Coordination polymers based on CuII and MnII complexes with 2-hydroxy-3,6-di(tert-butyl)-1,4-benzoquinone

The reactions of Mn^II and Cu^II ions with deprotonated 2-hydroxy-3,6-di(tert-butyl)-1,4-benzoquinone (L) afford bis(chelates) ML₂. In the solid phases of the compounds, the coordinated ligands L perform the bridging function leading to the formation of polymer structures: layered in MnL₂ and framework in CuL₂. In the coordination units ML₂ the chelate fragments are in the trans and cis positions relative to one another for MnL₂ and CuL₂, respectively. Paramagnetism of the polymer structures MnL₂ and CuL₂, for which the effective magnetic moments in the high-temperature region are 5.85 and 1.91 μ_B, respectively, is determined by the metal ions, because the energy level of the triplet state of the coordinated L lies much higher, according to the calculated data, than that of the singlet state.     

Antiferromagnetic coupling between rare earth ions and semiquinones in a series of 1:1 complexes

We use the strategy of diamagnetic substitution for obtaining information on the crystal field effects in paramagnetic rare earth ions using the homologous series of compounds with the diamagnetic tropolonato ligand, Ln(Trp)(HBPz(3))(2), and the paramagnetic semiquinone ligand, Ln(DTBSQ)(HBPz(3))(2), (DTBSQ = 3,5-di-tert-butylsemiquinonato, Trp = tropolonate, HBPz(3)= hydrotrispyrazolylborate) for Ln = Sm(iii), Eu(iii), Gd(iii), Tb(iii), Dy(iii), Ho(iii), Er(iii) or Yb(iii). The X-ray crystal structure of a new form of tropolonate derivative is presented, which shows, as expected, a marked similarity with the structure of the semiquinonate derivative. The Ln(Trp)(HBPz(3))(2) derivatives were then used as a reference for the qualitative determination of crystal field effects in the exchange coupled semiquinone derivatives. Through magnetisation and susceptibility measurements this empirical diamagnetic substitution method evidenced for Er(iii), Tb(iii), Dy(iii) and Yb(iii) derivatives a dominating antiferromagnetic coupling. The increased antiferromagnetic contribution compared to other radical-rare earth metal complexes formed by nitronyl nitroxide ligands may be related to the increased donor strength of the semiquinone ligand.     

Mixed‐ligand MnII and CuII complexes with alternating 2,2′‐bipyrimidine and terephthalate bridges

The novel polymeric complexes catena‐poly[[diaquamanganese(II)]‐μ‐2,2′‐bipyrimidine‐κ⁴N¹,N^1′:N³,N^3′‐[diaquamanganese(II)]‐bis(μ‐terephthalato‐κ²O¹:O⁴)], [Mn₂(C₈H₄O₄)₂(C₈H₆N₄)(H₂O)₄]_n, (I), and catena‐poly[[[aquacopper(II)]‐μ‐aqua‐μ‐hydroxido‐μ‐terephthalato‐κ²O¹:O^1′‐copper(II)‐μ‐aqua‐μ‐hydroxido‐μ‐terephthalato‐κ²O¹:O^1′‐[aquacopper(II)]‐μ‐2,2′‐bipyrimidine‐κ⁴N¹,N^1′:N³,N^3′] tetrahydrate], {[Cu₃(C₈H₄O₄)₂(OH)₂(C₈H₆N₄)(H₂O)₄]·4H₂O}_n, (II), containing bridging 2,2′‐bipyrimidine (bpym) ligands coordinated as bis‐chelates, have been prepared via a ligand‐exchange reaction. In both cases, quite unusual coordination modes of the terephthalate (tpht²⁻) anions were found. In (I), two tpht²⁻ anions acting as bis‐monodentate ligands bridge the Mn^II centres in a parallel fashion. In (II), the tpht²⁻ anions act as endo‐bridges and connect two Cu^II centres in combination with additional aqua and hydroxide bridges. In this way, the binuclear [Mn₂(tpht)₂(bpym)(H₂O)₄] entity in (I) and the trinuclear [Cu₃(tpht)₂(OH)₂(bpym)(H₂O)₄]·4H₂O coordination entity in (II) build up one‐dimensional polymeric chains along the b axis. In (I), the Mn^II cation lies on a twofold axis, whereas the four central C atoms of the bpym ligand are located on a mirror plane. In (II), the central Cu^II cation is also on a special position (site symmetry ). In the crystal structures, the packing of the chains is further strengthened by a system of hydrogen bonds [in both (I) and (II)] and weak face‐to‐face π–π interactions [in (I)], forming three‐dimensional metal–organic frameworks. The Mn^II cation in (I) has a trigonally deformed octahedral geometry, whereas the Cu^II cations in (II) are in distorted octahedral environments. The Cu^II polyhedra are inclined relative to each other and share common edges.     

