Volume 55, Issue 8

The crystal structures of two isomeric compounds, 2-endo-hydroxybornane-3-endo-carboxylic acid and 2 -exo -hydroxybomane-3 -endo-carboxylic acid, have been determined by X-ray single crystal analysis. The only difference between these two compounds is the disposition of the 2-hydroxy group with respect to the bomane skeleton. Both compounds show quite different hydrogen bonding schemes. In the endo-hydroxy-endo-carboxy isomer there is one intramolecular and one intermolecular hydrogen bond, which connects molecules into infinite chains, while in the exo-hydroxy-endo-carboxy isomer there are two intermolecular hydrogen bonds that form a more stable architecture of two kinds of chains which interconnect to close rings comprising four molecules. Due to these differences the melting point of 2 is ca. 30° higher than for 1 .

The tendency of forming mixed carboxyl-to-oxime hydrogen bonds was tested on the series of bornane derivatives: one with the acid function only (bornane-2-endo-carboxylic acid), one with the oxime function (2,2′-diethylthiobomane-3-oxime), and one with both oxime and carboxylic functions (bornane-2-oxime-3-endo-carboxylic acid). The crystal structures of these compounds were determined by means of X-ray diffraction. In bornane-2-endo-carboxylic acid and 2,2′-diethylthiobornane-3-oxime 'homogenic' hydrogen bonds were found, and these hydrogen bonds close eight-and six-membered rings, respectively. By contrast, in bornane-2-oxime-3-endo-carboxylic acid 'heterogenic' hydrogen bonds between carboxylic and oxime bonds were found. This carboxylic-oxime, or 'carboxyoxime' system is almost always present in compounds which have both oxime and carboxylic groups; therefore it can be regarded as an element of supramolecular structures (synthon). The presence of such synthons can break the tendency of carboxylic acids and oximes towards crystallizing in centrosymmetric structures.

The structure and properties of the thermal decomposition products of Fe[Fe(CN) 5 NO] · x H 2 O (x = 5 ~ 6) have been studied by Mössbauer and FT-IR spectroscopy, X-ray diffraction, and conductivity measurements. The valence state and coordination environment of the iron ions change dramatically when the nitrosyl ligand is eliminated by heat-treatment under vacuum at 200 °C. The dark blue product obtained by heat-treatment under vacuum at 250 °C is characteristic of the mixed-valence state in Prussian blue analogues. The electrical conductivity of the dark blue product is higher by a factor of 103 than that of the starting material because of the mixed-valence state between Fe(III)[Fe(II)(CN) 5 ] and Fe(II)[Fe(III)(CN) 5 ]. Heat-treatment under vacuum at 350°C yields a new product Fe(II)[Fe(II)(CN) 4 ] the crystal structure of which is different from that of the starting material. The electrical conductivity of the decomposition product obtained at 350 °C is about 10 5 times higher than that of the starting material.

By careful oxidation of trans-tetrafluorodichloroosmate(IV) with PbO 2 /trifluoroacetic acid in dichloromethane the corresponding osmium(V) complex anion rran5 -[OsF 4 Cl 2 ] - is for­ med. The X-ray structure determination on a single crystal has been performed of trans-(Et 4 N)[OsF 4 Cl 2 ] (triclinic, space group P1̄a = 7.190(5), b = 7.205(5), c = 7.732(5) Å, a = 71.28(1), β = 71.32(1), 7 = 70.76(1)°, Z = 1). Based on the molecular parameters of the X-ray determination the IR and Raman spectra of the complex have been assigned by normal coordi­ nate analysis. The valence force constants are: f d (OsCl) = 2.13 and f d (OsF) = 3.81 mdyn/Å.

The new ternary one-dimensional chain compounds K 2 ZrS 4 , Rb 2 ZrS 4 and Rb 2 HfS 4 were prepared at 350 °C by reacting A 2 S 3 and S with elemental M (A = K, Rb; M = Zr, Hf). They are isostructural, crystallizing in the orthorhombic space group Pbca with Z = 8 . The M atoms are in a distorted octahedral environment of four S 2− anions and one S 2 2− unit. The structure consists of infinite anionic chains comprised of edge-sharing M S 6 octahedra running parallel to the [001] direction separated by the alkali metal cations. The composition of the chain may be formulated as 1 ∞ [MS 4/ 2 (S 2 ) 2− ]. The two crystallographically independent alkali cations are in eight-and ninefold coordination of S atoms.

