Solvent effects in thermodynamically controlled multicomponent nanocage syntheses

The solvent effects on the condensation reaction between tetraformylcavitand 2 and ethylene-1,2-diamine 3 are reported. Earlier, it was found that the trifluoroacetic acid-catalyzed condensation of 2 and 2 equiv of 3 in CHCl(3) provides in 82% yield an octahedral nanocage 1 composed of 6 cavitands that are linked together by 12 -CH=N-CH(2)CH(2)-N=CH- linker groups (Liu, X.; Liu, Y.; Li, G.; Warmuth, R. Angew. Chem., Int. Ed. 2006, 45, 901). In tetrahydrofuran, the same reactants yield a tetrameric nanocage 4 (35% yield), which resembles a distorted tetrahedron built up from four cavitands that occupy the apexes. Each cavitand is doubly linked to one other cavitand and singly linked to the other two cavitands via -CH=N-CH(2)CH(2)N=CH- connectors. In CH(2)Cl(2), the reaction between 8 2 and 16 3 yields a square antiprismatic nanocage 5 (65% yield), in which each cavitand occupies one of the eight corners and is connected to four neighboring cavitands via -CH=N-CH(2)CH(2)-N=CH- linkers. Nanocage 5 is also the main product in CH(2)ClCH(2)Cl (26% yield) and CHCl(2)CHCl(2) (33% yield). Reduction of all imine bonds in 4 and 5 yields polyaminonanocontainers 7 and 8, respectively, which were isolated as trifluoroacetate salts. Contrary to the formation of larger capsules composed of four, six, or eight cavitands in the reaction between 2 and 3, the acid-catalyzed reaction of 2 with 2 equiv of H(2)N-X-NH(2) (X = (CH(2))(n)(=3,4,5), 1,3-C(6)H(4), 1,4-(CH(2))(2)C(6)H(4), or 1,3-(CH(2))(2)C(6)H(4)) quantitatively yields octaiminohemicarcerands 9-14, in which two cavitands are connected with four -CH=N-X-N=CH- linkers. The outcomes of these condensation reactions are rationalized with the different diamine structures and the relative orientation of cavitands in 1, 4, 5, and 9-14.     

Experimental and quantum-chemical studies of 1H, 13C and 15N NMR coordination shifts in Pd(II) and Pt(II) chloride complexes with quinoline, isoquinoline, and 2,2'-biquinoline

1H, 13C, and 15N NMR studies of platinide(II) (M=Pd, Pt) chloride complexes with quinolines (L=quinoline-quin, or isoquinoline-isoquin; LL=2,2'-biquinoline-bquin), having the general formulae trans-/cis-[ML2Cl2] and [M(LL)Cl2], were performed and the respective chemical shifts (delta1H, delta13C, delta15N) reported. 1H coordination shifts of various signs and magnitudes (Delta1Hcoord=delta1Hcomplex-delta1Hligand) are discussed in relation to the changes of diamagnetic contribution to the relevant 1H shielding constants. The comparison to the literature data for similar complexes containing auxiliary ligands other than chlorides exhibited a large dependence of delta1H parameters on electron density variations and ring-current effects (inductive and anisotropic phenomena). The influence of deviations from planarity, concerning either MN2Cl2 chromophores or azine ring systems, revealed by the known X-ray structures of [Pd(bquin)Cl2] and [Pt(bquin)Cl2], is discussed in respect to 1H NMR spectra. 15N coordination shifts (Delta15Ncoord=delta15Ncomplex-delta15Nligand) of ca. 78-100 ppm (to lower frequency) are attributed mainly to the decrease of the absolute value of paramagnetic contribution in the relevant 15N shielding constants, this phenomenon being noticeably dependent on the type of a platinide metal and coordination sphere geometry. The absolute magnitude of Delta15Ncoord parameter increased by ca 15 ppm upon Pd(II)-->Pt(II) replacement but decreased by ca. 15 ppm following trans-->cis transition. Experimental 1H, 13C, 15N NMR chemical shifts are compared to those quantum-chemically calculated by B3LYP/LanL2DZ+6-31G**//B3LYP/LanL2DZ+6-31G*, both in vacuo and in CHCl3 or DMF solution.     

