Showing papers in "Journal of The Chemical Society-dalton Transactions in 1999"

The phase behaviour of 1-alkyl-3-methylimidazolium tetrafluoroborates; ionic liquids and ionic liquid crystals

Abstract: Air- and water-stable 1-alkyl-3-methylimidazolium tetrafluoroborate salts with the general formula [Cn-mim][BF4] (n = 0–18) have been prepared by metathesis from the corresponding chloride or bromide salts. The salts have been characterised by 1H NMR and IR spectroscopy, microanalysis, polarising optical microscopy and differential scanning calorimetry. Those with short alkyl chains (n = 2–10) are isotropic ionic liquids at room temperature and exhibit a wide liquid range, whereas the longer chain analogues are low melting mesomorphic crystalline solids which display an enantiotropic smectic A mesophase. The thermal range of the mesophase increases with increasing chain length and in the case of the longest chain salt prepared, [C18-mim][BF4], the mesophase range is ca. 150 °C.

Solvent extraction of strontium nitrate by a crown ether using room-temperature ionic liquids†

Abstract: The preliminary results described here show that unprecedentedly large distribution coefficient (D) values can be achieved using ionic liquids as extraction solvents for the separation of metal ions by crown ethers. This work highlights the vast opportunities in separation applications for ionic liquids with crown ethers.

Negative thermal expansion materials

Abstract: The vast majority of materials have a positive coefficient of thermal expansion and their volume increases on heating. There has been considerable recent interest in materials which display the unusual property of contracting in volume on heating; i.e. those with a negative coefficient of thermal expansion. This Perspective gives an overview of some of the physical phenomena that can give rise to this unusual effect. Recent insights into negative thermal expansion materials and some of their unusual structural properties are discussed.

The bite angle makes the difference: a practical ligand parameter for diphosphine ligands

Abstract: Over the past twenty years, a correlation between the P–M–P bite angle in diphosphine complexes and selectivity has been observed in various catalytic reactions such as hydroformylation, hydrocyanation and cross coupling. The large number of examples indicates that this correlation is not fortuitous. In order better to understand the underlying principles of the bite angle effect, we have first analysed crystal structures available in the Cambridge Crystallographic Database. Systematic searches indicate that for many bidentate diphosphine ligands the P–M–P angles concentrate in surprisingly small ranges, even if complexes of different metals in various oxidation states are considered. Several examples in the literature show that continuous electronic changes associated with changing bite angles cannot only be verified by different spectroscopic techniques, but also explained on a theoretical level (Walsh diagrams). The ligand bite angle is a useful parameter for the explanation of observed rates and selectivities and likewise for the design of ligands for new catalytic reactions.

Electrochemical molecular recognition: pathways between complexation and signalling

Abstract: This perspective examines the mechanisms by which electrochemical recognition of various charged and neutral guest species by redox-active receptor molecules takes place. Particular emphasis is given to the intramolecular signalling pathway employed in each case. These include electrostatic interactions (through space or through conju-gated bonds), conformational changes in the redox centre in complexation and guest interference to an already present communication pathway in the host.

5,5′-Dicyano-2,2′-bipyridine silver complexes: discrete units or co-ordination polymers through a chelating and/or bridging metal–ligand interaction

Abstract: The ambidentate ligand 5,5′-dicyano-2,2′-bipyridine (L) was found to function as a bi-, tri- or tetra-dentate chelate or chelate/bridging ligand in the co-ordination of silver ions. The mode of co-ordination depends on the anion and the crystallization conditions and was elucidated by single crystal X-ray diffractometry. With metal-co-ordinating anions such as NO3– and CF3SO3– a tridentate co-ordination mode of L is observed which involves the two bipyridine nitrogen donor atoms and one cyano group. The latter bridges to a neighboring silver center so that a one-dimensional co-ordination polymer results. For NO3– this co-ordination polymer forms a 21 helix. With less co-ordinating anions such as BF4– and PF6– monomeric bis-chelate complexes are obtained, where L assumes a bidentate co-ordination mode involving only the bipyridine nitrogen donor atoms. In the case of the PF6– anion a variation in the solvent of crystallization also produced a two-dimensional hexagonal co-ordination polymer where L functions as a tetradentate ligand using all four nitrogen donor atoms in chelation and bridging to the silver centers.