Crystals of Hg 2 (H 2 AsO 4 )2 , which are isotypic with the corresponding dihydrogenphosphate Hg 2 (H 2 PO 4 ) 2 , were obtained from a concentrated arsenic acid solution. The crystal structure (P2 1 /n, a = 6.1838(4), b = 15.0987(9), c = 4.7989(3) Å, β = 91.977(1)°, Z = 2, R = 0.045 for 1318 structure factors, 56 variables) contains a Hg 2 2+ dumbbell with a distance d(Hg-Hg) = 2.5040( 10) Å and a symmetrical coordination of four oxygen atoms for each mercury atom. The oxygen atoms also belong to tetrahedral dihydrogenarsenate groups H 2 AsO 4 − , which stabilize the structure by hydrogen bonding. On heating Hg 2 (H 2 AsO 4 ) 2 condenses to give the mercury(I) metaarsenate Hg 2 As 2 O 6 . Crystals of that compound were obtained under hydrothermal conditions at 165 °C starting from elemental mercury in 60 wt% aqueous H 3 AsO 4 . The crystal structure (P3̄1m, a = 4.8411(2), c = 7.5961(9) Å, Z = 1, R = 0.037 for 376 structure factors, 13 variables) may be represented by sheets of edge sharing [AsO 6 ] octahedra and layers of Hg 2 2+ dumbbells, which alternate along the c axis. The dumbbells show a distance d(Hg-Hg) = 2.5190(10) Å and are coordinated symmetrically by six oxygen atoms at a distance d(Hg-O) = 2.374(4) Å. They are positioned above and below the vacant sites of adjacent [As 2 O 6 ] 2− layers. On further heating Hg 2 As 2 O 6 disproportionates into elemental mercury and mercury(II) metaarsenate, HgAs 2 O 6 . Single crystals of HgAs 2 O 6 were grown via chemical vapor transport from microcrystalline HgAs 2 O 6 with HgCl 2 as transport agent, using a temperature gradient of 650 → 550 °C. HgAs 2 O 6 (P3̄1m, a = 4.8482(2), c = 4.9789(10) Å, Z = 1, R = 0.031 for 367 structure factors, 12 variables) crystallizes in the PbSb 2 O 6 structure type, where anionic [Sb 2 O 6 ] 2− layers have the same arrangement. The divalent mercury atomsohave a pseudooctahedral environment of oxygen atoms with a distance d(Hg-O) = 2.353(3) Å.

Formal insertion of phenylethyne into Co-H functions of mer-octahedral acyl(enolato)-cobalt(III) hydrides 1-3 proceeds under ambient conditions affording η 1 -vinylcobalt(III) compounds where the dianionic acyl(enolato) ligands are derived from 2-formyl-4-phenyl-cyclohexanone (4), 1-formyl-cyclohexan-2-one (5), and 3-hydroxo-2,3-diphenyl-propenal (6). Dissociation and association of trimethylphosphane results in a reversible transformation of penta-coordinate complexes 4 -6 into hexa-coordinate ones 7 -9, respectively, involving different tautomeric vinyl species. In toluene solution 9 rearranges by reductive C,C coupling into a 5,6-η 2 -olefin(enolato)cobalt(I) complex 10. Trimethylsilylethyne undergoes a hydrolytic desilylation reaction which is followed by reductive C,C-coupling reactions of acyl and vinyl functions selectively producing chelating η 1 -enolato-5,6-η 2 -olefin ligands in cobalt(I) com ­ pounds 13 -16 where the (ax,eq)chelating ligands are derived from 1-formyl-cyclohexan-2-one (13), 3-hydroxo-2,3-diphenyl-propenal (14), 2-formyl-α-tetralone (15), and 2-formyl-4-tert-butyl-cyclohexanone (16). An axial position of the enolato-O donor in the trigonal bipyramidal configuration of complex 15 has been confirmed by X-ray diffraction analysis. With 1,4-bis(trimethylsilyl)buta-diyne 1,2-addition in cobalt(III) hydrides 2, 3, 11 (as deriverd from 2-formyl-α-tetralone), and 12 (as derived from 2-formyl-4-tert-butyl-cyclohexanone) produces 2-metalated vinyl groups in compounds 17 -20. Dissociation of trimethylphosphane from 17 and 19 does not activate C,C coupling at the cobalt(III) centre of penta-coordinate 21 and 22. Steric congestion in compounds 17, 18, and 20 favours exchange of trimethylphosphine for carbon monoxide affording the first octahedral carbonyl complexes of cobalt (d 6 ) (23 -25). In the crystal and in solution a meridional configuration is adopted by complex 23 with the CO group in a position opposite to the acyl function.

