Nitrogen Lone Pair Orbitals Research Articles

A Multireference Ab Initio Study of the Diradical Isomers of Pyrazine.

Three diradical pyrazine isomers were characterized using highly correlated, multireference methods. The lowest lying singlet and triplet state geometries of 2,3-didehydropyrazine ( ortho), 2,5-didehydropyrazine ( para), and 2,6-didehydropyrazine ( meta) were determined. Two active reference spaces were utilized. The complete active space (CAS) (8,8) includes the σ and σ* orbitals on the dehydrocarbon atoms as well as the valence π and π* orbitals. The CAS (12,10) reference space includes two additional orbitals corresponding to the in-phase and out-of-phase nitrogen lone pair orbitals. Adiabatic and vertical gaps between the lowest lying singlet and triplet states, optimized geometries, canonicalized orbital energies, unpaired electron densities, and spin polarization effects were compared. We find that the singlet states of each diradical isomer contain two significantly weighted configurations, and the larger active space is necessary for the proper physical characterization of both the singlet and triplet states. The singlet-triplet splitting is very small for the 2,3-didehydropyrazine ( ortho) and 2,6-didehydropyrazine ( meta) isomers (+1.8 and -1.4 kcal/mol, respectively) and significant for the 2,5-didehydropyrazine ( para) isomer (+28.2 kcal/mol). Singlet geometries show through-space interactions between the dehydocarbon atoms in the 2,3-didehydropyrazine ( ortho) and 2,6-didehydropyrazine ( meta) isomers. An analysis of the effectively unpaired electrons suggests that the 2,5-didehydropyrazine ( para) isomer also displays through-bond coupling between the diradical electrons.

Ibuprofen-thiadiazole hybrid compounds: Synthesis, vibrational analysis and molecular structure of 5-(1-(4-isobutylphenyl)ethyl)-1,3,4-thiadiazol-2-amine hydrochloride

The ibuprofen derivative 5-(1-(4-isobutylphenyl)ethyl)-1,3,4-thiadiazol-2-amine hydrochloride is prepared by via cyclization of ibuprofen with thiosemicarbazide in the presence of POCl3. The compound has been characterized by using FT-IR and multinuclear (1H and 13C) NMR spectroscopies, and elemental analysis. The molecular structure in crystalline phase has been determined by single crystal X-Ray diffraction. The compound crystallizes in the triclinic system with space group P-1 as discrete cations and chloride anions with two enantiomers present in the asymmetric unit. A full vibrational analysis of the FT-IR and FT-Raman spectra has been performed in conjunction with quantum chemical calculations. Experimental data agree with the occurrence of the thiadiazole NH protonated form in the solid phase. The observation of the ν(NN) and δ(CNN) normal modes as strong signals in the infrared and Raman spectra at 1189 (1180 cm−1) and 774 cm−1 suggests a NN bond with partial double bond character in the thiadiazole moiety, in good agreement with the computed values at the B3LYP/6-311++G(d,p) level of approximation. The NBO analysis showed that both, the sulfur lone pair and the exocyclic amine nitrogen lone pair orbitals contribute to strong resonance interactions with the adjacent π*(N2=C8) antibonding orbital of the protonated thiadiazole group.

Energy decomposition analysis of the metal-imine bond in [(CO) 4M–SB] (M = Cr, Mo, W; SB: RHC [dbnd]N–CH 2CH 2–N [dbnd]CHR)

The electronic and molecular structures of the metal-Schiff base complexes [(CO) 4M–SB] (M: Cr, Mo, W; SB: RHC N–CH 2CH 2–N CHR, R = C 6H 5, C 6F 5, Ortho-, Meta- and Para-XC 6H 4 (X = F, Cl, Br,CH 3)) have been investigated at the DFT level using the exchange correlation functional BP86. The nature of the TM−Schiff base interactions was analyzed with charge and energy decomposition methods. The octahedral equilibrium geometries have C 2v symmetry. The (CO) 4M–SB bond dissociation energies vary little for different substituents R. The calculated values indicate rather strong bonds which exhibit the trend for the different metals M = Mo ( D e = 59.8–65.4 kcal/mol) < Cr ( D e = 62.3–67.8 kcal/mol) < W ( D e = 69.9–75.8 kcal/mol). The energy decomposition analysis suggests that the (CO) 4M–SB attractive interactions come mainly from electrostatic attraction which provide ∼60% to ∆E int while ∼40% come from orbital interactions. The latter term arises mainly (∼70%) through (CO) 4M ← SB σ donation from the nitrogen lone-pair orbitals while a much smaller part (∼20%) comes from (CO) 4M→SB π backdonation. The transition metals carry large negative partial charges between −2.3 e for M = Cr and −1.1e for M = W.

