Manifestation of stereoelectronic effects on the calculated carbon-hydrogen bond lengths and one bond (1)J(C-H) NMR coupling constants in cyclohexane,six-membered heterocycles,and cyclohexanone derivatives

Cyclohexane (1), oxygen-, sulfur-, and/or nitrogen-containing six-membered heterocycles 2-5, cyclohexanone (6), and cyclohexanone derivatives 7-16 were studied theoretically [B3LYP/6-31G(d,p) and PP/IGLO-III//B3LYP/6-31G(d,p) methods] to determine the structural (in particular C-H bond distances) and spectroscopic (specifically, one bond (1)J(C-H) NMR coupling constants) consequences of stereoelectronic hyperconjugative effects. The results confirm the importance of n(X) --> sigma*(C-H)(app) (where X = O, N), sigma(C-H)(ax) --> pi*(C=O), sigma(S-C) --> sigma*(C-H)(app), sigma(C-S)-->sigma*(C-H)(app), beta-n(O) --> sigma*(C-H), and sigma(C-H) --> sigma*(C-H)(app) hyperconjugation, as advanced in previous theoretical models. Calculated r(C-H) bond lengths and (1)J(C-H) coupling constants for C-H bonds participating in more than one hyperconjugative interaction show additivity of the effects.     

Transformations of griseofulvin in strong acidic conditions--crystal structures of 2'-demethylgriseofulvin and dimerized griseofulvin

The structure of griseofulvic acid, C16H15ClO6, at 100 K has orthorhombic (P2(1)2(1)2) symmetry. It is of interest with respect to biological activity. The structure displays intermolecular O-H...O, C-H...O hydrogen bonding as well as week C-H...pi and pi...pi interactions. In strong acidic conditions the griseofulvin undergoes dimerization. The structure of dimerized griseofulvin, C34H32C12O12 x C2H6O x H2O, at 100 K has monoclinic (P2(1)) symmetry. The molecule crystallized as a solvate with one ethanol and one water molecule. The dimeric molecules form intermolecular O-H...O hydrogen bonds to solvents molecules only but they interact via week C-H...O, C-H...pi, C-Cl...pi and pi...pi interactions with other dimerized molecules.     

Silver(I) complexes in coordination supramolecular system with bulky acridine-based ligands: syntheses, crystal structures, and theoretical investigations on C-H...Ag close interaction

In our efforts to investigate the coordination architectures of transition metals and organic ligands with tailored structures, we have prepared two structurally related rigid bulky acridine-based ligands, 9-[3-(2-pyridyl)pyrazol-1-yl]- acridine (L(1)) and 9-(1-imidazolyl)acridine (L2), and synthesized and characterized four of their Ag(I) complexes, {[AgL1](ClO4)}2 (1), {[AgL1](NO3)}2 (2), [AgL2(2)](ClO4) (3), and {[(Ag3L2(3))(NO3)](NO3)2(H2O)}(infinity) (4). The single-crystal X-ray diffraction analysis shows that the structures of 1 and 2 are similar to each other, with the two intramolecular Ag(I) centers of each complex being encircled by two L1 ligands; this forms a unique boxlike cyclic dimer, which is further linked to form one-dimensional (1D) chains of 1 and a two-dimensional (2D) network of 2 by intermolecular face-to-face pi...pi stacking and/or weak C-H...O hydrogen-bonding interactions, respectively. 3 has a mononuclear structure, which is further assembled into a 2D network via intermolecular Ag...O and pi...pi stacking weak interactions. 4 possesses two different 1D motifs that are further interlinked through interlayer face-to-face pi...pi stacking and Ag...O weak interactions, resulting in a 2D network. It is worth noting that one of the interesting structural features of 1, 2, and 4 is the presence of obvious C-H...M hydrogen-bonding interactions between the Ag centers and some acridine ring H atoms identified by X-ray diffraction on the basis of the van der Waals radii. Furthermore, as a representative example, full geometry optimization on the basis of the experimental structure, the natural bond orbital (NBO), and topological analysis of 1 were carried out by DFT and AIM (Atoms in Molecules) calculations. The total C-H...Ag interaction energy in 1 is estimated to be about 14 kJ/mol. Therefore, this work offers three new rare examples (1, 2, and 4) that exhibit C-H...Ag weak interactions, in which the N donors of the acridine rings coordinate to Ag(I) ions. Also, these results strongly support the existence of C-H...Ag close interactions and allow us to have a better understanding of the nature of such interactions in the coordination supramolecular systems.     

