Ab initio MRD-CI calculations for breaking a chemical bond in a molecule in a crystal or other solid environment. III. Me2N?NO2 decomposition of dimethylnitramine in a large crystalline environment

Recently we extended our strategy for MRD-CI (multireference double excitation-configuration interaction) calculations, based on localized/local orbitals and an “effective” CI Hamiltonian, for molecular decompositions of large molecules to breaking a chemical bond in a molecule in a crystalline or other solid environment. Our technique begins with an explicit quantum chemical SCF calculation for a reference molecule surrounded by a number of other molecules in the multipole environment of more distant neighbors. The resulting canonical molecular orbitals are then localized, and the localized occupied and virtual orbitals in the region of interest are included explicitly in the MRD-CI with the remainder of the occupied localized orbitals being folded into an “effective” CI Hamiltonian. The MRD-CI calculations are then carried out for breaking a bond in the reference molecule. This method is completely general in that the space treated explicitly, as well as the surrounding space, may contain voids, defects, deformations, dislocations, impurities, dopants, edges and surfaces, boundaries, etc. Dimethylnitramine is the smallest prototype of the energetic R₂N—NO₂ nitramines, such as the 6-member ring RDX or the 8-member ring HMX. Decomposition of energetic compounds is initiated in the solid by a breaking of the target bond. Thus, it is crucial to know the difference in energy between breaking a bond in an isolated energetic molecule versus in the molecule in a solid. In the present study, we have carried out MRD-CI calculations for the Me₂N—NO₂ dissociation of dimethylnitramine in a dimethylnitramine crystal. The cases we investigated were one dimethylnitramine molecule (surrounded by 53 and 685 neighboring dimethylnitramine molecules represented by multipoles), three dimethylnitramine molecules, and three dimethylnitramine molecules (surrounded by 683 neighbors). All multipoles were cumulative atomic multipoles up through quadrupoles. The MRD-CI calculations on dimethylnitramine required large numbers of reference configurations from which were allowed all single and double excitations.     

DFT and CASPT2 study of two thermal reactions of nitromethane: C–N bond cleavage and nitro-to-nitrite isomerization. An example of the inverse symmetry breaking deficiency in density functional calculations of an homolytic dissociation

The reaction paths of nitromethane leading to the dissociation products or isomerization to methyl nitrite have been computationally investigated at the CAS-SCF and DFT levels of theory. Additionally, the CAS-SCF wave functions were used as reference in a second-order perturbation treatment, CASPT2, in order to obtain a good estimate for the activation energy of each reaction path. Both methods predict the isomerization as a concerted reaction. However, the behavior of the two approximations with respect to dissociation is rather different; while CASPT2 predicts a barrier height of (≈59 kcal/mol) in good accordance with the experimental activation energy (59.0 kcal/mol), B3-LYP/6-31G^* calculations overestimate the barrier for more than 30 kcal/mol. The DFT prediction of the dissociation channel exhibits inverse symmetry breaking, dissociating to the unphysical absurd CH₃^δ+ plus NO₂^δ−.     

Highly efficient nitration of phenolic compounds in solid phase or solution using Bi(NO3)3.5H2O as nitrating reagent

[reaction: see text] Bi(NO(3))(3).5H(2)O was used as an efficient nitrating reagent in the nitration of phenolic compounds to give nitrated phenols in good to high yields. The nitration reaction proceeded smoothly by grinding 1 equiv of phenol, 2-methylphenol, 4-methylphenol, or 4-chlorophenol and Bi(NO(3))(3).5H(2)O, and the nitration of other phenolic compounds could be performed in acetone at ambient temperature (22-30 degrees C).     

Neutral molecule/crown ether interactions 5. Comparison of the C−H acidic interactions of nitromethane and acetonitrile with 18-crown-6 and dibenzo-18-crown-6. Crystal structures of dibenzo-18-crown-6·2 CH3NO2 and dibenzo-18-crown-6·2 CH3CN

Complete structural characterization of dibenzo-18-crown-6·2 CH₃NO₂ and dibenzo-18-crown-6·2 CH₃CN have been carried out, including location and refinement of the methyl hydrogen atoms. Dibenzo-18-crown-6·2 CH₃NO₂ is monoclinic,P2₁/c, with (at –150°C)a=9.573(2),b=14.636(2),c=33.471(7) Å, =93.77(2)°, andD _calc=1.37 g cm^–3 forZ=8. Interactions between the solvent methyl groups and the crown ethers and other solvent nitro groups associate the 1 : 2 complexes into polymeric chains alongb. The acetonitrile adduct exists as discreet 1 : 2 complexes in the solid state with C–H...O interactions exlusively to the ether. This complex is triclinic,P 1, with (at –150°C)a=9.458(6),b=9.570(5),c=14.404(5) Å, =73.18(4), =79.85(5), =66.82(6)°, andD _calc=1.28 g cm^–3 forZ=2. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82070 (22 pages).For part 4, see reference [1].     