Magnetic Exchange Interactions in a 2D Grid-like Copper(II) Polymer with Bridging End-on Cyanato and Pyrazine Ligands: A DFT Study

The structure of a 2D grid-like copper(II) complex [Cu<TEX>$(NCO)_2$</TEX>(pyz)](pyz=pyrazine) (1) consists of 1D chains of Cu-pyz units connected by double end-on (EO) cyanato bridges. Each Cu(II) ion has a distorted octahedral coordination, completed by the four EO cyanato and two pyrazine ligands. Magnetic interactions through EO cyanato and pyrazine bridges in 1 are discussed on the basis of DFT broken-symmetry calculations at the B3LYP level. For model dicopper(II) complexes I (bridged by cyanato) and II (bridged by pyrazine), electronic structure calculations reproduce very well the experimental couplings for the S = 1/2 ferromagnetic and antiferromagnetic exchange-coupled 2D system: the calculated exchange parameters J are +1.25 <TEX>$cm^{-1}$</TEX> and -3.07 <TEX>$cm^{-1}$</TEX> for I and II, respectively. The <TEX>$\sigma$</TEX> orbital interactions between the Cu <TEX>$x^2-y^2$</TEX> magnetic orbitals and the nitrogen lone-pair orbitals of pyrazine are analyzed from the viewpoint of through-bond interaction. The energy splitting of 0.106 eV between two SOMOs indicates that the superexchange interaction should be antiferromagnetic in II. On the other hand, there are no bridging orbitals that efficiently connect the two copper(II) magnetic orbitals in I because the HOMOs of the basal-apical NCO bridge do not play a role in the formation of overlap interaction pathway. The energy separation in the pair of SOMOs of I is calculated to be very small (0.054 eV). This result is consistent with the occurrence of weakly ferromagnetic properties in I.

Effects of Hydrogen Bonding on Vibrational Normal Modes of Pyrimidine

The effects of weak intermolecular interactions on 10 vibrational normal modes of pyrimidine are investigated by Raman spectroscopy and electronic structure computations. Hydrogen-bonded networks of water induce a shift to higher energy in certain normal modes of pyrimidine with increasing water concentration, while other modes are relatively unaffected. Pyrimidine molecules also exhibit weak C-H...N interactions and shifted normal modes upon crystallization. The selective nature of the shifting of normal modes to higher energy allows for definitive assignments of the nearly degenerate nu(8a) and nu(8b) modes with polarized Raman spectroscopy. Natural bond orbital (NBO) analyses indicate that when water molecules donate hydrogen bonds to the nitrogen atoms of pyrimidine, there is significant charge transfer from pyrimidine to water, much of which can be accounted for by substantial decreases in the populations of the nitrogen lone pair orbitals. Despite the overall decrease of electron density in pyrimidine upon complexation with water, there are concomitant changes in NBO populations that polarize the pi-electron system toward the proton acceptor N atoms, as well as contractions of the bonds associated with the N-C-N and C-C-C regions of the pyrimidine ring.

STM fingerprint of molecule–adatom interactions in a self-assembled metal–organic surface coordination network on Cu(111)

A novel approach of identifying metal atoms within a metal-organic surface coordination network using scanning tunnelling microscopy (STM) is presented. The Cu adatoms coordinated in the porous surface network of 1,3,8,10-tetraazaperopyrene (TAPP) molecules on a Cu(111) surface give rise to a characteristic electronic resonance in STM experiments. Using density functional theory calculations, we provide strong evidence that this resonance is a fingerprint of the interaction between the molecules and the Cu adatoms. We also show that the bonding of the Cu adatoms to the organic exodentate ligands is characterised by both the mixing of the nitrogen lone-pair orbitals of TAPP with states on the Cu adatoms and the partial filling of the lowest unoccupied molecular orbital (LUMO) of the TAPP molecule. Furthermore, the key interactions determining the surface unit cell of the network are discussed.

