Methanol Ligands Research Articles

Synthesis, characterization and crystal structures of 2,4-di(2-aminopyridine)-6-methypyrimidine (dapmp), [Cu(dapmp)Cl 2] and [Cu(dapmp)(CH 3COO) 2] · H 2O

The new ligand dapmp ( 1) has been synthesized and the reactions of CuCl 2 · 2H 2O and Cu(CH 3COO) 2 · H 2O with the new ligand in methanol afforded two crystalline polymorphic forms: [Cu(dapmp)Cl 2] ( 2) and [Cu(dapmp)(CH 3COO) 2] · H 2O ( 3), where dapmp = 2,4-di(2-aminopyridine)-6-methylpyrimidine. Single crystal X-ray diffraction showed that ( 1) and ( 2) are each connected by hydrogen bonding to form a one-dimensional supermolecular compound and ( 3) is connected by hydrogen bonding to form a three-dimensional supermolecular compound.

Cobalt(II), nickel(II) and copper(II) complexes of isoquinoline-3-carboxylate.

The crystal structures of the title complexes, namely trans-bis(isoquinoline-3-carboxylato-kappa2N,O)bis(methanol-kappaO)cobalt(II), [Co(C10H6NO2)2(CH3OH)2], and the corresponding nickel(II) and copper(II) complexes, [Ni(C10H6NO2)2(CH3OH)2] and [Cu(C10H6NO2)2(CH3OH)2], are isomorphous and contain metal ions at centres of inversion. The three compounds have the same distorted octahedral coordination geometry, and each metal ion is bonded by two quinoline N atoms, two carboxylate O atoms and two methanol O atoms. Two isoquinoline-3-carboxylate ligands lie in trans positions, forming the equatorial plane, and the two methanol ligands occupy the axial positions. The complex molecules are linked together by O-H...O hydrogen bonds between the methanol ligands and neighbouring carboxylate groups.

Synthesis and solid-state molecular structures of nitrosoalkane complexes of iron porphyrins containing methanol, pyridine, and 1-methylimidazole ligands

Nitrosoalkanes belong to the family of C-nitroso compounds and are known to bind to the iron center in heme proteins. We have prepared and characterized a series of new nitrosoalkane heme model complexes of the form (por)Fe(RNO)(L) (por=porphyrinato dianion; R=isopropyl; L=MeOH, pyridine, 1-methylimidazole) by infrared and 1H NMR spectroscopy and X-ray crystallography. Within the set of octaethylporphyrinato (OEP) compounds, the infrared stretching frequencies of the NO groups decrease in the order (OEP)Fe( i PrNO)(MeOH) · MeOH (1433 cm −1) > (OEP)Fe( i PrNO)(py) (1429 cm −1) > (OEP)Fe( i PrNO)(1-MeIm) (1423 cm −1), reflecting the increased backdonation of electron density in the 1-methylimidazole derivative. The molecular structures of the compounds as determined by crystallography reveal N-binding of the nitrosoalkane ligands to the formally ferrous metal centers.

Synthesis and Characterization of a Novel Oxovanadium(IV) Complex and Conductometric Studies with N,N′‐bis(Salicylidene)‐1,2‐bis‐(p‐aminophenoxy)ethane

A new oxovanadium complex of the Schiff base obtained by the condensation of 1,2‐bis(p‐aminophenoxy)ethane with salicylaldehyde was synthesized. The complex has been characterized by elemental analyses, magnetic measurements, UV‐VIS and IR spectra. Stability constants and thermodynamic values for complexation between Cu(NO3)2, Zn(NO3)2 · 6H2O, and VOSO4 · 5H2O salts and the ligand synthesized by the method described in the literature in 80% dioxane–water and pure methanol were determined by conductance measurements. The stability constants (log K e) in 80% dioxane/water decrease in the order Cu(II) > (Zn(II). However, just the opposite behavior has been obtained for these metal complexes with the ligand in methanol (Zn(II) > (Cu(II)). The magnitudes of these ion association constants are related to the nature of solvation of the cation and of the complexed cation. The mobility of the complexes is also dependent, in part, upon solvation effects. Since the mobility of the VO(IV)L complex has been found to be higher than that of VO(IV) ion, assuming that the complex–solvent interaction in the VO(IV)‐L systems is comparatively weak. A major consequence of the complexation is the increase in the molar conductivity of the complex and a corresponding large decrease in κ values. For this reason, it was not obtained any stability constant values for VO(IV)‐L systems in two type of solvents.