Substituent effects in five oxo-centered trinuclear rhodium(III) clusters

We here report the rates of water substitution by methanol-d(4) for four new oxo-centered trinuclear rhodium(III) clusters with different carboxylate-bridging ligands, [Rh3(mu3-O)(mu-O2CR)6(OH2)3]+ (R = CH2CH3, CH2CH2Cl, CH2Cl, and CHCl2), and [Rh3(mu3-O)(mu-O2CCH3)6(OH2)3]+. By varying the R group alkyl chain, water substitution rates were found to span almost 3 orders of magnitude (k(298K) = 1.2 x 10(-2)-2.3 x 10(-5) s(-1)) and reflect the following trend R = CH2CH3 > CH3 > CH2CH2Cl > CH(2)Cl > CHCl2. Activation parameters for substitution point toward a dissociative activation pathway (DeltaH = 99-115 kJ mol(-1); DeltaS = 48-52 J mol(-1) K(-1)), indicating that there is little association with the incoming methanol molecule during the formation of the transition-state complex. Because the mechanism for substitution in all five trimers has a considerable dissociative character, substitution rates are likely very similar to water exchange rates. These data suggest that the kinetic reactivity of the ligated waters is heavily influenced by the inductive ability of the aliphatic substituents, but yet the mechanism of substitution remains virtually unchanged. Structural data are also reported for the four new rhodium(III) trimer salts as well as 103Rh NMR spectra. We find that 103Rh NMR chemical shifts span more than 200 ppm and mirror the same reactivity trend found for the rates of water substitution (103Rh delta (9406-9620 ppm): R = CH2CH3 < CH3 < CH2CH2Cl < CH2Cl < CHCl2). Taken together, these data suggest a means for estimating water exchange rates for other oxo-centered rhodium(III) trimers from chemical shift data alone.     

Towards new organometallic wires: tetraruthenium complexes bridged by phenylenevinylene and vinylpyridine ligands

The tetranuclear complexes [{(PiPr(3))(2)(CO)ClRu(mu-CH=CHpy)Ru Cl(CO)(PPh(3))(2)}(2)(mu-CH=CH-C(6)H(4)- CH=CH-1,4)] (3 a) and [{(PiPr(3))(2)(CO)ClRu(mu-CH=CHpy)RuCl(CO)(PPh(3))(2)}(2)(mu-CH=CH-C(6)H(4)-CH=CH-1,3)] (3b), which contain vinylpyridine ligands that connect peripheral Ru(PiPr(3))(2)(CO)Cl units to a central divinylphenylene-bridged diruthenium core, have been prepared and investigated. These complexes, in various oxidation states up to the tetracation level, have been characterized by standard electrochemical and spectroelectrochemical techniques, including IR, UV/Vis/NIR and ESR spectroscopy. A comparison with the results for the vinylpyridine-bridged dinuclear complex [PiPr(3))(2)(CO)ClRu(mu-CH=CHpy)RuCl(CO)(PPh(3))(2)(CH=CHPh)] (6) and the divinylphenylene-bridged complexes [{(EtOOCpy)(CO)Cl(PPh(3))(2)Ru}(2)(mu-CH=CH-C(6)H(4)-CH=CH-1,4)] (8a) and [{(EtOOCpy)(CO)Cl(PPh(3))(2)Ru}(2)(mu-CH=CH-C(6)H(4)-CH=CH-1,3)] (8b), which represent the outer sections (6) or the inner core (8a,b) of complexes 3a,b, and with the mononuclear complex [(EtOOCpy)(CO)(PPh(3))(2)RuCl(CH=CHPh)] (7) indicate that every accessible oxidation process is primarily centred on one of the vinyl ligands, with smaller contributions from the metal centres. The experimental results and quantum chemical calculations indicate charge- and spin-delocalization across the central divinylphenylenediruthenium part of 3a,b or the styrylruthenium unit of 6, but not beyond. The energy gap between the higher lying styryl- or divinylphenylenediruthenium-based and the lower occupied vinylpyridineruthenium-based orbitals increases in the order 6<3 b<3 a and thus follows the conjugation within the non-heteroatom-substituted aromatic vinyl ligand.     

