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Single-crystal X-ray structure determinations of the parent isoxindigo (1), C16H8O4, together with those of derivatives substituted in both benzene rings with ( i ) t-butyl groups in the 5- and 7-positions [derivative (2)] and (ii) methoxy and t-butyl groups in the 5- and 7- positions respectively [two polymorphs, (3α,8)] have been determined in order to examine the possibility of distortion of molecular planarity by substituent steric effects, and the spectroscopic consequences thereof. Crystals of (1) are monoclinic, P21/n, a 17.69(1), b 5.690(3), c5.693(3)Ǻ, β 100.52(5), Z 2; after least-squares refinement, a residual R 0.067 was obtained for No 385 ?observed? Independent reflections. For (2), C32H40O4, crystals are monoclinic, P21/n, a 16.402(8), b 12.313(6), c 13.913(8)Ǻ, β 96.75(4), Z4; R 0.088 for No 1261. For (3), C26H28O6 (α-form), crystals are orthorhombic, Pcab , a 10.449(4), b 12.477(4), c 17.825(6)Ǻ, Z 4; R 0.058 for No 959; in the case of the β-form of (3), crystals are monoclinic, P21/n, a 6.828(2), b 15.464(3), c 10.770(3) Ǻ, β 98.58(4), Z 2. In (1) and (3α,β), the molecules all lie disposed about crystallographically imposed symmetry elements, with one-half of the molecule, with a substantially planar fused-ring skeleton, comprising the asymmetric unit. In (2), the full molecule is the asymmetric unit; the fused-ring skeletons are substantially planar also, but the molecule exhibits a substantial twist about the bond connecting the two halves, with an interplanar dlhedral angle of 16.8°. This is ascribed to the steric effect of the large and more numerous t-butyl substituents.

The crystal and molecular structures of [1]benzopyrano[4,3- c][1]benzopyran-5,11-done (dibenzo-naphthyrone) and three of its symmetrically tetrasubstituted derivatives have been determined by single-crystal X-ray diffraction methods. Only the tetra-t-butyl-substituted dibenzonaphthyrone was found to deviate significantly from planarity by having the two carbonyl groups folded and 'syn'-oriented relative to the plane of the connecting ethylene double bond. The dihedral angle between the two aromatic rings was found to be 25. The molecular geometry of all the other dibenzo-naphthyrones in their crystalline states is characterized by planarity, and their structures are centrosymmetric.

The crystal structure of the title compound, C15H9NOS2, has been determined by single-crystal X-ray diffraction methods at 295 K, being refined to a residual of 0.057 for 2006 independent 'observed' reflections. Crystals are monoclinic, P21/n, a 13.467(5), b 9.426(3), c 20.680(9) , β 107.38(3), Z = 8. The two molecules are substantially planar; close intermolecular contacts as well as bond-order distributions are strongly suggestive of negative charge localization on the oxygen atoms with positive charge density localized in the S-C-S string.

The crystal structure of the title compound, C12H8N2O2, has been determined by single crystal X-ray diffraction methods at 295 K and refined by least-squares methods to a conventional residual of 0.050 for 1208 independent 'observed' reflections. Crystals are monoclinic, P21/a, a 14.375(10), b 6.330(8), c 10.780(8) , β 102.52(6), Z = 4. The molecular skeleton is substantially planar (σ(non-hydrogen atoms), 0.07 ) with a delocalization pattern representative of a betaine comprising a pyrazolinium cation and a delocalized ,β-diketone rather than an 8 π-electron delocalized system.

The crystal structures of the title compounds have been established by single-crystal X-ray diffraction techniques at 295 K, being refined by least squares to residuals of 0.043, 0.036, 0.036 for 2057, 3176 and 3468 independent 'observed' reflections respectively. Crystals of [Pd(diphos)2] C12 (1) (diphos = Ph2P(CH2)2PPh2) are monoclinic, P21/c, with a 12.779(9), b 18.084(10), c 12.942(6) , β 119.29(5), 22; for the isostructural platinum analogue (2), a 12.789(4), b 18.099(7), c 12.965(4) , β 1l9.39(2). Crystals of [PtCl2(diphos)].CH2Cl2, (3), are orthorhombic, P212121, with a 21.360(6), b 13.499(4), c 9.551(5) Z 4. Complexes (1) and (2) are also solvated but the nature of the solvation is complicated by disorder and less clearcut than in (3). In (1), Pd-P distances are 2.342(2), 2.347(2) in a centrosymmetric molecule; in (2), Pt-P distances are 2.332(2), 2.335(2) , while in (3), Pt-P distances are 2.230(2), 2.224(3) and Pt-Cl are both 2.355(2) [cf. 2.233(2), 2.226(2), (2.361(2), 2.357(2)) respectively for the previously studied palladium analogue].