Luminescence properties of salts of the [Pt(4′Ph-terpy)Cl]+ chromophore: crystal structure of the red form of [Pt(4′Ph-terpy)Cl]BF4 (4′Ph-terpy = 4′-phenyl-2,2′∶6′,2″-terpyridine)

Abstract: The complexes [Pt(4′Ph-terpy)Cl]A (4′Ph-terpy = 4′-phenyl-2,2′:6′,2″-terpyridine; A = SbF6, CF3SO3, or BF4) have been prepared by reaction of [Pt(PhCN)2Cl2] with the appropriate silver salt followed by addition of the 4′-phenyl-2,2′:6′,2″-terpyridyl ligand. The hexafluoroantimonate salt is yellow but, depending on the method of crystallisation, the triflate and tetrafluoroborate salts can be isolated in two forms, one yellow and the other red, the red forms only being stable at low temperatures. The crystal structure of red [Pt(4′Ph-terpy)Cl]BF4·CH3CN has been determined at 153 K by X-ray diffraction methods. The [Pt(4′Ph-terpy)Cl]+ cations are stacked face-to-face in an extended chain of stepped tetramers, with essentially equal Pt· · ·Pt distances of ca. 3.3 A within a tetramer and a Pt· · ·Pt distance of 4.680 A between successive tetramers. The spectroscopic and solid state emission properties of the salts have been recorded. The yellow salts are characterised by emission from an isolated chromophore in an excited state that reflects the admixture of 3MLCT (MLCT = metal-to-ligand charge-transfer) and 3IL (IL = intraligand) character. This assignment is supported by the presence of vibrational structure in the emission band as well as by a lifetime of ca. 1 µs for the emission. The red [Pt(4′Ph-terpy)Cl]BF4·CH3CN salt, in contrast, exhibits emission from a 3MMLCT (MMLCT = metal–metal–ligand charge-transfer) state as a consequence of the strong platinum dz2–dz2 orbital interactions. This assignment is consistent with the observation of a narrow, structureless and asymmetric band as well as an emission lifetime of ca. 0.1 µs. There is a systematic and substantial red-shift of 75 nm in the emission maximum on cooling the red salt from 280 to 80 K, an unexpected result since bathochromic shifts of this kind are normally associated with stacked structures with a uniform Pt· · ·Pt separation. The above assignments are further supported by measurements of the emission spectra of solutions of varying concentrations of the tetrafluoroborate salt in a dimethylformamide–methanol–ethanol glass at 77 K and by lifetime measurements. Interestingly, pressure in the form of grinding the salts modifies their luminescent properties. Thus, crushed samples of the yellow hexafluoroantimonate salt exhibit multiple emission at 80 K from both the 3MMLCT and the mixed parentage 3MLCT/3IL excited states, whereas at room temperature the emission spectrum is dominated by a broad band centred at 644 nm associated entirely with the 3MMLCT emission.

Interaction of polypyridyl ruthenium(II) complexes containing non-planar ligands with DNA

Abstract: 2-(2-Chlorophenyl)imidazo[4,5-f]1,10-phenanthroline (CIP) or 2-(2-nitrophenyl)imidazo[4,5-f]1,10-phenanthroline (NIP) and their complexes [Ru(bpy)2(CIP)]2+ and [Ru(bpy)2(NIP)]2+ (bpy = 2,2′-bipyridine) have been synthesized and characterized. The binding of the two complexes to calf thymus DNA has been investigated with spectrophotometric methods and viscosity measurements. The experimental results indicate that the two complexes bind to DNA through a partial intercalative mode that is different from the bonding mode for their parent compound, [Ru(bpy)2(PIP)]2+ (PIP = 2-phenylimidazo[4,5-f]1,10-phenanthroline). The crystal structure of [Ru(bpy)2(CIP)][ClO4]2·2H2O was determined by X-ray diffraction analysis; the imidazo[4,5-f]1,10-phenanthroline moiety is not coplanar with the 2-chlorophenyl ring, having a dihedral angle of 44.5° in the CIP.

Syntheses, structures and magnetism of α-Mn(dca)2, [Mn(dca)2(H2O)2]·H2O, [Mn(dca)2(C2H5OH)2]·(CH3)2CO, [Fe(dca)2(CH3OH)2] and [Mn(dca)2(L)2], where L = pyridine, CH3OH or DMF and dca– = dicyanamide, N(CN)2–†