A Discrete Supramolecular Conglomerate Composed of Two Saddle‐Distorted Zinc(II)‐Phthalocyanine Complexes and a Doubly Protonated Porphyrin with Saddle Distortion Undergoing Efficient Photoinduced Electron Transfer

Porphyrins (Por) and phthalocyanines (Pc) exhibit lightharvesting efficiency for producing charge-separated states as models of the reaction center in photosynthetic bacteria and photovoltaic cells for energy conversion. The use of supramolecular assemblies to model the functionality of the reaction center is an attractive and fruitful strategy to develop photofunctional materials and devices. Porphyrins exhibit strong Soret bands around 400 to 450 nm, whereas phthalocyanines show strong Q bands around 700 to 800 nm. Thus, the combination of those two p systems can cover nearly the whole range of the visible region and can be a useful strategy for development of photofunctional materials for efficient light-energy conversion. Attempts have so far been made to synthesize covalently linked Por–Pc heterodyad molecules and construct Por–Pc heterosupramolecules. Recently, ZnPor and ZnPc have been reported to form two-dimensional arrays on gold surfaces, and the formation of a cofacial ZnPor–ZnPc coordination tetrad has also been reported. However, a crystal structure determination of a discrete supramolecular assembly composed of both Por and Pc has yet to be reported. In addition, since the Q-band absorption of Pc usually overlaps the wavelength of fluorescence of Por, energy transfer is favored over electron transfer in most heterodyads. We have developed supramolecular assemblies based on a saddle-distorted nonplanar porphyrin, dodecaphenylporphyrin (H2DPP), and its metal complexes. [11–13] The saddle distortion facilitates protonation of pyrrole nitrogen atoms to allow access to a stable diprotonated porphyrin, which can act as an electron acceptor. In addition, the saddle distortion affords higher Lewis acidity at the metal center to maintain axial coordination of ligands, as a result of poor overlap of the pyrrole nitrogen lone pair orbitals with d orbitals of the metal center. In contrast, the Zn complex of the saddle-distorted phthalocyanine 1,4,8,11,15,18,22,25-octaphenylphthalocyanine (H2OPPc) exhibits a lower oxidation potential relative to the corresponding porphyrin complex. To construct supramolecular conglomerates composed of both porphyrin and phthalocyanine in a well-defined manner, we have taken advantage of saddle distortion of both components. Herein, we report formation of a discrete supramolecular assembly composed of H4DPP 2+ and [Zn(OPPc)] connected by 4-pyridinecarboxylate (4-PyCOO ) with coordination and hydrogen bonding (Figure 1). The supramolecular conglomerate [(H4DPP){Zn(OPPc)(k-N-4-PyCOO)}2] (1) was synthesized by reaction of [H4DPP](4-PyCOO)2 (2) and Zn(OPPc) (3) in toluene. We crystallized and isolated 1 in pure form by vapor diffusion of hexanes into solution of the mixture in toluene. X-ray crystallography of 1 unambiguously established its structure (Figure 2a).

Generalized van Vleck Perturbation Theory (GVVPT2) Study of the Excited States of Benzene and the Azabenzenes

Generalized van Vleck perturbation theory (GVVPT2) for molecular electronic structures is applied to examine the azabenzene series: benzene, pyridine, pyrazine, symmetric triazine and symmetric tetrazine. The spectra of azabenzenes are complex with large numbers of excited states at low energies comprising n --> pi* and pi --> pi* excited states and also doubly excited states of the n,n --> pi*,pi* type. The calculations are complicated due to strong correlation effects in the nitrogen lone-pair orbitals and the pi electrons. This study is the first to use GVVPT2 on conjugated systems. Comparison is made with experimental data and complete active space second-order perturbation theory, equation of motion coupled cluster and similarity transformed equation of motion coupled cluster theory data. Using polarized valence double split basis sets for benzene and pyrazine (cc-pVDZ) and pyridine (ANO-S) and polarized triple split basis sets (ANO-L) for triazine and tetrazine, the n --> pi* and pi --> pi* states are computed with an average error of 0.28 eV in comparison with available experimental data.

