Tetrazolato Ligand Research Articles

Tetrazolato Ligandı ve Pt(II) Kompleksinin DNA Etkileşiminin Moleküler Doking Yöntemi ile Belirlenmesi

Tetrazolato Ligandı ve Pt(II) Kompleksinin DNA Etkileşiminin Moleküler Doking Yöntemi ile Belirlenmesi

Synthesis and Photochemical Properties of Manganese(I) Tricarbonyl Diimine Complexes Bound to Tetrazolato Ligands

Ten manganese(I) tricarbonyl diimine complexes bound to variably functionalised 5‐aryl‐tetrazolato ligands were prepared, and their photochemical properties were investigated. Upon exposure to light at 365 nm, each complex decomposed to its free diimine and tetrazolato ligands, simultaneously dissociating three CO ligands, as evidenced by changes in the IR spectra of the irradiated complexes over time. The anti‐bacterial properties of one of these complexes were tested against Escherichia coli. While the complex displayed no effect on the bacterial growth in the dark, pre‐irradiated solutions inhibited bacterial growth. Comparative studies revealed that the antibacterial properties originate from the presence of free 1,10‐phenanthroline.

Mixed μ-azido-Schiff-base cyclometallated Pd (II) complexes as a template for novel palladacycles bearing bridging carbodiimido, tetrazolato ligands, and tetrazole-thiolato linkers

Mixed μ-azido-Schiff-base palladacycles [Pd{C,N-κ2-(4-R)C6H3CH = N-C6H3-2,6-i-Pr2}(μ2-N3)]2 (R = H, 1; OMe, 2) served as a metal-template for the synthesis of unusual dicarbodiimido bridged complexes [(μ2-NCN-Xyl)Pd{C,N-κ2-(4-R)C6H3CH = NC6H3-2,6-i-Pr2}]2 (R = H; OMe) and mixed tetrazolato-isocyanido complexes [Pd(C,N-κ2-(4-R)C6H3CH = NC6H3-2,6-i-Pr2)(CN4-Xyl)(CN-Xyl)] (R = H; OMe). Reactions of ethyl isothiocyanate with 1 and 2 gave the ditetrazole-thiolato bridged Pd complexes [(μ2-SCN4-C2H5)Pd(C,N-κ2-(4-R)C6H3CH = NC6H3-2,6-i-Pr2)]2. All these complexes were fully characterized by FT-IR, NMR spectroscopy, elemental analysis and/or X-ray crystallography.

Investigating Intracellular Localisation and Cytotoxicity Trends for Neutral and Cationic Iridium Tetrazolato Complexes in Live Cells.

A family of five neutral cyclometalated iridium(III) tetrazolato complexes and their methylated cationic analogues have been synthesised and characterised. The complexes are distinguished by variations of the substituents or degree of π conjugation on either the phenylpyridine or tetrazolato ligands. The photophysical properties of these species have been evaluated in organic and aqueous media, revealing predominantly a solvatochromic emission originating from mixed metal-to-ligand and ligand-to-ligand charge transfer excited states of triplet multiplicity. These emissions are characterised by typically long excited-state lifetimes (∼hundreds of ns), and quantum yields around 5-10 % in aqueous media. Methylation of the complexes caused a systematic red-shift of the emission profiles. The behaviour and the effects of the different complexes were then examined in cells. The neutral species localised mostly in the endoplasmic reticulum and lipid droplets, whereas the majority of the cationic complexes localised in the mitochondria. The amount of complexes found within cells does not depend on lipophilicity, which potentially suggests diverse uptake mechanisms. Methylated analogues were found to be more cytotoxic compared to the neutral species, a behaviour that might to be linked to a combination of uptake and intracellular localisation.