C28H4-nCln(n=1~3)与CH4-nCln(n=1~3)的结构和电子光谱的理论研究

用INDO系列方法对C28H3Cl, C28H2Cl2, C28HCl3, CH3Cl, CH2Cl2, CHCl3进行了几何构型优化, C28H3Cl, C28HCl3, CH3Cl, CH3Cl为C3v对称性,C28H2Cl2, CH2Cl2为C2v对称性, 这六个分子的基态都是稳定闭壳层分子, 以此构型为基础计算了上述分子的电子光谱, C28H4-nCln(n=1~3)的电子光谱属于理论预测性质。     

Microenvironmental and conformational structure of triblock copolymers in aqueous solution by 1H and 13C NMR spectroscopy

1H and 13C nuclear magnetic resonance (NMR) spectra of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers in D2O solutions have been systematically investigated. The detailed assignments of various 1H and 13C NMR signals are presented. The hyperfine structure of PO -CH2- protons was clearly assigned, the arising reason of this hyperfine structure was attributed to the influence of the chiral center of -CHCH3- groups and the direct coupling between the PO -CH2- and -CH3 protons. The external standard 2,2-dimethyl-2-silapentane-5-sulfonate sodium salt (DSS) was firstly applied in this system. Accurate chemical shift values referenced to the external standard DSS were obtained. 1H NMR chemical shift of PO -CH2- and -CH3 signals shows a larger decrease in ppm values than that of EO -CH2- signal with the increase of PPO/PEO ratio or temperature indicating that PO segments exist in a more hydrophobic microenvironment. A new resonance signal assigned to the PO -CH2- protons appeared when the temperature is above the CMT, which is attributed to the breakdown of the intra-molecular (C-H)...O hydrogen bond between the PO -CH2- protons and the ester oxygens. The breakdown of this intra-molecular hydrogen bond may result in a decrease of gauche conformers of the PPO chain. The increase of 13C NMR chemical shift of block copolymers validates this conformational change assumption. It can be inferred that the amount of gauche conformers decreases whereas that of trans conformers increases in both PO and EO chains when elevating the PPO/PEO ratio or temperature. The observed 13C NMR chemical shifts of PO segments show a bigger increase than those of EO segments, supporting the formation of a nonpolar microenvironment around PO segments.     

Characterization of covalent linkages in organically functionalized MCM-41 mesoporous materials by solid-state NMR and theoretical calculations

The covalent linkages formed during functionalization of MCM-41 mesoporous molecular sieves with five chloroalkylsilanes ((EtO)3Si(CH2Cl), (MeO)3Si(CH2CH2CH2Cl), Cl3Si(CH2CH2CH3), Cl2Si(CH3)(CH2Cl) and Cl2Si(CH3)2) have been investigated using high-resolution solid-state NMR spectroscopy and DFT calculations. Structural information was obtained from 1H-13C and 1H-29Si heteronuclear (HETCOR) NMR spectra, in which high resolution in the 1H dimension was obtained by using fast MAS. The 1H-13C HETCOR results provided the assignments of 1H and 13C resonances associated with the surface functional groups. Sensitivity-enhanced 1H-29Si HETCOR spectra, acquired using Carr-Purcell-Meiboom-Gill refocusing during data acquisition, revealed the identity of 29Si sites (Qn, Tn, and Dn) and the location of functional groups relative to these sites. Optimal geometries of local environments representing the Qn, Tn and Dn resonances were calculated using molecular mechanics and ab initio methods. Subsequently, DFT calculations of 29Si, 13C, and 1H chemical shifts were performed using Gaussian 03 at the B3LYP/6-311++G(2d,2p) level. The theoretical calculations are in excellent accord with the experimental chemical shifts. This work illustrates that state-of-the-art spectroscopic and theoretical tools can be used jointly to refine the complex structures of inorganic-organic hybrid materials.     

Free energies for degradation reactions of 1,2,3-trichloropropane from ab initio electronic structure theory