Flindercarpin-2, C32H40013, isolated from the bark of Flindersia laecicarpa C.T. White & Francis (Rutaceae) was shown by spectroscopic and crystallographic studies to be a pentanortriterpenoid, methyl (S)-(acetoxy){[3'S-(3α,3aα,4 α,5β,6α,6aα,7α,10aα,11aα)]-5',6'-diacetoxy-7'-(furan-3??-yl)-2',2'-3a',6a',11a'-pentamethyl-12'-methylene-9'-oxo-2',3',3a',4',',6',6a,9',10' 11a'-decahydro-7'H-4',10a'-methano-10a'H-furo[2,3-b]pyrano[3,4-g]oxocin-3'-yl}acetate (2).

The ()-benzyl(methyl)(4-methylphenyl)(naphthalen-1-yl)arsonium cation has been synthesized and subsequently resolved by fractional crystallization of monohydrogen [R-(R*,R*)]-2,3-bis(benzoyloxy)- butanedioate salts. The separated diastereoisomers were converted into the corresponding optically active arsonium bromides by ion-exchange column chromatography. The absolute configuration of the arsonium cation exhibiting a positive rotation at 589 nm (sodium D line) has been established as (R) by single-crystal X-ray analysis of both the bromide and hexafluorophosphate salts. The arsonium bromide with [α]D + 54.8(c, 0.62 in CH2Cl2) crystallizes in the orthorhombic space group P212121 (D24, No.19) with a 22.472(8), b 15.724(7), c 12.585(5) and U 4447(3) 3. The corresponding hexafluorophosphate with [α]D + 19.3 (c, 0.5 in CH2Cl2) crystallizes in the same space group with a 23.56(2), b 16.40(1), c 13.12(1) and U 5067(6) 3. Benzylidene transfer to benzaldehyde from the arsonium ylide derived from either of the arsonium salts produced optically pure (–)-(S)-methyl(4-methylphenyl)(naphthalen-1-yl)arsine, [α]D - 115.9 (c, 0.593 in CHCl3), and partly resolved [R-(R*,R*)]-2,3-diphenyloxiran.

The crystal structure of zerumbone, C15H22O, extracted from the rhizomes of Zingiber zerumbet Smith, has been determined by single-crystal X-ray diffraction at 295(1) K and refined by least squares to a residual of 0.051 for 925 'observed' reflections. Crystals are monoclinic, space group P21/c, a 9.036(3), b 9.712(5), c 15.643(6) , β 97.19(3), Z = 4. Although the molecule has no chiral centre, the presence of the three trans double bonds confers considerable distortion and rigidity on the eleven-membered ring and renders the whole molecule chiral and potentially resolvable.

The crystal structures of the title compounds are reported. In all cases, the coordination sphere of the nickel atom comprises three bidentate ligands. In (1), [Ni(bpy)2(O2N)] NO3, (Ni-N) is 2.M2 although there are small differences between those nitrogen atoms trans to the nitrite oxygen atoms and the other two. (Ni-O) is 2.12 . In (2), [Ni(bpy)3] NO2/NO3,xH2O, and (3), [Ni(bpy)3]- SO4,7.5H2O, a redetermination, Ni-N is shown to be c. 2.09 ; serious disorder is present among the non-cationic components of (2), precluding a definite assignment of stoichiometry.

The crystal structures of the title compounds are reported. The complex [Ni(C2H8N2)2(NO2)] ClO4 is found to be an infinite polymer with trans N,O-bridging nitrite groups. The zinc analogue of this contains mononuclear units involving a symmetrically chelated nitrite group. The two compounds formed with N,N,N',N'-tetramethylethane-1,2-diamine are isostructural, with the metal having a distorted octahedral ligand environment provided by the amine nitrogen atoms and two chelating nitrite groups. However, while the nitrite ions in the nickel complex are chelated approximately symmetrically, the Zn-O bonds trans to the amine nitrogen atoms (2.30 ) are much longer than those in the cis positions (2.07 ), and an alternative description of the geometry of the zinc complex is as a highly distorted tetrahedral arrangement involving essentially monodentate nitrito groups. The difference in stereochemistry between these two complexes is apparently caused by electronic rather than steric factors, and comparison is also made with the geometry reported for the iso-structural copper complex. The electronic spectra of the two nickel(II) complexes are discussed in relation to their structures, and the infrared frequencies reported for the nitrite groups are correlated with the observed coordination geometries.