Abstract: The dicyanamide anion has been observed to adopt two bridging co-ordination modes (µ and µ3) in α-Mn(dca)2, [Mn(dca)2(H2O)2]·H2O, [Mn(dca)2(C2H5OH)2]·(CH3)2CO, [Fe(dca)2(CH3OH)2] and [Mn(dca)2(L)2] [L = py, CH3OH or DMF; dca = dycanamide N(CN)2–], and generates weak ligand fields thus stabilising high spin configurations. The N- or O-bonded ligands L play an important role in the stabilisation of both the molecular structures and the three dimensional structure, via hydrogen bonding. The unsolvated α-Mn(dca)2 adopts a rutile-like single network structure, based on the near orthogonal packing of ‘ribbons’ of . . . Mn(NC–N–CN)2Mn . . ., similar to that found for the isomorphous analogues of Co, Ni, Fe and Cu. Magnetisation measurements confirmed a high spin manganese d5 system displaying antiferromagnetic coupling (θ = –25 K) above 25 K and undergoing long range magnetic ordering (TN = 16 K) to a spin-canted antiferromagnet (weak ferromagnet). Magnetisation and heat capacity measurements on some samples of α-Mn(dca)2 indicated a possible second transition at ≈6 K, the nature of which is under investigation. From the hysteresis data at 2 K (remnant magnetisation of 29 cm3 Oe mol–1 and coercive field of 406 Oe) a canting angle of 0.05° is estimated for this soft magnet. Other samples gave a higher value for the coercive field. The α-M(dca)2 series has a diverse range of ground states; CuII (d9) is a paramagnet, NiII (d8) and CoII (d7) are ferromagnets and FeII (d6) and MnII (d5) are canted antiferromagnets. Reasons for this diversity are given on the basis of the nature of exchange coupling pathways within the rutile structure and a mechanism for the long range magnetic ordering is proposed. A range of 1-D chain complexes of type [Mn(dca)2(L)2], containing ‘ribbons’ of doubly bridged Mn(NC–N–CN)2Mn have been structurally characterised. The complex [Fe(dca)2(CH3OH)2] is isostructural with the manganese analogue. 2-D Square grids are found in crystals of [Mn(dca)2(C2H5OH)2]·(CH3)2CO and in [Mn(dca)2(H2O)2]·H2O, the latter displaying, in addition, penetration of ribbons of trans-Mn(dca)2(H2O)2 through the grids. Dehydration or desolvation results in formation of the α-Mn(dca)2 phase. The Lewis-base adducts all display very weak antiferromagnetic coupling (J ≈ –0.12 cm–1) and no magnetic long-range order. Dissolution of the compounds in protic solvents leads to complete dissociation of the dicyanamide, and the axially co-ordinated ligands, L, can readily be exchanged by reaction or recrystallisation in different co-ordinating solvents.

Co-ordination engineering: when can one speak of an “understanding”? Case study of the multidentate ligand 2,2′-dimethyl-4,4′-bipyrimidine†

Abstract: The mode of co-ordination of the multidentate ligand 2,2′-dimethyl-4,4′-bipyrimidine (L) was found to depend on the metal ion, the crystallization conditions, the metal-to-ligand ratio, and the anion. With nickel a chelating co-ordination through the endo-dentate nitrogen donor set is observed in the molecular complex [NiCl2(L)(H2O)]·CH3NO2, derived from hot CH3NO2. With Cu(NO3)2 and CuI–CH3CN one- and two-dimensional (1-D and 2-D) co-ordination polymers of formula ∞ 1[Cu(NO3)2(µ-L)] and ∞ 2[Cu2(µ3-I)2(µ-L)] are obtained, where the bipyrimidine ligand is solely bridging through the two exo-dentate nitrogen atoms. On the other hand, a synthesis from CuI and crystallization from hot dimethyl sulfoxide leads to a 1-D iodide-bridged co-ordination polymer ∞ 1[Cu(µ-I)(L)] with a chelating ligand. With AgNO3 two different types of co-ordination polymers were found, depending on the silver-to-ligand ratio. At a 1∶1 ratio in the presence of a co-ordinating anion a 2-D network, ∞ 2[Ag(µ-NO3)2(µ-L)], with only bridging bipyrimidine ligands is observed. At a metal excess, a 3-D framework, ∞ 3[Ag3(µ3-NO3)3(µ3-L)2], forms where L functions both as a chelating and as bridging ligand. A tetradentate co-ordination mode of L towards silver is also found with non-co-ordinating anions, such as BF4– and PF6–, and gives rise to the isostructural 2-D co-ordination polymers of formula ∞ 2[Ag3(CH3CN)3(µ3-L)2]X3 (X = BF4 or PF6).

Metal–organic co-ordination frameworks based on mixed N- and O-donor ligands: crystal structures of [Co(phth)2(bipy)] and [Co2(mal)2(bipy)(H2O)2] (phth = phthalate, mal = malonate, bipy = 4,4′-bipyridine)†

Abstract: Two new metal–organic co-ordination frameworks have been prepared hydrothermally in mixed ligand systems and their crystal structures determined: [Co(phth)2(bipy)] is composed of a complex three-dimensional framework consisting of interlinked Co–phth–Co and Co–bipy–Co chains; [Co2(mal)2(bipy)(H2O)2] is also three-dimensional, being composed of Co–mal sheets which are pillared by bidentate bipy molecules (phth = phthalate, mal = malonate, bipy = 4,4′-bipyridine). Both frameworks enclose small void channels.