Exploring the lower limit in hydrogen bonds: analysis of weak C-H...O and C-H...pi interactions in substituted coumarins from charge density analysis

Experimental electron densities in coumarin, 1-thiocoumarin, and 3-acetylcoumarin have been analyzed based on the X-ray diffraction data at 90 K. These compounds pack in the crystal lattice with weak C-H...O and C-H...pi interactions, and variations in charge density properties and derived local energy densities have been investigated in the regions of intermolecular interactions. Theoretical charge density calculations on crystals using the B3LYP/6-31G* method show remarkable agreement with the derived properties and energy densities from the experiment. The intermolecular interactions follow an exponential dependence of electron density and energy densities at the bond critical points. The Laplacian follows a "Morse-like" dependence on the length of the interaction line. Based on the set of criteria defined using the theory of "atoms in molecules", it has become possible to distinguish between a hydrogen bond (C-H...O) and a van der Waals interaction (C-H...pi). This has resulted in the identification of a "region of overlap" in terms of electron densities, energy densities, and mutual penetration of the hydrogen and acceptor atoms with respect to the interaction length. This approach suggests a possible tool to distinguish between the two types of interactions.     

Roles of C-H...O=S and pi-stacking interactions in the 2-bromoacrolein complex with N-tosyl-(S)-tryptophan-derived oxazaborolidinone catalyst

[structures: see text] Ab initio and density functional calculations were employed to examine the structures and binding energies of various complexes between 2-bromolacrolein and N-tosyl-(S)-tryptophan-derived B-butyl-1,3,2-oxazaborolidin-5-one (NTOB), a catalyst commonly used for Diels-Alder reactions. Our calculations show that the chiral oxazaborolidinone catalyst serves as a tridentate complexation agent via B...O donor-acceptor, C-H...O hydrogen-bonded, and pi-stacking interactions. The most stable complex (1TS) is predicted to have a binding energy of -93 kJ mol(-1) (deltaG(298) = -29 kJ mol(-1)). The formyl C-H...O hydrogen bond and pi-stacking interaction are the key factors governing the relative stabilities of the four acrolein-NTOB complexes examined. The calculated structure and binding properties of 1TS are consistent with the experimental results on the absorption spectrum of the acrolein-NTOB complex and the effects of substituents on the reactivity of Diels-Alder reactions. 1TS differs from Corey's proposed model of transition-state assembly in two aspects: (1) it involves the s-trans-acrolein and (2) it favors a C-H...O interaction via the sulfonyl oxygen (C-H...O=S), rather than the ring oxygen (C-H...O-B). This calculated structure of the acrolein-catalyst complex provides an alternate explanation of the origin of stereoselectivity in the NTOB-catalyzed Diels-Alder reactions.     

Saturated hydrocarbon-benzene complexes: theoretical study of cooperative CH/pi interactions

High-level ab initio calculations at the CCSD(T)/aug-cc-pVTZ//MP2/aug(d,p)-6-311G(d,p) level were employed to investigate the cooperative CH/pi effects between the pi face of benzene and several modeled saturated hydrocarbons, propane, isobutane, cyclopropane, cyclobutane, cyclopentane, cyclohexane, cyclopentane, cyclooctane, and bicyclo[2.2.2]octane. In all cases, multiple C-H groups (2-4) are found to interact with the pi face of benzene, with one C-H group pointing close to the center of the benzene ring. The geometries of these complexes are governed predominantly by electrostatic interaction between the interacting systems. The calculated interaction energies (10-14 kJ mol(-1)) are 2-3 times larger than that of the prototypical methane-benzene complex. The trends of geometries, interaction energies, binding properties, as well as electron-density topological properties were analyzed. The calculated interaction energies correlate well with the polarizabilities of the hydrocarbons. AIM analysis confirms the hydrogen-bonded nature of the CH/pi interactions. Significant changes in proton chemical shift and stretching frequency (blue shift) are predicted for the ring C-H bond in these complexes.     