The preparation of a series of novel compounds of general formula [Ni5L4(NO2)8(OH)2] formed by ethane-1,2-diamine or one of five N-substituted ethane-1,2-diamines (L) is described. The crystal and molecular structures of the ethane-1,2-diamine, N,N'-diethylethane-1,2-diamine and N,N-dimethylethane-1,2-diamine complexes are reported. Each compound contains a planar, pentameric arrangement of nickel(II) ions, linked by bridging hydroxide and nitrite ligands. The details of the nitrite bridges differ among the complexes, causing differences in their electronic and infrared spectra. The structural variations are probably caused by the differing steric requirements of the amine substituents.

The crystal structures of the dimer [Ni(γmpy)2(NO2)2]2,2C6H6 and the trimer [Ni(βmpy)2(NO2)2]3,- C6Hs (γmpy = 4-methylpyridine, βmpy = 3-methylpyridine) are reported, the latter being the redetermination of a structure described previously. The ligand coordination geometry in each oligomer is essentially octahedral, with neighbouring nickel(II) ions being bridged by two nitrite groups, one through a single oxygen atom and the second through an oxygen and the nitrogen atom. The amine ligands occupy trans coordination sites with the terminal bond positions in both species being taken up by chelating nitrite ions. In both compounds the oligomers pack so that the amine rings form sheets with potential voids in the lattice being filled by clathrated benzene molecules. The electronic spectra of the complexes in the visible region are unusual, showing peaks centred at c. 17500 and c. 20500 cm-1, and the assignment of these is discussed. The infrared stretching frequencies of the nitrite groups in these and other compounds are found to correlate well with the observed nitrogen-oxygen bond lengths.

The crystal structures and spectroscopic properties of the complexes cis-tetrakis(2-methy1imidazole)-(nitrito-O,O')nickel(II) nitrate-methanol (2/1) and trans-tetrakis(2-methylimidazole)dinitritonickel(II) are reported. The nitrite group in the former compound chelates, giving a distorted octahedral ligand coordination geometry. The ligand stereochemistry in the second complex is also a distorted octahedron, with both anions coordinating as trans nitrito groups though with significantly different Ni-O bond lengths and the nickel(II) ion being raised out of the plane of the four imidazole ligand nitrogen atoms towards the closer nitrite group. The Ni-O bond directions also deviate substantially from the fourfold symmetry axis in this latter complex. These distortions apparently occur in order to minimize ligand-ligand repulsions, particularly those associated with the amine methyl substituents. The electronic spectra of both complexes show significant band splittings due to the departure of the ligand field from regular octahedral symmetry and these are discussed in terms of the relative field strengths of the imidazole and nitrito ligands. The structure of hexakis(imidazole)nickel(II) nitrate (redetermination) is also reported.

The crystal and molecular structures of the compounds [Ni(py)4(ONO)2],2py, [Ni(γmpy),(ONO)2] and [Ni(prz)4(ONO)2] are reported.All three are trans nitrito complexes, the pyridine (py) compound containing two pyridine molecules of solvation. The aromatic rings in the first two complexes adopt 'paddle wheel' conformations with pitch angles varying between 40 and 70. The nitrite ions are positioned so as to minimize repulsive interactions with the amines, and it seems likely that these groups bond through oxygen rather than nitrogen because this allows a lesser degree of interligand steric interference. The amine rings in [Ni(prz)4(ONO)2] are orthogonal to the plane containing the nickel and coordinated pyrazole nitrogen atoms; the nitrito groups are disordered between two inequivalent positions, each of which involves hydrogen bonding with the pyrazole NH groups. The nitrite infrared frequencies are similar to those observed for other nickel(II) nitrito complexes except that the antisymmetric NO stretching mode of one of the groups in the pyrazole complex is much lower in energy than expected, being in the range normally associated with a nitrogen-bonded or chelated nitrite group. It is suggested that this deviation may be caused by the hydrogen bonding in the complex. The electronic spectra of the compounds yield 10Dq values of 9100 and 8500 cm-1 for the nitrite ligands in [Ni(py)4(ONO)2] and Ni(prz)4(ONO)2], respectively, placing the nitrito group towards the weaker end of the spectro-chemical series.

