Theoretical Investigation on the Geometries and Properties of Guanine-BX3 （X = F, Cl） Complex

Geometries and binding energies were predicted at the B3LYP/6-311+G* level for the guanine-BX3 (X = F, Cl) systems and four isomers with no imaginary frequencies have been obtained for both guanine-BF3 and guanine-BCl3, respectively. Single energy calculations using much larger basis sets (6-311+G(2df,p) and aug-cc-pVDZ were carried out as well. It was found that the most stable isomer of guanine-BF3 is BF3 connected to N3 of guanine with the stabilization energy of –19.93 kcal/mol (BSSE corrected), while that of guanine-BCl3 is BCl3 connected to O10 of guanine having stabilization energy of –15.02 kcal/mol at the same level. The analyses for the combining interaction between BX3 and guanine with the atom-in-molecules theory (AIM) and natural bond orbital (NBO) methods have been performed. The results indicated that all the isomers are formed with σ-p type interactions between guanine and BX3, in which pyridine-type nitrogen or carbonyl oxygen or nitrogen atom of amino group offers its lone pair electrons to the empty p orbital of boron atom and the concomitance of charge transfer from guanine to BX3 has occurred. Still, one or two hydrogen bonds exist in some isomers of guanine-BX3 system and contribute to the stability of complex systems. Frequency analysis suggested that the stretching vibration of BX3 undergoes a red shift in complexes. Guanine-BF3 complex is more stable than guanine-BCl3 although the B–Y (Y=N, O) bond distance in the latter is shorter.     

Quantum Chemical Study of CnAl2^± （n=1～10） Clusters： Structure and Stability

Geometries, electronic structures and vibrational frequencies of CnAl2± clusters have been investigated by using the B3LYP-DFT method in the range of n = 1～10. At the B3LYP/6-311G level, the ground state structures of CnAl2± clusters are planar or linear with terminal aluminum atom. In these structures, the C–C bonds are alternately changed between double and triple. The changing magnitude of the averaged bond length decreases with the increase of cluster size. The energetic analysis showed that CnAl2± clusters with even n are more stable than those with odd n.     

Theoretical Studies on the M-M Bonding in Complexes [M2Cl4L2] and [M2Cl7L]- （M = Mo, Re; L = Ph2Ppy, （Ph2P）2py）

The structures of complexes [MⅡ2Cl4L2] and [MⅢ2Cl7L]- (M = Mo, Re; L = Ph2Ppy, (Ph2P)2py) were calculated by using density functional theory (DFT) PBE0 method. Based on the optimized geometries, the natural bond orbital (NBO) analyses were carried out to study the nature of Re-Re and Mo-Mo bonds. The conclusions are as follows: the M-M distances in two-Ph2Ppy or (Ph2P)2py complexes [MⅡ2Cl4L2] are shorter than those in mono-Ph2Ppy or (Ph2P)2py complexes [MⅢ2Cl7L]- due to the double bridged N-C-P interactions. For singlet of all complexes, there is ReⅢ-ReⅢ or MoⅡ-MoⅡ quadruply bond in complex [Re2Cl7L]- or [Mo2Cl4L2], while only ReⅡ-ReⅡ or MoⅢ-MoⅢ triply bond in complex [Re2Cl4L2] or [Mo2Cl7L]-. The most stable spin state of 2 and 6, triplet, only contains triple ReⅢ-ReⅢ bond. Because the LPCl → BD*Re-Re delocalizations weaken the Re-Re bond, the distance of ReⅢ-ReⅢ quadruple bonds in [Re2Cl7L]- is slightly longer than that of ReⅡ-ReⅡ triple bonds in [Re2Cl4L2]. Moreover, due to the delocalizations from the lone pair electrons of the remaining P' atom to the M-M antibonding orbitals, the M-M distance in (Ph2P)2py complexes is slightly longer than that in Ph2Ppy complexes.     