Controlling copper(I) halide framework formation using N-donor bridging ligand symmetry: use of 1,3,5-triazine to construct architectures with threefold symmetry

Abstract: The formation of co-ordination polymers between copper(I) halides and 1,3,5-triazine (tri), a potentially tridentate N-donor bridging ligand with threefold symmetry, has been studied. Complexes with both 3∶1 and 2∶1 molar ratios are formed by both CuBr and CuI. The compounds [Cu3X3(tri)]∞ (X = Br or I) are structurally similar, despite crystallising in different space groups. They are composed of (CuX)∞ columns linked by triazine molecules to generate three-dimensional constructions with non-crystallographically imposed threefold symmetry. The (CuX)∞ columnar motif can be described as a series of perpendicularly stacked Cu3X3 chairs, alternately rotated by 60° and linked by Cu–X contacts. The tetrahedral co-ordination geometry of the copper centres is completed by a tridentate triazine bridge which links two copper atoms in separate columns. Thus, each (CuX)∞ column is linked to six adjacent (CuX)∞ columns. The structure of [Cu2Br2(tri)]∞ comprises (CuBr)∞ columns and castellated (CuBr)∞ chains linked by triazine molecules to generate a construction with crystallographically imposed threefold symmetry. The (CuBr)∞ columns are similar to but more regular than those found in [Cu3Br3(tri)]∞. In this case, however, each column is linked to six adjacent chains. The (CuBr)∞ castellated chain motif is very unusual. The tetrahedral copper centres are co-ordinated by two adjacent bromide anions and by two triazine molecules each of which links a second chain and a column. Consequently, each chain is linked to four neighbouring chains and two neighbouring columns. Despite a stoichiometry identical to that of [Cu2Br2(tri)]∞, [Cu2I2(tri)]∞ has a completely different structure. The triazine molecules act as bidentate bridging ligands to link (CuI)∞ layers thereby giving alternating inorganic and organic layers. The tetrahedral co-ordination geometry of the copper centres in the (CuI)∞ layers, which are effectively undulating hexagonal nets, is provided by three iodide anions from the layers and by a bridging triazine molecule.

A three-dimensional network coordination polymer, (terephthalato)(pyridine)cadmium, with blue fluorescent emission

Abstract: The first terephthalato (TPT) bis-tridentate bridging cadmium coordination polymer, [(TPT)(py)Cd] 1, with blue fluorescent emission, was synthesized by a hydrothermal reaction between Cd(ClO4)2· 6H2O, 1,4-dicyanobenzene and pyridine (py).

A mechanistic and structural model for the formation and reactivity of a MnV=O species in photosynthetic water oxidation

Abstract: Photosynthetic water oxidation is carried out by a tetranuclear Mn cluster contained in the membrane-bound protein complex photosystem II (PSII). The mechanism of PSII catalysed water oxidation is unknown; however, several current models invoke a high-valent MnO species as a key intermediate in O–O bond formation. In part, these proposals are based on biophysical studies of the protein which suggest that the redox-active tyrosine residue, YZ, abstracts hydrogen atoms directly from substrate water molecules bound to the Mn4 cluster. In this paper, we consider organic oxidation and O–O bond-forming reactions catalysed by biomimetic Mn and Ru model complexes that are believed to proceed via MO intermediates. We also interpret biophysical data concerning the roles of Ca2+ and Cl– in photosynthetic water oxidation, proposing that they are involved in a hydrogen-bonded network between the Mn4 cluster and YZ. Connecting the observed reactivities of model complexes containing MO groups to spectroscopic information on the environment of the Mn4 cluster in the protein leads us to favour an O–O bond-forming step in photosynthetic water oxidation that occurs through nucleophilic attack of a calcium-bound hydroxide ligand on the electrophilic oxygen atom of a MnO intermediate. In addition, a new role for Cl– is proposed in which Cl– tunes the nucleophilicity of the calcium-bound hydroxide.