Complexes of platinum(II) containing neutral and deprotonated 9-methyladenine. Synthesis, x-ray structures, and NMR studies on the cyclic trimer cis-[L2Pt[9-MeAd([bond]H)]]3(NO3)3 and the Dinuclear cis-[L2Pt(ONO2)[9-MeAd([bond]H)]PtL2](NO3)2 (L = PMePh2)

The dinuclear hydroxo complex cis-[L(2)Pt(mu-OH)](2)(NO(3))(2) (L = PMePh(2), 1), in CH(2)Cl(2), CH(3)CN, or DMF solution, deprotonates the NH(2) group of 9-methyladenine (9-MeAd) to give the complex cis-[L(2)Pt[9-MeAd(-H)]](3)(NO(3))(3), 2, which was isolated in good yield. The X-ray structure shows that the nucleobase binds symmetrically the metal centers through the N(1),N(6) atoms forming a cyclic trimer with Pt...Pt distances in the range 5.202(1)-5.382(1) A. Dissolution of 2 in DMSO or DMF determines the partial (or total) dissociation of the cyclic structure to form several fragments. A multinuclear NMR analysis of the resulting mixture supports the presence of the mononuclear species cis-[L(2)Pt[9-MeAd(-H)]](+), 3, in which the deprotonated nucleobase chelates the metal center with the N(6),N(7) atoms. Addition of a stoichiometric amount of the nitrato complex cis-[L(2)Pt(ONO(2))(2)] (L = PMePh(2), 4) to a DMSO or DMF solution of 2 affords quantitatively the diplatinated compound cis-[L(2)Pt(ONO(2))[9-MeAd(-H)]PtL(2)](NO(3))(2), 5. The single-crystal X-ray analysis shows that the adenine behaves as a tridentate ligand bridging two cis-L(2)Pt units at the N(1) and N(6),N(7) sites, respectively [Pt(1)-N(1) = 2.109(5) A, Pt(2)-N(6) = 2.095(7) A, Pt(2)-N(7) = 2.126(7) A]. The N(1)-bonded metal center completes the coordination sphere through an oxygen atom of a nitrate group, and its coordination plane is arranged orthogonally with respect the second one. The Pt-O distance [2.109(5) A] is similar to those found in the nitrato complex 4 [2.110 A, average]. The related complex cis-[[L(2)Pt(ONO(2))](2)(9-MeAd)](NO(3))(2), 6, containing the neutral adenine platinated at the N(1),N(7) atoms, was isolated and its stability in solution investigated by NMR spectroscopy. In DMSO, 6 undergoes decomposition forming a mixture of the species 4, 5, and the adenine mono- and bis-adducts cis-[L(2)Pt(9-MeAd)(DMSO)](2+), 7, and cis-[L(2)Pt(9-MeAd)(2)](2+), 8, respectively. This last complex, quantitatively formed upon addition of 9-MeAd (Pt/adenine = 1:2) to the mixture, was also isolated and characterized.     

The crystal structures of α,ω-diaminoalkanecadmium(II) tetracyanonickelate(II)-aromatic molecule inclusion compounds. I. 1,4-diaminobutanecadmium(II) tetracyanonickelate(II)-2,5-xylidine (1/1): Cd(NH2(CH2)4NH2)Ni(CN)4. (CH3)2C6H3NH2

The title compound crystallizes in monoclinic space group P2₁/m with a=9.795(2), b=15.010(2), c=7.125(1) Å, =105.56(1)^o, and Z=2. The structure has been refined to the weighted Rw=0.042 for 2742 reflections collected by counter method. Two-dimensionally extended but wavy cyanometal complex layers are bridged by 1,4-diaminobutane (dabn) to give a three-dimensional host structure which provides a channel-like cavity with the guest 2,5-xylidine molecule. The skeleton of the bridging dabn takes a trans-cis conformation to make the packing efficient between the cavity and the guest molecule. The series of Hofmann-dabn-type Cd(NH₂ (CH₂)₄NH₂) Ni (CN)₄. nG inclusion compounds are described for several aromatic guest molecules G with various stoichiometric coefficients n. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82020 (22 pages).     

The crystal structures of α,ω-diaminoalkanecadmium(II) tetracyanonickelate(II)-aromatic molecule inclusion compounds. II. 1,6-diaminohexanecadmium(II) tetracyanonickelate(II)-o-toluidine (1/1): Cd(NH2(CH2)6NH2)Ni(CN)4.o-CH3C6H4NH2

The title inclusion compound crystallizes in monoclinic space group P2/m, with a=9.541(2), b=7.569(2), and c=7.199(1) Å, =100.3(1)^o, and Z=1. The structure has been refined to a conventional R=0.036 for 1973 independent reflections collected by counter method. The host metal complex has the structure similar to that of 1,4-diaminobutanecadmium(II) tetracyanonickelate(II)-2,5-xylidine (1/1) with respect to the two-dimensionally extended wavy cyanometal complex sheets bridged by the ,-diaminoalkane ligands at the respective Cd atoms in adjacent sheets providing a channel-like cavity with the guest aromatic molecule. The guesto-toluidine molecule is surrounded by four 1,6-diaminohexane bridges taking an all-trans conformation of the aliphatic chain and show disorder in the orientation in the cavity. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82021 (21 pages).     