Ultra-incompressible Ternary Diborides Re_（0.5）Ir_（0.5）B_2,Re_（0.5）Tc_（0.5）B_2,Os_（0.5）W_（0.5）B_2 and Os_（0.5）Ru_（0.5）B_2：Density Functional Calculation

In this paper, density functional computations have been applied to the structural, elastic and electronic properties of ternary transition metal diborides Re0.5Ir0.5B2, Re0.5Tc0.5B2, Os0.5W0.5B2 and Os0.5Ru0.5B2 in hexagonal (P63/mmc) and orthorhombic (Pmmn) structures with both local density approximation and generalized gradient approximation. LDA gives smaller lattice parameters and larger elastic moduli than GGA. Both results show that the hexagonal ones are more stable than orthorhombic ones except Os0.5Ru0.5B2. Moreover, the hexagonal structure has superior elastic property than orthorhombic one. Generally speaking, the calculated elastic moduli of Re0.5Ir0.5B2 and Os0.5Ru0.5B2 are smaller than those values of Re0.5Tc0.5B2 and Os0.5W0.5B2 within the same structure because of the filling of antibonding states. The relativistic effects result in weaker bonds of Tc-B (Ru-B) than those of Re-B (Os-B). All the diborides are ultra-incompressible. Re0.5Tc0.5B2 has the largest shear modulus and it is a promising superhard diboride like Os0.5W0.5B2. The elastic properties are in high correlation with the bond strength. The shear moduli are more sensitive than the bulk moduli to the bond strength.     

Pentazole anion cyclo-N_5~-: a rising star in nitrogen chemistry and energetic materials

正Nitrogen and carbon are common elements in nature. The development of nitrogen chemistry, however, is obviously left behind by that of carbon chemistry. Prof. Christ [1] attributed this reason to the stability difference between nitrogen-nitrogen bond and carbon-carbon bond. From N≡N,N=N to N–N bond, the bond dissociation energy increases significantly and the stability becomes worse rapidly, which is in contrast with stable C–C bond and unstable C≡C bond in carbon chemistry. Thus, lots of stable "polycarbon"     

POLYMER-SUPPORTED CLUSTER II SYNTHESIS, CHARACTERIZATION AND CATALYTIC PROPERTIES OF POLYMERSUPPORTED HETEROPENTAMETALLIC CLUSTER FeCO3 (CO)12 (μ3-AuPph2CH2■-■)*

The polymer-supported cluster FeCo3 (CO)_(12) (μ3-AuPph_2 CH_2) (4) has been synthesized through reaction of CH_2 ph_2 PAuCl with the cluster anion FeCo_3 (CO)_(12)~-. They are characterized through IR spectra, electronic spectra and XPS, with homogenous analog FeCo_3 (CO)_(12) (μ3-AuPph_3) (3) as reference compound. The cluster (3) and the polymer-supported cluster (4) are good catalysts for hydroformylation of olefins. They have better activity and selectivity than the cluster (1) and (2).The supported cluster (4) is more stable and has catalytic activity at higher temperature than its homogeneous analog (3). From the metal core level binding energies in XPS and λ_(max) in electronic spectra, it is found that the metal-metal bonds in (4) are reinforced bypolymer supporter. The cluster (3) and (4) can be reused , and possibly do not fragment to one metal species in the course of catalytic reaction.     

B20N20团簇的结构与稳定性

B3LYP/6-31G* density functional theory calculations have been carried out on the structure and stability of ten B20N20 clusters. It was found that two new proposed isomers with two octagons, twelve hexagons, eight squares in Cab and C2 symmetry were more stable than the isomer with sixteen hexagons and six squares in C2 symmetry which was previously deemed to the most stable by 79.5 and 13.8 kJ/mol respectively. The isomer with two decagons in S10 symmetry is much higher in energy than the most stable structure in C4h symmetry by 637.2 kJ/mol.     

COPOLYMERIZATION OF ETHYLENE AND PROPYLENE WITH CpCH2CH2CH=CH2)2MCl2(M=Zr,Hf)AND Cp2ZrCl2 CATALYSTS

(CpCH_2CH_2CH = CH_2)_2MCl_2(M=Zr, Hf)/MAO and Cp_2ZrCl_2/MAO (Cp=cyclopentadienyl; MAO=methylaluminoxane) catalyst systems have been compared for ethylene copolymerization to investigate the influence of theligand and transition metal on the polymerization activity and copolymer properties. For both CH_2CH_2CH=CH_2 substitutedcatalysts the catalytic activity decreased with increasing propene concentration in the feed. The activity of the hafnocenecatalyst was 6～8 times lower than that of the analogous zirconocene catalyst, ~(13)C NMR analysis showed that the copolymerobtained using the unsubstituted catalyst Cp_2ZrCl_2 has greater incorporatien of propene than those produced byCH_2CH_2CH=CH_2 substituted Zr and Hf catalysts. The melting point, crystallinity and the viscosity-average molecularweight of the copolymer decreased with an increase of propenc concentration in the feed. Both CH_2CH_2CH= CH_2 substitutedZr and Hf catalysts exhibit little or no difference in the melting point and crystallinity of the produced copolymers. However,there are significant differences between the two zirconocene catalysts. The copolymer produced by Cp_2ZrCl_2 catalyst havemuch lower T_m and X_c than those obtained with the (CpCH_2CH_2CH=CH_2)_2ZrCl_2 catalyst. The density and molecular weightof the copolymer decreased in the order: (CpCH_2CH_2CH=CH_2)_2HfCl_2>(CpCH_2CH_2CH=CH_2)_2ZrCl_2>Cp_2ZrCl_2. The kineticbehavior of copolymerizaton with Hf catalyst was found to be different from that with Zr catalyst.     