Preparation of bis(5-phenyltetrazolato) Pt(II) and Pt(IV) analogues of transplatin and in vitro evaluation for antitumor activity

To evaluate the 5-substituted tetrazolate (5R-tetrazolate) ligand for the development of novel antitumor active Pt(II) and Pt(IV) diamines, eight analogues of transplatin bearing 5-phenyltetrazolato and 5-(phenol)tetrazolato ligands were prepared by reacting transplatin with the 5-substituted tetrazolate in DMF in the presence of trimethylamine. Coordination to platinum was through the N2 position of the tetrazolato ligand, as evidenced by a X-ray crystal structure of trans-diamminobis[5-(phenyl-4-ol)tetrazolato-κN2]platinum(II). Attempts to synthesize the corresponding cis-coordinated analogues from cisplatin were unsuccessful due to isomerization to the more stable trans isomers. Hydrogen peroxide was used to oxidize trans-diamminobis(5-phenyltetrazolato) and trans-diamminobis(5-phenoltetrazolato)platinum(II) complexes to the trans-dihydroxo-Pt(IV) analogues; the hydroxo ligands were then further acylated. The binding of Pt to calf thymus DNA for trans,trans,trans-diamminodihydroxidobis(5-phenyltetrazolato-κN2)platinum(IV) was dependent on the presence of ascorbate; however, the Pt(II) analogue trans-diamminobis(5-phenyltetrazolato-κN2)platinum(II) itself bond only very weakly to DNA, indicating that this is not the product of the ascorbate induced reduction of the Pt(IV) complex. Evaluation of the antiproliferative activity on eight human cancer cells in vitro showed the Pt(IV) complexes to be more potent than the Pt(II) analogues but all complexes were still much less active than cisplatin. No cross resistance to cisplatin was observed in the A2870 ovarian cancer cell line.

Effect on catecholase activity and interaction with biomolecules of metal complexes containing differently tuned 5-substituted ancillary tetrazolato ligands

Four new metal complexes (one mononuclear and three dinuclear) viz. [NiL(5-phenyltetrazolato)] (1a), [Ni2L2{5-(2-cyanophenyl)-tetrazolato}2] (1b), [Cu2L2{5-phenyltetrazolato}2]·C6H5CN (2a) and [Cu2L2{5-(2-cyanophenyl)-tetrazolato}2] (2b) [HL=3-(2-dimethylamino-ethylimino)-1-phenyl-butan-1-one] have been synthesized by in-situ generation of tetrazolato ligands and characterized by X-ray crystallography, different spectroscopic techniques and elemental analyses. Introduction of one nitrile group in the 5-substituted phenyl ring makes the tetrazolato ligand comparatively weaker donor leading the complex to be more vulnerable towards dissociation facilitating subsequent substrate binding for catecholase oxidation study. Copper complex 2b has been found to be more active with respect to analogous nickel complex 1b as it provides the metal centered oxidation route rather than ligand centered oxidation in nickel complex. The comparative catalytic activities of complex 1b and 2b are further explored by DFT calculations which also support the experimental results. UV–Vis and fluorescence-based spectroscopic techniques revealed that two of the metal-tetrazolato complexes (1a and 2b) interact with double stranded DNA via intercalation and also with serum albumin protein BSA. A comparative assessment indicated that the Ni(II)-tetrazolato complex 1a displayed superior DNA binding. The interaction of these compounds with bovine serum albumin (BSA) suggested that the Cu(II)-tetrazolato complex 2b quenched the intrinsic fluorescence of BSA in a static quenching process and shows stronger binding constant.

Synthesis of six-coordinate mono-, bis-, and tris(tetrazolato) complexes via [3 + 2] cycloadditions of nitriles to silicon-bound azido ligands.

