Patrick McArdle

A method for the prediction of the crystal structure of ionic organic compounds—the crystal structures of o-toluidinium chloride and bromide and polymorphism of bicifadine hydrochloride

The crystal structures of o-toluidinium chloride (1), o-toluidinium bromide (2) and two polymorphs of bicifadine hydrochloride (3) have been determined. The polymorphs of 3 differ in their molecular conformation and in their mode of packing. Crystallisation studies and quantum mechanical calculations show that the more readily crystallisable polymorph grows from the thermodynamically most stable conformer. On heating, conversion to the second polymorph takes place just below the melting point. The crystal structures of 1, 2 and the first polymorph of 3 have been successfully predicted using a procedure that is suitable for simple ionic organics.

Asymmetric Organocatalytic 1,6‐Conjugate Addition of Aldehydes to Dienic Sulfones

An unprecedented 1,6-enamine conjugate addition exploiting the charge delocalization in 1,3-bis(sulfonyl) butadienes has been developed. By appropriately designing a Michael acceptor, unique reactivities were obtained for the formation of highly valuable dienes containing two versatile vinyl sulfones (see scheme, TMS=trimethylsilyl).

A reinvestigation of the reaction of [Fe2(η-C5H5)2(CO)4-n(CNR)n] (n = 1 or 2) with strong alkylating agents

Abstract The reaction of [Fe 2 (η-C 5 H 5 ) 2 (CO) 3 (CNR)] with R′OSO 2 CF 3 (R,R′  Me or Et) gives a mixture of cis and trans -[Fe 2 (η-C 5 H 5 ) 2 (CO) 2 (μ-CO)μ-CN(R′)R]SO 3 CF 3 . When R  R′  Me the isomer ratio is variable, but the cis always predominates and is the only product when R ≠ R′. The complexes [Fe 2 (η-C 5 H 5 ) 2 (CO) 2 (CNR) 2 ] react with R′OSO 2 CF 3 and the more reactive alkyl halides R′X to give a mixture of cis - [Fe 2 (η-C 5 H 5 ) 2 (CO)(CNR)(μ-CO)ν-CN(R′)R]X and cis -[Fe 2 (η-C 5 H 5 ) 2 (CO) 2 μ-CN(R′)R 2 ][X] 2 . In both series of cations the presence of μ-CN(R′)R ligands give rise to isomers that differ in respect of orientation about the CN bond. The cations are not fluxional and do not undergo cis - trans interconversion, bridge-terminal ligand exchange, or rotation about the μ-CN(R′)R double bond. The structure of the cations in the [Fe 2 (η-C 5 H 5 ) 2 (CO)(CNMe)(μ-CO)(μ-CNMe 2 )]BPh 4 and [Fe 2 (η-C 5 H 4 Me) 2 (CO) 2 (μ-CNMe 2 ) 2 ][SO 3 CF 3 ] 2 salts were confirmed as cis by X-ray diffraction studies. Their dimensions are similar to those previously found in cis - [Fe 2 (η-C 5 H 4 Me) 2 (CO) 2 (μ-CO)(μ-CNMe 2 )]I, but with variations due to the differing acceptor and donor abilities of the various ligands. Infrared and NMR spectra of the complexes are reported and discussed.

Design of Lead(II) Metal–Organic Frameworks Based on Covalent and Tetrel Bonding

Three solid materials, [Pb(HL)(SCN)2 ]⋅CH3 OH (1), [Pb(HL)(SCN)2 ] (2), and [Pb(L)(SCN)]n (3), were obtained from Pb(SCN)2 and an unsymmetrical bis-pyridyl hydrazone ligand that can act both as a bridging and as a chelating ligand. In all three the lead center is hemidirectionally coordinated and is thus sterically optimal for participation in tetrel bonding. In the crystal structures of all three compounds, the lead atoms participate in short contacts with thiocyanate sulfur or nitrogen atoms. These contacts are shorter than the sums of the van der Waals radii (3.04-3.47 Å for Pb⋅⋅⋅S and 3.54 Å for Pb⋅⋅⋅N) and interconnect the covalently bonded units (monomers, dimers, and 2D polymers) into supramolecular assemblies (chains and 3D structures). DFT calculations showed these contacts to be tetrel bonds of considerable energy (6.5-10.5 kcal mol(-1) for Pb⋅⋅⋅S and 16.5 kcal mol(-1) for Pb⋅⋅⋅N). A survey of structures in the CSD showed that similar contacts often appear in crystals of Pb(II) complexes with regular geometries, which leads to the conclusion that tetrel bonding plays a significant role in the supramolecular chemistry of Pb(II) .

