Mesoionic tetrazolium-5-aminides: Synthesis, molecular and crystal structures, UV-vis spectra, and DFT calculations.

Tetrazolium-5-aminides have been prepared by the tert-butylation of 5-aminotetrazole and its N-methyl derivatives by the t-BuOH/HClO4 system followed by the treatment of the tetrazolium salts by alkali. The mesoionic compounds have been found to show a higher reactivity of the exocyclic N atom in comparison with 5-aminotetrazoles. The compounds reacted with 1,2-dibromoethane and 5-(methylsulfonyl)-1-phenyl-1H-tetrazole with substitution of bromine and methylsulfonyl groups giving the corresponding tetrazolium salts or conjugate aminides. The obtained mesoionic tetrazoles have been characterized by elemental analysis, FTIR, NMR, and UV-vis spectroscopy, TGA/DSC analysis and for 1,3-di-tert-butyltetrazolium-5-aminide, its N,N'-ethylene-bridged bis-derivative and (1,3-di-tert-butyl-1H-tetrazol-3-ium-5-yl)(1-phenyl-1H-tetrazol-5-yl)amide by single crystal X-ray analysis. The structural and spectral features of the tetrazolium-5-aminides are discussed by using quantum-chemical calculations.

The first organocopper tetrazole derivative: synthesis and characterization.

1-(5-Amino-3-azapentyl)tetrazole dihydrochloride (HL·2HCl) was prepared by heterocyclization of diethylenetriamine with triethyl orthoformate and sodium azide followed by treatment with potassium carbonate and hydrochloric acid. The reaction of CuCl2, HL·2HCl and triethylamine (NEt3) in a molar ratio of 1 : 1 : 3 in water was found to generate a novel organometallic tetrazole derivative Cu2L2Cl2. This compound is present as a binuclear centrosymmetric molecular complex, in which C-deprotonated tetrazole L acts as a chelating ligand via the two amino N and tetrazole ring C coordination sites and the two copper atoms are linked together through two tetrazole ring N(4)-C(5) bridges. This complex is the first organocopper tetrazole derivative. When the molar ratio of the reagents in the abovementioned reaction was changed to 1 : 2 : 2, the complex Cu(HL)2Cl2 was formed along with Cu2L2Cl2. Pure Cu(HL)2Cl2 was isolated after reaction of the reagents in a molar ratio of 1 : 3 : 6. The complex Cu(HL)2Cl2 is present as a mononuclear molecular complex, with a chelating coordination mode of HL via the two amino N atoms only. Both complexes as well as HL·2HCl were characterized by single-crystal X-ray analysis.

5-(2-Mercaptoethyl)-1H-tetrazole: Facile Synthesis and Application for the Preparation of Water Soluble Nanocrystals and Their Gels.

A facile method for the preparation of the novel capping ligand 5-(2-mercaptoethyl)-1H-tetrazole for the stabilization of water-soluble nanocrystals was developed. This effective synthetic procedure is based on the cycloaddition of sodium azide to 3,3'-dithiobis(propionitrile) followed by the reductive cleavage of a S-S bond with triphenylphosphine. The structure of the synthesized compound was confirmed by single-crystal X-ray analysis. A target tetrazole was successfully applied for the direct aqueous synthesis of CdTe and Au nanocrystals. CdTe nanocrystals capped with 5-(2-mercaptoethyl)-1H-tetrazole were found to reveal high photoluminescence efficiencies (up to 77 %). Nanocrystals capped with this tetrazole ligand are able to build 3D structures in a metal-ion-assisted gelation process in aqueous solution. Critical point drying of the as-formed hydrogels allowed the preparation of the corresponding aerogels, while preserving the mesoporous structure.

Copper(II) tetrafluoroborate complexes with the N(3),N(4)-bridging coordination of 1-(tert-butyl)-1H-tetrazole: synthesis, crystal structure and magnetic properties.