A CLUSTER COMPOUND WITH DI-ENDOXYGEN LIGANDS——THE CRYSTAL AND MOLECULAR STRUCTURE OF [Fe(MOS_4O)_2][N(C_2H_5)_4]3

[Fe(MoS_4O)_2] [N(C_2H_3)_4]_3 cluster compound with di-end-oxygen ligands has been prepared and characterized by the X-ray diffraction method. The compound crystallizes in a monoclinic space group P2_1/n with lattice parameters a=13.019(4), b=16.959(5), c=18.234(5), β=97.34(2)(°), Z=4. The final agreement factors are R=0.0740, Rw=0.0598. The terminal bond length, Mo-S_t and bridged one, MO-S_b for the compound are much longer than the counterpart without end-oxygen ligand. It possibly suggests that low valence of molybdenum and smaller electronegativity of sulphur than oxygen lead to the charge transfer as S→Mo→O.     

Hierarchical self-assembly of crown ether based metal-carbene cages into multiple stimuli-responsive cross-linked supramolecular metallogel

The hierarchical self-assembly(HSA) strategy widely utilized in biological systems has been applied in artificial systems to orchestrate small building blocks into complex functional architectures. The non-interfering interactions glue various building blocks together and produce new species with attractive properties. Herein, we functionalized NHC-based assemblies with orthogonal host–guest interaction to fabricate metal-carbene based supramolecular polymer gel. A series of unique crown etherappended cylinder-like trinuclear AuIhexacarbene assemblies [Au_3(L)_2](PF_6)_3(L=D1–D4, A1–A4) were synthesized from the corresponding trisimidazolium salts H_3-L(PF_6)_3(L=D1–D4, A1–A4) in which the N-wingtip of the imidazole moieties were substituted with three identical crown ether groups of different sizes(B15C5, B18C6, B21C7, DB24C8). The gold carbene assembly is able to complex six ammonium salts without disrupting the underlying metal-carbene cylinders. In addition, the supramolecular polymer metallogel featuring a multiple-responsiveness can be formed by using [Au_3(A_4)_2](PF_6)_3 appended with DB24C8 as the core and bisammonium salt as the cross-linker. The case of introducing orthogonal interaction to NHC moiety by N-wingtip substitution demonstrates the feasibility and the power of such strategy to expand the NHC-based supramolecular system and endow them with novel properties.     

THE CLEAVAGE REACTION OF Mo≡Mo TRIPLE BOND.SYNTHESIS AND X-RAY CRYSTAL STRUCTURE OF[CpMo(CO)_2(N,S-C9H6NS)]·O=PPh3

The reaction of[CpMo(CO)_2]_2 with 8,8'-diquinolyl disulphideC_9H_6NSSNC_9H_6 resulted in the cleavage of Mo≡Mo triple bond to give a newnononuclear complex CpMo(CO)_2(N,S-C_9H_6NS)which was refluxed with PPh_3 inTHF to form the title complex.The crystal structure of the title complexwas determined by X-ray diffraction.     

Structures and stabilities of HPO_2 isomers

The potential energy surface of HPO2 system including eight isomers and twelve transition states is predicated at MP2/6-311++G(d, p) and QCISD(t)/6-311++G(3df,2p)(single-point) levels of theory. On the potential energy surface, cis-HOPO(E1) is found to be thermodynamically and kinetically most stable isomer followed by trans-HOPO(E2) and HPO(O)(C2v, E3) at 10.99 and 48.36 kJ/mol higher, respectively. Based on the potential energy surface, only E1 and E3 are thermodynamically stable isomers, and should be experimentally observable. The products cis-HPOO(E5) and frans-HPOO(E6) in the first-step reaction of HP with O2 can isomerize into isomer E1 that has higher stability. The reaction of OH with PO will directly lead to the formation of isomer E1. The computed results are well consistent with the previous experimental studies.     