Contributions to the Chemistry of Silicon—Sulphur Compounds. 66. Synthesis,crystal and molecular structure of bis(tri-tert-butoxysilanethiolato)(acetonitrile)cobalt(II)[(t-C4H9O)3SiS]2Co(NCCH3)

The title compound [(t-C₄H₉O)₃SiS]₂Co(NCCH₃)] 1 was obtained by reaction of anhydrous cobalt(II) chloride with tri-tert-butoxysilanethiol and triethylamine in acetonitrile as a solvent. The compound crystallizes as deep-blue orthorhombic plates with a = 17.779(4), b = 45.363(9), c = 9.096(2) Å, space group Fdd2 and Z = 8. The structure was solved by Patterson synthesis and refined to the R value of 0.0343. The crystal consists of mononuclear complexes in which the cobalt atom is five-fold coordinated to two sulphurs, two oxygens and one nitrogen in a distorted trigonal bipyramidal arrangement. The relevant bond distances and angles are: Co? S, 2.2680(7); Co? N, 2.065(4); Co? O1, 2.283(2); S? Si, 2.0666(8) Å; S? Co? S′, 119.14(4); N? Co? S, 120.43(2); O1? Co? O1′, 178.81(10)°.     

First example of a Sn-C bond cleaved product in the reaction of Ph3SnOSnPh3 with carboxylic acids. 3D-supramolecular network formation in the X-ray crystal structure of [Ph2Sn(OH)OC(O)(Rf)]2, Rf = 2,4,6-(CF3)3C6H2

A 1:2 reaction of Ph3SnOSnPh3 1 with RfCOOH 2 leads to the formation of [Ph2Sn(OH)OC(O)(Rf)]2 3, by means of a facile Sn-C bond cleavage process.     

Affinity of a new copper(II) complex to DNA/BSA and antioxidant/radical scavenging activities: crystal structure of [Cu(4,7-diphenyl-1,10-phenanthroline)(leucine)(NO3)(H2O)]

A new copper(II) complex, [Cu(Bphen)(Leu)(NO₃)(H₂O)] (Bphen = 4,7-diphenyl-1,10-phenanthroline, leu = L-leucine), has been synthesized and characterized by IR spectroscopy, CHN analysis, and single-crystal X-ray diffraction techniques. The CT-DNA binding properties of the complex have been investigated by both absorption and emission spectroscopy. The binding parameters for the fluorescence Scatchard plot were also determined. Further, the interaction of the complex with bovine serum albumin (BSA) has been investigated using absorption and emission spectroscopy. The thermodynamic parameters, free energy change (ΔG), enthalpy change (ΔH), and entropy change (ΔS), were calculated by the van’t Hoff equation and discussed. The distance between BSA and the complex has been obtained according to fluorescence resonance energy transfer. Conformational changes of BSA have been observed from synchronous fluorescence. Antioxidant and radical scavenging activities of the complex were determined by various in vitro assays such as 1,1-diphenyl-2-picryl-hydrazyl free radicals (DPPH˙), 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) radicals (ABTS˙⁺), and reducing ability determination by H₂O₂ scavenging methods.     

Synthesis (via reductive elimination or metathesis) and x-ray crystal structure of a tetrameric meso-tin(II) metallocycle Sn(CHSiMe3C6H4︹CHSiMe3−o)2, and characterisation of meso,meso−Sn(CHSiMe3C6H4︹CHSiMe3−o)2

A yellow, diamagnetic tin(II) metallocycle, $meso?S\stackrel{︹}{n(CHSiM{e}_3{C}_6{H}_4}CHSiM{e}_3?o)$ (I) showing a monomeric parent ion in its mass spectrum and a first ionisation energy at 7.6 eV in its photoelectron spectrum, is tetrameric in the solid with an Sn₄ ring (Sn—Sn 2.852(3)Å), as determined by X-ray structure analysis, and was isolated as a minor product on treating SnCl₄ with [{o-C₆H₄ (CHSiMe₃)₂}{Li(tmeda)}₂] (II) at ?78° C (but not +30° C) [tmeda = Me₂NCH₂CH₂NMe₂] in OEt₂. The major product is the spirocyclic complex $S\stackrel{︹}{n(CHSiM{e}_3{C}_6{H}_4}CHSiM{e}_3?o{)}_2$ in which both ligands are in the meso configuration; compound I was more conveniently obtained from II and Sn(OC₆H₂Me-4-Bu^t₂-2,6)₂     

13C?1H spin–spin couplings in cyclic α,β-unsaturated enones and their protonated derivatives. Measurements and quantum chemical calculations

Direct and long-range ¹³C? ¹H coupling constants are presented for the enone moieties of cyclopent-2-enone, cyclohex-2-enone and their protonated derivatives. A correlation is given between the experimental values and the results of quantum chemical calculations (CNDO/2, INDO). The existing calculations are modified in order to improve the relationship between the calculated and experimental results.