Affinity and nuclease activity of macrocyclic polyamines and their CuII complexes

The stability constants of Cu(II) complexes that consist of either an oxaaza macrocycle with two triamine moieties linked by dioxa chains, or two macrocyclic ligands with a polyamine chain which are connecting the 2 and 9 positions of phenanthroline, have been determined by means of potentiometric measurements. The results are compared to those reported for other ligands with a similar molecular architecture. Of the complexes that contain phenanthroline in their macrocycle, the Cu(II) ion of the complex with the smallest and most rigid macrocycle (L3) has an unsaturated coordination sphere, while in the complex with the largest macrocycle (L5) the Cu(II) ion is coordinatively almost saturated. These results are corroborated by the crystal structure of the [CuL5](ClO4)2 complex. The affinity of the ligands and the complexes towards nucleic acids was studied by measuring the changes in the melting temperature, which showed that the affinity of the macrocyclic ligands towards double-stranded DNA or RNA is generally smaller than that of their linear analogues that bear a similar charge, with a strong preference for polyA-polyU, a model for RNA. However, the complexes of two of the changed macrocyclic ligands which contain a phenanthroline unit (L4, L5) showed a distinctly larger increase in their melting temperature deltaTm with DNA (polydA-polydT), which is reversed again in favor of RNA upon metallation to the dinuclear copper complex with L5. Experiments with supercoiled plasmid DNA showed a particularly effective cleavage with a mononuclear Cu(II) complex that contains a phenanthroline unit (L6). Related ligands showed less activity towards DNA, but not so towards the biocidic bis(p-nitrophenyl)phosphate (BNPP). In both cases (with DNA and BNPP) the activity seemed to increase with decrease of coordinative saturation of the Cu(II) ion, with the exception of one particular ligand (L6). Experiments with radical scavengers in the DNA experiments showed some decrease in cleavage, which indicates the participation of redox processes.     

Synthesis,characterization, and polyphenol oxidase activity of CuII,MnII, and FeIII complexes with a N2O2 ligand

To explore the effect of the metal center on catechol oxidase and tyrosinase activities, four complexes, Cu₂(μ-Cl)₂(hbpg)₂ (1), [Cu₂(μ-OH₂)₂(hbpg)₂](NO₃)₂(H₂O)₂ (2), [Fe₂(μ-Cl)₂(hbpg)₂]Cl₂(H₂O)₂ (3), and [Mn₂(μ-Cl)₂(hbpg)₂](H₂O)₂ (4) (hbpg?=?N-(2-hydroxybenzyl)-N-(2-picolyl)glycine), were synthesized and characterized with elemental analysis, single-crystal X-ray diffraction, molar conductivity measurements, mass spectrometry, UV-Visible, and FT-IR spectroscopies. The X-ray crystal structural analysis indicates that 1 has a binuclear copper, coordinated with N₂O₂ ligands. Complementary characterizations suggested that 2, 3, and 4 have similar coordination sphere. Complex 3 exhibits much higher catechol oxidase and tyrosinase-like activity than 1, 2, and 4. The results suggested that with a similar coordination sphere, the redox potential of the metal center is critical for catalytic activity. This work provides valuable information for improving the polyphenol oxidase activity of metal complexes for phenolic degradation.     

Substituent effects on the proton spin-spin coupling of benzenes with side-chain interacting groups

Sixty MHz NMR proton spectra of 15 2,4-substituted benzaldehydes and 12 methylbenzenes dissolved in different solvents have been accurately analyzed. Substituent effects on the coupling constants have been determined and have been found to be additive in those trisubstituted compounds where there are neither internal hydrogen bonds or strong interacting groups present.     