A HeI photoelectron spectroscopy and theoretical study of 2,6-dichloropyrazine, 2,3-dichloropyrazine, 4,6-dichloropyrimidine and 3,6-dichloropyridazine

The electronic structures of C 4H 2Cl 2N 2 isomers have been studied by HeI photoelectron spectroscopy (PES) combined with the outer valence Green’s function (OVGF) calculations at 6-311++G(d,p) basis sets. The vertical first ionization potentials for 2,6-dichloropyrazine, 2,3-dichloropyrazine, 4,6-dichloropyrimidine and 3,6-dichloropyridazine are determined to be 9.93, 9.89, 10.45 and 10.07 eV, respectively, and the PE spectra were assigned based on molecular orbital analysis and by comparison with related compounds. The effects of chlorine substituent and different positions of nitrogen atoms in these C 4H 2Cl 2N 2 isomers have been carefully analyzed by comparing the C 4H 2Cl 2N 2 isomers with their matrixes (pyrazine, pyridazine, pyrimidine). The inductive effect of chlorine substituent leads to the stabilization of the nitrogen lone pair orbitals. The resonance effect predominates over the inductive effect, and the consequence is the destabilization of the π orbitals. Owing to the different positions, the effects of nitrogen atoms are different and lead to the different sequence of π orbitals.

Ionization potentials of nitriles — Photoelectron spectra of succinonitrile and glutaronitrile

The He(I) photoelectron spectra of succinonitrile (1) and glutaronitrile (2), both with extensive overlap of ionization bands in the low-energy region, are reported. To assign ionizations, we studied the conformational behaviour and resulting ionization energy dependence of 1 and 2 computationally with the B3LYP/6-31+G(d) model chemistry based on the fact that it reliably reproduces the ionization potentials of eleven mono- and di-nitriles, both saturated and unsaturated. The correlation of proton affinities with observed ionization potentials of 1, 2, and malononitrile establishes the orbital sequence of four C≡N π orbitals followed by two nitrogen lone pair orbitals as the highest occupied molecular orbitals for all three compounds.Key words: photoelectron spectrum, ionization potential, conformational dependence, nitrile, DFT.

Molecular and electronic structure of Tröger’s bases

Abstract The equilibrium conformations of Troger’s base and two new analogues were investigated at the MP2/6-31G(d, p) ab initio level of theory. The electronic structure of these rigid yet sharply folded molecules was investigated by means of their spectroscopic properties. The 13 C -NMR chemical shifts, calculated by the CSGT (continuous set of gauge transformations) formalism with the HF-B3LYP/6-311+G(2d, p) hybrid functional model, were fairly consistent with NMR observations. The He(I) photoelectron spectra were measured and interpreted by means of ab initio many-body OVGF (outer valence Green’s function) calculations. The theoretical results satisfactorily reproduced the energies and splittings of the uppermost bands, associated with the two nitrogen lone pair orbitals and the phenyl π orbitals. Electron transmission spectroscopy, with the support of calculated π ∗ virtual orbital energies, was employed to characterize the empty molecular levels. The 2,3,8,9-tetramethoxy analogue of Troger’s base exhibits a complex conformational situation. Whereas its NMR spectrum indicates a predominance of trans–trans arrangements of the two o-dimethoxy groups in CDCl3 solution, its photoelectron spectrum should be interpreted in terms of a mixture of the trans–trans and twisted conformers in the gas phase.

On the structure and spectroscopic properties of bispidine, N, N′-dimethylbispidine and a bis-bispidine macrocycle

The equilibrium conformations of bispidine and its N, N ′-dimethyl derivative were investigated with the ab initio MP2 formalism and the density functional theory (DFT) ansatz B3LYP. For bispidine, the chair–chair (cc) ( exo, endo) is the most stable conformer. On the contrary, for its N, N ′-dimethyl derivative, the energy difference between the cc and chair–boat (cb) conformers is small, allowing for conformational mobility of the bicyclo rings. For tetraaza-macrocycle with four nitrogen lone pair orbitals (LPOs) pointing into the molecular cavity, the C 2h structure with stepped ethylene bridges is preferred over the twisted structure of D 2 symmetry. Mono- and di-protonated forms of this base are characterized by intramolecular asymmetric hydrogen bonds. All the theoretical conformational predictions are consistent with the available experimental results. The NMR chemical shifts, calculated by the continuous set of gauge transformations (CSGT) formalism with the DFT/B3LYP method, are fairly consistent with NMR observation. The He(I) photoelectron (PE) spectra were measured and assigned by means of ab initio outer valence Green's function (OVGF) calculations. The predominance of the lowest energy conformation of bispidine and tetraaza-macrocycle is supported by the spectroscopic results. The conformational situation for N, N ′-dimethyl-bispidine is more complex. Whereas its NMR spectrum indicates a predominance of the cc conformer in THF-d 8 solution, the vibrational and PE spectra should be interpreted in terms of a mixture of the cc and cb conformers in the neat liquid and gas-phase.

