Molecular and multidimensional polyoxotungstates functionalized by {Cu(bpy)}2+ groups

Five new materials built from polyoxotungstates and Cu(ii) ions as linkers have been synthesized by hydrothermal reactions from a mixture of sodium tungstate, copper chloride and bipyridine. The value of the initial pH, the nature of the heteroelement (P or Si) and of the ligand (2,2'- and/or 4,4'-bipyridine) permit the control of the nature of the polyoxotungstate clusters and their connectivity via the copper ions, and hence the dimensionality of the framework. A single phase has been obtained with silicon as heteroelement at an initial pH of 5, namely the 2D material [SiW(12)O(40)][Cu(2,2'-bpy)(2)](2).10H(2)O (1) with saturated Keggin polyoxotungstates linked by {Cu(2,2'-bpy)(2)}(2+) groups. With phosphorous as heteroelement and at the same initial pH, three different structures have been isolated according to the nature of the ligand. Indeed, the two 1D materials [{Cu(5)(2,2'-bpy)(5)(H(2)O)(HPO(4))(PO(4))}PW(11)CuO(39)].6H(2)O (2) with 2,2'-bpy and [4,4'-Hbpy][{Cu(2)(2,2'-bpy)(2)(4,4'-bpy)(2.5)}PW(11)CuO(39)].16H(2)O (3) with a mixture of 2,2'- and 4,4'-bpy have been characterized, and a coordination polymer with polyoxometalate guests Na(3)[4,4'-Hbpy]{Cu(4)(4,4'-bpy)(8)(H(2)O)(8)}[PW(11)CuO(39)(H(2)O)][PW(10)Cu(2)O(38)(H(2)O)(2)].38H(2)O (4) with 4,4'-bpy has been obtained. Finally, in basic medium (pH = 10) the unprecedented molecular cluster Na(2)[{Cu(8)(2,2'-bpy)(8)}(PW(8)O(31))(2)].15H(2)O (5) has been evidenced. Magnetic studies of compound 2 revealed that the predominant interactions involve only 4 paramagnetic centers, which are interacting within pairs, among the 6 Cu(ii) centers. The chi(M)T=f(T) curve can be fitted using the dinuclear expression appropriate to the HDVV isotropic exchange Hamiltonian H=-JS(1)xS(2), with S(1)=S(2)=(1/2) and J=-105.4 cm(-1), showing strong antiferromagnetic interactions within the two Cu(ii) pairs.     

Resonance hyper-Raman scattering from conjugated organic donor-acceptor "push-pull" chromophores with large first hyperpolarizabilities

Resonance hyper-Raman spectra have been obtained using 1064 nm excitation for several electron donor-acceptor-substituted, pi-conjugated "push-pull" molecules that have large second harmonic hyperpolarizabilities. The hyper-Raman spectra are nearly identical to the resonance Raman spectra measured with 532 nm excitation. This indicates that both the second harmonic hyperpolarizability and the linear absorption are dominated by the same, single electronic transition that is both one- and two-photon allowed. Comparison of resonance Raman and resonance hyper-Raman spectra is proposed as an experimental test of the common two-electronic-state model for the first hyperpolarizability.     

X-ray crystallographic determination of the structure and conformation of trans-2-tribromomethyl-5-trichloromethyl-1,3-dioxolan-4-one: an analogue of chloralide

trans-2-Tribromomethyl-5-trichloromethyl-1,3-dioxolan-4-one is monoclinic,P2₁/c,a=6.381(6),b=17.116(6),c=10.598(5) Å,=94.07(6)°,Z=4. The structure was solved by direct methods from data collected at room temperature on an Enraf-Nonius CAD4 diffractometer, and refined by full-matrix least squares to a finalR value of 0.042 using 1274 reflections. The conformation of the molecule is very similar to that of chloralide with the 5-mem-bered ring being almost planar. Evidence is provided for a possible C-HO intermolecular interaction. The average C-Br distance is 1.931(11) Å and the average Br-C-Br angle is 109.7(9)°. A table of average C-Br bond lengths and Br-C-Br angles, with the ranges for these parameters, in compounds containing -CBr₃ groups is given. Some¹H NMR and mass spectra data are included for the title compound and for chloralide.     

C−H...π(Ar)...H−C host-guest interactions in a novel air-stable cyanoborate clathrate

The host compound forms a coordinato-clathrate in a coordination assisted host lattice. The host lattice is provided by hydrogen bonding between the nitrogen atom of the cyano group and two hydrogen atoms from the phosphonium methyl group. Guest molecules ofp-xylene occupy constricted channels in the lattice. The twop-xylene molecules participate in C–H...(Ar)...H–C interactions. Results from searches of the Cambridge Structural Database for other C–H...(Ar)...H–C and C–H...(Ar) interactions are presented.     

Synthesis and X-ray crystal structure of three polyazamacrocycles having sulfonate pendant groups: Piperazinyl-monomethanesulfonic acid,sodium hydrogen 1,4,7-triazacyclononane-N,N′-di(methanesulfonate) and 1,4,7,10-tetraazacyclododecane-N,N′-di(methanesulfonic acid)

C₅H₁₀N₂O₃S,1, monoclinicC2/c,a=17.545(5),b=6.822(8),c=13.928(2),=108.36(7),Z=8, MoK, =0.7107 Å,=3.56cm^–1,R=0.061,R _w =0.099. C₈H₁₆N₃O₆S₂Na·2H₂O,2, orthorhombicPna2₁,a=17.964(8),b=10.157(1),c=8.263(4),Z=4, MoK, =0.7107 Å,=4.07 cm^–1,R=0.040,R _w =0.043. C₁₀H₂₀N₄O₆S₂·2H₂O,3, monoclinicP2₁/n,a=9.142(9),b=13.576(7),c=14.028(8),=94.096(8),Z=4, MoK, =0.7107 Å,=3.37 cm^–1,R=0.063,R _w =0.074. Compounds1, 2, and3 were prepared from the pH-dependent sulfomethylation of the di- and polyazamacrocycles.     