Investigation of the Substituent Effects on π-Type Pnicogen Bond Interaction

Intermolecular interactions between PH_2Cl and Ar–R(R = H,OH,NH_2,CH_3,Br,Cl,F,CN,NO_2) were calculated by using MP2/aug-cc-p VDZ quantum chemical method.It has been shown from our calculations that the aromatic rings with electron-withdrawing groups represent much weaker binding affinities than those with electron-donating groups.The charge-transfer interaction between PH_2Cl and Ar–R plays an important role in the formation of pnicogen bond complexes,as revealed by NBO analysis.Nevertheless,AIM analysis shows that the nature of the interactions between PH_2Cl and Ar–R is electrostatic,and the interaction energies of the complexes are correlated positively with the electron densities in the bond critical points(BCPs).RDG/ELF graphical analyses were performed to visualize the positions and strengths of the pnicogen bonding,as well as the spatial change of the electron localization upon the formation of complexes.The π-type halogen bond was also calculated,and it has been revealed that the π-type pnicogen bond systems are more stable than the halogen bond ones.     

CRYSTAL AND MOLECULAR STRUCTURE OF ISOMORPHOUS Cp_2Cr_2(CO)_4(μ-η2-P_2)[M(CO)_5]_2(M=Mo,W)

<正> Cp_2Cr_2(CO)_4(μ-η~2-P_2)C(M(CO)_5]_2(M=Mo(3),W(4)) are isostruc-tural to Cp2Cr2 (CO)4 (μ-η2-P2) [Cr (CO)5]2 (2) and crystallize in space group C2/c (No. 15) with a=18. 553(5),b=10. 462,c=16. 786(2)(2)A ,β=109. 84(1)°,V= 3064. 5(8)A3,Z=4,Mr = 880. 16,F(000) = 1712,and Dc=1.907 g/cm3 for 3,and a -18. 552(6),b= 10. 471 (2),c= 16. 768(2) A, β=109. 77(2)°,V = 3065(1) A3,Z = 4,Mr= 1055. 98,F(000) = 1968,and Dc = 2. 288g/cm3 for 4. This series of complexes share a virtually invariant Cr2(μ-η2-P2) central core with their parent complex Cp2Cr2-(CO)4(μ-η2-P2)(1).The Mo-P (2. 506(1) A) and W-P (2. 511(3) A) distances are longer than the corresponding Cr - P distance (2. 397(1)A) in complex 2 in accordance with the increase in covalent radii of the M atoms.     

Syntheses and Characterization of Two Diiron Dithiolate Complexes with Electron-withdrawing and Electron-donating Substitution

Two diiron dithiolate complexes [Fe_2(CO)_6(1,8-S_2-2-CH_2OOCPhC_(10)H_5)] 1 and[Fe_2(CO)_6(1,8-S_2-2-CH_2OOCPh-4-NO_2C_(10)H_5)]2 were synthesized in high yield. The complexes have been confirmed by single-crystal X-ray diffraction and characterized by IR, UV-Vis, ~1H NMR spectroscopy and cyclic voltammetry. They contain a butterfly Fe_2S_2 core with the Fe1–Fe_2 distances of 2.5237(7) ? in 1 and 2.5125(12) ? in 2, falling in the normal range of Fe–Fe bond length(2.49 ~ 2.57 ?). The cyclic voltammetry has been used to investigate the electrochemical properties and the electrocatalytic proton reduction for 1 and 2. The complexes display reduction peaks at –1.074 V, –1.535 V(1) and –0.869 V, –1.247 V(2) vs. Fc/Fc+, respectively. With using p-Ts OH acid of different concentration, the reduction peak of complex 2 grows non-linear; on the contrary, that of complex 1 is linear with the addition of the acid. Cyclic voltammetry revealed the two complexes are good catalysts in the CH_3CN/NBu_4PF_6 solution.     

Two Novel Isomers of HPS3 System

Two new isomers of HPS3 system, FIP(S)S2 and HSSPS, are predicted by means of B3LYP method with 6-311 G(3df,3pd) basis set. The two isomers can isomerize into thermodynamically the most stable species HSPS2, which have been experimentally identified,with relatively higher reaction barriers. In view of their higher thermodynamical and kinetic stability and the experimental observation for I-IP(O)O2 and HOOPO in previous study, we can reasonably believe that the two species can be spectrosymmetrically characterized in future experiments.     