1-(tert-Butyl)-1H-tetrazole (L) reacts with copper(ii) tetrafluoroborate hexahydrate to give the complexes [Cu2L8(H2O)2](BF4)4 (1) or [Cu3L6(H2O)6](BF4)6 (2) depending on the reaction conditions. These complexes, as well as compound L, were characterized using single crystal X-ray analysis. Complex 1 was found to comprise a dinuclear complex cation [Cu2L8(H2O)2](4+) (the Ci symmetry point group), with six tetrazole ligands L showing monodentate N(4)-coordination, and two ligands L providing two tetrazole ring N(3),N(4) bridges between the copper(ii) cations; water molecules complete the distorted octahedral coordination of the metal ions. Complex 2 includes a linear trinuclear complex cation [Cu3L6(H2O)6](6+) (the S6 symmetry point group), in which neighbouring copper(ii) cations are linked by three ligands L via tetrazole ring N(3),N(4) bridges; central and terminal metal ions show octahedral CuN6 and CuN3O3 coordination cores, respectively. The temperature-dependent magnetic susceptibility measurements of complex 2 revealed that the copper(ii) ions were weakly ferromagnetically coupled showing a coupling constant J of 2.2 cm(-1) {H = -2J(S1S2 + S2S3)}. The quantum-chemical investigation of the electronic structure and basicity of ligand L was carried out.

Tetrazoles: Unique Capping Ligands and Precursors for Nanostructured Materials.

Capping agents play an important role in the colloidal synthesis of nanomaterials because they control the nucleation and growth of particles, as well as their chemical and colloidal stability. During recent years tetrazole derivatives have proven to be advanced capping ligands for the stabilization of semiconductor and metal nanoparticles. Tetrazole-capped nanoparticles can be prepared by solution-phase or solventless single precursor approaches using metal derivatives of tetrazoles. The solventless thermolysis of metal tetrazolates can produce both individual semiconductor nanocrystals and nanostructured metal monolithic foams displaying low densities and high surface areas. Alternatively, highly porous nanoparticle 3D assemblies are achieved through the controllable aggregation of tetrazole-capped particles in solutions. This approach allows for the preparation of non-ordered hybrid structures consisting of different building blocks, such as mixed semiconductor and metal nanoparticle-based (aero)gels with tunable compositions. Another unique property of tetrazoles is their complete thermal decomposition, forming only gaseous products, which is employed in the fabrication of organic-free semiconductor films from tetrazole-capped nanoparticles. After deposition and subsequent thermal treatment these films exhibit significantly improved electrical transport. The synthetic availability and advances in the functionalization of tetrazoles necessitate further design and study of tetrazole-capped nanoparticles for various applications.

3D assembly of silica encapsulated semiconductor nanocrystals.

Non-ordered porous networks, so-called aerogels, can be achieved by the 3D assembly of quantum dots (QDs). These materials are well suited for photonic applications, however a certain quenching of the photoluminescence (PL) intensity is observed in these structures. This PL quenching is mainly attributed to the energy transfer mechanisms that result from the close contact of the nanoparticles in the network. Here, we demonstrate the formation of a novel aerogel material with non-quenching PL behaviour by non-classical, reversible gel formation from tetrazole capped silica encapsulated QDs. Monitoring of the gelation/degelation by optical spectroscopy showed that the optical properties of the nanocrystals could be preserved in the 3D network since no spectral shifts and lifetime shortening, which can be attributed to the coupling between QDs, are observed in the gels as compared to the original colloidal solutions. In comparison with other QD-silica monoliths, QDs in our gels are homogeneously distributed with a distinct and controllable distance. In addition we show that the silica shell is porous and allows metal ions to pass through the shell and interact with the QD core causing detectable changes of the emission properties. We further show the applicability of this gelation method to other QD materials which sets the stage for facile preparation of a variety of mixed gel structures.

2-tert-Butyl-5-(2-pyridyl)-2H-tetrazole as a chelating ligand in the direct synthesis of novel Cu(II) and heterobimetallic Cu(II)/Mn(II) complexes.