Sodium hydrotris(methimazolyl)borate, a novel soft, tridentate ligand: preparation, structure and comparisons with sodium hydrotris(pyrazolyl)borate†

Abstract: The hydrotris(methimazolyl)borate anion (Tm), a soft analogue of the hydrotris(pyrazolyl)borate anion (Tp), has been synthesized. This novel ligand system has been designed to maintain the tripodal geometry around the boron while allowing the replacement of the three nitrogen donor atoms by three sulfur (thione) donor atoms, thus providing a complementary soft, tridentate, face capping ligand system. The two ions, Tm and Tp were compared by X-ray analysis and ab initio calculations in an attempt to explore the effects of exchanging the hard donor atoms for soft donor atoms in this type of ligand. The compound NaTm is essentially salt like with discrete anions and hydrated sodium cations. The structure of NaTp crystallised under identical conditions is observed to be an infinite ribbon containing monodentate, bridging and pendant pyrazolyl units. The co-ordination sphere of the sodium cation in NaTp is completed by two water molecules. Ab initio calculations at the Hartree–Fock level using a 6-31G* basis set on these anions and their sodium complexes suggested that while both ions are in general similar in nature, there are subtle differences which will influence their chemistry. Ab initio calculations were also used to provide a rational analysis of the formation of the two sodium salts obtained and on the analogous copper complexes further to clarify the hard and soft nature of the two ligand systems.

Structural families in nitride chemistry

Abstract: Recent progress in the area of nitride chemistry has been rapid and incresingly diverse. Advances in ternary transition metal nitride research have been significant in the last several years to the point where the chemist can begin to correlate these compounds in terms of certain favoured structure types. It is a facet of the often intermediate bonding behaviour in these solids that the structure types so far exhibited are an intriguing mix of covalent (carbide-like), ionic (oxide-like) and unique motifs. While new motifs continue to be discovered with astonishng regularity, an attempt is made to summarise and classify just some of the major emerging ternary nitride structural families.

The first co-ordinatively unsaturated Group 8 allenylidene complexes: insights into Grubbs’ vs. Dixneuf–Fürstner olefin metathesis catalysts

Abstract: The reactions of [MCl2(PPh3)3] with HCCCPh2OH provided [MCl2(CCCPh2)(PPh3)2] (M = Ru 1a or Os 1b) the first examples of co-ordinatively unsaturated allenylidene complexes of Group 8 metals. The phosphine ligands of 1a are labile and readily replaced by PCy3 to give [RuCl2(CCCPh2)(PCy3)2] 1c. Heating 1a with NaPF6 in chloroform gave the known bimetallic salt [Ru2(µ-Cl)3(CCCPh2)2(PPh3)4]PF6 2·PF6. The reaction of 1a with carbon monoxide provided [RuCl2(CCPh2)(CO)(PPh3)2] 3 which may also be prepared from [RuCl2(CO)(dmf)(PPh3)2] and HCCCPh2OH. The first macrocycle coligated allenylidene complex [RuCl(CCCPh2)(PPh3)([9]aneS3)]Cl 4·Cl ([9]aneS3 = 1,4,7-trithiacyclononane) was obtained from the reaction of 1a with [9]aneS3. Alternatively, 4·PF6 is also obtained by treating [RuCl2(PPh3)([9]aneS3)] sequentially with NaPF6 in acetonitrile followed by HCCCPh2OH. The reaction of 1a with dppe and NaPF6 yielded the known salt trans-[RuCl(CCCPh2)(dppe)2]PF6 5·PF6. The complex [RuCl(CCCPh2)(PCy3){HB(pz)3}] 6 (pz = pyrazol-1-yl) was obtained from the reaction of 1c with K[HB(pz)3], whilst the related benzylidene complex [RuCl(CHPh)(PCy3){HB(pz)3}] 7 was obtained similarly from [RuCl2(CHPh)(PCy3)2] and K[HB(pz)3]. Heating [Ru2(µ-Cl)2Cl2(η-cym)2] (cym = iPrC6H4Me-4) with PCy3 and HCCCPh2OH in refluxing benzene provided a mixture of 1c and the bimetallic complex [Ru2(µ-Cl2)Cl2(CCCPh2)(η-cym)] 8 and other unidentified products. The complex 8 may however be obtained quantitatively from the reaction of 1c with [Ru2(µ-Cl)2Cl2(η-cym)2]. These results suggest that the active species in ring-closure olefin metathesis processes mediated by the allenylidene pre-catalyst [RuCl(CCCPh2)(PCy3)(η-cym)]+ in non-polar arene solvents may be allenylidene analogues of the Grubbs’ alkene metathesis catalyst, viz. 1c and 8.

1-Ethyl-3-methylimidazolium halogenoaluminate ionic liquids as solvents for Friedel–Crafts acylation reactions of ferrocene

Abstract: Friedel–Crafts acylations of ferrocene in 1-ethyl-3-methylimidazolium halogenoaluminate ionic liquids, [emim]I–(AlCl3)x are described.3 The effect of varying the “bulk” Lewis acidity of the ionic liquids used as solvents in these reactions and the effect of varying the relative amounts of acylating agent with respect to the amount of ferrocene in these reactions is also described. The use of a variety of different acylating agents in our studies demonstrates the scope of this reaction performed in these ionic liquid systems.