The crystal and molecular structure of the complex cis-aquabis[N,N-dimethyl(ethane-l,2-diamine)]- nitronickel(11) perchlorate is reported and the stereochemistry is compared with those observed for other nickel nitrite complexes formed by substituted amines. The electronic spectrum of the complex in the visible region is unusual, showing bands with maxima at 17750 and 21000 cm-1. The latter peak consists of a poorly resolved vibrational progression having an interval of c.600cm-1. While the lower energy band is assigned to the second spin-allowed 'd-d' transition of an octahedral nickel(11) complex, it is suggested that the band at 21000 cm-1 is due either to a metal → ligand charge-transfer transition, or to an internal n(O)→ π* nitrite transition.

The crystal and molecular structures of the complexes [Ni(mstien),(NO2)(H2O)] ClO4 and [Ni(mstien)2(O2N)] Cl are reported (mstien = meso-stilbenediamine, 1,2-diphenylethane-1,2-di-amine). Both compounds contain nickel(II) in an essentially octahedral ligand environment. In the latter complex, the nitrite ion chelates, while in the former it is present as a nitro group situated trans to a coordinated water molecule. In both complexes the conformations observed for the amine chelate rings can be rationalized on the basis that they minimize intramolecular ligand repulsions. The complex [Ni(mstien)2(O2N)] NO2 is isomorphous with the analogous chloride compound, and spectral evidence suggests that the complex [Ni(mstien)2(O2N)] ClO4 also contains a chelating nitrite group. The electronic spectra of single crystals of [Ni(mstien),(O2N)] X (X = Cl- and NO2-) show bands centred at c. 25000 cm-l which exhibit vibrational fine structure. The energies of the progressional spacings are c.600cm-l, which suggests that the bands are probably due to n → π* internal nitrite transitions. The band centred at c. 20500 cm-1 in [Ni(mstien)2(NO2)(H2O)] ClO4 also shows well resolved vibrational fine structure with a progressional spacing of c. 630 cm-1. This implies that the band is not due to a 'd-d' transition, but must be caused by the excitation of an electron into the nitrite π* orbital, either from a non-bonding nitrite orbital, or more probably from the nickel ion.

The crystal structures of the complexes cis-bis(ethane-1,2-diamine)(nitrito-O,O')zinc(II) nitrite and trans-bis[N,N-dimethyl(ethane-l,2-diamine)]dinitritozinc(II) are described. The former compound contains one chelating nitrite, the second group being present as a counter ion. In this complex the coordination polyhedron about the metal ion may be described either as a distorted trigonal bi-pyramid or an octahedron, depending upon whether the chelated nitrite is considered to occupy one or two coordination sites. The second compound is a trans nitrito complex, having an octahedral ligand geometry, though with three markedly different metal-ligand bond lengths. The structures of the complexes are compared with those of analogous nickel(II) nitrite complexes, and the differences are discussed in terms of the electron configurations of the two metal ions.

The crystal structures of the trans complexes bis(ethane-1,2-diamine)dinitronickel(II) (1), bis[N,N-dimethyl(ethane-1,2-diarnine)]dinitritonickel(II) (2) and bis[N,N'-dimethyl(ethane-1,2-diamine)]dinitronickel(II) monohydrate (3) are described, (1) and (2) being redeterminations of previously reported structures. The complexes formed by the substituted amines have significantly different geometries, both in the manner of coordination of the nitrite ligands, and in the conformations adopted by the diamine chelate rings. These differences can be explained in terms of the particular steric requirements of the amine substituents. The changes in nitrite geometry which occur upon coordination, and the spectroscopic properties of the complexes are discussed.

A single-crystal X-ray structure determination on the diacetate derivative of the major diterpene ester isolated from the neutral extract of P. lepidota (Verbenaceae) has shown it to be methyl (13E)-6α,18-diacetoxycleroda-3,13-dien-15-oate.

On the basis of physical data, an acid isolated from the title plant is found to be ent-3β-acetoxy- 15,16-epoxylabda-8(17),13(16),14-trien-18-oic acid (1) or its enantiomer. The crystal structure of the acid, C22H28O6, was determined from single-crystal diffractometer data at 295(1) K, being refined by least squares to a residual of 0·056 for 922 'observed' reflections; crystals are orthorhombic, P212121, a 16·22(1), b 12·212(5), c 9·976(3) , Z 4.

3β-Hydroxyolean-18-en-28-oic acid (morolic acid) has been isolated from the leaves of Eucalyptus grossa Benth. The crystal structure of methyl morolate acetate has been determined and some distortions of the angular geometry in the A/B trans-decalin moiety have been noted.

