Synthese,Kristallstruktur und Magnetismus von [(CH3)2NH2][NdCl4(H2O)2]

Preparation, Crystal Structure, and Magnetism of [(CH₃)₂NH₂][NdCl₄(H₂O)₂] The complex water containing chloride [(CH₃)₂NH₂][NdCl₄(H₂O)₂] was prepared for the first time and the crystal structure was determined by X‐ray methods from single crystals. The compound crystallizes in the orthorhombic space group Cmca (Z = 8) with a = 1793.5(2) pm, b = 936.6(2) pm and c = 1232.8(2) pm. The anionic part of the structure is built up by chains of edge connected [NdCl_4/2Cl₂(H₂O)₂]^– trigondodecahedra. In order to study the interactions between the neodymium cation and the ligands magnetic measurements were carried out. The magnetic data were interpreted by ligand field calculations applying the angular overlap model.     

Synthese,Kristallstruktur und Magnetismus von [(CH3)2NH2][PrCl4(H2O)2]

Preparation, Crystal Structure, and Magnetism of [(CH₃)₂NH₂][PrCl₄(H₂O)₂] The complex water containing chloride [(CH₃)₂NH₂][PrCl₄(H₂O)₂] has been prepared for the first time and the crystal structure has been determined from single crystal X‐ray diffraction data. The compound crystallizes orthorhombically in the space group Cmca (Z = 8) with a = 1796.6(2) pm, b = 940.7(1) pm, and c = 1238.4(2) pm. The anionic part of the structure is built up by chains of edge‐connected trigondodecahedra [PrCl₆(H₂O)₂]^3– according to [PrCl_4/2Cl₂(H₂O)₂]^–, which are held together by dimethylammonium cations ([(CH₃)₂NH₂]⁺). In order to study the interactions between the praseodymium cation (Pr³⁺) and the ligands magnetic measurements were carried out. The magnetic data were interpreted by ligand field calculations applying the angular overlap model.     

Density functional theory investigation of the binding interactions between phosphoryl,carbonyl, imino,and thiocarbonyl ligands and the pentaaqua nickel(II) complex: Coordination affinity and associated parameters

Density Functional Theory (UB3LYP/6‐311++G(d,p)) calculations of the affinity of the pentaaqua nickel(II) complex for a set of phosphoryl [O?P(H)(CH₃)(PhR)], imino [HN?C(CH₃)(PhR)], thiocarbonyl [S?C(CH₃)(PhR)] and carbonyl [O?C(CH₃)(PhR)] ligands were performed, where R?NH₂, OCH₃, OH, CH₃, H, Cl, CN, and NO₂ is a substituent at the para‐position of a phenyl ring.The affinity of the pentaaqua nickel(II) complex for these ligands was analized and quantified in terms of interaction enthalpy (ΔH), Gibbs free energy (ΔG²⁹⁸), geometric and electronic parameters of the resultant octahedral complexes. The ΔH and ΔG²⁹⁸ results show that the ligand coordination strength increases in the following order: carbonyl < thiocarbonyl < imino < phosphoryl. This coordination strength order is also observed in the analysis of the metal‐ligand distances and charges on the ligand atom that interacts with the Ni(II) cation. The electronic character of the substituent R is the main parameter that affects the strength of the metal‐ligand coordination. Ligands containing electron‐donating groups (NH₂, OCH₃, OH) have more exothermic ΔH and ΔG²⁹⁸ than ligands with electron‐withdrawing groups (Cl, CN, NO₂). The metal‐ligand interaction decomposed by means of the energy decomposition analysis (EDA) method shows that the electronic character of the ligand modulates all the components of the metal‐ligand interaction. The absolute softness of the free ligands is correlated with the covalent contribution to the instantaneous interaction energy calculated using the EDA method. © 2013 Wiley Periodicals, Inc.     

