Comparing a mononuclear Zn(II) complex with hydrogen bond donors with a dinuclear Zn(II) complex for catalysing phosphate ester cleavage

Introducing ligand based hydrogen bond donors to increase the activity of a mononuclear Zn(II) complex for catalysing phosphate ester cleavage can be a more effective strategy than making the dinuclear analogue.     

Synthesis and properties of one-dimensional Ni(II) and Ni(II)Cu(II) complexes linked by hydrogen bond

Four dithiooxalato (Dto) bridged one-dimensional Ni(ll) and Ni(ll)Cu(ll) complexes (Me₆[14]dieneN₄)Ni₂(Dto)₂) (1), (Me₆[14]dieneN₄)CuNi(Dto)₂ (2), (Me₆[14]aneN₄)Ni₂(Dto)₂ (3), and (Me₆[14]aneN₄)CuNi(Dto)₂ (4), were synthesized. These complexes have been characterized by elemental analysis, IR, UV and ESR spectra. The crystal structure of complex3 was determined. It crystallizes in the monoclinic system, space group C2/c with a = 2. 2425(4) nm,b = 1.0088(2) nm,c= 1.4665(3) nm, β= 125.32(3)δ Z = 4;R = 0.076, R_w = 0.079. In the complex, Ni(1) coordinates four sulphur atoms of two Dto ligands in plane square environment. Ni(2) lies in the center of macrocyclic ligand. For Dto ligand, two sulphur atoms coordinate Ni(1), and O(1) coordinates Ni(2) and forms weak coordination bond. O(2) is linked to N(2) of macrocyclic ligand through hydrogen bond.     

Copper(II) and zinc(II) complexes with 2-formylpyridine-derived hydrazones

In the present work 2-formylpyridine-para-chloro-phenyl hydrazone (H2FopClPh) and 2-formylpyridine-para-nitro-phenyl hydrazone (H2FopNO₂Ph) were obtained, as well as their copper(II) and zinc(II) complexes [Cu(H2FopClPh)Cl₂] (1), [Cu(2FopNO₂Ph)Cl] (2), [Zn(H2FopClPh)Cl₂] (3) and [Zn(H2FopNO₂Ph)Cl₂] (4). Upon re-crystallization in DMSO:acetone conversion of 2 into [Cu(2FopNO₂Ph)Cl(DMSO)] (2a) and of 4 into [Zn(2FopNO₂Ph)Cl(DMSO)] (4a) occurred. The crystal structures of 1, 2a, 3 and 4a were determined.     

The effectiveness of solvents as hydrogen bond donors

Taft and Kamlet's -scale of solvent hydrogen bond donation ability is reexamined with regard to its correlations with three widely used polarity scales: Dimroth and Reichardt's E _T (30), Kosower's Z and Mayer's A _N , as well as with the _m values of the solvents when present as monomeric solutes. The correlation with E _T serves to extend the solvent -scale according to the expression:

A general high-yield route to bis(salicylaldimine) zinc(II) complexes: application to the synthesis of pyridine-modified salen-type zinc(II) complexes

A general, direct, and high-yield synthesis of bis(salicylaldimine) zinc complexes from the ligands and Et(2)Zn is reported. This synthetic method is particularly valuable, not only because it allows the efficient preparation of salen-type complexes of zinc but also because it can be used to prepare bifunctional pyridine-modified zinc(II) bis(salicylidene) complexes, which are potentially useful compounds for applications in asymmetric catalysis and materials chemistry. The synthesis and complete structural characterization of a new series of pyridine-modified zinc(II) bis(salicylidene) ligands is discussed.     

Extended chains via hydrogen bond linkages of dinuclear copper(II) and cadmium(II) complexes with a new flexible disulfoxide ligand

A new flexible disulfoxide ligand 1,6-bis(benzylsulfinyl)hexane (L), which is a mixture of the meso and rac isomers, was treated with Cu^II or Cd^II nitrate and obtained dimeric complex [Cu₂(L)₃(H₂O)₂(NO₃)₄] 2 or [Cd₂(L)₃(H₂O)₂(NO₃)₄] 3. In the reacting system the crystals of meso isomer 1 of L together with 2 or 3 were obtained. 2 and 3 have similar molecular structures. In the neutral dimer, three ligands present two kinds of coordination models: monodentate and bis-monodentate. The neutral dimeric units in 2 and 3 are linked by hydrogen bonds to yield a chain structure. Crystal structures of all three compounds were determined by single-crystal X-ray diffraction methods. Crystal data for 1: monoclinic, space group Cc, a=41.95(2), b=5.132(2), c=8.660(4) Å, β=94.898(9)°, V=1857.7(15) Å³, Z=4, final refinement (I>2σ(I)): R1=0.0659, wR2=0.1415. Crystal data for 2: triclinic, space group P-1, a=9.242(4), b=9.539(4), c=21.042(9) Å, α=83.888(9), β=87.971(8), γ=74.177(9)°, V=1774.6(13) Å³, Z=2, final refinement (I>2σ(I)): R1=0.0577, wR2=0.0954. Crystal data for 3: triclinic, space group P-1, a=9.203(4), b=9.831(3), c=20.860(7) Å, α=84.313(6), β=86.432(7), γ=74.188(6)°, V=1805.9(11) Å³, Z=2, final refinement (I>2σ(I)): R1=0.0548, wR2=0.1192.     