Trifluoromethyliodine(III) bis-trifluoracetate [CF 3 I(OCOCF 3 ) 2 ] was obtained by reaction between CF 3 IF 2 and (CH 3 ) 3 SiOCOCF 3 at -50 °C. It crystallises in the triclinic space group P1̄ with a = 520.8(1), b = 1042.9(1), c = 1087.5(1) pm, α = 65.22(0)°, β = 81.18(0)°, γ = 80.09(0)°, and two formula units per unit cell. The compound has also been characterised by its Raman and IR spectra.

In the search for soluble and reactive ruthenium nitrosyl complexes, [Ru(NO)('py bu S 4 ')]Br ([2]Br) was synthesized by template alkylation of NBu 4 [Ru(NO)(' bu S 2 ') 2 ] with py(CH 2 ,Br) 2 ['py bu S 4 ' 2- = 2,6-bis(2-mercapto-3,5-di-tert-butyl-phenylthio)dimethylpyridine(2-); ' bu S 2 ' 2- = 2-mercapto-3,5-di-tert-butylphenylthiolate(2-); py(CH 2 Br) 2 = 2,6-bis(bromomethyl)pyridine]. The solid state structure of 2 has been determined by X-ray diffraction, which reveals a head-to-head O-O interaction between the linear Ru-NO entities. The ligand CH 2 protons of [2] + are activated and exchange with D + under ambient conditions. The ν (NO) band of [2]Br appears at 1841 cm -1 in the solid state (KBr or hostaflon mull) and is significantly blue-shifted in solution (1879 cm -1 in MeOH, 1886 cm -1 in DMF). A similar blue-shift (1866 cm -1 in KBr vs. 1888 cm -1 in MeOH) has been found for [Ru(NO)('pyS 4 ')]Br ([1]Br) which contains the parent [Ru(NO)('pyS 4 ')] + cation ['pyS 4 ' 2- = 2,6-bis(2-mercaptophenylthio)dimethylpyridine(2-)]. These ν(NO) shifts can be explained either by an interionic charge-transfer between the bromide anions and the nitrosyl complex cation or by O-O interactions between two NO ligands as found for solid-state [2]Br. These interactions are not found for [1]OTs which exhibits a ν(NO) band at ca. 1890 cm -1 in the solid state (KBr, hostaflon) as well as in MeOH solution.

The preparation and spectroscopic data of the new ternary amide LiAl(NHCH 3 ) 4 are reported. The structure of the title compound has been determined from X-ray powder diffraction data (tetragonal, 14 1 , a = 14.000(4) Å, c = 9.275(2) Å, 210 reflections, R = 3.75%, weighted R = 5.10%). Both the lithium and the aluminium atoms are coordinated tetrahedrally by nitrogen atoms. Edge-sharing pairs of lithium centered and aluminium centered tetrahedra are connected to each other in helical chains forming a 3D-framework via the remaining vertices. A comparison of the projection of the crystal structure of LiAl(NHCH 3 ) 4 along the c-axis to those of cristobalite and of hollandite, (Ba,K) 2 (Mn,Fe) 8 O 16 , reveals similarities with respect to both the connectivity and the topology of ring structures.

The synthesis of the first stable phosphanidovanadium(V) complex t BuN=V[P(SiMe 3 ) 2 ] 3 is described. The compound has been investigated by 1 H, 13 C , 31 P, 51 V NMR spectroscopy. The results indicate an eighteen-electron complex.