A convenient synthetic route to poly(tetrazolato) silicon complexes is described based on the four reactive centres of the N-rich, highly endothermic tetraazides of the type Si(N3)4(L2). Hypercoordinate azido(tetrazolato) silicon complexes Si(N3)2(N4C-R)2(L2), R = CH3, C6H5, 4-C6H4CH3 (4a, 5, 6, 7) and Si(N3)2(N4C-L)2 (9, L = 2-C5H4N), L2 = 2,2'-bipyridine, 1,10-phenanthroline, with SiN6 skeletons were synthesised via multiple [3 + 2] dipolar cycloaddition reactions starting from Si(N3)4(L2) and a nitrile. The isolated new complexes were characterised by standard analytical methods, single crystal X-ray diffraction and differential scanning calorimetry (4a,b). Tetrazolato ligand linkage isomerism was observed for complex 4a. The crystallographically characterised methyl tetrazolato complexes and plausible configurational and linkage isomers were evaluated by DFT calculations at the B3LYP/6-311G(d,p) level.

Ligand-Induced Structural, Photophysical, and Electrochemical Variations in Tricarbonyl Rhenium(I) Tetrazolato Complexes

Treatment of [Re(CO)5X] (X = Cl, Br) with 2-(2-tert-butyltetrazol-5-yl)pyridine yielded neutral mononuclear complexes by exchange of two CO ligands for the chelating tetrazolato ligand. Treatment of [Re(CO)5Br] with phenyltetrazolate resulted in the assembly of an anionic dinuclear rhenium tricarbonyl species bridged by three tetrazole rings. The reaction of [Re(CO)5Br] with (2-tert-butyltetrazol-5-yl)benzene formed an analogous neutral dinuclear complex bridged by a tetrazole ring as well as two bromide ligands; however this complex was found to be rather unstable in solution and was only structurally characterized via X-ray diffraction. The first three complexes were investigated for their photophysical properties, highlighting phosphorescent emission from their triplet metal-to-ligand charge transfer excited states, although in the case of the dinuclear species the quantum yield was found to be extremely low. The complexes are also characterized for their electrochemical behavior, and while the neutral...

Preparation and Characterization of Dinuclear Nickel(II) Complexes Containing N3Ni(μ1, 3‐SO3R)2(μ‐RCN4)NiN3 Cores: Crystal Structures and Magnetic Properties

AbstractThe preparation and characterization of three new mixed ligand macrocyclic [Ni2L2(L′)]+ complexes are described, where (L2)2– represents a supporting macrocyclic hexaaza‐bis(phenylsulfonato) ligand and L′ a tetrazolato ligand. The complexes [Ni2(L2)(CN4H)]BPh4 (4), [Ni2(L2)(CN4Me)]BPh4 (5), and [Ni2(L2)(CN4Ph)]BPh4 (6) were synthesized by H2O2 oxidation of the corresponding [Ni2(L1)(CN4H)]BPh4 (1), [Ni2(L1)(CN4Me)]BPh4 (2), and [Ni2(L1)(CN4Ph)]BPh4 (3) complexes supported by the corresponding hexaaza‐bis(thiophenolate) macrocycle. The compounds were characterized by means of elemental analysis, mass spectrometry, IR, and UV/Vis spectroscopy. The crystal structures of compounds 4–6 show that the bridging thiophenolate functions in 1–3 are in all cases converted to μ1, 3‐bridging sulfonate groups to generate N3Ni(μ1, 3‐SO3R)2(μ‐RCN4)NiN3 cores. The conversion to the phenylsulfonato groups is accompanied by a drastic increase of the Ni···Ni distances from 3.455(1) Å in 1, 3.425(1) Å in 2, and 3.443(1) Å [3.450(1) Å] in 3 to 4.2796(5) Å [4.3375(6) Å] in 4, 4.3402(6) Å in 5, and 4.2607(4) Å in 6. Upon oxidation the magnetic properties are affected. In contrast to 1–3, which exhibit an intramolecular ferromagnetic exchange interaction (S = 2 ground state), the spins of the nickel(II) (Si = 1) ions in 4–6 are antiferromagnetically coupled, the coupling constants J being –1.39 cm–1 (4), –1.43 cm–1 (5), and –1.60 cm–1 (6) (H = –2JS1S2) to yield a diamagnetic S = 0 ground state. DFT (density functional theory) calculations were carried out to substantiate the experimental results.