Electronic structure methods were used to calculate the gas and aqueous phase reaction energies for reductive dechlorination (i.e., hydrogenolysis), reductive β-elimination, dehydrochlorination, and nucleophilic substitution by OH? of 1,2,3-trichloropropane. The thermochemical properties ΔH(f)°(298.15 K), S°(298.15 K, 1 bar), and ΔG(S)(298.15 K, 1 bar) were calculated by using ab initio electronic structure calculations, isodesmic reactions schemes, gas-phase entropy estimates, and continuum solvation models for 1,2,3-trichloropropane and several likely degradation products: CH3?CHCl?CH2Cl, CH2Cl?CH2?CH2Cl, C?H2?CHCl?CH2Cl, CH2Cl?C?H?CH2Cl, CH2═CCl?CH2Cl, cis-CHCl═CH?CH2Cl, trans-CHCl═CH?CH2Cl, CH2═CH?CH2Cl, CH2Cl?CHCl?CH2OH, CH2Cl?CHOH?CH2Cl, CH2═CCl?CH2OH, CH2═COH?CH2Cl, cis-CHOH═CH?CH2Cl, trans-CHOH═CH?CH2Cl, CH(═O)?CH2?CH2Cl, and CH3?C(═O)?CH2Cl. On the basis of these thermochemical estimates, together with a Fe(II)/Fe(III) chemical equilibrium model for natural reducing environments, all of the reactions studied were predicted to be very favorable in the standard state and under a wide range of pH conditions. The most favorable reaction was reductive β-elimination (ΔG(rxn)° ≈ ?32 kcal/mol), followed closely by reductive dechlorination (ΔG(rxn)° ≈ ?27 kcal/mol), dehydrochlorination (ΔG(rxn)° ≈ ?27 kcal/mol), and nucleophilic substitution by OH? (ΔG(rxn)° ≈ ?25 kcal/mol). For both reduction reactions studied, it was found that the first electron-transfer step, yielding the intermediate C?H2?CHCl?CH2Cl and the CH2Cl?C?H?CH2Cl species, was not favorable in the standard state (ΔG(rxn)° ≈ +15 kcal/mol) and was predicted to occur only at relatively high pH values. This result suggests that reduction by natural attenuation is unlikely.     

Atmospheric chemistry of t-CF3CH=CHCl: products and mechanisms of the gas-phase reactions with chlorine atoms and hydroxyl radicals

FTIR-smog chamber techniques were used to study the products and mechanisms of the Cl atom and OH radical initiated oxidation of trans-3,3,3-trifluoro-1-chloro-propene, t-CF(3)CH=CHCl, in 700 Torr of air or N(2)/O(2) diluent at 296 ± 2 K. The reactions of Cl atoms and OH radicals with t-CF(3)CH=CHCl occur via addition to the >C=C< double bond; chlorine atoms add 15 ± 5% at the terminal carbon and 85 ± 5% at the central carbon, OH radicals add approximately 40% at the terminal carbon and 60% at the central carbon. The major products in the Cl atom initiated oxidation of t-CF(3)CH=CHCl were CF(3)CHClCHO and CF(3)C(O)CHCl(2), minor products were CF(3)CHO, HCOCl and CF(3)COCl. The yields of CF(3)C(O)CHCl(2), CF(3)CHClCOCl and CF(3)COCl increased at the expense of CF(3)CHO, HCOCl and CF(3)CHClCHO as the O(2) partial pressure was increased over the range 10-700 Torr. Chemical activation plays a significant role in the fate of CF(3)CH(O)CHCl(2) and CF(3)CClHCHClO radicals. In addition to reaction with O(2) to yield CF(3)COCl and HO(2) the major competing fate of CF(3)CHClO is Cl elimination to give CF(3)CHO (not C-C bond scission as previously thought). As part of this study k(Cl + CF(3)C(O)CHCl(2)) = (2.3 ± 0.3) × 10(-14) and k(Cl + CF(3)CHClCHO) = (7.5 ± 2.0) × 10(-12) cm(3) molecule(-1) s(-1) were determined using relative rate techniques. Reaction with OH radicals is the major atmospheric sink for t-CF(3)CH=CHCl. Chlorine atom elimination giving the enol CF(3)CH=CHOH appears to be the sole atmospheric fate of the CF(3)CHCHClOH radicals. The yield of CF(3)COOH in the atmospheric oxidation of t-CF(3)CH=CHCl will be negligible (<2%). The results are discussed with respect to the atmospheric chemistry and environmental impact of t-CF(3)CH=CHCl.     

A simple molecule with a complex crystal structure: interplay of 31P solid-state NMR spectroscopy and single-crystal x-ray diffraction in the structure determination of a ruthenium diphosphine diamine complex

A comprehensive 31P solid-state NMR study of Ru(eta1-Ph2PCH2CH2OCH3)2(eta2-en)Cl2 (en = ethylenediamine) (1), by 1D (contact time variation, inversion-recovery, SPARTAN) and 2D techniques (homonuclear J-resolved, SECSY) indicated that the crystal structure of 1 should be complex. The single-crystal x-ray structure determination confirmed the presence of eight independent molecules in the asymmetric unit, with 31P isotropic chemical shifts in the range 27.3-40.1 ppm, while the spans of the phosphorus chemical shift tensors are of the order of 170 ppm. Based on unique structural features and NMR data, one molecule has been tentatively assigned.     