Magnitude and nature of interactions in benzene-X (X=ethylene and acetylene) in the gas phase: significantly different CH/pi interaction of acetylene as compared with those of ethylene and methane

The accurate interaction energies of the CH/pi interaction in the benzene-X clusters (X = ethylene and acetylene) were experimentally and theoretically determined. Two-color multiphoton ionization spectroscopy was applied, and the binding energies in the neutral ground state of the clusters were evaluated from the dissociation threshold measurements of the cluster cations. The experimental binding energies of the clusters (D0) were 1.4+/-0.2 and 2.7+/-0.2 kcal/mol, respectively. Estimated CCSD(T) interaction energies for the clusters at the basis set limit (De) were 2.2 and 2.8 kcal/mol, respectively. Calculated D0 values (1.7 and 2.4 kcal/mol, respectively) are close to the experimental values. Large electron correlation contributions (Ecorr=-3.6 and -2.8 kcal/mol, respectively) show that dispersion is the major source of the attraction in both clusters. The electrostatic interaction in the ethylene cluster is very small (-0.38 kcal/mol), as in the case of the benzene-methane cluster, whereas the electrostatic interaction in the acetylene cluster is large (-1.70 kcal/mol). The shifts of the S1-S0 transition also suggest that the ethylene cluster is a van der Waals-type cluster, but the acetylene cluster is a pi-hydrogen-bonded cluster. The nature of the CH/pi interaction of the "activated" alkyne C-H bond is significantly different from that of the "nonactivated" (or typical) alkane and alkene C-H bonds.     

Rapid and accurate evaluation of the binding energies and the individual N-H···O=C, N-H···N, C-H···O=C, and C-H···N interaction energies for hydrogen-bonded peptide-base complexes

The binding energies of thirty-six hydrogen-bonded peptide-base complexes, including the peptide backbone-ase complexes and amino acid side chain-base complexes, are evaluated using the analytic potential energy function established in our lab recently and compared with those obtained from MP2, AMBER99, OPLSAA/L, and CHARMM27 calculations. The comparison indicates that the analytic potential energy function yields the binding energies for these complexes as reasonable as MP2 does, much better than the force fields do. The individual N H…O=C, N H…N, C H…O=C, and C H…N attractive interaction energies and C=O…O=C, N H…H N, C H…H N, and C H…H C repulsive interaction energies, which cannot be easily obtained from ab initio calculations, are calculated using the dipole-dipole interaction term of the analytic potential energy function. The individual N H…O=C, C H…O=C, C H…N attractive interactions are about 5.3±1.8, 1.2±0.4, and 0.8 kcal/mol, respectively, the individual N H … N could be as strong as about 8.1 kcal/mol or as weak as 1.0 kcal/mol, while the individual C=O…O=C, N H…H N, C H…H N, and C H…H C repulsive interactions are about 1.8±1.1, 1.7±0.6, 0.6±0.3, and 0.35±0.15 kcal/mol. These data are helpful for the rational design of new strategies for molecular recognition or supramolecular assemblies.     

Pointers toward the occurrence of C-F...F-C interaction: Experimental charge density analysis of 1-(4-fluorophenyl)-3,6,6-trimethyl-2-phenyl-1,5,6,7-tetrahydro-4H-indol-4-one and 1-(4-fluorophenyl)-6-methoxy-2-phenyl-1,2,3,4-tetrahydroisoquinoline

A charge density study of crystalline 1-(4-fluorophenyl)-3,6,6-trimethyl-2-phenyl-1,5,6,7-tetrahydro-4H-indol-4-one (A) and 1-(4-fluorophenyl)-6-methoxy-2-phenyl-1,2,3,4-tetrahydroisoquinoline (B) has been carried out using high-resolution X-ray diffraction data collected at 113(2) K. Weak intermolecular interactions of the type C-H...O, C-H...pi, and pi...pi hold the molecules together in the crystal lattice along with interactions of the type C-H...F and unusual C-F...F-C examined via charge density analysis. The topological features are evaluated in terms of Bader's theory of atoms in molecules through the first four criteria of Koch and Popelier. The C-F...F-C contact is observed to be across the center of symmetry in B and not in A, and further, this interaction appears to possess a certain correlation with the electron density properties at the critical point which suggests that such an interaction fits into the hierarchy of weak interactions.     

Preparation, solid-state characterization, and computational study of a crown ether attached to a squaramide

[structure: see text] Crystals of a disecondary squaramide covalently linked to a crown ether presents a great variety of inter- and intramolecular nonbonded interactions including C-H/pi contacts, C-H...O and N-H...O hydrogen bonds, and pi-pi stacking between squaramide rings. Latter interaction, the stacking between squaramide rings, can be considered as an experimental evidence for the proposed aromaticity of squaramide when it is forming hydrogen bonds, either as acceptor or donor.     