Cuprous Halide Coordination Polymers Based on Cationic [Cu4X2] and [Cu3X] Clusters and [Cu2Br]n Layers with Tetrazolates as Assembling Ligands: Highly Connected Networks and Halide‐Dependent Luminescence

AbstractFive tetrazolate‐based coordination polymers with cationic copper(I) halide motifs, namely, Cu4(tta)2Cl2 (1, tta = tetrazolate), Cu4(tta)2Br2 (2), Cu2(tta)I (3), Cu3(mtta)2Cl (4, mtta = 5‐methyltetrazolate), and Cu2(tta)Br (5) were prepared by hydro(solvo)thermal reactions of CuX2 or CuX with tetrazolato ligands in the presence of HX. Compounds 1, 2, and 3 show eight‐connected square‐planar layered structures constructed with butterfly‐like [Cu4X2]2+ (X = Cl, Br, I) clusters and μ4‐tta groups. Isomorphs 1 and 2 crystallize in the orthorhombic space group Pbca, but 3 crystallizes in the orthorhombic space group Pbam, because each μ4‐tta group is coordinated to three butterfly‐like clusters rather than four in 1 and 2. To the best of our knowledge, 1, 2, and 3 represent the only 2D coordination polymers with eight‐connected square planar topology to date. Compound 4 is a [Cu3Cl]2+ cluster based on the undocumented ten‐connected ZrIn2 topological framework. Compound 5 has a 3D pillar layered framework constructed with [Cu2Br]nn+ cationic layers. Compounds 1, 2, 4, and 5 exhibit strong green‐blue emission in the solid state at room temperature, whereas cuprous iodide complex 3 shows strong red luminescence.

Synthesis, Structural, and Photophysical Investigation of Diimine Triscarbonyl Re(I) Tetrazolato Complexes.

The synthesis, structural, and photophysical properties of a novel family of neutral fac-[Re(N(∧)N)(CO)(3)(L)] complexes, where N(∧)N is either 2,2'-bipyridine or 1,10-phenanthroline and L is a para functionalized 5-aryltetrazolate [namely, 5-phenyltetrazolate (Tph(-)), 4-(tetrazolate-5-yl)benzaldehyde (Tbdz(-)), 5-(4-acetylphenyl)tetrazolate (Tacy(-)), and methyl 4-(tetrazolate-5-yl)benzoate (Tmeb(-))] are reported. The complexes were prepared by direct addition of the corresponding tetrazolate anion to the acetonitrile solvated fac-[Re(N(∧)N)(CO)(3)](+) precursor. NMR data demonstrate that the coordination of the metal fragment is regiospecific at the N2 atom of the tetrazolate ring. These conclusions are also supported by X-ray structural determinations. Photophysical data were obtained in diluted and deaerated dichloromethane solutions displaying broad and structureless profiles with emission maxima ranging from 566 to 578 nm. The absorption profiles indicate the presence of higher energy intraligand (IL) π-π* transitions and lower energies ligand-to-ligand charge transfer (LLCT) and metal-to-ligand charge transfer (MLCT). As the last two transitions are mixed, they are better described as a metal-ligand-to-ligand charge transfer (MLLCT), a result that is also supported by density functional theory (DFT) calculations. The complexes show excited state lifetime values ranging from 102 to 955 ns, with associated quantum yield between 0.012 and 0.099. Compared to the parent neutral chloro or bromo [Re(N(∧)N)(CO)(3)X], the complexes show a slightly improved performance because of the π accepting nature of the tetrazolato ligand. The metal-to-ligand backbonding is in fact depleting the Re center of electron density, thus widening the HOMO-LUMO gap and reducing the non-radiative decay mechanism in accordance with the energy gap law. Finally, the electron-withdrawing or donating nature of the substituent on the phenyltetrazolato ligand allows the fine-tuning of the photophysical properties.