Transition-metal Schiff-base complexes as ligands in tin chemistry. Part 7. Reactions of organotin(IV) Lewis acids with [M(L)]2 [M=Ni, Cu and Zn; H2L=N,N′-bis(3-methoxysalicylidene)benzene-1,3-diamine and its -1,4-diamine analog]

Dinuclear complexes [M(3MeO-sal- m -phen)(H 2 O)] 2 [M=Cu, Ni and Zn; 3MeO–H 2 sal- m -phen= N,N ′-bis(3-methoxysalicylidene)benzene-1,3-diamine] and [M(3MeO-sal- p -phen)(H 2 O)] 2 [M=Cu, Ni and Zn; 3MeO–H 2 sal- p -phen= N,N ′-bis(3-methoxysalicylidene)benzene-1,4-diamine] were synthesised and reacted with diorganotin(IV) dihalides, dinitrates and dithiocyanates. Only in the case of those reactions involving [M(3MeO-sal- m -phen)(H 2 O)] 2 with M=Ni or Zn were adducts obtained as the sole products of reaction; the adducts were all tetranuclear complexes. The tetranuclear adduct {(SnBu n 2 ).[Ni(3MeO-sal- m -phen)(NCS) 2 ]} 2 · 6MeCN results from salicylaldimine ligands, related by a 2-fold axis, adopting bridging roles by co-ordinating to each of the symmetry related nickel atoms through phenolic oxygen and imine nitrogen atoms, while their phenolic and methoxy oxygen atoms form donor bonds to the tin atoms of symmetry related dibutyltin cations. The salicylaldimine ligands, related by inversion, adopt the same bridging role towards the nickel atoms in the adduct {[SnBz 2 (NO 3 )]·[Ni(3MeO-sal- m -phen)(NO 3 )]} 2 .6MeCN (Bz=benzyl), but as a result of the bidentate role of the nitrate co-ordinated to nickel, the arrangement of the phenolic and methoxy oxygens is such that each tin is co-ordinated quite strongly by a bidentate nitrate, a methoxy and two phenolic oxygen atoms while a second methoxy oxygen provides a weak Sn–O interaction, thus resulting in pseudo eight co-ordinate tin. 119 Sn Mossbauer parameters indicate that all of the adducts of di- and triorganotin halides are organotin aqua adducts with the donor water engaged in hydrogen bonding with Schiff-base oxygen atoms.

Planar [Ni7] discs as double-bowl, pseudo metallacalix[6]arene host cavities

We report three heptanuclear [Ni7] complexes with planar disc-like cores, akin to double-bowl metallocalix[6]arenes, which form molecular H-bonded host cavities.

α-Keto amides as precursors to heterocycles—generation and cycloaddition reactions of piperazin-5-one nitrones

alpha-Keto amides 10a,b, formed from reaction of pyruvic or benzoylformic acid with allyl amine are found to present as single rotameric forms whilst their tertiary amido analogues 10c, d present as two rotamers in solution at rt. The hydroxyimino derivatives 8 share the conformational characteristics of their parents. The geometrical make-up of the new alpha-amidooximes is seen to depend on the structure of the starting acid and on the degree of substitution of the amido group. The oxime 8a derived from pyruvic acid and allyl amine is formed solely as the (E)-isomer whilst its tertiary amido analogue 8c is formed as both (E)- and (Z)-isomers. Oximes derived from benzoylformic acid have the opposite selectivity with both geometrical isomers forming from the secondary amide 8b and only the (Z)-isomer from the tertiary amide 8d. With the exception of 8b all oximes were configurationally stable with (Z)-isomers reacting to form isoxazolopyrrolidinones 11--compounds with a relatively rare bicyclic nucleus and (E)-isomers cyclising to piperazin-5-one nitrones 1--ketopiperazine N-oxides have to date only appeared once in the literature. New nitrones were trapped with phenyl vinyl sulfone, dimethyl acetylenedicarboxylate and methyl propiolate yielding isoxazolidine and isoxazoline fused piperazinones 13, 15, 21 and 22. Cycloadducts from dimethyl acetylenedicarboxylate and 8a, b are thermally labile and their rearrangement provides a novel route to pyrrolopiperazinones 16. The structure of a representative isoxazolopyrrolidinone, 11c, and a 2,3-dihydroisoxazoline fused piperazinone, 21b, are unambiguously solved following x-ray structural analysis.