Bonding properties and electronic structures of glycylglycinato copper(II) complexes. Molecular structure of acetylhistaminegly-cylglycinatocopper(II) dihydrate

Summary Mixed ligand diglycinatocopper(II) complexes of the Cu(glygly)L·nH₂O type, where glygly stands for [NH₂-CH₂ CONCH₂CO₂]^2– and L for imidazole (n = 1.5), N-methylimidazole (n = 1), 2-methylimidazole (n = 2), 4-methylimidazole (n = 2), 4-phenylimidazole (n = 2), N-acetylhistamine (n = 2) and NH₃ (n = 2), were prepared and characterized by elemental analyses, i.r., vis. and e.p.r. spectroscopic measurements. The molecular structure of [Cu(glygly)(achmH)]·2H₂O (achmH = acetylhistamine) was determined using three dimensional XRD data. The structure consists of distorted square planar [Cu(glygly)-(achmH)] units interconnected via the peptide oxygen at the apex to complete a square pyramidal structure, Cu—O-(peptide) 2.477(2) Å. The H₂O molecules, not binding directly to the copper ion, involve in intermolecular hydrogen bonding with the copper units. The dianionic glygly ligand and the imidazole ring bind strongly to the central copper ion with Cu—N(amino) 2.045(6) Å, Cu—N-(peptide) 1.891(5) Å, Cu—O(carboxylate) 2.001(4) Å and Cu—N(imidazole) 1.956(5) Å. The dihedral angle between the imidazole nucleus and the CuN₃O xy plane is 6.0°. Similar structures with a CuN₃O coordination plane are proposed for the imidazole complexes, based on spectroscopic data. The bonding properties of the glygly ligand and the unidentate imidazole ligands are elucidated and discussed with reference to the electronic structures of the complexes deduced from Gaussian analyses.     

FeIII Quinolylsalicylaldimine Complexes: A Rare Mixed‐Spin‐State Complex and Abrupt Spin Crossover

A new synthesis of (8‐quinolyl)‐5‐methoxysalicylaldimine (Hqsal‐5‐OMe) is reported and its crystal structure is presented. Two Fe^III complexes, [Fe(qsal‐5‐OMe)₂]Cl ? solvent (solvent=2 MeOH ? 0.5 H₂O ( 1 ) and MeCN ? H₂O ( 2 )) have been prepared and their structural, electronic and magnetic properties studied. [Fe(qsal‐5‐OMe)₂] Cl ? 2 MeOH ? 0.5 H₂O ( 1 ) exhibits rare crystallographically independent high‐spin and low‐spin Fe^III centres at 150 K, whereas [Fe(qsal‐5‐OMe)₂]Cl ? MeCN ? H₂O ( 2 ) is low spin at 100 K. In both structures there are extensive π–π and C? H???π interactions. SQUID magnetometry of 2 reveals an unusual abrupt stepped‐spin crossover with T_1/2=245 K and 275 K for steps 1 and 2, respectively, with a slight hysteresis of 5 K in the first step and a plateau of 15 K between the steps. In contrast, 1 is found to undergo an abrupt half‐spin crossover also with a hysteresis of 10 K. The two compounds are the first Fe^III complexes of a substituted qsal ligand to exhibit abrupt spin crossover. These conclusions are supported by ⁵⁷Fe Mössbauer spectroscopy. Both complexes exhibit reversible reduction to Fe^II at ?0.18 V and irreversible oxidation of the coordinated qsal‐5‐OMe ligand at +1.10 V.     

Two isomorphous imidazole (Him) complexes: [MCl2(Him)2(H2O)2] (M = Co and Ni)

The structures of aqua­di­chloro­bis(1H‐imidazole)­cobalt(II), [CoCl₂(Him)₂(H₂O)₂] (Him is 1H‐imidazole, C₃H₄N₂), (I), and aqua­di­chloro­bis(1H‐imidazole)­nickel(II), [NiCl₂(Him)₂(H₂O)₂], (II), are isomorphous and consist of monomers with inversion symmetry. The three monodentate ligands (imidazole, chlorine and aqua), together with their symmetry equivalents, define almost perfect octahedra. Hydro­gen‐bonding interactions via the imidazole and aqua H atoms lead to a three‐dimensional network.     