An efficient synthesis of polyynyl and polyynediyl complexes of ruthenium(II)

Abstract: The fluoride-induced desilylation of trimethylsilyl-substituted alkynes and polyynes and subsequent reactions with RuCl(PPh3)2Cp have been used to synthesize complexes containing unsaturated chains containing up to six carbons. Reactions with Co2(CO)8 or tetracyanoethene have been further used to characterise the products. Structural confirmation of RuX(PPh3)2Cp [X = CCC6H4CCSiMe3 2, CCCCPh 4, CCC2Ph{Co2(CO)6} 8, CCC2H{Co2(µ-dppm)(CO)4} 9, CCC{C(CN)2}CPhC(CN)2 10 or CCC{C(CN)2}C{C(CN)2}CCPh 11] and {Ru(PPh3)2Cp}2(µ-Cn) [n = 4 (6) or 6 (7)] is reported.

Crystallisation of H3BTC, H3TPO or H2SDA with MII (M = Co, Mn or Zn) and 2,2′-bipyridyl: design and control of co-ordination architecture, and magnetic properties (H3BTC = benzene-1,3,5-tricarboxylic acid, H3TPO = tris(4-carboxylphenyl)phosphine oxide, H2SDA = cis-stilbene-4,4′-dicarboxylic acid)†

Abstract: The hydrothermal reaction of benzene-1,3,5-tricarboxylic acid (H3BTC) with MII (M = Mn, Co or Zn), tris(4-carboxyphenyl)phosphine oxide (H3TPO) or cis-stilbene-4,4′-dicarboxylic acid (H2SDA) with CoII and 2,2′-bipyridyl (BIPY) gave 1-D co-ordination networks formulated as: [M(HBTC)(BIPY)(H2O)] (M = Mn 1, Co 2, or Zn 3; [Co3(BTC)2(BIPY)2(H2O)6]·4H2O 4, [Co3(TPO)2(BIPY)2(H2O)6]·xH2O 5 and [Co(SDA)(BIPY)(H2O)] 6. Structures 1 and 2 consist of double stranded chains of alternating HBTC dianions and dimeric units MII–MII linked by two µ-(1,1) bridging carboxylates. Magnetic properties of 1 and 2 indicate the presence of ferromagnetic exchange interactions within the dimers. Structures 4 and 5 consist of chains with a molecular ladder motif which are stacked creating large channels lined by hydrated cobalt(II) ions. The H2O/D2O solvent exchange in structure 5, studied by infrared spectroscopy and thermal gravimetric analysis–mass spectrometry, provides evidence for the porosity and zeolitic nature of the material.

Self-assembly of novel co-ordination polymers containing polycatenated molecular ladders and intertwined two-dimensional tilings

Abstract: Four novel co-ordination polymers have been obtained from the reactions of MII(NO3)2 salts (MII = Zn, Co or Cd) and the bidentate spacer ligands 1,2-bis(4-pyridyl)ethyne (bpethy) and trans-4,4′-azobis(pyridine) (azpy), all exhibiting the same metal-to-ligand molar ratio of 2∶3. Crystal structure analyses, however, have revealed two quite different polymeric motifs, in spite of the presence of similar co-ordination geometries of the metal ions, that are bound to three pyridyl groups, with a T-shaped disposition, and to the oxygen atoms of two η2-nitrates, thus resulting in a distorted pentagonal-bipyramidal seven-co-ordination. The species [M2(bpethy)3(NO3)4] (M = Zn or Co) consist of ladder-like polymers that interpenetrate in an unprecedented fashion to produce an overall three-dimensional array. On the other hand, the species [Cd2(bpethy)3(NO3)4]·CH2Cl2 and [Cd2(azpy)3(NO3)4] contain undulated two-dimensional layers with an unprecedented tiled pattern, that give threefold interpenetration in a parallel fashion.

Syntheses and crystal structures of lithium and niobium complexes containing a new type of monoanionic “scorpionate” ligand†

Abstract: The synthesis of a novel lithium compound [{Li(H2O)(bdmpza)}4] [bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate], containing a new “scorpionate” ligand, and its reaction with a niobium complex to give [NbCl3(bdmpza)(PhCCMe)] have been reported.