Transition metal Schiff-base complexes as ligands in tin chemistry: IV. Reactions of triphenyltin chloride with divalent metal salicylaldimine complexes and the molecular structures of [SnPh3Cl · H2O][Ni(3-MeOsal1,3pn) · H2O] (1:1) and [SnPh3Cl · H2O]Ni(3-MeOsal1,3pren) (1:1) [H23-MeOsal1,3pn N,N′-bis(3-methoxysalicylidene)propane-1,3-diamine]

Abstract Unlike diorganotin(IV) dihalides, triphenyl- and tribenzyl-tin chlorides do not react with Schiff-base complexes M(SB) (M  Cu II , Ni II and Zn II ; SB  N , N ′-ethylenebis-salicylideneaminato and related salicylaldimine ligands). Triphenyltin chloride does however form 1:1 addition complexes with 3,3′-methoxy substituted salicylaldimines of Ni II and Cu II , but only in the presence of water. Each of these complexes contains the aquo adduct SnPh 3 Cl · H 2 O, with the donor water molecule engaged in hydrogen bonding interactions with the four oxygen atoms of the divalent metal salicyaldimine. These structural features were confirmed crystallographically for (SnPh 3 Cl · H 2 O)Ni(3-MeOsal1,3pn) (1:1) [H 2 3-MeOsal1,3pn  N,N′-bis(3-methoxysalicylidene)propane-1,3-diamine]. In the case of [SnPh 3 Cl · H 2 O][Ni(3-MeOsal1,3pn) · H 2 O] (1:1) both the water molecule coordinated to nickel and the water molecule coordinated to tin engage in hydrogen bonding interactions with the Schiff-base oxygen atoms, thereby creating centrosymmetric hydrogen-bonded dimers.

Predicting and understanding crystal morphology: the morphology of benzoic acid and the polymorphs of sulfathiazole

Crystals of benzoic acid grown from dichloromethane and acetonitrile are greatly extended along the b-axis. The enhanced growth is not related to hydrogen bonding as benzoic acid is respectively dimeric and monomeric in these solvents. A mechanism is suggested for enhanced growth in the π-stacking direction for flat π-stacking systems. Facilities have been added to the Oscail software package which provide attachment energy calculations, crystal surface analysis and crystal visualization. Crystal surface analysis can be used to find the π-stacking direction and to identify the density of available hydrogen bond donors and acceptors on crystal faces. Observed and calculated morphologies for crystals of sulfathiazole form 2 grown from ethanol are in good agreement. Differences in the observed and calculated shapes of sulfathiazole forms 1, 3, 4 and 5 are attributed to solvent effects which correlate with the density of available hydrogen bond acceptors on crystal faces.

Transition-metal Schiff-base complexes as ligands in tin chemistry. Part 3. An X-ray crystallographic and tin-119 Mössbauer spectroscopic study of adduct formation between tin(IV) Lewis acids and nickel 3-methoxysalicylaldimine complexes

1:1 Addition complexes of [NiIIL]·H2O [H2L =N,N′-bis(3-methoxysalicylidene)ethylenediamine (3MeO-H2salen), N,N′-bis(3-methoxysalicylidene)propane-1,2-diamine (3MeO-H2salpn) or N,N′-bis(3-methoxysalicylidene)-o-phenylenediamine (3O-H2salphen)] with SnR2Cl2(R = Me or Ph), SnBunCl3, or SnCl4 have been found to be generally monoaqua adducts of the tin Lewis acids with the water engaged in hydrogen bonding with the methoxy and phenolic oxygen atoms of the Schiffbase ligand. Both water and methoxy oxygen atoms are involved in donor-bond formation to tin in the polymeric structures 2SnMe2Cl2·[Ni(3MeO-salen)]·H2O and SnMe2Cl2·[Ni(3MeO-salphen)]·H2O, each of which has two very different tin environments. The two octahedral tin sites in the structure of SnMe2Cl2·2[Ni(3MeO-salphen)·H2O] appear to result from two isomeric forms of the adduct co-existing in a lattice as a result of hydrogen-bonding interactions. Crystal-structure determinations revealed that the monoaqua adducts of dimethyltin dichloride which exist in the structures SnMe2Cl2·[Ni(3MeO-salen)]·H2O and SnMe2Cl2·[Ni(3MeO-salon)]·H2O differ in that, in the former tin is in a trigonal-bipyramidal environment, whereas in the latter it is in an octahedral environment as a result of an intermolecular Sn ⋯ Cl contact of 3.615 A.