On the structure and spectroscopic properties of the cis- and trans-isomers of cyclen- and cyclam-glyoxal

The equilibrium structures of the cis- and trans-isomeric derivatives of the cyclen and cyclam condensation products with glyoxal were investigated with the density functional theory (DFT) model B3LYP/6-31G(d,p). According to calculations, the trans-fused condensation product is more stable than the cis product by 2kcalmol−1 in the case of cyclam. For cyclen, the stability order is instead inverted, the cis-fusion being much more preferred by 9.8kcalmol−1. The 13C NMR chemical shifts were recorded and analyzed by means of continuous set of gauge transformations (CSGT) calculations performed with the HF-B3LYP/6-311+G(2d,p) hybrid functional model. The He(I) photoelectron spectra were measured and interpreted by means of ab initio outer valence Green function (OVGF) calculations, which give a consistent, overall description of the uppermost bands, associated with the four nitrogen lone pair orbitals.

On the structure and spectroscopic properties of free and protonated adamanzanes

The equilibrium structures of a selection of tetraazatricyclo-alkanes, containing a small, medium or macro-intramolecular cavity, were investigated with the density functional theory ansatz B3LYP/6-31G+(d,p). The four nitrogen lone pair orbitals (LPOs) are outwardly oriented in the smallest two members of the class (hexamethylenetetramine and next homologue), while they point towards the inside in the larger cages (hexaethylenetetramine and next homologues). These conformational arrangements are maintained in the monoprotonated derivatives, whose theoretical structural models are consistent with evidence obtained from IR, NMR and X-ray spectroscopic data. The case of inside-coordination is characterized by a relatively strong five-centre intramolecular hydrogen bond, which involves asymmetric protonation at one nitrogen and nearly equivalent interaction with the other three unprotonated nitrogens. The NMR chemical shifts, calculated by the continuous set of gauge transformations formalism with the B3LYP/6-311+G(2d,p) method, are fairly consistent with NMR observation, in particular for the very low-field signal of the encapsulated proton. The electronic structure of the free bases was also studied by means of ab initio outer valence Green function calculations, which give a consistent, overall description of the different manifolds of photoionization, associated with the nitrogen LPOs.

A study of the molecular structure and spectroscopic properties of polycyclic polyaza-compounds with diamond-lattice conformations

The equilibrium structures of a selection of polycyclic polyaza-compounds, characterized by diamond-lattice arrangements and conformational flexibility, were investigated with the density functional method B3LYP/6-31G(d,p). The 10- or 12-membered central ring in two tricyclic tetraaza-compounds, formally derived from tricyclo-hexadecane and tricyclo-octadecane, respectively, prefers a “square” geometry. The 16- or 24-membered central ring in nonacyclic octaaza-compounds, related to pentacyclo-octacosane, and in nonacyclic dodecaaza- and hexadecaaza-compounds, both related to nonacyclo-tetratetracontane, can instead adopt two or three alternative conformations with “square” or “rectangular” geometry. The theoretical structural models are consistent with evidence from NMR and X-ray spectroscopy. In addition, they provide a satisfactory account of the 13C NMR chemical shifts, which were predicted with a continuous set of gauge transformation calculations performed with the B3LYP/6-311+G(2d,p) formalism. The electronic structure was also studied by means of ab initio outer valence Green function calculations, which give a consistent, overall description of the different manifolds of photoionizations, associated with the nitrogen lone pair orbitals. Electron transmission spectroscopy was employed to detect the low-lying temporary anion states of some representative compounds. © 2001 John Wiley & Sons, Inc. Int J Quant Chem, 2001

THE COORDINATION OF AMINOPHOSPHONATES TO CHROMIUM(III)

Abstract Attempts to induce coordination of the amine group in aminophosphonate complexes of chromium(III) were unsuccessful. However, N-phosphonomethylglycine forms a stable complex in which the amine, the carboxylate, and one phosphonate oxygen are coordinated. A similarly coordinated complex of N,N-diphosphonomethylglycine is unstable and reverts to an isomer in which the amine group is free. Several potential reasons for the failure of the amine group to coordinate in aminophosphonates in contrast to analogous aminocarboxylate complexes were explored. Steric factors appear unimportant. Contributing factors are (1) there is a driving force for the transfer of a proton from a phosphonate oxygen to the amine, establishing a preference for oxygen coordination; (2) coordination of the phosphonate end of an aminophosphonate appears to lower the basicity of the amine group much more than carboxylate coordination in an aminocarboxylate; (3) in an aminophosphonate the nitrogen lone pair orbitals lie lower in e...