A molecular orbital study of the electronic structure and stereochemistry of dithiocyanate diamine and dicyanate diamine cupric complexes

CNDO/2—UHF molecular orbital calculations have been performed with the aim of studying the electronic structure and stereochemistry of the complexes Cu(NH₃)₂(NCX)₂ (X = O, S). Orbital energies, atomic charges, Wiberg indices, spin densities, total molecular energies and their partitioning into metal—ligand and ligand—ligand interactions have been calculated for three model structures of each complex. The role of axial interactions in stabilizing the planar arrangement of theCuN₄ chromophore is discussed. The harmonic force constants of some deformation vibrations of coordinated NCX groups have been estimated for the trans isomers and these estimates are compared with the values for the free ligands.     

Synthesis,Structure, and Magnetic Characterization of a Series of Iron(II) Coordination Frameworks with 2, 6‐Bis(1, 2,4‐triazole‐4‐yl)pyridine

Based on the bis‐triazole ligand 2, 6‐bis(1, 2,4‐triazole‐4‐yl)pyridine (L), the triazole‐iron(II) complexes [Fe(L)₂(dca)₂(H₂O)₂] · 2H₂O ( 1 ) (Nadca = sodium dicyanamide), {[Fe(μ₂‐L)₂(H₂O)₂]Cl₂}_n ( 2 ), and {[Fe(μ₂‐L)₂(H₂O)₂](ClO₄)₂ · L · H₂O}_n ( 3 ) were isolated by solvent diffusion methods. When iron(II) salts and Nadca were used, compound 1 was isolated, which contains mononuclear Fe(L)₂(dca)₂(H₂O)₂ units. When FeCl₂ or FeClO₄ were used, one‐dimensional (1D) cation iron(II) chains ( 2 ) and two‐dimensional (2D) cation iron(II) networks ( 3 ) were isolated indicating anion directing structural diversity. Moreover, variable‐temperature magnetic susceptibility data of 1 – 3 were recorded in the temperature range 2–300 K. The magnetic curve of complex 2 was fitted by using the classical spin Heisenberg chain model indicating anti‐ferromagnetic interactions (J = –5.31 cm^–1). Obviously complexes 1 – 3 show no detectable thermal spin crossover behaviors, the lack of spin‐crossover behavior may be correlated with FeN₄O₂ coordination spheres in 1 – 3 .     

trans‐Diaquabis(1H‐imidazole‐4,5‐di­carboxyl­ate‐κ2N3,O4)­manganese(II)

In the title compound, [Mn(C₅H₃N₂O₄)₂(H₂O)₂], the Mn^II atom lies on an inversion centre, is trans‐coordinated by two N,O‐bidentate 1H‐imidazole‐4,5‐di­carboxyl­ate monoanionic ligands [Mn—O = 2.202 (3) Å and Mn—N = 2.201 (4) Å] and two water mol­ecules [Mn—O = 2.197 (4) Å], and exhibits a distorted octahedral geometry, with adjacent cis angles of 76.45 (13), 86.09 (13) and 89.20 (13)°. The complete solid‐state structure can be described as a three‐dimensional supramol­ecular framework, stabilized by extensive hydrogen‐bonding interactions involving the coordinated water mol­ecules, the carboxy O atoms and the protonated imidazole N atoms of the imidazole‐4,5‐di­carboxyl­ate ligands.     

Syntheses,Structures, and Magnetic Properties of Two DMTCNQ and DETCNQ Gadolinium Complexes

