Crystal synthesis of hybrid organometallic-inorganic hydrogen bonded salts of acid oxoanions

Partially deprotonated inorganic oxoanions derived from sulfuric and phosphoric acids have been used to assemble organometallic cations in inorganic-organometallic hybrid systems. The organometallic sandwich cations [(eta(5)-C(5)H(5))(2)Co]+, [(eta(5)-C(5)Me(5))(2)Co]+ and [(eta(5)-C(5)Me(5))(2)Fe]+ have been used because they do not interfere with hydrogen bonding formation forcing self-assembling of the inorganic acids anions HSO(4)(-) and H(2)PO(4)(-) into hydrogen bonded mono- and bi-dimensional networks.     

Anions derived from squaric acid form interionic pi-stack and layered, hydrogen-bonded superstructures with organometallic sandwich cations: the magnetic behaviour of crystalline

Depending on the stoichiometric ratio, squaric acid (3,4-dihydroxy-3-cyclobutene-1,2-dione, H2SQA) reacts with [(eta6-C6H6)2Cr] in THF to form the crystalline material [(eta6-C6H6)2Cr][HSQA] (1) and in water to yield [[(eta6-C6H6)2Cr]2][SQA] x 6H2O (3); it also reacts with [(eta5-C5H5)2Co][OH] in water to form [[(eta5-C5H5)2Co]2][SQA] x 6H2O (4). Compound 1 is almost isostructural with the previously reported salt [(eta5-C5H5)2Co][HSQA] (2); its structure is based on pi-pi stacks between the benzene ligands and the hydrogen squarate anionic chains (pi-pi distance 3.375 A). Compounds 3 and 4 are isomorphous and have a structure in which layers of organometallic cations intercalate with layers of water molecules hydrogen bonded to squarate dianions. All crystals contain charge-assisted C-Hdelta+...Odelta- hydrogen bonds between the organometallic and the organic components, while negative O-H(-)...O(-) and O-H...O(2-) interactions are present in the pairs 1/3 and 2/4, respectively. In constrast to most organic salts of [(eta6-C6H6)2Cr]+ and [(eta5-C5H5)2Co]+ which are yellow, crystals of compounds 1-4 are orange. Reflectance spectra measured on the crystalline material 1 show the presence of an intense tail that can be assigned to a charge-transfer transition through the [(eta6-C6H6)2Cr]+/[HSQA]- pi-stacking interactions, while the pi stacking in 2 causes only a broadening of the band. The magnetic behaviour of 1 and 3 has been investigated by SQUID magnetometry. Both compounds are characterised by a weak antiferromagnetic interaction between the S=1/2 Cr centres of the [(eta6-C6H6)2Cr]+ cations, which is significantly stronger in 1 due to the pi-stacking with the HSQA- anions.     

Making crystals from crystals: a green route to crystal engineering and polymorphism

Supramolecular reactions between crystalline materials as well as reactions between a crystalline material and a vapour can be used to generate new crystalline substances. These solvent-free processes can be exploited to prepare both hydrogen-bonded co-crystals and coordination networks. Solid-vapour reactions do not differ from solid-vapour uptake/release processes, and can also be used to prepare polymorphs and solvates. It is argued that solvent-less reactions involving molecular crystals represent a green route to supramolecular solid-state chemistry and crystal engineering.     

Hydrogen bonding and dynamic behaviour in crystals and polymorphs of dicarboxylic-diamine adducts: a comparison between NMR parameters and X-ray diffraction studies

Fumaric, malonic, maleic, and hydromuconic (HOOCCH2(CH)2CH2COOH) acids were used to prepare a series of hydrogen-bonded adducts or salts, depending on whether acid-base proton transfer takes place, with the dibase [N(muCH2CH2)3N] in various stoichiometric ratios. The resulting compounds have been investigated by using the 1H MAS, 15N, and 13C cross polarisation magic-angle spinning (CPMAS) methods and discussed in relation to X-ray diffraction studies to ascertain the nature of the O-HO, NH-O, and N+-HO- hydrogen bonds between the various species. In addition, two polymorphic forms of the malonic compound and a hydrate in the maleic case were examined. We also present the correlations between the chemical shifts of the hydrogen-bonded protons and those from the proton transfer reaction (acid-to-base) with the heavy atom distances. The dynamic behaviour in the solid-state of the [N(muCH2CH2)3N] adducts with fumaric 2:1, maleic 1:1 hydrate, and hydromuconic acids, and a malonate 2:1 polymorph adduct have been investigated by using variable-temperature 1H spin-lattice relaxation times. A substantial agreement between the activation energies obtained from fitting the T1 data and the results of potential energy barrier calculations demonstrates that the facile reorientation of the [N(muCH2CH2)3N] molecule occurs in several of the adducts.     

Ferrocenyl-functionalised terpyridines and their transition-metal complexes: syntheses,structures and spectroscopic and electrochemical properties

Terpyridine ligands of the type Fc'-X-tpy (Fc'=ferrocenyl or octamethylferrocenyl, X=rigid spacer, tpy'=4'-substituted 2,2':6',2'-terpyridine) were prepared, crystallographically characterised and used for the synthesis of di- and trinuclear bis(terpyridine) complexes of RuII, FeII and ZnII. Donor-sensitiser dyads and triads based on RuII were thoroughly investigated by (spectro)electrochemistry, UV/Vis, transient absorption and luminescence spectroscopy, and an energy level scheme was derived on the basis of the data collected. Intramolecular quenching of the photoexcited RuII complexes by the redox-active Fc' groups can occur reductively and by energy transfer. Both the redox potential of the donor Fc' and the nature of the spacer X have a decisive influence on excited-state lifetimes and emission properties of the complexes. Some of the compounds show room-temperature luminescence, which is unprecedented for ferrocenyl-functionalised compounds of this kind.     

