three complexes coupled with the determination of the hydrodynamic radius based on the diffusion coefficient of 1 that matches that observed in the crystal structure, demonstrate this structure is retained in solution.

Tris(pyrazolyl)methane and 1,8-naphthalimide-functionalized dialkynylgold(I) anionic complexes.

The reaction of tetrapropylammonium bis(acetylacetonato)gold(I) with alkyne derivatives of the tris(pyrazolyl)methane and 1,8-naphthalimide functional groups yielded two new compounds, both bridged by the linear C[triple-bond]C-Au-C[triple-bond]C spacer, namely tetrapropylammonium bis{3-[2,2,2-tris(1H-pyrazol-1-yl)ethoxy]prop-1-yn-1-yl}aurate(I), (C16H28N)[Au(C14H13N6O)2], and tetrapropylammonium {η(2)-μ-3-[2,4-dioxo-3-azatricyclo[7.3.1.

Homochiral helical metal-organic frameworks of group 1 metals.

The reactions of (S)-2-(1,8-naphthalimido)propanoic acid (HL(ala)) and (S)-2-(1,8-naphthalimido)-3-hydroxypropanoic acid (HL(ser)), protonated forms of ligands that contain a carboxylate donor group, an enantiopure chiral center, and a 1,8-naphthalimide π···π stacking supramolecular tecton and in the case of HL(ser) an alcohol functional group, with the appropriate alkali metal hydroxide followed by a variety of crystallization methods leads to the formation of crystalline K(L(ala))(MeOH) (1), K(L(ala))(H2O) (2), Na(L(ala))(H2O) (3), KL(ser) (4), CsL(ser) (5), and CsL(ala) (6). Each of these new complexes has a solid state structure based on six-coordinate metals linked into homochiral helical rod secondary building unit (SBU) central cores. In addition to the bonding of the carboxylate and solvent (in the case of L(ser) the ligand alcohol) to the metals, both oxygens on the 1,8-naphthalimide act as donor groups.

Dinuclear complexes containing linear M-F-M [M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II)] bridges: trends in structures, antiferromagnetic superexchange interactions, and spectroscopic properties.

The reaction of M(BF(4))(2)·xH(2)O, where M is Fe(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II), with the new ditopic ligand m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene (L(m)*) leads to the formation of monofluoride-bridged dinuclear metallacycles of the formula [M(2)(μ-F)(μ-L(m)*)(2)](BF(4))(3). The analogous manganese(II) species, [Mn(2)(μ-F)(μ-L(m)*)(2)](ClO(4))(3), was isolated starting with Mn(ClO(4))(2)·6H(2)O using NaBF(4) as the source of the bridging fluoride. In all of these complexes, the geometry around the metal centers is trigonal bipyramidal, and the fluoride bridges are linear.

Homochiral helical metal-organic frameworks of potassium.

Two trifunctional ligands built from enantiopure amino acids and containing a 1,8-naphthalimide group have been used to prepare two new complexes of potassium that have extended structures based on homochiral-rod secondary building units. One structure is a three-dimensional metal-organic framework (MOF), while the other is a two-dimensional solid that is organized into a supramolecular MOF by strong π···π-stacking interactions of the naphthalimide groups in the third dimension.

Halide and hydroxide linearly bridged bimetallic copper(II) complexes: trends in strong antiferromagnetic superexchange interactions.

Centrosymmetric [Cu(2)(μ-X)(μ-L(m)*)(2)](ClO(4))(3) (X = F(-), Cl(-), Br(-), OH(-), L(m)* = m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene)], the first example of a series of bimetallic copper(II) complexes linked by a linearly bridging mononuclear anion, have been prepared and structurally characterized. Very strong antiferromagnetic exchange coupling between the copper(II) ions increases along the series F(-) < Cl(-) < OH(-) < Br(-), where -J = 340, 720, 808, and 945 cm(-1). DFT calculations explain this trend by an increase in the energy along this series of the antibonding antisymmetric combination of the p orbital of the bridging anion interacting with the copper(II) d(z(2)) orbital.

Copper(II) carboxylate dimers prepared from ligands designed to form a robust π···π stacking synthon: supramolecular structures and molecular properties.