Effects of isolobal substitution in cyclopentadienyl ligands: The azacyclopentadienyl system C 4R 4N. Comparative photoelectron spectra of the tetra-tert-butyl ferrocene derivatives

The He(I) photoelectron (PE) spectra of tetra-tert-butylferrocene ( 7) and tetra-tert-butyl-diazaferrocene ( 8) are reported. A comparison with the PE spectrum of ferrocene and pyridine reveals that (i) the hyperconjugative donor effect of a tert-butyl group is about twice that of a methyl or trimethylsilyl group, (ii) the electron-withdrawing potential of the nitrogen atom is very similar to that of the phosphorus atom in diphosphaferrocenes, (iii) there is no significant interaction between the nitrogen lone-pair orbitals. An explanation for the marked instability of diazaferrocenes compared to stable diphosphaferrocenes is offered. The PE spectra of 7 and 8 could be reproduced with an INDO/S theoretical calculation.

Compounds with bridgehead nitrogen. Part 72—NMR spectra and stereochemistry of 8,9,10,11,11a,11b,12,13‐octahydro‐7aH‐quino [1,2‐c][1,3]benzoxazines and perhydropyrido [1,2‐c][1,3]benzoxazines. NMR chemical shifts of methylene group protons adjacent to a nitrogen atom

AbstractThe positions of conformational equilibria in the four diastereoisomers of 8,9,11,11a,11b,12,13‐octahydro‐7aH‐quino [1,2‐c] [1,3] benzoxazines were investigated using 13C and 1H NMR spectroscopy. Comparison of the NMR chemical shifts of these isomers with those in the corresponding isomers of perhydropyrido [1,2‐c] [1,3]benzoxazine shows the effect on NMR shifts of fusion of the aromatic ring on to the fully saturated system. The Δδ values are discussed in terms of degree of overlap of the nitrogen lone pair orbitals with the aromatic π‐system.

Infrared reflection‐absorption spectroscopy of polyacrylonitrile on copper and aluminium surfaces

AbstractInfrared reflection‐absorption spectroscopy has been used to study the chemical structure of thin films of pyrolyzed polyacrylonitrile (PAN) on copper and aluminium surfaces. The formation of a conjugated CCC backbone occurs at temperatures as low as 200°C for PAN on copper, whereas the same reaction on aluminium requires pyrolysis at 300°C in order to be completed. These temperatures are, respectively, about 200 and 100°C lower than those previously reported for bulk PAN. Pyrolysis of PAN on copper at 200°C also results in diffusion of copper atoms (ions) into the polymer network followed by Cu(I)N°C complexing. Conclusive evidence is obtained for end‐on coordination through nitrogen lone pair orbitals of the CN groups. We propose a chemical structure of PAN on copper that is different to that in the bulk and on aluminium.

Transport and optical properties of the hydrazine intercalation complexes of TiS2, TiSe2and ZrS2

The authors have performed weight-gain resistivity Hall effect and room-temperature optical transmission measurements on the layered-structure group IV transition-metal dichalcogenides, TiS2, TiSe2 and ZrS2 and on there hydrazine (N2H4) intercalation complexes. They find good metallic behaviour for the intercalated compounds, with room-temperature carrier concentrations of the order of 1022cm-3. This increase in carrier concentration over that in the pristine materials is explained in terms of a charge transfer process from the intercalated hydrazine molecules to the 'd' band of the host, within the framework of a rigid-band model. The mechanism of the charge transfer process is discussed and is thought to be through covalent bonding between the nitrogen lone-pair orbitals of the hydrazine molecules and some host layer states which are probably the chalcogen 'p' states. Apart possibly from the hydrazine intercalation complexes of ZrS2, which show a weak anomaly at about 275 K in the resistivity data, no firm evidence has been found for any charge-density-wave distortions in these intercalation complexes.