Magnetic Properties of Mixed Ligand NiII2 and NiII4 Complexes Composed of Macrocyclic Hexaamine‐Dithiophenolato and Bridging Tetrazolato Ligands

AbstractThe magnetic properties of the dinuclear and tetranuclear nickel(II) tetrazolato complexes [Ni2L(RCN4)][BPh4] (R = H (4), Me (5), Ph (6)) and [(Ni2L)2(1,4‐(CN4)2‐C6H4)][BPh4]2 (7), where (L)2– represents a 24‐membered macrocyclic N6S2 supporting ligand, are reported. Analysis of temperature‐dependent magnetic susceptibility measurements over the temperature range from 2 to 300 K revealed the presence of weak ferromagnetic exchange interactions between the NiII ions in the binuclear [Ni2L(μ‐L′)]+ subunits with magnetic exchange coupling constant values of J1 = 13.5 cm–1 for 4, J1 = 20.0 cm–1 for 5, J1 = 19.2 cm–1 for 6, and J1 = 15.2 cm–1 for 7 (H = –2JS1S2). The exchange coupling J2 across the bistetrazolato bridge in 7 is less than 0.1 cm–1, which suggests that no significant interdimer coupling occurs in this compound. The synthesis and crystal structure of the new complex 7·2MeCN is also reported.

Synthesis, X-ray structures and luminescence properties of three multidimensional metal–organic frameworks incorporating the versatile 5-(pyrimidyl)tetrazolato bridging ligand

The hydrated sodium salt of the novel and versatile 5-(pyrimidyl)tetrazolato ligand (pmtz(-)), Na(pmtz).H(2)O (1), has been prepared in very mild conditions from 2-cyanopyrimidine and NaN(3). Two coordination polymers [Cd(pmtz)(2)]n (2)and [Cd(pmtz)(micro-Cl)(0.5)(micro-N(3))(0.5)(H(2)O)](n)(3), , have been synthesized from (1)under conventional or hydrothermal conditions, respectively, and fully characterized by single-crystal or powder X-ray diffraction methods. Compounds and consist of mono-dimensional polymeric chains, further stabilized by interchain pi-pi stacking and hydrogen bond interactions. Compound , containing octacoordinated Cd ions of crystallographic D(2) symmetry, exhibits neutral (4, 4) layers formed by square units of the metallacalix[4]arene type in 1,3-alternate conformation. Species , and display intense, room temperature, photoluminescence in the solid state.

Synthesis, structural characterization, and properties of chromium(iii) complexes containing amidinato ligands and η2-pyrazolato, η2-1,2,4-triazolato, or η1-tetrazolato ligands

Treatment of anhydrous chromium(III) chloride with 2 or 3 equivalents of 1,3-di-tert-butylacetamidinatolithium or 1,3-diisopropylacetamidinatolithium in tetrahydrofuran at ambient temperature afforded Cr(tBuNC(CH3)NtBu)2(Cl)(THF) and Cr(iPrNC(CH3)NiPr)3 in 78% and 65% yields, respectively. Treatment of Cr(tBuNC(CH3)NtBu)2(Cl)(THF) with the potassium salts derived from pyrazoles and 1,2,4-triazoles afforded Cr(tBuNC(CH3)NtBu)2(X), where X=3,5-disubstituted pyrazolato or 3,5-disubstituted 1,2,4-triazolato ligands, in 65-70% yields. X-Ray crystal structure analyses of Cr(tBuNC(CH3)NtBu)2(Me2pz) (Me2pz=3,5-dimethylpyrazolato) and Cr(tBuNC(CH3)NtBu)2(Me2trz) (Me2trz=3,5-dimethyl-1,2,4-triazolato) revealed eta2-coordination of the Me2pz and Me2trz ligands. Treatment of Cr(tBuNC(CH3)NtBu)2(Cl)(THF) with trifluoromethyltetrazolatosodium (NaCF3tetz) in the presence of 4-tert-butylpyridine afforded Cr(tBuNC(CH3)NtBu)2(CF3tetz)(4-tBupy) in 30% yield. An X-ray crystal structure determination showed eta1-coordination of the tetrazolato ligand through the 2-nitrogen atom. The complexes Cr(iPrNC(CH3)NiPr)3 and Cr(tBuNC(CH3)NtBu)2(X) are volatile and sublime with <1% residue between 120 and 165 degrees C at 0.05 Torr. In addition, these complexes are thermally stable at >300 degrees C under an inert atmosphere such as nitrogen or argon. Due to the good volatility and high thermal stability, these new compounds are promising precursors for the growth of chromium-containing thin films using atomic layer deposition.