Two DMTCNQ (DMTCNQ = 2,5‐dimethyl‐7,7,8,8‐tetracyano‐p‐quinodimethane) and DETCNQ (DETCNQ = 2,5‐diethyl‐7,7,8,8‐tetracyano‐p‐quinodimethane) gadolinium complexes [Gd(DMTCNQ)₂(CH₃OH)(H₂O)₆][DMTCNQ] · 4H₂O ( 1 ) and [Gd(DETCNQ)(H₂O)₇][2DETCNQ] ( 2 ) were synthesized by reactions of GdCl₃ · 6H₂O with Li(DMTCNQ) or Li(DETCNQ). X‐ray diffraction analysis reveals that complexes 1 and 2 are discrete complexes. The central metal atom in 1 is coordinated by two DMTCNQ ligand radicals whereas that in 2 is coordinated by just one DETCNQ ligand radical. The adjacent molecules are connected by the intermolecular hydrogen bonds to form the two‐dimensional (2D) supramolecular layer structures, which are further packed into a three‐dimensional (3D) supramolecular architecture through the π–π interactions between ligand radicals in 1 and 2 . Magnetic investigation indicates that the antiferromagnetic interactions between spin carriers exists in 1 and 2 .     

Four Metal Complexes Based on Bulky Imidazole Ligands: Solvothermal Syntheses,Crystal Structures,and Fluorescence Properties

In order to explore the influences of (de‐)protonation of the imidazole ring on the structural diversity of the resulting complexes, the imidazole‐based ligands 4, 5‐diphenylimidazole (Hdpi) and 1H‐phenanthro[9, 10‐d]imidazole (Hpi) were utilized as bulky building blocks to construct four complexes by solvothermal reactions, i.e. [Ag(Hdpi)₂](NO₃) · (H₂O) ( 1 ), [Cu(dpi)]_∞ ( 2 ), [Cu(Hpi)(NO₃)]_∞ ( 3 ), and [(H₂pi)(NO₃)] · H₂O ( 4 ). In complex 1 , two Hdpi ligands adopt a monodentate pattern and coordinate with one Ag^I ion to form a mononuclear unit, which is further connected by hydrogen bonds into a 1D supramolecular helix. The deprotonated dpi ligand of 2 acts in bidentate mode, and bridges Cu^I ions to afford a 1D chain. In 3 , the NO₃^– ion, acts as a monodentate bridging ligand and joins Cu^I ions to generate a 1D chain. The Hpi ligand employs a monodentate mode to bond with Cu^I ions of the 1D chain. 4 is protonated and two H₂pi nitrogen atoms are free of coordination. Interestingly, hydrogen bonds among the NO₃^– ion, the H₂pi ligand, and the water molecule yield a macro ring R⁴₄(14). The resulting structural diversity reveals that the (de‐)protonation of imidazole ring directly steers the coordination number of ligand, and thus causes a significant effect on the structure, especially the dimensionality. Furthermore, the solid‐state fluorescence properties of the free ligands and compounds 1 – 4 were studied at room temperature.     

Mixed Adenine/Guanine Quartets with Three trans‐a2PtII (a=NH3 or MeNH2) Cross‐Links: Linkage and Rotational Isomerism,Base Pairing,and Loss of NH3

Of the numerous ways in which two adenine and two guanines (N9 positions blocked in each) can be cross‐linked by three linear metal moieties such as trans‐a₂Pt^II (with a=NH₃ or MeNH₂) to produce open metalated purine quartets with exclusive metal coordination through N1 and N7 sites, one linkage isomer was studied in detail. The isomer trans,trans,trans‐[{Pt(NH₃)₂(N7‐9‐EtA‐N1)₂}{Pt(MeNH₂)₂(N7‐9‐MeGH)}₂][(ClO₄)₆] ? 3H₂O ( 1 ) (with 9‐EtA=9‐ethyladenine and 9‐MeGH=9‐methylguanine) was crystallized from water and found to adopt a flat Z‐shape in the solid state as far as the trinuclear cation is concerned. In the presence of excess 9‐MeGH, a meander‐like construct, trans,trans,trans‐[{Pt(NH₃)₂(N7‐9‐EtA‐N1)₂}{Pt(MeNH₂)₂(N7‐9‐MeGH)₂}][(ClO₄)₆] ? [(9‐MeGH)₂] ? 7 H₂O ( 2 ) is formed, in which the two extra 9‐MeGH nucleobases are hydrogen bonded to the two terminal platinated guanine ligands of 1 . Compound 1 , and likewise the analogous complex 1 a (with NH₃ ligands only), undergo loss of an ammonia ligand and formation of NH₄⁺ when dissolved in [D₆]DMSO. From the analogy between the behavior of 1 and 1 a it is concluded that a NH₃ ligand from the central Pt atom is lost. Addition of 1‐methylcytosine (1‐MeC) to such a DMSO solution reveals coordination of 1‐MeC to the central Pt. In an analogous manner, 9‐MeGH can coordinate to the central Pt in [D₆]DMSO. It is proposed that the proton responsible for formation of NH₄⁺ is from one of the exocyclic amino groups of the two adenine bases, and furthermore, that this process is accompanied by a conformational change of the cation from Z‐form to U‐form. DFT calculations confirm the proposed mechanism and shed light on possible pathways of this process. Calculations show that rotational isomerism is not kinetically hindered and that it would preferably occur previous to the displacement of NH₃ by DMSO. This displacement is the most energetically costly step, but it is compensated by the proton transfer to NH₃ and formation of U(?H⁺) species, which exhibits an intramolecular hydrogen bond between the deprotonated N6H^? of one adenine and the N6H₂ group of the other adenine. Finally the question is examined, how metal cross‐linking patterns in closed metallacyclic quartets containing two adenine and two guanine nucleobases influence the overall shape (square, rectangle, trapezoid) and the planarity of a metalated purine quartet.     