Multinuclear solid-state high-resolution and 13C -{27Al} double-resonance magic-angle spinning NMR studies on aluminum alkoxides

A combination of 27Al magic-angle spinning (MAS)/multiple quantum (MQ)-MAS, 13C-1H CPMAS, and 13C-{27Al} transfer of population in double-resonance (TRAPDOR) nuclear magnetic resonance (NMR) were used for the structural elucidation of the aluminum alkoxides aluminum ethoxide, aluminum isopropoxide, and aluminum tertiarybutoxide. Aluminum alkoxides exist as oligomers with aluminum in different coordinations. High-resolution 27Al MAS NMR experiments with high-spinning speed distinguished the aluminum atoms in different environments. The 27Al MAS NMR spectrum gave well-resolved powder patterns with different coordinations. Z-filter MQ-MAS was performed to obtain the number and types of aluminum environments in the oligomeric structure. 13C-1H CPMAS chemical shifts resolved the different carbon species (-CH3, =CH2, =CH-, and =C=) in the structures. 13C-{27Al} TRAPDOR experiments were employed to obtain relative Al-C dipolar interactions and to distinguish between terminal and bridging alkoxides in the crystallographic structures. The complete characterization of selected aluminum alkoxides using advanced NMR methods has evidenced the tetrameric structure for aluminum isopropoxide and the dimeric structure for aluminum tertiary-butoxide, as reported in the literature, and proposed a polymeric structure for aluminum ethoxide.     

Nuclear magnetic resonance shielding constants and chemical shifts in linear 199Hg compounds: a comparison of three relativistic computational methods

We investigate the importance of relativistic effects on NMR shielding constants and chemical shifts of linear HgL(2) (L = Cl, Br, I, CH(3)) compounds using three different relativistic methods: the fully relativistic four-component approach and the two-component approximations, linear response elimination of small component (LR-ESC) and zeroth-order regular approximation (ZORA). LR-ESC reproduces successfully the four-component results for the C shielding constant in Hg(CH(3))(2) within 6 ppm, but fails to reproduce the Hg shielding constants and chemical shifts. The latter is mainly due to an underestimation of the change in spin-orbit contribution. Even though ZORA underestimates the absolute Hg NMR shielding constants by ～2100 ppm, the differences between Hg chemical shift values obtained using ZORA and the four-component approach without spin-density contribution to the exchange-correlation (XC) kernel are less than 60 ppm for all compounds using three different functionals, BP86, B3LYP, and PBE0. However, larger deviations (up to 366 ppm) occur for Hg chemical shifts in HgBr(2) and HgI(2) when ZORA results are compared with four-component calculations with non-collinear spin-density contribution to the XC kernel. For the ZORA calculations it is necessary to use large basis sets (QZ4P) and the TZ2P basis set may give errors of ～500 ppm for the Hg chemical shifts, despite deceivingly good agreement with experimental data. A Gaussian nucleus model for the Coulomb potential reduces the Hg shielding constants by ～100-500 ppm and the Hg chemical shifts by 1-143 ppm compared to the point nucleus model depending on the atomic number Z of the coordinating atom and the level of theory. The effect on the shielding constants of the lighter nuclei (C, Cl, Br, I) is, however, negligible.     

Chlorophosphonates: inexpensive precursors for stereodefined chloro-substituted olefins and unsymmetrical disubstituted acetylenes

New chlorophosphonates bearing a 1,3,2-dioxaphosphorinane ring which are useful for the stereospecific synthesis of 5-chlorofurfuryl substituted olefins and chloro-substituted dienes have been obtained by an easy, inexpensive route. The utility of some of these in the synthesis of ferrocenyl- and anthracenyl-substituted unsymmetrical acetylenes has been explored. The structures of the phosphonates (OCH(2)CMe(2)CH(2)O)P(O)CH(2)(C(4)H(2)ClO) (4) and (OCH(2)CMe(2)CH(2)O)P(O)(CH=CHCH(Cl)Ph (7) have been determined; in addition, the stereochemistry of (5-chlorofurfuryl)CH=CH(4-ClC(6)H(4)) (13b) and 2, 4-Cl(2)C(6)H(3)-CH=CH-CH=C(Ph)Cl (14a) is unambiguously proved by the X-ray structure determination.     

