Hazel A. Sparkes

Effects of diphosphine structure on aurophilicity and luminescence in Au(I) complexes

The effects of diphosphine flexibility and bite angle on the structures and luminescence properties of Au(I) complexes have been investigated. A range of diphosphines based on heteroaromatic backbones [bis(2-diphenylphosphino)phenylether (dpephos), 9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene (xantphos), and 4,6-bis(diphenylphosphino)dibenzofuran (dbfphos)] has been used to prepare mono- and digold derivatives. A clear relationship between the presence of aurophilic contacts and the emission properties of dinuclear complexes has been observed, with one of the complexes studied, [Au(2)Cl(2)(micro-xantphos)], exhibiting luminescence thermochromism.

Syntheses and crystal structures of CuIIBiIII, CuIIBaIICuII, [CuIIPbII]2 and cocrystallized (UVIO2)2.4CuII complexes: structural diversity of the coordination compounds derived from N,N′-ethylenebis(3-ethoxysalicylaldiimine)

Syntheses, characterization and structures of heterodinuclear compound [CuIIL1BiIII(NO3)3] (1), sandwich type heterotrinuclear compound [(CuIIL1)2BaII(NO3)2]·0.2H2O (2), heterotetranuclear compound [{CuIIL1PbII(µ-NO3)(NO3)}2] (3) and heterohexanuclear [2 × 1 + 1 × 4] cocrystal [(UVIO2)2(µ-H2O)2(NO3)4]·4[CuIIL1⊂(H2O)] (4) are described in this investigation (H2L1 = N,N′-ethylenebis(3-ethoxysalicylaldiimine)). Compounds 1 and 4 crystallize in orthorhombic P212121 and triclinic Pī systems, respectively, while the space group of compounds 2 and 3 is monoclinic P21/c. The structure of 1 consists of a diphenoxo-bridged CuIIBiIII dinuclear core containing three chelating nitrates and a 10-coordinate bismuth(III) centre. The dinuclear cores are self-assembled to two dimensions through intermolecular nitrate oxygen⋯copper(II) semicoordination and weak C–H⋯O hydrogen bonds. Compound 2 is a double-decker CuIIBaIICuII system in which a barium(II) ion is sandwiched between two mononuclear [CuIIL1] moieties. The barium(II) centre is 11-coordinate, four phenoxo and four ethoxy oxygen atoms and one chelating and one monodentate nitrate ions. Compound 3 is a tetranuclear system (dimer of two dinuclear moieties) in which one nitrate is chelating, while the second nitrate behaves as both a chelating and bridging ligand. The lead(II) centre is 9-coordinate in this compound. Compound 4 is a [2 × 1 + 1 × 4] cocrystal of one diaqua-bridged diuranyl(VI) moiety, containing two chelating nitrates and 8-coordinated hexagonal bipyramidal uranium(VI) centres and four inclusion species [CuIIL1⊂(H2O)]. The governing factor for the self-assembled cocrystallization in 4 are the C–H⋯·π and C–H⋯O hydrogen bonds. The compounds reported in this investigation and other heteronuclear systems derived from N,N′-ethylenebis(3-ethoxysalicylaldiimine) indicate that this ligand system is an important example which gives rise to structurally diverse heteronuclear compounds. In addition to the structural diversity, the structural resemblance of bismuth(III) with lanthanides(III) and utilization of noncovalent interactions to form self-assembly and cocrystals are the major outcomes of the present investigations.

Syntheses and crystal structures of dinuclear, trinuclear [2 × 1 + 1 × 1] and tetranuclear [2 × 1 + 1 × 2] copper(II)–d10 complexes (d10 ⇒ ZnII, CdII, HgII and AgI) derived from N,N′-ethylenebis(3-ethoxysalicylaldimine)