Effect of Chelate Ring Size in Iron(II) Isothiocyanato Complexes with Tetradentate Tripyridyl‐alkylamine Ligands on Spin Crossover Properties

Iron(II) complexes of the type [Fe(L)(NCS)₂] with tetradentate ligands L are well known to show spin crossover properties. However, this behavior is quite sensitive in regard to small changes of the ligand system. Starting from the thoroughly investigated complex [Fe(tmpa)(NCS)₂] [tmpa = tris(2‐pyridylmethyl)amine, also abbreviated as tpa in the literature] we modified the ligand by increasing systematically the chelate ring sizes from 5 to 6 thus obtaining complexes [Fe(pmea)(NCS)₂], [Fe(pmap)(NCS)₂], and [Fe(tepa)(NCS)₂] [pmea = N,N‐bis[(2‐pyridyl)methyl]‐2‐(2‐pyridyl)ethylamine, pmap = N,N‐bis[2‐(2‐pyridyl)ethyl]‐(2‐pyridyl)methylamine, and tepa = tris[2‐(2‐pyridyl)ethyl]amine]. All complexes were structurally characterized and spin crossover properties were investigated using Mößbauer spectroscopy, magnetic measurements, and IR/Raman analyses. The results demonstrated that only the iron complexes with tmpa and pmea showed spin crossover properties, whereas the complexes with the ligands pmap and tepa only formed high spin complexes. Furthermore, DFT calculations supported these findings demonstrating again the strong influence of ligand environment. Herein the effect of increasing the chelate ring sizes in iron(II) isothiocyanato complexes with tetradentate tripyridyl‐alkylamine ligands is clearly demonstrated.     

mer‐Diaquabis(1H‐imidazole‐κN3)[orotato(2–)]cobalt(II)

In the title complex, mer‐diaqua[2,6‐dioxo‐1,2,3,6‐tetrahydropyrimidine‐4‐carboxylato(2−)]bis(1H‐imidazole‐κN³)cobalt(II), [Co(C₅H₂N₂O₄)(C₃H₄N₂)₂(H₂O)₂], the Co^II ion is coordinated by a deprotonated N atom and the carboxylate O atom of the orotate ligand, two imidazole N atoms and two aqua ligands in a distorted octahedral geometry. The title complex exists as discrete doubly hydrogen‐bonded dimers, and a three‐dimensional network of O—H...O and N—H...O hydrogen bonds and weak π–π interactions is responsible for crystal stabilization.     