Substituent effects on methane activation and elimination by high-valent Zr complexes

A computational study of substituent effects on methane activation and elimination by high-valent zirconium complexes is reported. Substituent (Z) effects (in a structural, electronic, and enthalpic sense) are substantially less important for the imido (L_nZr(DOUBLE BOND)NZ) and imidolike TS than the amido (L_nM(SINGLE BOND)NHZ). For the microscopic reverse reaction, methane CH activation, it suggests that tailoring imido reactivity through electronic modification of nitrogen substituents will be difficult. Analysis of the earliest part of the reaction coordinate for methane elimination entails structural deformation of the Zr—amido to assume an appropriate geometry for elimination, which, in some cases, is directly reflected in substantially higher elimination barriers. Lower elimination barriers correlate with stronger agostic bonding, providing further support for the crucial importance of agostic bonding in facilitating alpha-elimination processes for high-valent transition-metal complexes. © 1996 John Wiley & Sons, Inc.     

Substituent and coupling effects in the IR spectra of arylidenecyclanones

By studying the IR spectra of arylidenecyclanones possessing exocyclic CC double bonds, a correlation has been found between the wave number and intensity values of the ν CO and ν CC vibrations and the substituent constants. Transmissive factors of the CC double bond have been calculated and these indicated that the most pronounced conjugation occurs in the case of the indanones and the smallest for 1-thiochromanones. It has also been established that the substituent effect transmitted by the CC double bond is mainly of a resonant character. Coupling of the ν CO and ν CC vibrations has been studied by the method of Taylor and Smith. It has been concluded that in the case of arylidene-indanones possessing strong coupling, of the two intense bands between 1600 and 1800 cm⁻¹ the one found at higher wave number is a result of an out-of-phase (ν_as) coupling of the ν CO and ν CC vibrations while the other originates from an in-phase (ν_s) coupling. Coupling was less in the case of the other compounds investigated. Our studies prove that for the evaluation of the substituent effects the coupling phenomena should be taken into consideration.     

Substituent effects on carbohydrate coupling reactions promoted by insoluble silver salts

Coupling reactions were performed in the α-D-glucopyranosyl bromide series (i.e. compounds $\text{1}$ a–c, $\text{2}$ a, b, $\text{3}$ and $\text{4}$) and the α-D-mannopyranosyl bromide series (i.e. compounds $\text{7}$ a–c, $\text{8}$ a, b, $\text{9}$) with aglycons $\text{5}$ or $\text{10}$ in the presence of insoluble silver salt promotors. (i.e. silver silicate and silver zeolite). The insoluble silver salt promotes the formation of the β-glycosidic linkage, while a non-participating group is present at C-2 of the glycon. It was found that in both series 4-O-acyl functions increase the β/α ratio of the glycosidic bond formation relative to 4-O-alkyl functions, whereas 3-O and 6-O-acyl functions decrease this ratio. We assume that inductive effects are responsible for the influence exerted by 3-O-substituents, but that through-bond interactions are essential for the effects exerted by 4-O and 6-O substituents. Another unexpected finding was that coupling of α-D-mannopyranosyl bromide derivatives gave much higher β/α ratios than the corresponding reactions of α -D-glucopyranosyl bromides.     

New chiral CuII complexes and their catalytic activity in enantioselective Henry reaction

New chiral polydentante ligands capable of complexation of Cu²⁺ ions were synthesized using readily available derivatives of (S)-proline, d-glyceraldehyde, and imidazole as the starting materials. The synthesized complexes are efficient catalysts for enantioselective nitroaldol condensation (the Henry reaction).     

New complexes of fullerences C60 and C70 with CoII and MnII tetraphenylporphyrinates and their ESR study

Complexes of fullerenes C₆₀ and C₇₀ with cobalt(II) and manganese(II) tetraphenylporphyrinates of compositions Mn(TPP)·(C₆₀)₂(CS₂)_1.5 (1), Mn(TPP)·C₇₀(CS₂) _x , wherex<=1.25 (2), Co(TPP)·C₆₀(CS₂)_0.5 (3), and Co(TPP)·C₇₀(CS₂) _x , wherex<0.25 (4), were synthesized and studied by ESR spectroscopy. At 77 K, complexes1 and2 have singlet ESR spectra characteristic of the low-spin (S=1/2) state of Mn^II, withg=2.002 and linewidths of 250 G and 300 G, respectively, and differing significantly from that of the initial Mn^II(TPP) (g ₁=5.9 andg=2.0,S=5/2). The spectra of complexes1 and2 exposed to oxygen exhibit hyperfine structure due to interaction with⁵⁵Mn and¹⁴N nuclei. The ESR spectra of complexes3 and4 are asymmetric (<g>=2.4, ΔH _pp=(500–600) G), which is due to the overlap of parallel and perpendicular spectral components. The absence of ESR signals from C₆₀ ^.− and C₇₀ ^.− radical anions makes it possible to conclude that the formation of complexes1–4 is not accompanied by electron transfer from Co(TPP) and Mn(TPP) to fullerences C₆₀ and C₇₀. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 722–725, April, 1999.     