The reactions of bifunctional carboxylate ligands (1,8-naphthalimido)propanoate, (L(C2)(-)), (1,8-naphthalimido)ethanoate, (L(C1)(-)), and (1,8-naphthalimido)benzoate, (L(C4)(-)) with Cu(2)(O(2)CCH(3))(4)(H(2)O)(2) in methanol or ethanol at room temperature lead to the formation of novel dimeric [Cu(2)(L(C2))(4)(MeOH)(2)] (1), [Cu(2)(L(C1))(4)(MeOH)(2)]·2(CH(2)Cl(2)) (2), [Cu(2)(L(C4))(4)(EtOH)(2)]·2(CH(2)Cl(2)) (3) complexes. When the reaction of L(C1)(-) with Cu(2)(O(2)CCH(3))(4)(H(2)O)(2) was carried out at -20 °C in the presence of pyridine, [Cu(2)(L(C1))(4)(py)(4)]·2(CH(2)Cl(2)) (4) was produced. At the core of complexes 1-3 lies the square Cu(2)(O(2)CR)(4) "paddlewheel" secondary building unit, where the two copper centers have a nearly square pyramidal geometry with methanol or ethanol occupying the axial coordination sites.

Zinc paddlewheel dimers containing a strong π···π stacking supramolecular synthon: designed single-crystal to single-crystal phase changes and gas/solid guest exchange.

The ligand 4-(1,8-naphthalimido)benzoate, L(C4)(-), containing a linear link between the strong π···π stacking 1,8-naphthalimide supramolecular synthon and the carboxylate donor group, reacts with Zn(O(2)CCH(3))(2)(H(2)O)(2) in the presence of dimethylsulfoxide (DMSO) to yield [Zn(2)(L(C4))(4)(DMSO)(2)]·2(CH(2)Cl(2)). This compound contains the "paddlewheel" Zn(2)(O(2)CR)(4) secondary building unit (SBU) that organizes the rigid phenylene and naphthalimide rings of the carboxylate ligands in a square arrangement. The supramolecular architecture is dominated by π···π stacking interactions between naphthalimide rings of one dimer with four adjacent dimers, essentially at right angles, forming an open three-dimensional network structure.

Syntheses and characterization of copper(II) carboxylate dimers formed from enantiopure ligands containing a strong π···π stacking synthon: enantioselective single-crystal to single-crystal gas/solid-mediated transformations.

Tri- and tetrafunctional enantiopure ligands have been prepared from 1,8-naphthalic anhydride and the amino acids L-alanine, D-phenylglycine, and L-asparagine to produce (S)-2-(1,8-naphthalimido)propanoic acid (HL(ala)), (R)-2-(1,8-naphthalimido)-2-phenylacetic acid (HL(phg)), and (S)-4-amino-2-(1,8 naphthalimido)-4-oxobutanoic acid (HL(asn)), respectively. Reactions of L(ala)(-) with copper(II) acetate under a variety of solvent conditions has led to the formation and characterization by X-ray crystallography of three similar copper(II) paddlewheel complexes with different axial ligands, [Cu(2)(L(ala))(4)(THF)(2)] (1), [Cu(2)(L(ala))(4)(HL(ala))] (2), and [Cu(2)(L(ala))(4)(py)(THF)] (3). A similar reaction using THF and L(phg)(-) leads to the formation of [Cu(2)(L(phg))(4)(THF)(2)] (4).

Copper(II) carboxylate tetramers formed from an enantiopure ligand containing a π-stacking supramolecular synthon: single-crystal to single-crystal enantioselective ligand exchange.

An enantiopure ligand built from connecting the π···π stacking 1,8-naphthalimide supramolecular synthon with L-asparagine, L(asn)(-), forms tetrameric [Cu(4)(L(asn))(8)(py)(MeOH)]. The methanol ligand, located in a chiral pocket, is replaced enantioselectively when exposed to racemic ethyl lactate vapor to yield [Cu(4)(L(asn))(8)(py)((S)-ethyl lactate)], in a single-crystal to single-crystal gas/solid transformation.

Homochiral, helical supramolecular metal-organic frameworks organized by strong π · · · π stacking interactions: single-crystal to single-crystal transformations in closely packed solids.

Enantiopure, trifunctional carboxylate ligands synthesized by linking the strong π · · · π stacking 1,8-naphthalimide supramolecular synthon to three naturally occurring amino acids using the azide/alkyne click reaction have been prepared [amino acid = glycine (L(gly)(-)), alanine (L(ala)(-)), and serine (L(ser)(-))]. These ligands have been used to form complexes of the formula [M(L(amino acid))2(4,4'-bipy)(H2O)2] · xH2O (M = Fe, Co, Ni, Cu, Zn; x = 4.25-5.

Synthesis, structural and spectroscopic characterization and biomimetic properties of new copper, manganese, zinc complexes: identification of possible superoxide-dismutase mimics bearing hydroxyl radical generating/scavenging abilities.