Weak Carbon−Hydrogen−Nitrogen Interactions Affect the Heterocyclic Ligand Bonding Modes in Barium Complexes Containing η2-Tetrazolato and η2-Pentazolato Ligands

Treatment of Ba[N(SiMe3)2]2(THF)2 with 2 equiv of dimethylaminotetrazole or diisopropylaminotetrazole and 1 equiv of 18-crown-6 afforded Ba[CN4(NMe2)]2(18-crown-6) (87%) and Ba[CN4(NiPr2)]2(18-crown-6) (79%) as colorless crystalline solids. Ba[CN4(NMe2)]2(18-crown-6) contains two 1,2-eta2-tetrazolato ligands and one eta6-18-crown-6 ligand. The molecular structure of Ba[CN4(NiPr2)]2(18-crown-6) is similar to that of Ba[CN4(NMe2)]2(18-crown-6), except that the tetrazolato ligands exhibit the isomeric 2,3-eta2-coordination mode and the tetrazolato ligand CN4 cores are bent significantly toward the 18-crown-6 ligands. Molecular orbital calculations were carried out on the model complexes Ba(azolate)2(18-crown-6) (azolate = 1,2-eta2-CHN4, 2,3-eta2-CHN4, and eta2-N5) and demonstrate that the ligand coordination modes are influenced by intramolecular interactions between filled nitrogen orbitals on the azolato ligands and empty C-H sigma* orbitals on the 18-crown-6 ligands.

Reactions of palladium(ii) and platinum(ii) bis(azido) complexes with isocyanides: synthesis and structural characterization of palladium(ii) and platinum(ii) complexes containing carbodiimido (or bis(carbodiimido)) and bis(tetrazolato) ligands

Bis(azido)palladium(II) complexes Pd(N3)2L2 (L = PMe3, PMe2Ph, PEt3, PMePh2) reacted with two equivalents of 2,6-dimethylphenyl isocyanide to give the Pd(II) complexes, trans-Pd[CN4(R)](NCN–R)L2 (R = 2,6-Me2C6H3, L = PMe3, 1; PMe2Ph, 2; PEt3, 3; PMePh2, 4) containing a carbodiimido ligand and a C-coordinated 5-membered tetrazolato ligand. X-Ray structures of 1 and 2 identified the formation of palladium(II) complexes with a carbodiimido group, in which a nitrogen of the linear NCN moiety is bonded to the metal center, and with a tetrazolato ring formed via 1,3-dipolar cycloaddition of the isocyanide to the coordinated azido bond. Heating the isolated complexes 1 and 3 at 60 °C for 5 h converted them into the bis(carbodiimido)palladium(II) complexes, trans-Pd[NCN–R]2L2 (R = 2,6-Me2C6H3, L = PMe3, 5; PEt3, 6). The reactions of 2,6-dimethylphenyl isocyanide with Pd(N3)2L2 (L = PMe3, PEt3) also gave the same complexes directly. Reaction of Pd(N3)2(dppe) with 2,6-dimethylphenyl isocyanide also caused the formation of the bis(carbodiimido) complex Pd[NCN–2,6-Me2C6H3]2(dppe), 7 in 75% yield. However, reactions of M(N3)2(PMe3)2 (M = Pd or Pt) with tert-butyl isocyanide resulted in the formation of bis(tetrazolato) compounds, M[CN4(R)]2(PMe3)2 (R = tert-butyl, M = Pd, 8; Pt, 9) by the cycloaddition of isocyanide to the coordinated azido bond. The same reactions with other isocyanides such as cyclohexyl and n-butyl isocyanides afforded bis(tetrazolato) complexes, trans-M[CN4(R)]2L2 (M = Pd, R = C6H11, L = PMe3: 10anti,syn; M = Pd, R = n-Bu, L = PMe3: 11anti,syn; M = Pt, R = n-Bu, L = PMe3: 12anti,syn; M = Pt, R = n-Bu, L = PEt3: 13anti,syn), which show a mixture of syn and anti isomers in solution. Molecular structures of 11anti, 12anti, and 13syn have been determined by X-ray crystallography.