Ruthenium trihydrides with N-heterocyclic carbene ligands: effects on quantum mechanical exchange coupling

Ruthenium trihydrides containing N-heterocyclic carbene ligands display large quantum mechanical exchange couplings in their 1H NMR spectra: DFT calculations are used to explore this phenomenon and to compare them to their phosphine congeners.     

On the relationship between the structures of CuII complexes and their chemical transformations

The thermal decomposition of the complexes M ₂ ^I Cu(SO₄)₂ · 6 H₂O and M₂Ni(SO₄)₂ · · 6 H₂O (M^I=NH₄, K, Rb, Tl) containing the complex cation M^II(H₂O)₆ ²+ (M^Il = =Cu, Ni) was studied. The values of the experimental activation energyE obtained for the dehydration reactions of both complex cations were found to be influenced in different ways by the outer-sphere cations present. It was therefore concluded that the activation energy of the decomposition of Cu(H₂O)₆ ²⁺ depends on the degree of tetragonal distortion of this cation, which increases with the ionic radius of cation M^I. TheΔH values of the studied reactions depend less on the structures of the coordination polyhedra.     

Substituent effects on some physicochemical properties of chalcones and their vinylogues

Carbonyl stretching frequencies (ν_CO), dipole moments (μ), longwave maxima (λ_max), half-wave potentials (°_1/2), and relative intensities (Z/Z₀) of benzoyl-ion in mass-spectra oftrans chalcones and their vinylogues of the general type PhCO(CH=CH)_nC₆H₄R-p (I) were measured. Contrary to the previously investigated polyenes of the type R(CH=CH)_nR′ (R′ = CHO or COOEt) variation of the substituent R in compounds I has little influence on properties of I in the ground state and a satisfactory linear relationship between (ν_CO) or μ and σ constants exists only in the case of I (n = 0, 1); the best correlation with σ⁺ indicates that the mesomeric mechanism plays a great part in the transmission of electronic effects. λ_max.,E_1/2, orZ/Z₀ of all series I (n = 0–3) correlate with σ_p or σ⁰ constants, and the separation of mesomeric and inductive effects by multiparametric correlation reveals that in this case inductive effect is of great importance in the transmission of electronic effects. These features were accounted for by the non-planar structure of molecules of I, which was confirmed by X-ray analysis of I (R = Br). The Pariser-Parr-Pople method has also been applied to the calculation of π-electronic density in molecules I and it was found that the introduction of various substituents in para position of I exercises a very little influence on the electronic distribution in compounds I.     

Substituent effects on the intramolecular charge transfer and fluorescence of bimetallic platinum complexes

An investigation of a series of platinum-containing organometallic complexes for the study of fluorescence phenomena in organometallic chromophores controlled by the intramolecular charge transfer (ICT) is presented in this work. We report steady-state and time-resolved spectroscopic experiments as well as quantum chemistry calculations to investigate the substituent effects on the ICT and fluorescence emission. We demonstrate that the fluorescence maximum and lifetimes greatly depend on different substituents and the presence of bimetallic platinum donor. This work paves the way for an understanding of the fluorescence phenomena controlled by molecular ICT characters of these kinds of platinum-containing organometallic complexes.     

Polymeric heterometallic CuII dimethylmalonate complexes with potassium and cadmium ions

A reaction of (HPiv)₂Cu₂(Piv)₄ with dimethylmalonic acid dipotassium salt (K₂Me₂mal) leads to the formation of a cage coordination polymer {(μ-H₂O)₆K₈[(μ-H₂O)Cu-(μ₃,κ²-Me₂mal)(μ₆,κ²-Me₂mal)]₂[Cu₂(μ₅,κ²-Me₂mal)₂(μ₅,κ²-Me₂mal)₂]}n (1). It was found that when 1 reacted with CdSO₄·8H₂O in a mixture of EtOH-H₂O (3: 1), the potassium ions in 1 were displaced with cadmium(ii) ions with the formation of a heterometallic 1D-polymer [(κ¹-H₂O)₄CdCu(μ,κ²-Me₂mal)₂] _n (2). Compounds 1 and 2 were characterized by X-ray crystallography and ESR spectroscopy.