Synthesis,Crystal Structure and Spectroscopy Studies on Complex cis-Os~Ⅱ(bpy)_2Cl_2 and Its Oxidation Product [cis-Os~Ⅲ(bpy)_2Cl_2](PF_6)

The treatment of(NH_4)_2 OsCl_6 with 2 equiv of bpy in ethylene glycol produced complex 1, cis-Os~Ⅱ(bpy)_2Cl_2(bpy = 2,2?-bipyridine). Its one-electron oxidation product 2, [cis-Os~Ⅲ-(bpy)_2Cl_2](PF_6), was obtained by the oxidation of 1 with(Cp)_2 FePF_6. Complex 1 crystallizes in the orthorhombic space group Pbca, and adopts distorted [MCl_2 N_4] octahedral coordination, in which four coordination sites are occupied by four nitrogen atoms from two bpy ligands and the other two sites are occupied by two chlorine atoms in a cis-position. Complex 2 crystallizes in monoclinic space group C2/c, and contains one [Os(bpy)_2Cl_2]~+ cation, one PF_6~- anion and two uncoordinated water solvent molecules.     

Three Novel Isomers of FCH2CP System

Three new isomers of FCH2CP system, F(H)CCPH (1), F-cCPC-H(H) (2) and F-cCC(H)P-H (3), are predicted by means of B3LYP and CCSD(T) (single-point) methods with 6-311 G(d,p) and 6-311 G(2df,2p) basis sets, respectively. The three calculated isomers can isomerize into thermodynamically the most stable species F-cPC(H)C-H, which has been suggested in previous theoretical studies, with relatively higher reaction barriers. In view of their higher thermodynamic and kinetic stability, we believe that the three species can be detected in future experiments.     

Bonding and Reactivity in RB-As R Systems(R=H,F,OH,CH_3,CMe_3,CF_3,SiF_3,BO): Substituent Effects

Density functional theory-based calculations have been carried out to study the bonding and reactivity in RB-As R(R=H,F,OH,CH3,CMe_3,CF_3,SiF_3,BO)systems.Our calculations demonstrated that all the studied systems adopted bent geometry(DR-B-As≈180°andDB-As-R≈90°or less).The reason for this bending was explained with the help of a valence-orbital model.The potential energy surfaces for three possible isomers of RB-As R systems were also generated,indicating that the RB-As R isomer was more stable than R_2B-As R when R=SiF_3,CMe_3,and H.The B-As bond character was analyzed using natural bond orbital(NBO)and Wiberg bond index(WBI)calculations.The WBI values for B-As bonds in F3Si B-As SiF_3 and HB-As H were 2.254 and 2.209,respectively,indicating that this bond has some triple-bond character in these systems.While the B centers prefer nucleophilic attack,the As centers prefer electrophilic attack.     

MOLYBDENUM-IRON MIXED METAL CLUSTERS (Ⅰ)——THE SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF (η~5-C_5H_5)_2Mo_2Fe_2(μ_4-Te)(μ_3-Te)_2(CO)_6

The reaction of Fe_2(μ_3-Te)_2(CO)_9 with Mo_2(CO)_6(η~5-C_5H_5) affords the title compound. Its X-ray analysis shows a butterfly structure for the Mo_2Fe_2 core; the two molybdenum atoms occupy the hinge with a Mo—Mo bond distance of 2.819 and the two iron atoms are on the tops of the wings with an average Mo—Fe bond distance of 2.932(2). Each molybdenum is bonded to a Cp ring, and three CO ligands are terminally bonded to each iron atom. One tellurium atom quadruply bridges Mo_Fe_2 with Mo—Te(μ_4)=2.625(2). and Fe—Te(μ_4)=2.713(2). Two tellurium atoms triply bridge the two triangular Mo_2Fe faces with Mo—Te(μ_3)=2.678(1) and Fe—Te(μ_3)=2.513(3). The molecule has C_(2v) symmetry and a bicapped triangle bipyramidal skeleton. Crystallographic parameters are as follows: space groupImm2(orthorhombic), a=14.562(3), b=10.391(1), c=7.139(4), V=1080.2(i)~3, Z=2, ρ(cald)=1.819g·cm~(-3). The final R factor was 2.2％ for 620 independent reflections(I>2σ(I)).