Syntheses of highly functionalized cube-octameric polyhedral oligosilsesquioxanes (R8Si8O12)

Abstract: Reactions of [H2N(CH2)3]8Si8O12 or its octahydrochloride salt with a variety of electrophiles, including anhydrides, lactones, acid chlorides, α,β-unsaturated esters and isocyanates, afforded functionalized R8Si8O12 frameworks in good to excellent yields. Practical methods for the synthesis of [HO(CH2)3]8Si8O12, [OCN(CH2)3]8Si8O12 and [(Ph2PCH2)2N(CH2)3]8Si8O12 are also reported.

The heterogenization of homogeneous metallocene catalysts for olefin polymerization

Abstract: Metallocene complexes of titanium, zirconium and hafnium are very active and versatile catalysts for olefin polymerization and are already contributing to commercial production. Owing to a variety of catalyst parameters a wide range of polymers with various properties are accessible. Since metallocene complexes are homogeneous in solution they can easily be studied by spectroscopic methods. However, for industrial application they must be heterogenized.

Structures and photoluminescence of dinuclear platinum(II) and palladium(II) complexes with bridging thiolates and 2,2′-bipyridine or 2,2′∶6′,2″-terpyridine ligands

Abstract: A series of mononuclear and dinuclear platinum(II) thiolates with 2,2′-bipyridine (bpy) and 2,2′∶6′,2″-terpyridine (terpy) ligands having emissive LLCT (ligand-to-ligand charge-transfer) excited states were prepared and characterized by X-ray diffraction analyses. The [M2(dtbpy)2(NS)2][ClO4]2 (M = Pt or Pd; dtbpy = 4,4′-di-tert-butyl-2,2′-bipyridine, NS– = pyridine-2-thiolate) complexes are isostructural to each other with intramolecular Pt· · ·Pt and Pd· · ·Pd distances being 2.917(2) and 2.891(4) A, respectively. Assignment of LLCT absorption bands for the platinum(II) complexes was based on the shift in absorption energy with the substituents on the diimine and thiolate ligands. In the solid state or in solution at room temperature the platinum(II) complexes show photoluminescence with λmax ranging from 603 to 710 nm. The PtII· · ·PtII and/or ligand–ligand interactions are not primarily responsible for the emissions of the dinuclear platinum(II) thiolates which have intramolecular metal–metal separations greater than 2.9 A.

Synthesis and characterisation of titanium silasesquioxane complexes: soluble models for the active site in titanium silicate epoxidation catalysts†

Abstract: Titanium silasesquioxane complexes have been prepared as models for the catalytically active centres in titanium silicate oxidation catalysts. Complexes [TiL(R7Si7O12)] [R = c-C6H11, L = CH2Ph 5, NMe2 6, OSiMe3 7, OPri 8 or OBut 9; R = c-C5H9, L = CH2Ph 13 or OPri 14] were prepared from the reactions of incompletely condensed silasesquioxanes R7Si7O9(OH)3 1, 2 with homoleptic complexes TiL4. Aryloxy derivatives [TiL(R7Si7O12)] [R = c-C6H11, L = OPh 10, O-C6H4F-p 11 or O-C6H4NO2-p 12] were prepared from the reaction of 8 with the corresponding aryl alcohols. The 29Si and 13C NMR spectroscopic data obtained on 5–14 indicate that the local C3v symmetry of the silasesquioxane ligand is retained at titanium, consistent with the formation of monomeric complexes possessing tripodal geometry. The monomeric nature of 7 was confirmed by X-ray crystallography. For complexes 8–12 solution NMR spectroscopy reveals the presence of a dimer, containing µ-alkoxy ligands, in equilibrium with the monomer. The zirconium analogue of 9, [Zr(OBut){(c-C6H11)7Si7O12}] 15, was similarly isolated as a monomer–dimer mixture from the reaction of the incompletely condensed silasesquioxane (c-C6H11)7Si7O9(OH)3 with [Zr(OBut)4]. Reaction of the disilanol (c-C6H11)7Si7O9(OSiMe3)(OH)2 4 with an excess of [Ti(OPri)4] afforded [Ti(OPri)2{(c-C6H11)7Si7O11(OSiMe3)}] 16, containing a bidentate silasesquioxane ligand, while reactions with TiL4 (L = CH2Ph, NMe2 or OSiMe3) afforded [Ti{(c-C6H11)7Si7O11(OSiMe3)}2] 17, independent of the stoichiometry of the reactants. Complexes 5–14 serve as soluble models for putative tripodal (open lattice) sites in titanium silicates, while 16 and 17 represent models for bipodal and tetrapodal (closed lattice) sites, respectively. From a study of the catalytic properties of complexes 5–17 in the epoxidation of oct-1-ene with tert-BuOOH (TBHP), revealing high activity for 5–14 and low activity for 16 and 17, it is concluded that the most active site in titanium silicate epoxidation catalysts corresponds to a four-co-ordinate site possessing tripodal geometry. Studies using IR and NMR spectroscopy show that, in the absence of olefins, putative alkylperoxo complexes formed by the addition of TBHP to tripodal complexes decompose rapidly at ambient temperature. Based on the high TBHP-to-epoxide selectivities observed under epoxidising conditions, it is apparent that the rate of epoxidation is significantly greater than that of alkylperoxo intermediate decomposition.