Origin of the attraction in aliphatic C-H/pi interactions: infrared spectroscopic and theoretical characterization of gas-phase clusters of aromatics with methane

An attractive intermolecular interaction between an aliphatic C-H bond and a pi-electron system (C-H/pi interaction) was characterized on the basis of infrared spectroscopy and high level ab initio calculations. Infrared spectroscopy was applied to several isolated methane clusters with benzene, toluene, p-xylene, mesitylene, and naphthalene in the gas phase, and the spectral changes of the C-H stretch bands in the methane moiety upon the cluster formation were observed. In the theoretical approach, interaction energies of the clusters were evaluated by high-level ab initio calculations. The forbidden symmetric C-H stretch transition weakly appeared in the IR spectra of the clusters, and it confirmed the small deformation of the methane moiety from the T(d)() symmetry, which was predicted by the ab initio calculations. On the other hand, the degenerated asymmetric C-H stretch band showed complicated splitting, which is qualitatively interpreted by a hindered rotor model. Low-frequency shifts upon the cluster formation were seen in the symmetric C-H stretch frequency, though the magnitude of the shifts was extremely small and no clear correlation with the interaction energy was found. On the other hand, the size of the calculated interaction energy well correlates with the polarizability of aromatics. The S(1)-S(0) electronic transition of the aromatic moiety was also observed, and it showed low-frequency shifts upon cluster formation. These results support the dominance of the dispersion interaction over the electrostatic and charge-transfer terms in the aliphatic C-H/pi interaction.     

Characterizing the properties of the N7,N9-dimethylguaninium chloride ion pairs: prospecting for the design of a novel ionic liquid

The structures, infrared spectra, and electronic properties of the N7,N9-dimethylguaninium chloride have been studied. The interaction of one cation with one to four Cl anions and one Cl anion with two cations were investigated. Fifteen stable conformers are obtained. It is found that there are four acidic regions in the vicinity of the guaninium cations. In these regions, the cation could H-bond with one to three Cl anions but no more than three nearest anions. One Cl anion could H-bond with two cations. Additionally, evidence of a Cl...pi interaction between the anion and cation is observed. Among these structures, one cation interaction with two anions and two cations interaction with one anion have the larger interaction energies than the other series. Natural bond orbital analyses and molecular orbitals reveal that the charge transfer from anion(s) to the cation(s) occurs mainly through either the Cllp --> sigma C-H, Cllp --> sigma N-H, or Cllp --> pi C8-N7 interactions. The interaction between Cl and sigma (C/N-H) or pi C-N produces a small bond order. This indicates that the Cl...H (Cl...pi) interaction exhibits a weak covalent character and suggests a strong ionic H-bond (Cl...pi bond). What's more, formation of Cl...H/Cl...pi bond decreases the bond order of the associated C/N-H bond or C8-N7 bond. In addition, examination of vibrational spectrum of each conformer explains the origin of H-bonding character.     

Synthesis and characterization of a tripodal amide ligand and its binding with anions of different dimensionality

Synthesis and crystal structure of a tren-based amide, L(1), N,N',N'-tris[(2-amino-ethyl)-3-nitro-benzamide] is reported. The crystallographic results show intramolecular hydrogen bonding and aromatic pi...pi stacking among tripodal arms which prevent opening of the receptor cavity. Intermolecular hydrogen bonding in L1 generates the sheetlike network in the solid state. The structural aspects of binding halides (1 and 2), nitrate (3), perchlorate (4), and hexafluorosilicate (5) with the protonated L1 are examined crystallographically. Protonation at the apical nitrogen of L1 in the presence of anions shows a structural transformation from sheet to bilayer network. Anion binding with multiple receptor units is observed via amide N-H...anion and aryl C-H...anion hydrogen-bonding interactions in all the complexes. The aryl group having nitro functionality that contributes to anion binding in complexes 1-5 through CH...anion interactions (either para or meta to nitro C-H) is noteworthy. These studies also show higher anion coordination of chloride (8) and hexafluorosilicate (14) with L1H+.     