Remote substituents influence both the thermodynamics and kinetics of zinc binding to tris-pyridyl methanol derivatives.

[reaction: see text] Three families of tris-pyridyl methanol ligands were synthesized. An analysis of the Zn(2+) binding properties of the ligands revealed that both steric and electronic properties of the pyridine substituents, as well as the nature of the group on the tertiary alcohol oxygen, control the thermodynamics and kinetics of complex formation.

Bis(2,2′-diamino-4,4′-bi-1,3-thiazole-κ2N,N′)(isothiocyanato-κN)(methanol)nickel(II) chloride

The title compound, [Ni(NCS)(C6H6N4S2)(CH4O)]Cl, consists of an NiII complex cation and a Cl− anion. The NiII complex has an octahedral coordination, with the iso­thio­cyanate and methanol ligands in cis positions. The di­amino­bi­thia­zole ligands are each nearly planar, but the NiII atom is out of the planes of the thia­zole rings, the deviations ranging from 0.113 (5) to 0.389 (4) A.

A paradigm shift in the construction of heterobimetallic complexes: synthesis of group 2 & 4 metal-calix[6]arene complexes.

Deprotonation of calix[6]arenes with barium in methanol followed by the addition of [Ti(OPr(i))(4)] or [Zr(OBu(n))(4)] is effective in the formation of novel dimeric 2:1 barium-titanium(IV)/zirconium(IV) calix[6]arene complexes. In these complexes a central Ti(IV)/Zr(IV) coordinated in the exo-position connects the two calix[6]arenes in the 1,3-alternate conformation, each with an endo-barium sharing common phenolate groups with the titanium/zirconium centre and participating in cation-pi interactions. A homometallic barium calix[6]arene dimer was also prepared wherein the calix[6]arenes are in the 1,3-alternate conformation with each coordinating one endo- and one exo-barium centre. The exo-barium cations connect the two calix[6]arenes through bridging methanol ligands. In this and the heterometallic complexes, cation-pi complexation of the Ba(2+) ion within the 1,3 alternate conformation of calix[6]arene facilitates the formation of the dimeric complexes in methanol. In contrast, the smaller Sr(2+) ion did not form similar complexes in methanol, and the formation of an analogous 2:1 strontium-titanium calixarene complex required the use of the more sterically demanding donor alcohol, isopropanol, the resulting complex being devoid of cation-pi interaction. The results show (i) that a subtle interplay of solvation strength, coordination array type and cavity/cation size influences the accessibility of heterobimetallic complexes based on calix[6]arenes, and (ii) a synergistic endo-exo binding behaviour.

Trans-Bis(methanol-κO)bis(2-quinolinecarboxylato-κ2N,O)zinc(II)

The title complex, [Zn(C10H6NO2)2(CH3OH)2], is a neutral mononuclear complex containing a ZnII ion in a six-coordinate environment. The ZnII center, located on a crystallographic center of symmetry, displays a distorted octahedral geometry, with two 2-quinoline­carboxyl­ate and two methanol ligands, all in trans configurations. The complex mol­ecules are linked together by O—H⋯O hydrogen bonds between methanol mol­ecules and carboxyl­ate groups to form a two-dimensional framework.