Crystal structures and magnetic properties of the interpenetrating rutile-related compounds M(tcm)2 [M = octahedral, divalent metal; tcm– = tricyanomethanide, C(CN)3–] and the sheet structures of [M(tcm)2(EtOH)2] (M = Co or Ni)

Abstract: The isomorphous structures of M(tcm)2 [MII = Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd or Hg; tcm– = tricyanomethanide, C(CN)3–] contain two interpenetrating rutile-related networks generated by octahedral six-connecting metal ions and trigonal three-connecting tcm– anions. The detailed variable temperature and variable field magnetic properties of this series of high-spin complexes generally point to the existence of very weak intraframework coupling with no evidence for long range magnetic order or interframework effects. The compound Cr(tcm)2 is the most strongly coupled and displays a field independent maximum in susceptibility at 14.5 K and a J value of –1.6 cm–1 (using a –2JS1·S2 Heisenberg chain model); Co(tcm)2 displays high temperature magnetic moments typical of essentially uncoupled octahedral centres but with a most unusual field dependence in µCo observed below 10 K, probably due to very weak ferromagnetic coupling, and an Msat value in high fields, at 2 K, which is significantly less than that expected for S = 3/2. Doping of M(tcm)2 with another M′ member of the series leads to a crystal structure isomorphous with M(tcm)2 in which the dopant metal M′ occupies the M site in a random fashion. The resultant magnetism is simply intermediate between those of the parent phases. The isomorphous structures of [M(tcm)2(EtOH)2] (MII = Co or Ni) contain pseudo square-grid sheets in which the tcm– ligands are each co-ordinated to two metal ions and act as a kinked bridge. Each metal is co-ordinated to four tcm– anions in an equatorial arrangement and to two axial ethanol ligands. Extensive intrasheet hydrogen bonding exists between the ethanol molecules and the unco-ordinated nitrile of the tcm– bridges.

Blue luminescent zinc(II) complexes with polypyridylamine ligands: crystal structures and luminescence properties

Abstract: A series of blue luminescent zinc(II) complexes, [Zn(dpa)X2] [dpa = di-2-pyridylamine, X = OAc 1a, Cl 1b, CN 1c or 4-MeC6H4S 1d], [Zn(dpa)2][CF3SO3]2 2, [Zn(tpda)X2] [tpda = 2,6-bis(2-pyridylamino)pyridine, X = OAc 3a or Cl 3b] and [Zn(tpda)(CF3SO3)2] 4 has been prepared. Their molecular structures, except complex 4, have been established by X-ray crystallography. In the crystal lattice of 2 the [Zn(dpa)2]2+ cations and CF3SO3– anions are disposed in pairs via intermolecular hydrogen bonds [N(2)· · ·O(2) 2.865(4) A]. The crystal packing of [Zn(dpa)(OAc)2] 1a revealed that two adjacent molecules associate in pairs through intermolecular hydrogen bonding [N(2)· · ·O(4′) 2.816(3) A]. However, the crystal lattice of its tpda derivative 3a shows that the molecules are linked by extensive intermolecular hydrogen bonding between the amino groups and the acetate ligands [N(2)· · ·O(2′) 2.805(3) and N(4)· · ·O(4′) 2.860(3) A] resulting in an interlocking hydrogen bond network. Polymeric one-dimensional tapes are generated through extended π–π stacking interactions between the molecules of [Zn(dpa)(4-MeC6H4S)2] 1d, and the thiolate groups are aligned in an all-anti conformation along the metal chain. In the case of [Zn(dpa)(CN)2] 1c, co-operative intermolecular hydrogen bonds and aromatic π–π interactions in its solid state lead to a supramolecular two-dimensional sheet. All the zinc(II) complexes display high energy intraligand 1(π–π*) fluorescence in degassed MeOH at 298 K, and intraligand 3(π–π*) phosphorescence in a glassy solution (MeOH–EtOH 1∶2 at 77 K). An emission band observed for 1c (418 nm) and 1d (481 nm) in their solid state emission spectra is ascribed to excimeric emission due to aromatic π–π interactions.