Synthesis and spectroscopy of N3P3X5OCH=CH2 (X = Cl, F, OCH3, OCH2CF3, N(CH3)2) and N3P3X4(OCH=CH2)2 (X = Cl, N(CH3)2). Correlations of ultraviolet photoelectron spectroscopy and nuclear magnetic resonance data to electronic and geometrical structure

The syntheses of the vinyloxycyclotriphosphazene derivatives N3P3X5OCH=CH2 (X = OMe, OCH2CF3) and the N3P3(NMe2)4(OCH=CH2)2 isomeric mixture along with improved preparations of N3P3X5OCH=CH2 (X = F, NMe2) are reported. The interactions between the vinyloxy function and the cyclophosphazene in these and the previously reported N3P3Cl5 (OCH=CH2) and N3P3F6-n(OCH=CH2)n (n = 1-4) have been examined by ultraviolet photoelectron spectroscopy (UPS) and NMR spectroscopy. The UPS data for the chloro and fluoro derivatives show a strong electron-withdrawing effect of the phosphazene on the olefin that is mediated with decreasing halogen substitution. The 1H and 13C NMR data for N3P3X5OCH=CH2 (X = F, Cl, OMe, OCH2CF3, NMe2) show significant changes as a function of the phosphazene substituent. There is a linear correlation between the beta-carbon chemical shift on the vinyloxy unit and the phosphorus chemical shift at the vinyloxyphosphorus centers. The chemical shifts of the different phosphorus centers on each ring are also related in a linear fashion. These relationships may be understood in terms of the relative electron donor-acceptor abilities of the substituents on the phosphazene ring. The 1H NMR spectra of the N3P3(NMe2)4(OCH-CH2)2 isomeric mixture allow for assignment of the relative amounts of cis and trans isomers. A model for the observed cis preference in the formation of N3P3Cl4(OCH=CH)2 is presented.     

含茂基、烷氧基及氯离子混合配镧系金属有机化合物的合成及表征

本文通过二茂基镧不金属氯化物Ｃｐ２ＬｎＣｌ（Ｃｐ＝Ｃ５Ｈ５；Ｌｎ＝Ｄｙ，Ｙｂ）与烷基醇ＲＯＨ（Ｒ＝－ＣＨ２ＣＨ２ＣＨ３，－ＣＨ２ＣＨ＝ＣＨ２）在四氢呋喃中反应，合成了四个新的含三种不同配位基的镧系金属有机化合物；元素分析，红外光谱及质谱分析表明这些化合物可能具有三聚体结构，即：［ＣｐＬｎ（ＯＲ）Ｃｌ］３。     

High-accuracy thermochemistry of atmospherically important fluorinated and chlorinated methane derivatives

High-precision quantum chemical calculations have been performed for atmospherically important halomethane derivatives including CF, CF(3), CHF(2), CH(2)F, CF(2), CF(4), CHF, CHF(3), CH(3)F, CH(2)F(2), CCl, CCl(3), CHCl(2), CH(2)Cl, CCl(2), CCl(4), CHCl, CHCl(3), CH(3)Cl, CH(2)Cl(2), CHFCl, CF(2)Cl, CFCl(2), CFCl, CFCl(3), CF(2)Cl(2), CF(3)Cl, CHFCl(2), CHF(2)Cl, and CH(2)FCl. Theoretical estimates for the standard enthalpy of formation at 0 and 298.15 K as well as for the entropy at 298.15 K are presented. The determined values are mostly within the experimental uncertainty where accurate experimental results are available, while for the majority of the considered heat of formation and entropy values the present results represent the best available estimates.     