A series of Cu(II), Zn(II) and Mn(II) coordination compounds has been synthesized by reaction of the corresponding metal salts and pyrazolyl-based ligands, i.e. the neutral 1-(2-(4-((2,2,2-tri(1H-pyrazol-1-yl)ethoxy)methyl)benzyloxy)-1,1-di(1H-pyrazol-1-yl)ethyl)-1H-pyrazole {p-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2), (L(1)), and the anionic hydridotris(3-phenyl-5-methylpyrazolyl)borate (L(2))(-), bis(pyrazolyl)acetate (L(3)) and bis(3,5-dimethylpyrazolyl)acetate (L(4))(-): the species [L(1)(CuCl(2))(2)] (1), [L(1)(Cu(OAc)(2))(2)] (2), [L(1)(Zn(OAc)(2))(2)] (3), [(CuCl(L(2))(Hpz(Ph,Me))] (4), [Mn(L(3))(2)].

Structural impact of multitopic third-generation bis(1-pyrazolyl)methane ligands: double, mononuclear metallacyclic silver(I) complexes.

The reaction of 1,2,4,5-tetrakis(bromomethyl)benzene and hexakis(bromomethyl)benzene with the alkoxide of 2,2-bis(1-pyrazolyl)ethanol leads to the synthesis of the new polytopic ligands 1,2,4,5-C(6)H(2)[CH(2)OCH(2)CH(pz)(2)](4) (L(tetra), pz = pyrazolyl ring) and C(6)[CH(2)OCH(2)CH(pz)(2)](6) (L(hexa)). Reactions of these ligands and the appropriate silver(I) salt lead to the preparation of [Ag(2)L(tetra)](BF(4))(2) (1), [Ag(2)L(tetra)](SO(3)CF(3))(2) (2), [Ag(3)L(hexa)](BF(4))(3) (3), and [Ag(3)L(hexa)](ClO(4))(3) (4). The solid-state structures of four different complexes crystallized from solutions of 1 or 2 yield five independent structures of the [Ag(2)L(tetra)](2+) cation, all with similar structures.

Monofluoride bridged, binuclear metallacycles of first row transition metals supported by third generation bis(1-pyrazolyl)methane ligands: unusual magnetic properties.

The reaction of M(BF(4))(2).xH(2)O, where M is Fe, Co, Cu, and Zn, and the ditopic, bis(pyrazolyl)methane ligand m-[CH(pz)(2)](2)C(6)H(4), L(m), where pz is a pyrazolyl ring, yields the monofluoride bridged, binuclear [M(2)(mu-F)(mu-L(m))(2)](BF(4))(3) complexes. In contrast, a similar reaction of L(m) with Ni(BF(4))(2).

Homochiral, helical metal-organic framework structures organized by strong, non-covalent pi-pi stacking interactions.

A new trifunctional ligand, L(ala), containing a carboxylate donor group, a homochiral center derived from L-alanine and a strong pi-pi stacking, 1,8-naphthalimide synthon, has been used to prepare the copper(II) complex [Cu(L(ala))2(4,4'-bipy)(H2O)2].4.25H2O that has a homochiral, helical, supramolecular metal-organic framework 3-D structure, organized in one dimension solely by strong non-covalent forces.

Structural, magnetic, and Mössbauer spectral study of the electronic spin-state transition in [Fe{HC(3-Mepz)2(5-Mepz)}2](BF4)2.

The complex [Fe{HC(3-Mepz)(2)(5-Mepz)}(2)](BF(4))(2) (pz = pyrazolyl ring) has been prepared by the reaction of HC(3-Mepz)(2)(5-Mepz) with Fe(BF(4))(2) x 6 H(2)O. The solid state structures obtained at 294 and 150 K show a distorted iron(II) octahedral N(6) coordination environment with the largest deviations arising from the restrictions imposed by the chelate rings. At 294 K the complex is predominately high-spin with Fe-N bond distances averaging 2.

Highly organized structures and unusual magnetic properties of paddlewheel copper(II) carboxylate dimers containing the pi-pi stacking, 1,8-naphthalimide synthon.

The substituted carboxylate compounds N-(3-propanoic acid)-1,8-naphthalimide (HL(C2)) and N-(4-butanoic acid)-1,8-naphthalimide (HL(C3)) react with Cu(2)(O(2)CCH(3))(4)(H(2)O)(2) in the presence of either pyridine (py) or 4,4'-bipyridine (bipy) to produce the dimeric complexes [Cu(2)(L(C2))(4)(py)(2)].2(CH(2)Cl(2)).(CH(3)OH) (1), [Cu(2)(L(C3))(4)(py)(2)].