Heterobimetallic Calix[4]arene Complexes: Interconversion of Dimeric (Ca, Sr or Ba)/TiIV Complexes with a Monomeric K/TiIV Complex

AbstractReaction of calix[4]arene with alkaline earth metals (Ca/Sr/Ba) in methanol followed by the addition of various titanium(IV) sources afforded novel dimeric 1:1 alkaline earth/titanium(IV) calix[4]arene complexes. In each complex the central core of the crystallographically imposed centrosymmetric dimer consists of a rhombus of alternating alkaline earth metals and μ3‐oxo‐centres. Five terminal methanol ligands form seven‐coordinate calcium and strontium centres, while the barium centres are bridged by two additional methanol ligands, making them nine‐coordinate. Each oxo centre is the apical ligand of a square‐pyramidal titanium(IV) centre, whose basal plane ligands are the four phenolate oxygens from a calix[4]arene in the symmetrical cone‐conformation. Deprotonation of calix[4]arene with potassium metal, followed by the addition of a titanium(IV) source containing at least one acetylacetonate ligand, formed a mixed potassium/titanium complex based on one calix[4]arene. The potassium cation in this complex binds within the π‐basic calix[4]arene cavity, whilst titanium is octahedrally complexed in the exo‐position, by four phenolates and one acetylacetonate. The alkaline earth titanium dimers and potassium/titanium monomers could be interconverted merely by changing the solvent, with the appropriate cations and ligands present in solution. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Cover Picture: Heterobimetallic Calix[4]arene Complexes: Interconversion of Dimeric (Ca, Sr or Ba)/TiIV Complexes with a Monomeric K/TiIV Complex (Eur. J. Inorg. Chem. 23/2003)

AbstractThe cover picture shows the structures of two new types of calix[4]arene complexes obtained by deprotonating the calixarene with an alkaline earth metal, or potassium metal, followed by reaction with selected titanium(IV) compounds. The alkaline earth metals form dimeric alkaline earth‐titanium(IV) complexes, containing at the core a rhombus of alternating alkaline earth metal and μ3‐oxo centres. Each oxo centre of the rhombic core is the apical ligand of a square‐pyramidal titanium(IV) centre, whose basal plane donors are the four phenolate oxygen atoms from a calix[4]arene arrayed in the symmetrical cone conformation. Terminal methanol ligands surround the alkaline earth centres, and simultaneously hydrogen‐bond to the adjacent phenolate oxygen atoms. Potassium reacts with calix[4]arene and the titanium(IV) source to give a monomeric mixed potassium‐titanium complex. The potassium cation binds within the κ‐basic calix[4]arene cavity, whilst the titanium centre is octahedrally complexed in the exo position by four phenolate and one acetylacetonate ligands. A solution pathway exists for the interconversion between the potassium‐titanium calix[4]arene monomer and the alkaline earth‐titanium dimers, where the product is dictated by the choice of solvent. Details are discussed in the article by R. N. Lamb et al. on p. 4153 ff.

Incremental binding free energies of aluminum (III) vs. magnesium (II) complexes

A sequential ligand addition to the aluminum (III) cation has been studied using the B3LYP functional and a combined all-electron/pseudopotentials basis set. The aluminum complexes are compared with analogous magnesium (II) complexes. Different thermodynamical data, such as incremental binding energies, enthalpies, entropies and free energies, are presented for these addition reactions. While the magnesium (II) cation can only accommodate three negatively charged ligands, aluminum (III) accommodates four even after including bulk solvent effects. The main differences between both cations complexing with the neutral ligands, is that aluminum (III) is not able to form complexes with methanol until the number of methanol ligands is equal to 3. Magnesium (II) prefers to bind methanol and formamide when the number of ligands is small, while aluminum prefers formamide. For the largest complexes both cations prefer to bind water.