Syntheses, characterization and crystal structures of heterotetranuclear [2 × 1 + 1 × 2] co-crystals [{CuIILZnII(H2O)2}{CuIIL}2](ClO4)2 (1) and [{CuIILCdII(H2O)2(CH3CN)}{CuIIL}2](ClO4)2 (2), dinuclear compound [CuIILHgII(CH2COCH3)](ClO4) (3) and heterotrinuclear [2 × 1 + 1 × 1] co-crystal [{CuIILAgI(H2O)}{CuIIL}](ClO4) (4) derived from N,N′-ethylenebis(3-ethoxysalicylaldimine) (H2L) are reported herein. Compounds 3 and 4 crystallize in the orthorhombic Pbca and monoclinic P21/c systems, respectively, while the space group of compounds 1 and 2 is monoclinic C2/c. The structure of 3 consists of a monophenoxo-bridged CuIIHgII dinuclear core in which the mercury(II) centre is dicoordinated by the bridging phenoxo oxygen atom and the CH2 carbon atom of the mono-deprotonated acetone anion. The coordination environment of HgII in this compound is almost linear. In the CuII2AgI compound 4, one diphenoxo-bridged [CuIILAgI(H2O)]+ cation is co-crystallized with one mononuclear [CuIIL] moieties. On the other hand, the structures of the CuII3MII compounds 1 (M = Zn) and 2 (M = Cd) consist of one diphenoxo-bridged dinuclear CuIIMII unit and two mononuclear [CuIIL] moiety; the composition of the dinuclear unit being [CuIILZnII(H2O)2]2+ and [CuIILCdII(H2O)2(CH3CN)]2+ for 1 and 2, respectively. The AgI (in 4), ZnII (in 1) and CdII (in 2) ions in the diphenoxo-bridged dinuclear cores are tri-, tetra- and heptacoordinated, respectively. The metal ions are coordinated to two bridging phenoxo oxygen atoms, with the silver(I) and zinc(II) centres being additionally coordinated to one and two water molecules, respectively. While in the case of cadmium(II), the additional five coordination positions are occupied by two ethoxy oxygen atoms, two water oxygen atoms and one acetonitrile nitrogen atom. The coordination environment of silver(I) in 4 is pyramidal with a scalene O3 triangle as the base, whereas those of zinc(II) and cadmium(II) in 1 and 2 are distorted tetrahedral and distorted pentagonal bipyramidal, respectively. The coordinated water molecule in 4 and each of the two coordinated water molecules in 1 and 2 are encapsulated into the O4 compartment of a [CuIIL] moiety resulting in the [2 × 1 + 1 × 1] (for 4) or [2 × 1 + 1 × 2] (for 1 and 2) cocrystallization and self-assemblies. Clearly, the encapsulation of the coordinated water molecule(s) is the governing force for the formation of dinuclear-mononuclear co-crystals in 1, 2 and 4. In addition all four compounds 1–4 have π–π stacking interactions which form dimers between pairs of adjacent molecules in the structure of 3 consisting of CuIIHgII dimers, while one-dimensional stacks are formed in the CuII3ZnII (1), CuII3CdII (2) and CuII2AgI (4) complexes. The compositions of the title compounds are compared with the related systems derived from the same ligand. The [2 × 1 + 1 × 1] co-crystal, 4, is a new type of system in terms of the number of components. Again, in spite of the tri-, tetra- and hepta-coordinated nature of the second metal ion in the dinuclear cores, co-crystallization in 1, 2 and 4, respectively, are new observations. The accommodation/coordination of varieties of metal ions by the O4 compartment of H2L has also been highlighted in the present investigation.

Carbonyl⋯carbonyl interactions in first-row transition metal complexes

Carbonyl⋯carbonyl interactions involving Tr–CO moieties (Tr = first-row transition element) have been studied using crystal structure data retrieved from the Cambridge Structural Database and by use of DFT calculations. By comparison with organic ketones, Tr–CO systems show an increased tendency to form close CO⋯CO interactions, with 45% of these forming pairwise interactions in a sheared antiparallel dimer motif and 55% having a perpendicular (single interaction) geometry. The bulky Tr and steric hindrance arising from other ligands at Tr play a significant role in the formation and geometry of the interactions. DFT calculations for the antiparallel dimer indicate that interaction energies for Tr–CO systems are slightly stronger than for organic ketones, and there is evidence of a stronger CO bond dipole in Tr–CO systems. With interaction energies comparable to those for medium strength hydrogen bonds, we conclude that CO⋯CO interactions in Tr–CO species may have a role to play in the design of novel carbonyl-containing inorganic and metal–organic structures.

Trans-4-(trifluoromethyl) cinnamic acid

The crystal structure of trans-4-(trifluoromethyl) cinnamic acid (1) has been determined in the triclinic space groupP. Differential scanning calorimetry showed that 1 undergoes a single fully reversible temperature induced phase transition at around 132/131 K (cooling/heating). Single crystal structure determinations, carried out at 200, 145 and 120 K, revealed that the volume of the unit cell quadruples as the crystal is cooled through the phase transition with Z′ increasing from 2 to 8. The structures are stabilised by the presence of O–H⋯O hydrogen bonding and C–H⋯O interactions. The results of DSC, single crystal and powder X-ray diffraction studies on 1 are reported.