Two acetylamino derivatives of 2,4-bis(trichloromethyl)-1,3-benzdioxin showing different types of hydrogen bonding: (a) (C13C)CH⋯O=C and (b) N-H⋯O=C

8-Acetylamino-6-methyl-2,4-bis(trichloromethyl)-1,3-benzdioxin, (I), is monoclinic,P2₁/c,a=15.174(4),b=11.977(7),c=9.911(3)Å,=99.72(2)°. 6-Acetylamino-2,4-bis(trichloromethyl)-1,3-benzdioxin, (II), is monoclinic,P2₁/_n,a=5.927(4),b=40.623(1),c =7.120(3)Å,=91.39(4)°. In compound (I) the imino hydrogen atom is locked in an intramolecular hydrogen bond to the proximate oxygen atom of the heterocyclic ring and is not available for intermolecular hydrogen bonding. Instead the weakly acidic hydrogen atom [Cl₃C-C(2)]H takes part in a hydrogen bond to the carbonyl oxygen atom in another molecule. In compound (II) a normal intermolecular hydrogen bond of the type N-HO=C occurs. The 6-acetylam-ino group is twisted about the (C_Ar-N) bond such that the angles NHO=C, C_ArH_ArO=C, NHOH_ArC_Ar, at the carbonyl oxygen group total 360° (where NH is in the related molecule). The packing in both compounds takes the form of infinite chains and in compound (II) partial overlap of the aromatic ring and the acetylamino group, with very little offset, also occurs.     

Isomerism in some 1-oxa-3,5-dithians and the X-ray structure determination of 2,6-bis(trichloromethyl)-4-dichloromethylene-1-oxa-3,5-dithian

2,6-bis (trichloromethyl)-4-dichloromethylene-1-oxa-3,5-dithian is triclinic,P¯1,a=10.125(3),b=10.294(3),c=14.631(10) Å,=92.84(5),=96.51(5), =96.18(2)°,V=1503 ų,Z=4. The structure was solved by direct methods, from data collected at room temperature on an Enraf-Nonius CAD4 diffractometer, and refined by least squares to a finalR value of 0.035 using 3961 reflections. The conformation of the molecules is twist-boat, one molecule being almost symmetrically twisted about the O-C(Cl₂) direction. The range of endocyclic O-C-S angles is 111.8(3) to 115.1(3)° and data are given which support the possibility of there being a correlation between the endocyclic O-C(X)-S angle, the C-O-C(X)-C(Cl₃) torsion angle, and the C-S-C(X)-C(Cl₃) torsion angle. The -CCl₃ groups are in pseudoequatorial positions. Average bond lengths (Å) for the two molecules are C-O 1.405, C(sp ³)-S 1.822, C(sp ²)-S 1.759, C-C_eq 1.529 and average endocyclic angles (°) are O 117.3, C (sp ³) 113.5, S 97.4, C(sp ²) 119.3, the esds on the individual bond lengths and angles being in the ranges of 0.003–0.004 Å and 0.2–0.4° respectively.     

Structure and conformation of 6-nitro-2-trichloromethyl-1,3-benzdioxin-4-one: X-ray crystallographic determination

6-nitro-2-trichloromethyl-1,3-benzdioxin-4-one is monoclinic,P2₁/n;a=5.969(2),b=11.646(1),c=16.953(1) Å;=98.03(2)°;Z=4. The structure was solved by direct methods, from data collected at room temperature on an Enraf-Nonius CAD4 diffractometer, and refined by least squares to a finalR value of 0.030 using 1530 reflections.The heterocyclic ring is a distorted half-boat and is substituted equatorially by a trichloromethyl group. Dihedral angles are (a) 4.87(7)° between the mean plane of the aromatic ring and the plane containing the two carbon atoms common to both rings plus the two atoms bonded to these, and (b) 16.8(2)° between the carbonyl group and the aromatic ring. The conformation is discussed with reference to the two previously reported X-ray structures of 1,3-benzdioxin-4-ones and to two isocoumarins.     

Structure and conformation of 6-nitro-2,4-bis(dichloromethyl)-1,3-benzdioxin

6-Nitro-2,4-bis(dichloromethyl)-1,3-benzdioxin is monoclinic,P2₁/c, witha=8.514(1),b=22.187(3),c=7.931(1) Å,=117.96(1)°,Z=4. The structure was solved, from data collected with MoK radiation on an Enraf-Nonius CAD4 diffractometer, by direct methods and refined by full-matrix least squares using 2170 unique reflections to give a finalR factor of 0.032. The heterocyclic ring in the title compound has an envelope conformation with thecis-dichloromethyl groups in pseudoequatorial positions. The average C-C(HCl₂) distance is 1.516(4) Å. A comparison is given with the structure of the analogous compound 6-nitro-2,4-bis(trichloromethyl)-1,3-benzdioxin (Irving, A., and Irving, H. M. N. H. (1986)J. Crystallogr. Spectrosc. Res. 16, 703) which also containscis-halogenoalkyl groups but in which the –CCl₃ group at the 4-position occupies a pseudoaxial position.     

Portfolio Optimization With a Guaranteed Minimum Maturity Benefit and Risk-Adjusted Fees

Methodology and Computing in Applied Probability - We study a portfolio optimization problem involving the loss averse policyholder of a variable annuity with a guaranteed minimum maturity benefit....