Metal complexes of 3-acetamido-5-methylpyrazole

In this paper, we present the complete synthesis of the 3-Acetamido-5-methylpyrazole (3-Ac-AMP) from 3-amino-5-methylpyrazole and acetic acid anhydride, including its full spectroscopic characterization. The solid-state structure shows extensive H-bonding involving the acyl and pyrazole moieties. Upon coordination to Co 2+, Zn 2+, and Cd 2+, the system adopts a geometry that allows it to bind to metal centres as a O, N-chelate. 3-Ac-AMP coordination to Zn and Cd was monitored by 1H NMR showing the formation of presumably tetrahedral 2:1 complexes. In the solid state, Co and Zn complexes are centrosymmetric and octahedral having two 3-Ac-AMP ligands in the equatorial plane and two methanol ligands occupying axial positions. The systems form a layered structure in which the ClO 4 − counter ion links the layers via H-bonding.

Trans-Bis(isoquinoline-3-carboxylato-κ2N,O)bis(methanol-κO)iron(II)

In the crystal structure of the title complex, [Zn(C10H6NO2)2(CH3OH)2], the Zn atom at a center of inversion has distorted octa­hedral coordination geometry and is bonded to two quinoline N atoms, two carboxyl­ate O atoms and two methanol O atoms. Two isoquinoline-3-carboxyl­ate ligands lie in trans positions, forming the equatorial plane, and the two methanol ligands occupy the axial positions. The complex mol­ecules are linked together by O—H⋯O hydrogen bonds between the methanol ligands and neighboring carboxyl­ate groups.

Intermediates in the NiII(2,4,9,11-Tetramethyl-Napho2[14]-2,4,6,9,11,13-hexaeneN4)-catalyzed photoreduction of CO2 to CO: A pulse-radiolytic and flash-photochemical study

The photoreduction of CO2 to CO was catalyzed by Ni(II) complexes of the 2,4,9,11-tetramethyl-Napho2[14]-2,4,6,9,11,13-hexaeneN4 and 2,4,9,11-tetra(1,1′-dimethylethyl)-Napho2[14]-2,4,6,9,11,13-hexaeneN4 ligands in methanol. In the experiments, the charge transfer excited state of Ru(bipy) was used as the reductant of the Ni(II) complexes and 2,2′,2′′-nitrilotriethanol was used as a sacrificial reagent. Intermediates in these reactions were investigated by pulse-radiolytic and flash-photochemical procedures. Flash irradiations of the Ni(II) and Co(III) complexes in methanolic solutions at 350 nm resulted in oxidation of methanol. Transient species with a coordinated macrocyclic radical were observed in the photolysis and when radiolytically generated •CH2OH radicals reacted with the complexes. The pulse-radiolytically and flash-photochemically generated transients of the Ni(II) complex incorporated CO2 and the resulting species could mediate in the formation of CO.

Dimethanoltetrakis[5,10,15,20-tetrakis(2,6-dichlorophenyl)porphinato]manganese(III) hexacyanooctaselenidorhenate(III) tridecahydrate

The crystal structure of the title compound, [Mn(TDC)]4[Re6Se8(CN)6]·13H2O, contains discrete [Re6Se8(CN)6]4− and Mn(TDC)+ moieties [TDC is the tetrakis(2,6-di­chloro­phenyl)­porphinate dianion, C44H20Cl8N42−]. The anion as well as two of the cations lie on crystallographic centers of symmetry. Each Mn(TDC)+ cation is octahedral with two axial methanol ligands. The coordinated methanol groups form O—H⋯O hydrogen bonds to solvent water mol­ecules of crystallization in the lattice.

Prototype Microsolvation of Aromatic Hydrocarbon Cations by Polar Ligands: IR Spectra of Benzene+−Ln Clusters (L = H2O, CH3OH)