For the first time, a representative of the 2,5-disubstituted tetrazoles, namely, 2-tert-butyl-5-(2-pyridyl)-2H-tetrazole (L), has been found to participate in oxidative dissolution of copper powder in homometalic systems Cu0­L­NH4X­DMSO (X = Cl, SCN, ClO4) and heterobimetallic ones Cu0­Mn(OAc)2­L­NH4OAc­Solv (Solv = DMSO, DMF), providing the formation of molecular homometallic complexes [CuL2Cl2] (1), [CuL2(SCN)2] (2), and [CuL2(H2O)](ClO4)2 (3), heterobimetallic complex [Cu2MnL2(OAc)6] (4) from DMF solution and its mixture with complex [Cu2MnL2(OAc)6]·2DMSO (5) from DMSO solution. Free ligand L and complexes 1­4 were characterized by elemental analysis, IR spectroscopy, thermal and X-ray single crystal analyses, whereas complex 5 was characterized by X-ray analysis only. Compounds 1­3 are mononuclear complexes, with chelating coordination mode of L via the tetrazole ring N4 and pyridine ring N7 atoms. Heterobimetallic complexes 4 and 5 possess trinuclear structures, with a linear Cu­Mn­Cu arrangement of the metal atoms, linked by the acetate anions; each copper(II) atom is decorated by a chelating unit of L via the tetrazole ring N1 and pyridine ring N7 atoms in complex 4, and via the N4, N7 atoms in complex 5. Temperature-dependent magnetic susceptibility measurements of complex 4 revealed a weak antiferromagnetic coupling between the paramagnetic copper(II) and manganese(II) ions (J = −2.5 cm(−1), g(Cu) = 2.25 and g(Mn) = 2.01), with magnetic exchange through the acetato bridges.

3D assembly of semiconductor and metal nanocrystals: hybrid CdTe/Au structures with controlled content.

A 3D metal ion assisted assembly of nanoparticles has been developed. The approach relies on the efficient complexation of cadmium ions and 5-mercaptomethyltetrazole employed as the stabilizer of both colloidal CdTe and Au nanoparticles. It enables in a facile way the formation of hybrid metal-semiconductor 3D structures with controllable and tunable composition in aqueous media. By means of critical point drying, these assemblies form highly porous aerogels. The hybrid architectures obtained are characterized by electron microscopy, nitrogen adsorption, and optical spectroscopy methods.

CdTe nanocrystals capped with a tetrazolyl analogue of thioglycolic acid: aqueous synthesis, characterization, and metal-assisted assembly.

A novel ligand, 5-mercaptomethyltetrazole, is applied to the direct colloidal synthesis of highly luminescent (quantum yield of up to 60%) water-soluble CdTe nanocrystals. In the synthesis the 5-mercaptomethyltetrazole behaves analogously to the widely used thioglycolic acid, providing the additional advantage of solubility of the resulting nanocrystals in methanol. Moreover, the 5-mercaptomethyltetrazole-capped nanocrystals possess the unique ability to reversibly form fine 3D networks (hydrogels) upon the addition of metal salts.

A tetrazol-5-yl analogue of glycine, 5-ammoniomethyl-1H-tetrazolide, and its copper(II) complex.

A nonclassical tetrazole isostere of glycine, viz. zwitterionic 5-ammoniomethyl-1H-tetrazolide, C(2)H(5)N(5), (I), crystallizes in the chiral P3(1) space group, similar to gamma-glycine. The crystal packing of (I) is determined by a set of classical hydrogen bonds, forming a three-dimensional network that is practically the same as that in gamma-glycine. The Cu(II) complex of (I), poly[[bis(mu(2)-5-aminomethyl-1H-tetrazolido-kappa(3)N(1),N(5):N(4))copper(II)] dihydrate], {[Cu(C(2)H(4)N(5))(2)].2H(2)O}(n), (II), is a layered coordination polymer formed as a result of tetrazole ring bridges. The Cu(II) cations lie on inversion centres, are surrounded by four anions and adopt elongated octahedral coordination. Water molecules are located in the interlayer space and connect the layers into a three-dimensional network via a system of hydrogen bonds.

Bis(1-methyl-1H-tetrazol-5-yl)diazene and two its copper(I) chloride complexes poly[[[mu-1,2-bis(1-methyl-1H-tetrazol-5-yl)diazene-kappa4N',N4:N,N4']dicopper(I)]-di-mu-chloro] and catena-poly[[chlorocopper(I)]-mu-1,2-bis(1-methyl-1H-tetrazol-5-yl)diazene-kappa4N',N4:N,N4'].