As an exercise in crystal engineering, low-temperature X-ray structures were determined for six rationally designed ionic solids of general formula BH + (MeSO 2 ) 2 N − , where BH + is 2-aminopyridinium (2, monoclinic, space group P2 1 /c, Z = 4), 2-aminopyrimidinium (3, orthorhombic, Pbca, Z = 8), 2-aminothiazolium (4, orthorhombic, Pbcn, Z = 8), 2-amino-6-methylpyridinium (5, solvated with 0.5 H 2 0, monoclinic, C2/c, Z = 8), 2-amino-1,3,4-thiadiazolium (6, triclinic, P1̄, Z = 2), or 2-amino-4,6-dimethylpyrimidinium (7, orthorhombic. Fdd2, Z = 16). The onium cations in question exhibit a trifunctional hydrogen-bond donor sequence H − N (H*)-C (sp 2 ) − N − H , which is complementary to an O − S (sp 3 )−N fragment of the anion and simultaneously expected to form a third hydrogen bond via the exocyclic N − H* donor. Consequently, all the crystal packings contain cation-anion pairs assembled by an N − H ∙∙∙ N and an N −H ∙∙∙ O hydrogen bond, these substructures being mutually associated through an N − H* ∙∙∙ O bond. For the robust eight-membered ring synthon within the ion pairs [graph set N 2 = R 2 2 (8), antidromic], two supramolecular isomers were observed: In 2 and 3, N − H ∙∙∙ N originates from the ring NH donor and N − H ∙∙∙ O from the exocyclic amino group, whereas in 4-7 these connectivities are reversed. The third hydrogen bond, N − H*∙∙∙ O , leads either to chains of ion pairs (generated by a 2 1 transformation in 2-4 or by a glide plane in 5) or to cyclic dimers of ion pairs (C i symmetric in 6, C 2 -symmetric in 7). The overall variety of motifs observed in a small number of structures reflects the limits imposed on the prediction of hydrogen bonding patterns. Owing to the excess of potential acceptors over traditional hydrogen-bond donors, several of the structures display prominent non-classical secondary bonding. Thus, the cyclodimeric units of 6 are associated into strands through short antiparallel O ∙∙∙ S(cation) interactions. In the hemihydrate 5, two independent C-H(cation) ∙∙∙ O bonds generate a second antidromic R 2 2 (8) pattern, leading to sheets composed of N − H ∙∙∙ N/O connected catemers; the water molecules are alternately sandwiched between and O - H ∙∙∙ O bonded to the sheets to form bilayers, which are cross-linked by a third C − H (cation ) ∙∙∙ O contact. The roof-shaped cyclodimers occurring in 7 occupy the polar C 2 axes parallel to z and build up hollow C ar − H ∙∙∙ O bonded tetrahedral lattices; in order to fill their large empty cavities, five translationally equivalent lattices mutually interpenetrate.

In order to study crystal packings and hydrogen bonding frameworks, low-temperature X-ray structures were determined for three onium salts of general formula B H + (MeSO 2 ) 2 N − , where BH + is acetamidinium (1, monoclinic, space group P2 1 /c, Z = 4), guanidinium (2, monoclinic, P2 1 /c, Z = 4), or 4,6-diamino-2-thioxo-2,3-dihydropyrimidinium (3, monoclinic P2 1 /n, Z = 4). In every case the ions create three-dimensional N − H ∙∙∙ N/O networks, in which all N − H donors of the cations and four (in 1) or five (2, 3) acceptors of the anion are involved; non-conventional secondary bonds, e.g. C − H ∙∙∙ O/N, do not play an important role in the packings. For the isotypic structures 1 and 2, congruencies and dissimilarities of the hydrogen bonding patterns are discussed in detail. Despite the structural and chemical differences between the cations and the way in which they are attached to the anion, each of the three structures displays a robust eight-membered ring synthon [N 2 = R 2 2 (8), antidromic] constructed via two-centre hydrogen bonds from a syn, syn-sequence H − N − C (sp 2 ) −N −H of the respective cation and a V-shaped O − S (sp 3 ) − N fragment of the anion. Although the networks in 2 and 3 contain several N − H (∙∙∙ O) 2 three-centre interactions, the two-point connectivity of the synthon is distinctly preserved. The results indicate that the (MeSO 2 ) 2 N − ion may be utilized in crystal engineering as a dependable building block.

By reaction of hexamethyldisilazane with aluminium trichloride in hexane hexamethyldisilazane-trichloroaluminum [(H 3 C) 3 Si] 2 NH • AlCl 3 is formed. The adduct has been characterized by MS, IR, Raman, 1 H, 13 C, 27 Al, 29 Si NMR spectroscopy, and by a crystal structure determination (1425 independent reflections, R = 0.035). The space group is Pbca with a = 1312,6(5), b = 1182,9(5), c = 1964,7(5) pm; Z = 8. [(H 3 C) 3 Si] 2 NH • AlCl 3 forms monomeric units which have point symme­try C 1 and exhibit an Al − N bond length of 193,9(3) pm.

Lantana camara L. var. aculeata yielded a triterpenoid, pomonic acid (1). The acid-catalyzed lactonization of this γ-hydroxy acid afforded a rearranged lactone 3, the structure of which was as­ signed by detailed 2D-NMR studies. A reaction mechanism involving a 1,3-butadiene intermediate is proposed.