IR photodissociation spectra of clusters composed of the benzene cation (Bz+) solvated by several water (H2OW) and methanol (CH3OHM) ligands are recorded in the O−H and C−H stretch ranges to investigate the microsolvation process of an aromatic hydrocarbon cation by polar ligands. The Bz+−L (L = W, M) spectra are consistent with H-bound dimer equilibrium structures, in which the ligand L approaches Bz+ in the aromatic plane to form two H-bonds between the lone pairs of the oxygen atom of L and adjacent protons of Bz+. This charge−dipole structure corresponds to the global minimum of the dimer potential and is the only isomer identified in the IR spectrum. In contrast to the dimers, the spectra of larger Bz+−Ln clusters (n ≤ 4 for L = W, n ≤ 2 for L = M) provide clear evidence for the presence of two classes of isomers. Isomer class I corresponds to interior Bz+ solvation and is characterized by cluster geometries in which n single ligands form separate H-bonds to the central Bz+ cation. Isomer class II clusters show the onset of the formation of an H-bonded solvent network, because at least one ligand forms an H-bond to a second ligand. As the Bz+−L interaction is much stronger than the L−L interaction, class I isomers are probably more stable than class II isomers. Comparison between Bz+−Ln and Bz−Ln reveals the drastic influence of ionization of the aromatic solute on both the dimer properties and the microsolvation process.

A Study of the Equilibrium and Kinetics of Urea Binding by a Biomimetic Dinickel(II) Complex

AbstractThe equilibrium and kinetics of urea binding by model dinickel complexes have been studied, which is relevant to the activity of the urease enzyme. The pyrazolate‐based, O2H3‐bridged dinuclear nickel(II) complex [LNi2(OH)(H2O)]2+ (1) binds urea reversibly in organic solvents with the formation of an N,O‐bridged urea anion complex [LNi2[OC(NH2)NH)]2+ (2) and two water molecules. The equilibrium constant has been measured as 4.3(4) in acetone, 2.7(5) in acetonitrile, and 3(1) in methanol at 25 °C. Upon dissolving 1 in anhydrous methanol, the O2H3 bridge is substituted for an O2Me2H bridge to give [LNi2(OMe)(MeOH)]2+ (4),which has been crystallized as 4·(ClO4)2 and characterized by X‐ray diffraction. Both NiII ions in 4 are five‐coordinate with geometries intermediate between square‐pyramidal and trigonal‐bipyramidal. The H atom in the Me2O2H bridging unit is located in an asymmetric position. The exchange of water and methanol ligands in complexes 1 and 4 is very fast in solution at 25 °C (kobsd. > 103 s−1). Binding of urea by complexes 1 and 4 are slower reactions (kobsd. ≈︁ 10−1 to 101 s−1 under the concentration conditions used) and can be monitored by stopped‐flow techniques. Detailed kinetic studies indicate that binding of urea is a multi‐step process. Steady‐state intermediates of the tentative formula [LNi2(OR)(urea)n]2+ (n = 1, 2) are formed in fast preequilibrium with the starting complexes 1 (R = H) and 4 (H = Me), respectively. The bidentate N,O‐coordination and deprotonation of an O‐bound urea ligand constitute the overall rate‐limiting step. The kinetic data suggest that both mono‐ and bis(urea) complexes participate in the formation of the chelate 2, and that the latter are substantially more reactive. The bis(urea) pathway was unexpected because only one urea molecule is incorporated into the final product 2. Reactive intermediates [LNi2(OH)(urea)n]2+ are close analogs of the reactive intermediate of urease, which also has the hydroxide and urea ligands bound at a dinickel core. However, the reactivities of the intermediates are different. The hydroxide ligand in our model complex acts as a base towards urea, and the urea anion complex 2 is formed. In urease, the hydroxide ligand attacks urea as a nucleophile leading to the hydrolysis of urea. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

A ruthenium(II)-porphyrin-carbene complex with a weakly bonded methanol ligand.

The title diphenylcarbene porphyrin complex (diphenylcarbenyl-kappaC)(methanol-kappaO)(5,10,15,20-tetra-p-tolylporphyrinato-kappa(4)N)ruthenium(II) methanol solvate, [Ru(C(13)H(10))(C(48)H(36)N(4))(CH(4)O)].CH(4)O, has a six-coordinate Ru atom with a methanol molecule as the second axial ligand. The carbene fragment is slightly distorted from an ideal sp(2) configuration, with a C(phenyl)-C(carbene)-C(phenyl) angle of 112.2 (3) degrees. The Ru-C bond length of 1.845 (3) A is comparable with other carbene complexes. The two phenyl rings of the carbene ligand are perpendicular to the carbene plane. Methanol solvate molecules link the methanol ligands of adjacent porphyrin complexes via hydrogen bonds.