The physicochemical and biological properties of zinc(II) complexes

Spectroscopic (IR), thermoanalytical (TG/DTG, DTA) and biological methods were applied to investigate physicochemical and biological properties of seven zinc(II) complex compounds of the following formula Zn(HCOO)₂·2H₂O (I), Zn(HCOO)₂·tph (II), Zn(CH₃COO)₂·2H₂O (III), Zn(CH₃COO)₂·tph (IV), Zn(CH₃COO)₂·2phen (V), Zn(CH₃CH₂COO)₂·2H₂O (VI), Zn(CH₃CH₂CH₂COO)₂·2H₂O (VII), where tph=theophylline, phen=phenazone. The formation of various intermediates during thermal decomposition suggests the dependence on the length of aliphatic carboxylic chain and type of N-donor ligand (tph, phen). The final product of the thermal decomposition was ZnO. The antimicrobial activity of these complexes were tested against G⁺ and G^– bacteria. Strong inhibitive effect was observed towards E. coli, salmonellae and Staph. aureus.     

Formation constants of zinc(II) complexes with Semi-Xylenol Orange

A potentiometric and spectrophotometric investigation on the formation of zinc(II) complexes with Semi-Xylenol Orange (SXO or H(4)L) is reported. In an aqueous solution (mu = 0.1), three 1:1 complex species, MH(2)L, MHL(-), ML(2-), and a 1:2 complex, ML(6-)(2), seem to exist. In a strongly alkaline medium (above pH 12.5) the complexes may dissociate to give zinc hydroxide and L(4-). The formation of a hydroxy complex is not observed. The absorption maxima are at 445 nm (MH(2)L), 466 nm (MHL(-)) and 561 nm (ML(2-)), the molar absorptivities being 2.34 x 10(4), 2.42 x 10(4) and 3.14 x 10(4) 1.mole(-1) .cm(-1) respectively. The formation constants are (at 25 +/- 0.1 degrees ) log K(M)(ML) = 11.84, log K(M)(MHL) = 7.13, log K(M)(MH(2)L) = 2.70, log K(M)(ML(2)) = 16.60.     

Phenolate-bridged zinc(II) complexes relevant to biological phosphoester cleavage

Three zinc complexes based on 2,6-bis(N-2-pyridylmethyl)formimidoyl-4-methylphenolate (HL) by employing Zn(ClO₄)₂, Zn(CH₃COO)₂, and ZnCl₂ have been synthesized and investigated as functional models of phosphoesterases. The molecular structure of [{Zn₂L(µ ³-OH)(H₂O)}₂](ClO₄)₄ (1) obtained by reacting zinc perchlorate with HL was determined by X-ray diffraction analysis, revealing a tetranuclear species with four zinc centers and two ligands. Two zinc ions are accommodated within the two compartments of each ligand and are bridged by an additional hydroxide leading to Zn–Zn distances of 3.1235(9) and 3.1268(9)?Å, respectively. The hydroxide is involved in an additional bridge to the second LZn₂ moiety forming a µ ³-OH. A water molecule is coordinated to two of the four zinc ions. The occurrence of a hydroxide group and of a coordinated water is relevant to the structure found in the native enzyme. The hydrolysis of the phosphoester bis(p-nitrophenol)phosphate ester (BNPP) in a mixture of DMSO and water at 50°C catalyzed by the three zinc compounds has been investigated. High hydrolytic activity was found for all three compounds but differed significantly depending on the nature of the counterion; the chloro derivative was found to be most active, while the perchlorate compound showed the least activity.     