Early transition metal complexes containing 1,2,4-triazolato and tetrazolato ligands: synthesis, structure, and molecular orbital studies.

Several early transition metal complexes bearing 1,2,4-triazolato and tetrazolato ligands have been prepared by reaction of the pyrazolato complexes Ti(tBu(2)pz)(4-x)Cl(x) (tBu(2)pz = 3,5-di-tert-butylpyrazolato; x = 1, 2) and M(tBu(2)pz)(5-x)Cl(x) (M = Nb, Ta: x = 2, 3) with the sodium or potassium salts derived from 1,2,4-triazoles and tetrazoles. The X-ray structure analysis of Ti(tBu(2)pz)(2)(Me(2)C(2)N(3))(2) shows eta(2)-coordination of the 1,2,4-triazolato ligands, while in Ti(tBu(2)pz)(3)(C(2)H(2)N(3)) and Nb(tBu(2)pz)(3)(Me(2)C(2)N(3))(2) the analogous groups are joined in a eta(1)-fashion in the solid-state structure. Solution NMR studies at different temperatures suggest transition states involving eta(2)-1,2,4-triazolato ligands for the complexes containing eta(1)-1,2,4-triazolato ligands in the solid state. X-ray crystal structures of analogous tetrazolato complexes Ti(tBu(2)pz)(3)(PhCN(4)) and Nb(tBu(2)pz)(3)(PhCN(4))(2) show eta(1)-coordination of the 2-nitrogen atoms of the tetrazolato ligands. Molecular orbital calculations have been carried out on several model titanium complexes and provide detailed insight into the bonding between early transition metal centers and 1,2,4-triazolato and tetrazolato ligands. The eta(2)-coordination mode of 1,2,4-triazolato and tetrazolato ligands is predicted to be more stable than the eta(1)-coordination mode by 13.8-5.2 kcal/mol.

Synthesis, spectroscopic and electrochemical properties of tetrazolatomanganese(III) porphyrins

The synthesis, spectroscopic characterization and electrochemical properties of four tetrazolatomanganese(III) porphyrins are reported. The investigated compounds are represented by (TPP)Mn[N 4C(R)], where TPP is the dianion of tetraphenylporphyrin and R is CH 2CH 3, C 6H 5, CHCH 2 or CHCHCN. Each complex was characterized by IR, UV-vis and 1H NMR spectroscopy, as well as by mass spectrometry. Variable-temperature 1H NMR data demonstrate that the electron-withdrawing effect of the tetrazolato ligand in (TPP)Mn[N 4C(R)] is higher than that of the azido axial ligand in (TPP)MnN 3. The reductions of each σ-bonded (TPP)Mn[N 4C(R)] derivative were also examined in four non-aqueous solvents (dichloromethane, benzonitrile, tetrahydrofuran and pyridine) and the resulting data compared with data in the literature for manganese(III) porphyrins containing an ionic axial ligand such as Cl − or ClO 4 −.