SYNTHESIS AND CHARACTERIZATION OF METAL COMPLEXES OF P,P′-DI[3-(TRIMETHYLSILYL)-1-PROPYL] METHYLENEDIPHOSPHONIC ACID

ABSTRACT The silicon-substituted diphosphonic acid P,P′-di[3-(trimethyl-silyl)-1-propyl] methylenediphosphonic acid, H2DTMSP-[MDP], reacts with metal nitrates in methanol to form complexes M2(DTMSP[MDP])3 for M˭Fe, Eu and Yb and M(DTMSP[MDP])2 for M˭Th. The sodium salt, Na2-(DTMSP[MDP]), forms upon neutralization of H2DTMSP-[MDP] with NaOH. The calcium salt, Ca(DTMSP[MDP]), forms upon addition of the aqueous metal nitrate to an equivalent amount of the neutralized ligand in methanol. Elemental analysis, infrared spectroscopy and magnetic susceptibility measurements were used to characterize the compounds. Frequency shifts in the asymmetric and symmetric POO− stretching bands of the Fe, Eu, Yb and Th compounds indicate symmetrical coordination of the phosphonate groups through chelate and/or bridging interactions. The frequency difference between these stretching bands becomes smaller as the ionic potential (e/r) of the metal ion increases.

Supramolecular architecture and magnetic properties of copper(II) and nickel(II) porphyrinogen-TCNQ electron-transfer salts.

The compounds [Cu(Tz)-(MeOH)2](TCNQ)2 (1), [Ni(Tz)-(MeOH)2](TCNQ)2 (2), [Cu(Tz)2]-(TCNQ)7 (3) and [Ni(Tz)2](TCNQ)7 (4) (Tz = 2,7,12,17-tetramethyl-1,6,11,16-tetraazaporphyrinogen) were obtained by metathesis reaction of [M(Tz)](ClO4)2 with LiTCNQ and Et3NH(TCNQ)2, respectively. They were characterized by a combination of spectroscopic and physical methods. Compound 1 crystallizes in the monoclinic space group P2(1)/n with a = 8.310(2), b = 25.180(4), c = 20.727(4) A, beta = 93.58(2) degrees; Z = 4. Compound 3 crystallizes in the triclinic space group P1 with a = 11.244(1), b = 16.700(1), c = 17.321(1) A, a = 113.47(1), beta = 108.52(1), gamma = 96.12(1) degrees; Z = 2. The asymmetric unit of the compound 1 is formed by cationic [Cu(Tz)(MeOH)2]2+ and by two crystallographically non equivalent TCNQ.- anions; these anions form dimeric units by overlap of the pi clouds. The dimers form hydrogen bonds with the metal-lomacrocyclic cation through the methanol ligands. According to this structure the compound is paramagnetic and behaves as an insulator in the temperature range studied. The paramagnetism arises only from the metal-complex moieties. Compound 3 shows an unprecedented structure due to the steric requirements of the macrocycle that favors the stacking of the TCNQ groups. The structure consists of infinite stacks of TCNQ units separated by the metal-macrocyclic units; there are seven TCNQ molecules per formula unit, one of which is formally mono-anionic, while the other six bear one half of an electron per molecule. The copper is six-coordinate in a very distorted octahedral environment. The Tz ligand is located in the equatorial plane and the apical nitrogens of the nitrile groups of two TCNQ molecules complete the coordination around the copper. The compound is a semiconductor and its magnetic behavior can be explained by the sum of the Curie contribution of the metal complex and the contribution arising from the magnetic-exchange interactions of the spins located on the TCNQ units. The latter is found to be typical of one-dimensional antiferromagnetic distorted chains of S = 1/2 spins and can be fitted according to a one-dimensional Heisenberg antiferromagnetic model.