Cadmium(II) and zinc(II) complexes of S-confused thiaporphyrin

The synthesis of 5,10,15,20-tetraphenyl-2-thia-21-carbaporphyrin [S-confused thiaporphyrin, (SCPH)H] was optimized. The formation of the phlorin was detected, which was saturated at the meso carbon adjacent to thiophene. Phlorin converted readily to (SCPH)H in the final oxidation process. Insertion of cadmium(II) and zinc(II) into S-confused thiaporphyrin yielded (SCPH)Cd(II)Cl and (SCPH)Zn(II)Cl complexes. The macrocycle acted as a monoanionic ligand. Three nitrogen atoms and the C(21)H fragment of the inverted thiophene occupied equatorial positions. The compensation of the metal charge required the apical chloride coordination. The characteristic C(21)H resonances of the inverted thiophene ring were located at 1.71 and 1.86 ppm in the 1H NMR spectra of (SCPH)Cd(II)Cl and (SCPH)Zn(II)Cl, respectively. The proximity of the thiophene fragment to the metal ion induced direct scalar couplings between the spin-active nucleus of the metal (111/113Cd) and the adjacent 1H nucleus (J(CdH) = 8.97 Hz). The interaction of the metal ion and C(21)H also was reflected by significant changes of C(21) chemical shifts: (SCPH)Zn(II)Cl, 92.9 ppm and (SCPH)Cd(II)Cl, 88.2 ppm (free ligand (SCPH)H, 123.7 ppm). The X-ray analysis performed for (SCPH)Cd(II)Cl confirmed the side-on cadmium-thiophene interaction. The Cd...C(21) distance (2.615(7) A) exceeded the typical Cd-C bond lengths, but was much shorter than the corresponding van der Waals contact. The density functional theory (DFT) was applied to model the molecular structures of zinc(II) and cadmium(II) complexes of S-confused thiaporphyrin. Subsequent AIM analysis demonstrated that the accumulation of electron density between the metal and thiophene, which is necessary to induce these couplings, was fairly small. A bond path linked the cadmium(II) ion to the proximate C(22) carbon of the thiophene.     

N-acetyl-DL-leucinate cobalt(II), nickel(II) and zinc(II) complexes

Summary Complexes of the type M(AcLeu)₂ · B₂ (M = Co^II, Ni^II or Zn^II; B = H₂O, py, 3-pic, 4-pic; AcLeu =N-acetyl-DL-leucinate ion) and M(AcLeu)₂ B (M = Co^II or Zn^II and B = o-phen) were prepared and investigated by means of magnetic and spectroscopic measurements. The i.r. spectra of all the complexes are consistent with bidentate coordination of the amino acid to the metal ion. The room temperature solid state electronic spectra indicate that the symmetry of this species is closer toD _4h and that MO₆ and MO₄N₂ chromophores are present in the M(AcLeu)₂ · 2 H₂O and M(AcLeu)₂B_n · x H₂O (B = py, 3-pic, 4-pic, n=2 and x=0 for M = Ni^II; B = o-phen, n=1 and x=0 for M = Co^II; B = py, 3-pic, 4-pic, n=1 and x=1 for M = Co^II) complexes, respectively. By comparing the Dq values of the amino acid and those of other N-substituted amino acids previously studied, a spectrochemical series of the the cobalt(II) and nickel(II) complexes is proposed. The¹ H n.m.r. spectra of the zinc(II) complexes confirm the proposed stereochemistry.     

Barriers to energy migration in mixed-ligand zinc(II) complexes

Spectroscopic investigations of Zn(4-Cl-PhS)₂(dmphen) (4-Cl-PhS = anion of 4-chlorobenzenethiol; DMPHEN = 2,9-dimethyl-1,10-phenanthroline) in the p2₁/N and p2₁/C crystal phases and in polymethylmethacrylate (PMMA) are reported. The results demonstrate the existence of an intramolecular barrier to energy migration between 3ππ* and ligand-to-ligand charge-transfer levels.     

Energetics of lead(II), cadmium(II) and zinc(II) complexes with amino acids

The molar heat capacity and the standard (p ⁰ = 0.1 MPa) molar enthalpies of formation of the crystalline of bis(glycinate)lead(II), Pb(gly)₂; bis(dl-alaninate)lead(II), Pb(dl-ala)₂; bis(dl-valinate)lead(II), Pb(dl-val)₂; bis(dl-valinate)cadmium(II), Cd(dl-val)₂ and bis(dl-valinate)zinc(II), Zn(dl-val)₂, were determined, at T = 298.15 K, by differential scanning calorimetry, and high precision solution-reaction calorimetry, respectively. The standard molar enthalpies of formation of the complexes in the gaseous state, the mean molar metal–ligand dissociation enthalpies, M(II)–amino acid, \( \langle D_{\text{m}} \rangle \)(M–L), were derived and compared with analogous copper(II)–ligand and nickel(II)–ligand.θθ