Carboxylic acid clathrate hosts of Diels-Alder adducts of phencyclone and 2-alkenoic acids. Role of bidentate C-H ... O hydrogen bonds between the phenanthrene and carbonyl groups in host-host networks

Carboxylic acid host compounds (3) having a phenanthrene-condensed bicyclo[2.2.1]hept-2-en-7-one skeleton have been synthesized by the [4 + 2]pi cycloaddition of phencyclone (1a) with 2-alkenoic acids (2) and their inclusion behavior was investigated. The endo [4 + 2]pi cycloadducts (3) enclathrated alcohols and ethers besides aromatics and ketones. The X-ray crystallographic analysis of the inclusion compound (3ac-dioxane) of the endo [4 + 2]pi cycloadduct (3ac) of phencyclone and trans 2-butenoic acid (2c) indicated that dioxanes are located at the opposite side of the bridged carbonyl of the bicyclo[2.2.1]hept-2-en-7-one moiety, in which the O-H...O and C-H...O hydrogen bonds play an important role in the inclusion complex formation. Similarly, a pair of 3-pentanone molecules were included in the endo [4 + 2] pi cycloadduct (3ae) of 1a and cinnamic acid (2e). In both cases, the hosts are linked by the edge-to-face interaction between the phenanthrene and phenyl rings and the "bidentate" C-H...O hydrogen bonds between the phenanthrene-ring hydrogens and the bridged carbonyl or the carboxylic carbonyl group. The endo [4 + 2] pi cycloadduct (3bl) of tetracyclone (1b) and acrylamide (2l) also showed a wide-range inclusion behavior, in which alcohols are included by making a hydrogen-bond loop with the amide groups. The inclusion behavior of the carboxylic acid Diels-Alder hosts is discussed on the basis of the single crystal X-ray analysis, thermal analysis and semiempirical molecular orbital calculation data.     

Understanding the structural properties of a homologous series of bis-diphenylphosphine oxides

A homologous series of bis-diphenylphosphine oxides (C6H5)2PO(CH2)(n)PO(C6H5)2 (with n = 2-8; denoted 2-8] have been investigated to explore the effects of a range of competing and cooperative intermolecular and intramolecular interactions on the structural properties in the solid state. The important factors influencing the structural properties include intramolecular aspects such as the conformation of the aliphatic chain and the intramolecular interaction between the two P=O dipoles in the molecule, and intermolecular aspects such as long-range electrostatic interactions (dominated by the arrangement of the P=O dipoles), C-H...O interactions, C-H...pi interactions and pi...pi interactions. Compounds 3 and 5 could be crystallized only as solvate co-crystals (3 water and 5 x (toluene)2], whereas the crystal structures of all the other compounds contain only the bis-diphenylphosphine oxide molecule. The crystal structures have been determined from single-crystal X-ray diffraction data, with the exception of 7 (which has been determined here from powder X-ray diffraction data) and 4 (which was known previously). The compounds with even n represent a systematic structural series, exhibiting characteristic, essentially linear P=O...P=O...P=O dipolar arrays, together with C-H...O and C-H...pi interactions. For the compounds with odd n, on the other hand, uniform structural behaviour is not observed across the series, although certain aspects of these crystal structures contribute in a general sense to our understanding of the structural properties of bis-diphenylphosphine oxides. Importantly, for the compounds with odd n, there is "frustration" with regard to the molecular conformation, as the preferred all-anti conformation of the aliphatic chain gives rise to an unfavourable parallel alignment of the two P=O dipoles within the molecule. Clearly the importance of avoiding a parallel alignment of the P=O dipoles becomes greater as n decreases. Local structural aspects (investigated by high-resolution solid-state 31P NMR spectroscopy) and thermal properties of the bis-diphenylphosphine oxide materials are also reported.     

Symmetry switching of the fluorescent excited state in alpha,omega-diphenylpolyynes