Synthesis and characterization of nickel(II) bis(alkylthio)salen complexes

NiX2(2-RSC6H4CH=NCH2CH2N=CHC6H4SR-2) (NiX2L; L = 5) (1a, X = Br, R = C6H13; 1b, X = Cl, R = C12H25) and NiX2(2-C6H13SC6H4CH2NHCH2CH2NHCH2C6H4SC6H13-2) (NiX2L; L = 6) (2a, X = Br; 2b, X = Cl; 2c, X = OClO3) were prepared from ligands 5 and 6, respectively. The 1:2 metal-ligand complex Ni(OClO3)2(2-RSC6H4CH2NHCH2CH2NHCH2C6H4SR-2)2 3, was obtained from an EtOH solution of 2c. The characterization of paramagnetic 1-3 included single-crystal X-ray diffraction studies of 1a and 3. Complex 2c converted into 3 in the presence of excess ligand 6 in CHCl3.     

1H, 13C and 15N NMR coordination shifts in gold(III), cobalt(III), rhodium(III) chloride complexes with pyridine, 2,2'-bipyridine and 1,10-phenanthroline

Au(III), Co(III) and Rh(III) chloride complexes with pyridine (py), 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) of the general formulae [M1LCl3], trans-[M2L4Cl2]+, mer-[M2L3Cl3], [M1(LL)Cl2]+, cis-[M2(LL)2Cl2]+, where M1=Au; M2=Co, Rh; L=py; LL=bpy, phen, were studied by 1H--13C HMBC and 1H--15N HMQC/HSQC. The 1H, 13C and 15N coordination shifts (the latter from ca-78 to ca-107 ppm) are discussed in relation to the type of metal, electron configuration, coordination sphere geometry and the type of ligand. The 13C and 15N chemical shifts were also calculated by quantum-chemical NMR methods, which reproduced well the experimental tendencies concerning the coordination sphere geometry and the ligand type.     

Packing interactions in hydrated and anhydrous forms of the antibiotic Ciprofloxacin: a solid-state NMR, X-ray diffraction, and computer simulation study

We present an experimental NMR, X-ray diffraction (XRD), and computational study of the supramolecular assemblies of two crystalline forms of Ciprofloxacin: one anhydrate and one hydrate forming water wormholes. The resonance assignment of up to 51 and 54 distinct (13)C and (1)H resonances for the hydrate is reported. The effect of crystal packing, identified by XRD, on the (1)H and (13)C chemical shifts including weak interionic H-bonds, is quantified; (1)H chemical shift changes up to ～-3.5 ppm for CH···π contacts and ～+2 ppm (CH···O((-))); ～+4.7 ppm (((+))NH···O((-))) for H-bonds. Water intake induces chemical shift changes up to 2 and 5 ppm for (1)H and (13)C nuclei, respectively. Such chemical shifts are found to be sensitive detectors of hydration/dehydration in highly insoluble hydrates.     

Stereoelectronic and inductive effects on 1H and 13C NMR chemical shifts of some cis-1,3-disubstituted cyclohexanes

This work presents the substituent effects on the 1H and 13C NMR chemical shifts in the cis-isomer of 3-Y-cyclohexanols (Y = Cl, Br, I, CH3, N(CH3)2 and OCH3) and 3-Y-1-methoxycyclohexanes (Y = F, Cl, Br, I, CH3, N(CH3)2 and OCH3). It was observed that the H-3 chemical shift, due to the substituent alpha-effect, increases with the increase of substituent electronegativity when Y is from the second row of the periodic table of elements, (CH3 *sigma(C3--H3a) interaction energy. This interaction energy, for the halogenated compounds, decreases with an increase in size of the halogen, and this is a possible reason for the largest measured chemical shift for H-3 of the iodo-derivatives. The beta-effect of the analyzed compounds showed that the chemical shift of hydrogens at C-2 and C-4 increases with the decrease of n(Y) --> *sigma(C2-C3) and n(Y) --> *sigma(C3-C4) interaction energies, respectively, showing a behavior similar to H-3. The alpha-effect on 13C chemical shifts correlates well with substituent electronegativity, while the beta-effect is inversely related to electronegativity in halogenated compounds. NBO analysis indicated that the substituent inductive effect is the predominant effect on 13C NMR chemical shift changes for the alpha-carbon. It was also observed that C-2 and C-4 chemical shifts for compounds with N(CH3)2, OCH3 and F are more shielded in comparison to the compounds having a halogen, most probably because of the larger interaction of the lone pair of more electronegative atoms (n(N) > n(O) > n(F)) with *sigma(C2-C3), *sigma(C3-C4) and *sigma(C3-H3a) in comparison with the same type of interaction with the lone pair of the other halogens.