M(II)–amino acid	\( \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \)(cr)/kJ mol?1
Bis(glycinate)lead(II), Pb(gly)2	?998.9 ± 1.9
Bis(dl-alaninate)lead(II), Pb(ala)2	?1048.7 ± 1.8
Bis(dl-valinate)lead(II), Pb(val)2	?1166.3 ± 2.5
Bis(dl-valinate)cadmium(II), Cd(val)2	?1243.7 ± 2.7
Bis(dl-valinate)zinc(II), Zn(val)2	?1306.1 ± 2.3

     

Sulfadrug complexes of zinc(II), cadmium(II) and mercury(II)

Summary Zn^II, Cd^II and Hg^II complexes of sulfadrugs,viz., sulfathiazole, sulfadiazine, sulfamerazine and sulfamethazine were prepared and characterized by analytical and spectroscopic data. The complexes are insoluble and melt with decomposition. The drugs act as bidentate ligands yielding polymeric complexes except for the Zn^II(sulfamethazine) complex in which the drug is monodentate.     

Iron(II) and zinc(II) monohelical binaphthyl salen complexes

A new chiral binaphthyl salen ligand with rigid polyaromatic sidearms gives monohelical complexes (Fe(II) and Zn(II)) of predetermined handedness.     

Macrocyclic copper(II) and zinc(II) complexes incorporating phosphate esters

Slow evaporation of solutions prepared by adding either Cu(ClO(4))(2).6H(2)O or Zn(ClO(4))(2).6H(2)O to solutions containing appropriate proportions of Me(3)tacn (1,4,7-trimethyl-1,4,7-triazacyclononane) and sodium phenyl phosphate (Na(2)PhOPO(3)) gave dark blue crystals of [Cu(3)(Me(3)tacn)(3)(PhOPO(3))(2)](ClO(4))(2).(1)/(2)H(2)O (1) and colorless crystals of [Zn(2)(Me(3)tacn)(2)(H(2)O)(4)(PhOPO(3))](ClO(4))(2).H(2)O (2), respectively. Blue crystals of [Cu(tacn)(2)](BNPP)(2) (3) formed in an aqueous solution of [Cu(tacn)Cl(2)], bis(p-nitrophenyl phosphate) (BNPP), and HEPES buffer (pH 7.4). Compound 1 crystallizes in the triclinic space group P1 (No. 2) with a = 9.8053(2) A, b = 12.9068(2) A, c = 22.1132(2) A, alpha = 98.636(1) degrees, beta = 99.546(1) degrees, gamma = 101.1733(8) degrees, and Z = 2 and exhibits trinuclear Cu(II) clusters in which square pyramidal metal centers are capped by two phosphate esters located above and below the plane of the metal centers. The trinuclear cluster is asymmetric having Cu...Cu distances of 4.14, 4.55, and 5.04 A. Compound 2 crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 13.6248(2) A, b = 11.6002(2) A, c = 25.9681(4) A, beta = 102.0072(9) degrees, and Z = 4 and contains a dinuclear Zn(II) complex formed by linking two units of [Zn(Me(3)tacn)(OH(2))(2)](2+) by a single phosphate ester. Compound 3 crystallizes in the monoclinic space group C2/c (No. 15) with a = 24.7105(5) A, b = 12.8627(3) A, c = 14.0079(3) A, beta = 106.600(1) degrees, and Z = 4 and consists of mononuclear [Cu(tacn)(2)](2+) cations whose charge is balanced by the BNPP(-) anions.     

Effects of the intramolecular NH...S hydrogen bond in mononuclear platinum(II) and palladium(II) complexes with 2,2'-bipyridine and benzenethiol derivatives

A series of complexes, [M(bpy)(SAr)2] (M = platinum(II) or palladium(II), bpy = 2,2'-bipyridine, SAr = 2- or 4-(acylamino)benzenethiolate, or 2-(alkylcarbamoyl)benzenethiolate), were synthesized and characterized on the basis of 1H NMR, IR, and electrochemical properties. The structures of [Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1) and [Pt(bpy)(S-2-t-BuNHCOC6H4)2] (3) were determined by X-ray analysis. The complexes have intramolecular NH...S hydrogen bonds between the amide NH group and the sulfur atom. A weak NH...S hydrogen bond in these complexes and [Pd(bpy)(S-2-Ph3CCONHC6H4)2] (4) is detected from the 1H NMR spectra and the IR spectra in chloroform and in the solid state. [Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1) exhibits a remarkably high-energy-shifted lowest-energy band in UV-visible spectra and has a positively shifted oxidation potential. The blue-shift of 42 nm and the positive shift of +0.24 V, as compared to those of [Pt(bpy)(SC6H5)2), are due to the effect of the NH...S hydrogen bond.