Zweidimensionale Polymere mit hydrophober Umhüllung: Kristallstrukturen der isostrukturellen Metallkomplexe [M{C6H4(SO2)2N}(H2O)] (M = K,Rb) und des strukturverwandten Ammoniumsalzes [(NH4){C6H4(SO2)2N}(H2O)]

Metal Salts of Benzene‐1,2‐di(sulfonyl)amine. 4. Hydrophobically Wrapped Two‐Dimensional Polymers: Crystal Structures of the Isostructural Metal Complexes [M{C₆H₄(SO₂)₂N}(H₂O)] (M = K, Rb) and of the Structurally Related Ammonium Salt [(NH₄){C₆H₄(SO₂)₂N}(H₂O)] The previously unreported compounds KZ · H₂O ( 1 ), RbZ · H₂O ( 2 ) and NH₄Z · H₂O ( 3 ), where Z^– is Ndeprotonated ortho‐benzenedisulfonimide, are examples of layered inorgano‐organic solids, in which the inorganic component is comprised of metal or ammonium cations, N(SO₂)₂ groups and water molecules and the outer regions are formed by the planar benzo rings of the anions. The metal complexes 1 and 2 were found to be strictly isostructural, whereas 3 is structurally related to them by a non‐crystallographic mirror plane ( 1 – 3 : monoclinic, space group P2₁/c, Z = 4; single crystal X‐ray diffraction at low temperatures). In each structure, the five‐membered 1,3,2‐dithiazolide heterocycle possesses an envelope conformation, the N atom lying about 40 pm outside the mean plane of the S–C–C–S moiety. The metal complexes feature two‐dimensional coordination networks interwoven with O–H…O hydrogen bonds originating from the water molecules. The metal centres adopt an irregular nonacoordination formed by five sulfonyl O atoms, two N atoms and two μ₂‐bridging water molecules; each M⁺ is connected to four different anions. When NH₄⁺ is substituted for M⁺, the metal–ligand bonds are replaced by N⁺–H…O hydrogen bonds, but the general topology of the lamella is not affected. In the three structures, the lipophilic benzo groups protrude obliquely from the surfaces of the polar lamellae and display marked interlocking between adjacent layers.     

Synthesis,Structure and Characterization of Dinuclear Pentacoordinate Molybdenum(V) Complexes with Thiosemicarbazone Ligands

New dinuclear pentacoordinate molybdenum(V) complexes, [Mo₂^VO₃L₂] [L = thiosemicarbazonato ligand: C₆H₄(O)CH:NN:C(S)NHR′ and C₁₀H₆(O)CH:NN:C(S)NHR′; R′ = H, CH₃, C₆H₅) were obtained either by oxygen atom abstraction from Mo^VIO₂L with triphenylphosphine or by using [Mo₂O₃(acac)₄] in the reaction with the corresponding ligands H₂L. Crystal and molecular structure of [Mo₂O₃{C₆H₄(O)CH:NN:C(S)NHC₆H₅}₂] · CH₃CN has been determined by the single‐crystal X‐ray diffraction method.     

Ligand‐Exchange Processes on Solvated Zinc Cations: Water Exchange on [Zn(H2O)4(L)]2+⋅2 H2O (L=Heterocyclic Ligand)

The water‐exchange mechanisms of [Zn(H₂O)₄(L)]²⁺?2 H₂O (L=imidazole, pyrazole, 1,2,4‐triazole, pyridine, 4‐cyanopyridine, 4‐aminopyridine, 2‐azaphosphole, 2‐azafuran, 2‐azathiophene, and 2‐azaselenophene) have been investigated by DFT calculations (RB3LYP/6‐311+G**). The results support limiting associative reaction pathways that involve the formation of six‐coordinate intermediates [Zn(H₂O)₅(L)]²⁺?H₂O. The basicity of the coordinated heterocyclic ligands shows a good correlation with the activation barriers, structural parameters, and stability of the transition and intermediate states.     