While bis(1-methyl-1H-tetrazol-5-yl)diazene, C4H6N10, (I), has no crystallographically imposed symmetry, in the two title chlorocopper(I) complexes, [Cu2Cl2(C4H6N10)]n, (II), and [CuCl(C4H6N10)]n, (III), the organic ligands lie across centres of inversion; in (III), the Cu and Cl atoms additionally lie about a twofold rotation axis in the space group P2/c. Complex (II) forms a two-dimensional coordination polymer containing tetrahedrally coordinated Cu(I) atoms, and complex (III) forms a one-dimensional coordination polymer containing five-coordinate square-pyramidal Cu(I) atoms.

Bis[1,3-bis(2-methyltetrazol-5-yl-kappaN4)triazenido-kappaN2]nickel(II).

The title compound, [Ni(BMTT)2], where BMTT is 1,3-bis(2-methyltetrazol-5-yl)triazenide (C4H6N11), presents a molecular complex with tridentate ligands. The tridentate mode of the ligand is realised through the central N atom of the triazene group and two N atoms of the two tetrazole rings. The [Ni(BMTT)2] molecule is the meridional isomer, with crystallographic 4 symmetry in space group P4(2)/n. The nickel centre has a distorted octahedral environment, with two axial Ni-N bonds of 2.041 (2) A and four equatorial Ni-N bonds of 2.0739 (14) A. The molecules are linked together by van der Waals interactions only.

1-phenyl-5-(piperidinomethyl)-1H-tetrazole.

In the molecule of the title 1,5-disubstituted tetrazole, C(13)H(17)N(5), the tetrazole and benzene rings are not coplanar, having a dihedral angle of 42.96 (5) degrees between them. The piperidine fragment adopts a chair conformation, and there is a non-classical intramolecular contact between the benzene H atom and the piperidine N atom. Intermolecular C-H...pi interactions involving the piperidine C-H groups and the benzene rings are responsible for the formation of two-dimensional networks, extending parallel to the ab plane. These networks are linked together into a three-dimensional polymeric structure via pi-pi stacking interactions between the tetrazole rings of two adjacent molecules.

catena-Poly[[bis[mu-1,2-bis(1-methyltetrazol-5-yl)ethane-kappa(2)N(4):N(4')]bis[chlorocopper(II)]]-di-mu-chloro].

In the title compound, [Cu(2)Cl(4)(C(6)H(10)N(8))(2)](n), the ligand has C(2) symmetry, and the Cu and Cl atoms lie on a mirror plane. The coordination polyhedron of the Cu atom is a distorted square pyramid, with the basal positions occupied by two N atoms from two different ligands [Cu-N = 2.0407 (18) A] and by the two Cl atoms [Cu-Cl = 2.2705 (8) and 2.2499 (9) A], and the apical position occupied by a Cl atom [Cu-Cl = 2.8154 (9) A] that belongs to the basal plane of a neighbouring Cu atom. The [CuCl(2)(C(6)H(10)N(8))](2) units form infinite chains extending along the a axis via the Cl atoms. Intermolecular C-H.Cl contacts [C.Cl = 3.484 (2) A] are also present in the chains. The chains are linked together by intermolecular C-H.N interactions [C.N = 3.314 (3) A].

Zwitterionic 5-(1-piperidiniomethyl)-1H-tetrazolide.

The title compound, C(7)H(13)N(5), a tetrazole analogue of betaines, exists as a zwitterion, with the H atom of the tetrazole ring being transferred to the piperidine ring N atom. The tetrazole ring symmetry is close to C(2v), which suggests strong charge delocalization in the N-C-N fragment of the ring. There are classical hydrogen bonds in the structure which are responsible for the formation of two-membered aggregates.

Dichloro[N,N-dimethyl-1-(1-methyl-1H-tetrazol-5-yl-kappaN4)methanamine-kappaN]copper(II).

The title compound, [CuCl(2)(C(5)H(11)N(5))], is the first structurally characterized molecular chelate complex involving an alpha-aminoalkyltetrazole. There are two complex molecules in the asymmetric unit. The ligand molecules are bidentate. Both Cu atoms reveal rather distorted square-planar coordinations. The complex molecules are linked together by van der Waals interactions only.