Arsenobetaine has been isolated from the tail muscle of the western rock lobster (Panulirus cygnus George) and from the flesh of the dusky shark (Carcharhinus obscurus Le Sueur), both of which are commercially important seafoods. Trigonelline has also been isolated from the lobster and both arsenobetaine and trigonelline have been isolated from human urine obtained after ingestion of cooked rock lobster. The crystal structures of the monohydrates of arsenobetaine and trigonelline have been determined and a simple synthesis of arsenobetaine has been developed.

The crystal structures of the hemi-ethanolate of nitron, C20H16N4(C2H6O)0.5, and of a non-stoichiometric hydrochloride of nitron, C20H16N4(HCl)1.7(H2O)3.3, have been determined by X-ray diffraction from diffractometer data at 295 K and refined by block diagonal least squares to residuals of 0.069 (2049 'observed' reflections) and 0.055 (1915), respectively. Crystals of the hemi-ethanolate of nitron are monoclinic P21/n, a 12.697(6), b 15.821(5), c 19.064(6) Ǻ, β 108.79(3)°, Z 8. Crystals of the non-stoichiometric hydrochloride of nitron are also monoclinic C2/c, a 25.41(1), b 5.968(6), c 29.40(2) Ǻ, β 103.53(5)°, Z 8. Despite some unusual features in their molecular geometry, these structures are consistent with the mesoionic character of nitron.

Crystal structures of (Z)-O-β-D-xylopyranosyl(1→6)-β-D- glucopyranosyloxy-NNO-azoxymethane (macrozamin) (1) and 5-O-methy-myo-inositol (sequoyitol) (4)-both of which are constituents of Macrozamia riedlei (Fisch. ex Gaud.) C. A. Gardn.-have been determined by X-ray diffraction. Diffractometer data at 295 K were refined by least-squares techniques to residuals of 0.050 (1537 'observed' reflections) for macrozamin and 0.060 (1052) for sequoyitol. Crystals of macrozamin are monoclinic, P2I, a 8.315(3), b 10.410(4), c 10.423(5) Ǻ, β 106.42(3)°, Z 2. Crystals of sequoyitol are triclinic, Pī, a 4.780(5), b 6.502(6), c 14.668(10) Ǻ, α 96.43(7), β 94.20(8), γ 109.31(8)°, Z 2.

A new diterpene, 1,18-dihydroxydecipi-14-en-19-oic acid, has been isolated from an unclassified Eremophila sp. Chemical and X-ray diffraction evidence is presented which confirms its structure and relative configuration.

In order to permit a comparative study of the structure and bonding behaviour of dimethylglyoxime in its neutral and monoanionic forms, both 'free' and complexed to transition metals, redeterminations of the crystal structures of dimethylglyoxime, dmgH2, and the complexes Cu(dmgH2)Cl2 and Cu(dmgH2)Br2 have been carried out, together with an initial determination of the structure of the hydrated sodium salt Na2(dmg),8H2O. Crystals of dmgH2 are triclinic, space group Pī, a 6.078(3), b 6.319(3), c 4.492(2) Ǻ, α 122.69(3), β 91.71(4), γ 77.72(4)°, Z 1 the structure was refined to a residual of 0.049 for 748 'observed' reflections. Crystals of Na2(dmg),8H2O are monoclinic, P21/c, a 11.317(7), b 12.995(7), c 4.901(4) Ǻ, β 100.55(5)°, Z 2, the structure being refined to a residual of 0.040 for 942 ?observed? reflections. Crystals of Cu(dmgH2)Cl2 are triclinic, Pī, a 8.163(4), b 8.109(3), c 7.701(2) Ǻ, α 110.88(3), β 101.31(3), γ 108.04(3)°, Z 2; for the isomorphous bromide a 8.628(3), b 8.276(4), c 7.757(2) Ǻ, α 111.18(3), β 101.02(3), γ 108.55(3)°. The two structures were refined to residuals of 0.052 and 0.045 for 964 and 1597 'observed' reflections respectively.

The crystal structure of the title compound, trans- [Co(C2N2H8)2(NH3)(SO3)] ClO4, has been determined by single-crystal X-ray diffraction methods at 295(1)K and refined by least squares to a residual of 0.061 for 2989 'observed' reflections. Crystals are monoclinic, P21/n, a 6.863(3), b 14.713(6), c 13.279(8) Ǻ, β 104.45(4)°, Z 4. Whereas the Co-S bond has the common value of 2.227(2) Ǻ, Co-N is remarkably long, being 2.070(3) Ǻ, this being ascribed to a structural trans effect.