Cyanide‐Bridged Tetranuclear REIII2FeIII2 (RE = Y,Tb, Dy) Molecular Squares with 2, 2′:6′,2′′‐Terpyridine as a Capping Ligand

Self‐assembly reaction between hydrated rare‐earth (RE) nitrates RE(NO₃)₃ · 6H₂O with K₃Fe(CN)₆ in H₂O/DMF solution by employing the tridentate ligand 2, 2′:6′,2′′‐terpyridine (terpy) as a capping ligand has yielded three cyanide‐bridged compounds [RE(terpy)(DMF)(H₂O)₂][Fe(CN)₆] · 6H₂O [RE = Y ( 1 ), Tb ( 2 ), Dy ( 3 )]. FT‐IR spectra confirmed the presence of terpy ligands and cyanide groups in compounds 1 – 3 . Single‐crystal X‐ray structural analysis indicated that these compounds are isomorphous and adopt neutral [RE₂Fe₂] molecular squares, which are further linked through hydrogen bonding interactions to generate a three‐dimensional supramolecular network. Magnetic susceptibility measurements revealed that significant single ion magnetic anisotropy dominates the properties of these compounds.     

Synthesis and Selected Reactions of Hydrazides Containing an Imidazole Moiety

The preparation of two types of imidazole derivatives bearing a hydrazide group was achieved by treatment of the corresponding esters with NH₂NH₂?H₂O in MeOH at room temperature. In the case of 4‐(ethoxycarbonyl)‐1H‐imidazole 3‐oxides 3 , hydrazides of type 1 were formed with retention of the N‐oxide structure (Scheme 1). Interestingly, due to a strong H‐bonding, no deoxygenation of the N→O function could be achieved even by treatment of 3 with Raney‐Ni. The second type, 2‐[(1H‐imidazol‐2‐yl)sulfanyl]acetohydrazides 2 , was obtained from 1H‐imidazole‐2(3H)‐thiones 4 in two steps via S‐alkylation with methyl bromoacetate, followed by treatment with NH₂NH₂?H₂O (Scheme 2). An imidazole 7 , containing both types of hydrazide groups, was prepared analogously from ethyl 2,3‐dihydro‐2‐thioxo‐1H‐imidazole‐4‐carboxylate 4d (Scheme 4). Both types of hydrazides, 1 and 2 , were transformed successfully to the corresponding acylhydrazones 8 and 9 , respectively (Scheme 5). Furthermore, it has been shown that hydrazides of type 1 are useful starting materials for the synthesis of 1,2,4‐triazole‐3‐thiones 11 and 1,3,4‐thiadiazole‐2‐amines 12 , bearing an imidazole 3‐oxide moiety (Scheme 7).     

Synthesis of Bis‐Heterocyclic 1H‐Imidazole 3‐Oxides from 3‐Oxido‐1H‐imidazole‐4‐carbohydrazides

The reaction of 1H‐imidazole‐4‐carbohydrazides 1 , which are conveniently accessible by treatment of the corresponding esters with NH₂NH₂?H₂O, with isothiocyanates in refluxing EtOH led to thiosemicarbazides (=hydrazinecarbothioamides) 4 in high yields (Scheme 2). Whereas 4 in boiling aqueous NaOH yielded 2,4‐dihydro‐3H‐1,2,4‐triazole‐3‐thiones 5 , the reaction in concentrated H₂SO₄ at room temperature gave 1,3,4‐thiadiazol‐2‐amines 6 . Similarly, the reaction of 1 with butyl isocyanate led to semicarbazides 7 , which, under basic conditions, undergo cyclization to give 2,4‐dihydro‐3H‐1,2,4‐triazol‐3‐ones 8 (Scheme 3). Treatment of 1 with Ac₂O yielded the diacylhydrazine derivatives 9 exclusively, and the alternative isomerization of 1 to imidazol‐2‐ones was not observed (Scheme 4). It is important to note that, in all these transformations, the imidazole N‐oxide residue is retained. Furthermore, it was shown that imidazole N‐oxides bearing a 1,2,4‐triazole‐3‐thione or 1,3,4‐thiadiazol‐2‐amine moiety undergo the S‐transfer reaction to give bis‐heterocyclic 1H‐imidazole‐2‐thiones 11 by treatment with 2,2,4,4‐tetramethylcyclobutane‐1,3‐dithione (Scheme 5).