Experimental charge density study into C–C σ-interactions in a Binor-S rhodium complex

Transition-metal complexes containing (C-C)→M σ-interactions have potential applications in both catalysis and the activation and cleavage of C-C bonds. Fully characterising the bonding and interactions in complexes containing such (C-C)→M σ-interactions is vital to understand their chemical behaviour. As a result a high-resolution experimental X-ray charge density study has been undertaken on [Rh(Binor-S)(PCy(3))][HCB(11)Me(11)] (Binor-S = 1,2,4,5,6,8-dimetheno-s-indacene) which contains a (C-C)→Rh interaction. The data are analysed using Baders Atoms in Molecules (AIM) approach with particular attention paid to the interactions around the rhodium centre. The results provide clear evidence for the σ(C-C)→Rh interaction in the solid-state which is classified as a weak covalent interaction. These results are supported by theoretical calculations.

Bond catastrophes in rhodium complexes: experimental charge-density studies of [Rh(C7H8)(PtBu3)Cl] and [Rh(C7H8)(PCy3)Cl]

Rhodium complexes have potential uses in both catalysis and promoting the cleavage of C-C bonds. In order to further our understanding of these species and their potential applications, it is vital to obtain insight into the bonding within the species, particularly the Rh-C interactions, and to this end experimental charge-density studies have been undertaken on the title complexes. High-resolution single-crystal datasets to sin θ/λ = 1.06 A(-1) were obtained at 100 K and analysed using Baders Atoms in Molecules (AIM) approach. The results of the studies have provided unique insights into the bonding involving rhodium and highlight the importance of undertaking such investigations for transition metal compounds.

[Rh(C7H8)(PPh3)Cl]: an experimental charge-density study.

In order to gain a deeper understanding into the bonding situation in rhodium complexes containing rhodium-carbon interactions, the experimental charge-density analysis for [Rh(C(7)H(8))(PPh(3))Cl] (1) is reported. Accurate, high-resolution (sin theta/lambda = 1.08 A(-1)), single-crystal data were obtained at 100 K. The results from the investigation were interesting in relation to the interactions between the rhodium metal centre and the norbornadiene fragment and illustrate the importance of such analyses in studying bonding in organometallic complexes.

Controlled photochemical reaction of 4-oxo(phenylacetyl)morpholine and 1-(phenylglyoxylyl)piperidine in solid supramolecular systems

Six inclusion compounds containing a photoreactive guest molecule, 4-oxo(phenylacetyl)morpholine or 1-(phenylglyoxylyl)piperidine, with different host molecules have been crystallized. The guest molecules underwent photochemical reaction upon irradiation. Examining their structures suggests that γ-hydrogen abstraction by an oxygen, the first step in cyclization of α-oxoamides, should be possible in all cases. In four cases crystallinity was maintained during and at the end of the conversion process i.e. the process was a single-crystal to single-crystal transformation. The crystal structure of the product crystals revealed that in two of the inclusion compounds the product obtained is a result of enclosure to a four-membered ring while in the other two the product obtained results from enclosure to a five-membered ring. The morpholine molecules adopt two different conformations. The photochemical reaction may take different courses either as a result of the different conformation or as a result of the different shapes of the cavities provided by the host molecules.

4-Bromo-trans-cinnamic acid

4-Bromo-trans-cinnamic acid (1) displays some interesting behaviour in the solid-state undergoing a photo-induced head-to-head [2 + 2] cycloaddition reaction in addition to a reversible phase transition. Differential scanning calorimetry established that the thermal phase transition shows a slight hysteresis occurring at 252 K upon cooling and 256 K upon warming. Interestingly it was noted that upon photoirradiation above the phase transition temperature the compound appears to undergo a conversion to the low temperature form, prior to undergoing a cycloaddition reaction. Crystal structures of 1 were determined at 120, 240 and 300 K and found to be in the monoclinic space group P21/n at all three temperatures. The crystal structure of 1i was obtained, after recrystallisation of a powdered sample of 1 that had been irradiated at room temperature, and was found to be in the triclinic space group P. In all cases, the structures were found to be stabilised by the presence of O–H⋯O hydrogen bonding and C–H⋯O interactions. The results of these investigations are presented herein.