By using MO calculations based on DFT, absorption, and fluorescence spectroscopy, we have comprehensively studied the low-lying excited singlet states of alpha,omega-diphenylpolyynes (DPY) having 1-6 triple bonds. The a(g) vibrational modes of the C(triple bond)C stretching and of the phenyl ring motion were observed in the fluorescence spectra of diphenylacetylene and 1,4-diphenylbutadiyne. On the other hand, in the fluorescence spectra of the long DPY with the triple-bond number (N) more than two, the phenyl ring motion with a(g) symmetry disappeared and the b(1g) modes of the phenyl ring twisting (approximately 400 cm(-1)) and of the C-H bending (approximately 900 cm(-1)) were detected. The observed fluorescent states of DPY with N < or = 2 and N > or = 3 are assigned to the 1(1)B(1u) (pi(x)pi(x*)) and 1(1)A(u) (pi(x)pi(y*) and/or pi(y)pi(x*)) states, respectively, based on the vibronic structures, the relatively short lifetimes, and the solvatochromic shifts of the fluorescence spectra. Not only the allowed transition of 1(1)B(1u) <-- S(0) but also the forbidden transition of 1(1)A(u) <-- S(0) was detected in the fluorescence excitation spectra of the long DPY with N > or = 3. The low-lying excited state with A(u) symmetry is characteristic in polyyne, which does not exist in polyene. The oscillator strength (f) of the first absorption band in DPY decreases with an increase in N, which is the opposite behavior of the all-trans-alpha,omega-diphenylpolyenes. The N-dependence of the f value is understood by the configuration interaction between the 1(1)B(1u) and 2(1)B(1u) (pi(y)pi(y*)) states, which is consistent with the reduction of the nonlinear optical response of polyyne.     

Characteristics of antiaromatic ring pi multi-hydrogen bonds in (H2O)n-C4H4 (n = 1, 2) complexes

By counterpoise-corrected optimization method, the six antiaromatic ring pi multi-hydrogen bond structures with diversiform shapes for (H2O)n-C4H4 (n = 1,2) have been obtained at the MP2/aug-cc-pVDZ level. At the CCSD(T)/aug-cc-pVDZ level, the interaction energy obtained mainly depends on the numbers of H2O and fold numbers of the pi multi-hydrogen bond. The interaction energy order is -2.342 (1a with pi mono-hydrogen) < -2.777 (1b with pi bi-hydrogen) < -4.683 (2a with pi bi-hydrogen) < -4.734 (2b with pi tri-hydrogen) < -4.782 (2c with pi tri-hydrogen) < -5.009 kcal/mol (2d with pi tetra-hydrogen bond). Strangely, why is the interaction energy of the pi bi-hydrogen bond in 1b close to that of the pi mono-hydrogen bond in 1a (their difference is only 15.7%)? The reason is that a pi-type H-bond (as an accompanying interaction) between two lone pairs of the O-atom and a near pair of H-atoms of C4H4 exists shoulder by shoulder in structures 1a, 2a, 2b, and 2c and contributes to the interaction energy. Another accompanying interaction, a repulsive interaction between the pi H-bond (using the H-atom(s) of H2O) and the near pair of H-atoms of C4H4, is also found. For the structures and interaction energies, the pi-type H-bond produces four effects: bending the strong pi H-bond, attracting the pair of H-atoms of C4H4 so that they deviate from the C4 ring plane, showing the interaction energy contribution, and bringing the larger electron correlation contribution. The repulsive interaction also produces four effects: pushing the pair of H-atoms of C4H4 so that they deviate from its ring plane, elongating the distance of the pi H-bond, promoting the formation of pi-type H-bond, and slightly influencing the interaction energy. In the present paper, one C=C bond with two H2O (over and below the ring plane) forms a pi H-bond link in two ways: a strong-weak pi H-bond link and a strong-strong pi H-bond link. The stability contribution of the former is more favorable than the latter. One H2O forms a pi H-bond with C4H4 in two ways. One strong pi H-bond part (over or below the ring plane) always is accompanied by another H-bond part. The accompanying part is either a weak pi H-bond or pi-type H-bond.     

Nonlinear optical material of a low-dimensional coordination polymer: Synthesis, structure, NLO and fluorescence properties

Employing unsymmetrical 2-mercapto-5-methyl-1,3,4-thiadiazole and 2,2′-bipyridine as mixed ligands, a new low-dimensional coordination polymer [Zn(MMTA) 2 (2,2′-bipy)] n (MMTA = 2-mercapto-5-methyl-1,3,4-thiadiazole, 2,2′-bipy = 2,2′-bipyridine), has been synthesized under solvothermal condition and characterized by single crystal X-ray diffraction. This compound crys- tallizes in the noncentrosymmetric space group Cc, with cell parameters: a = 8.291(4) , b = 15.483(9) , c = 15.620(6) , = 96.00(5)°, V = 1994.1(2) 3 , and Z = 4. The mixed ligands link the zinc center into a mononuclear unit, which is futher linked by weak C-H···N and C-H···S hydrogen bonds into a three-dimensional noncentrosymmetric framework. The compound exhibits intense photoluminescence and distinct NLO properties at room temperature. The intensity of the green light produced by the powder sample of the compound is about 3.2 times that produced by KDP powder. On the basis of the results of TG analysis, the structure is thermally stable up to ～260 °C.     

Magnitude and directionality of the interaction energy of the aliphatic CH/pi interaction: significant difference from hydrogen bond

The CCSD(T) level interaction energies of CH/pi complexes at the basis set limit were estimated. The estimated interaction energies of the benzene complexes with CH(4), CH(3)CH(3), CH(2)CH(2), CHCH, CH(3)NH(2), CH(3)OH, CH(3)OCH(3), CH(3)F, CH(3)Cl, CH(3)ClNH(2), CH(3)ClOH, CH(2)Cl(2), CH(2)FCl, CH(2)F(2), CHCl(3), and CH(3)F(3) are -1.45, -1.82, -2.06, -2.83, -1.94, -1.98, -2.06, -2.31, -2.99, -3.57, -3.71, -4.54, -3.88, -3.22, -5.64, and -4.18 kcal/mol, respectively. Dispersion is the major source of attraction, even if substituents are attached to the carbon atom of the C-H bond. The dispersion interaction between benzene and chlorine atoms, which is not the CH/pi interaction, is the cause of the very large interaction energy of the CHCl(3) complex. Activated CH/pi interaction (acetylene and substituted methanes with two or three electron-withdrawing groups) is not very weak. The nature of the activated CH/pi interaction may be similar to the hydrogen bond. On the other hand, the nature of other typical (nonactivated) CH/pi interactions is completely different from that of the hydrogen bond. The typical CH/pi interaction is significantly weaker than the hydrogen bond. Dispersion interaction is mainly responsible for the attraction in the CH/pi interaction, whereas electrostatic interaction is the major source of attraction in the hydrogen bond. The orientation dependence of the interaction energy of the typical CH/pi interaction energy is very small, whereas the hydrogen bond has strong directionality. The weak directionality suggests that the hydrogen atom of the interacting C-H bond is not essential for the attraction and that the typical CH/pi interaction does not play critical roles in determining the molecular orientation in molecular assemblies.     

Copper(II), cobalt(II), and nickel(II) complexes with a bulky anthracene-based carboxylic ligand: syntheses, crystal structures, and magnetic properties

To systematically explore the influence of the bulky aromatic ring skeleton with a large conjugated pi-system on the structures and properties of their complexes, six CuII, CoII, and NiII complexes with the anthracene-based carboxylic ligand anthracene-9-carboxylic acid (HL1), were synthesized and characterized, sometimes incorporating different auxiliary ligands: [Cu2(L1)4(CH3OH)2](CH3OH) (1), [Cu4(L1)6(L2)4](NO3)2(H2O)2 (2), {[Cu2(L1)4(L3)](CH3OH)0.25}infinity (3), [Co2(L1)4(L4)2(micro-H2O)](CH3OH) (4), {[Co(L1)2(L5)(CH3OH)2]}infinity (5), and {[Ni(L1)2(L5)(CH3OH)2]}infinity (6) (L2 = 2,2'-bipyridine, L3 = 1,4-diazabicyclo[2.2.2]octane, L4 = 1,10-phenanthroline, and L5 = 4,4'-bipyridine). 1 has a dinuclear structure that is further assembled to form a one-dimensional (1D) chain and then a two-dimensional (2D) network by the C-H...O H-bonding and pi...pi stacking interactions jointly. 2 takes a tetranuclear structure due to the existence of the chelating L2 ligand. 3 possesses a 1D chain structure by incorporating the related auxiliary ligand L3, which is further interlinked via interchain pi...pi stacking, resulting in a three-dimensional (3D) network. 4 also has a dinuclear structure and then forms a higher-dimensional supramolecular network through intermolecular pi...pi stacking and/or C-H...pi interactions. 5 and 6 are isostructural complexes, except they involve different metal ions, showing 1D chain structures, which are also assembled into 2D networks from the different crystallographic directions by interchain pi...pi stacking and C-H...pi interactions, respectively. The results reveal that the steric bulk of the anthracene ring in HL1 plays an important role in the formation of 1-6. The magnetic properties of the complexes were investigated, and the very long intermetallic distances result in weak magnetic coupling, with the exception of 1 and 3, which adopt the typical paddle-wheel structure of copper acetate and are thus strongly coupled.