Novel hetero-bimetallic metalla-macrocycles based on the bis-1-pyridyl ferrocene [Fe(eta 5-C5H(4)-1-C5H4N)2] ligand. Design,synthesis and structural characterization of the complexes [Fe(eta 5-C5H(4)-1-C5H4N)2](AgI)2(2+)/(CuII)2(4+)/(ZnII)2(4+)

The bidentate sandwich ligand [Fe(eta 5-C5H(4)-1-C5H4N)2] has been prepared, structurally characterized and employed in the preparation of the novel supramolecular heterobimetallic metalla-macrocycles [Fe(eta 5-C5H(4)-1-C5H4N)2]Ag2(NO3)(2).1.5H2O, [Fe(eta 5-C5H(4)-1-C5H4N)2]Cu2(CH3COO)(4).3H2O and [Fe(eta 5-C5H(4)-1-C5H4N)2]Zn2Cl4.     

Assembly of hybrid organic-organometallic materials through mechanochemical acid-base reactions

Manual grinding of the organometallic complex [Fe(eta(5)-C(5)H(4)COOH)(2)] with a number of solid bases, namely 1,4-diazabicyclo[2.2.2]octane, C(6)H(12)N(2), 1,4-phenylenediamine, p-(NH(2))(2)C(6)H(4), piperazine, HN(C(2)H(4))(2)NH, trans-1,4-cyclohexanediamine, p-(NH(2))(2)C(6)H(10), and guanidinium carbonate [(NH(2))(3)C](2)[CO(3)], generates quantitatively the corresponding adducts, [HC(6)H(12)N(2)][Fe(eta(5)-C(5)H(4)COOH)(eta(5)-C(5)H(4)COO)] (1), [HC(6)H(8)N(2)][Fe(eta(5)-C(5)H(4)COOH)(eta(5)-C(5)H(4)COO)] (2), [H(2)C(4)H(10)N(2)][Fe(eta(5)-C(5)H(4)COO)(2)] (3), [H(2)C(6)H(14)N(2)][Fe(eta(5)-C(5)H(4)COO)(2)].2 H(2)O, (4.2 H(2)O), and [C(NH(2))(3)](2)[Fe(eta(5)-C(5)H(4)COO)(2)].2 H(2)O, (5.2 H(2)O), respectively. Crystallization from methanol in the presence of seeds of the ground sample allows the growth of single crystals of these adducts; therefore we were able to determine the structures of the adducts by single-crystal X-ray diffraction. This information was used in turn to identify and characterize the polycrystalline materials obtained by the grinding process. In the case of [HC(6)N(2)H(12)][Fe(eta(5)-C(5)H(4)COOH)(eta(5)-C(5)H(4)COO)] (1), the base can be removed by mild treatment regenerating the starting dicarboxylic acid, while in all other cases decomposition is observed. The solid-solid processes described herein imply molecular diffusion through the lattice, breaking and reassembling of hydrogen-bonded networks, and proton transfer from acid to base.     

O-H...O interactions involving doubly charged anions: charge compression in carbonate-bicarbonate crystals

The O-H...O interaction formed by the anions HCO(3)(-) and CO(3)(2-) has been investigated on the basis of data retrieved from the Inorganic Crystal Structure Database (ICSD) and by means of ab initio computations. It has been shown that the O-H...O separations associated with HCO(3)(-)...(3)(2-) interactions are shorter than those found in crystals containing hydrogen carbonate monoanions such as HCO(3)(-)...HCO(3)(-). Ab initio MP2/6-311G++(2d,2p) computations on the crystal Na(3)(HCO(3))(CO(3)).2H(2)O have shown that the interaction between the monoanion donor and the dianion acceptor, for example HCO(3)(-)...CO(3)(2-), is more repulsive than that between singly charged ions, for example HCO(3)(-)...HCO(3)(-), but is largely overcompensated for by anion-cation electrostatic attractions. The shortening of the (-)O-H...O(2-) interaction relative to the (-)O-H...O(-) interaction has been explained as a consequence of the increased charge compression, that is of the stronger cation-anion interactions established by the CO(3)(2-) dianions with respect to those established by monoanions, and does not reflect an increase in the strength of the (-)O-H ...O(-) interaction. To expand the structural sample in the crystal packing analysis, the structure of the novel mixed salt K(2)Na(HCO(3))(CO(3)).2H(2)O has been determined by single-crystal X-ray diffraction and compared with the structure of the salt Na(3)(HCO(3))(CO(3)).2H(2)O used in the computations.     

Phosphine and phosphonite complexes of a Ru(II) porphyrin. 2. Photophysical and electrochemical studies

The photophysical and electrochemical properties of a series of mono- and bis-phosphine complexes of a 5,15-diphenyl-substituted ruthenium porphyrin, (MeOH)Ru(II)(CO)(DPP) 1, were investigated. The ligands used were diphenyl(phenylacetenyl)phosphine (DPAP), diethyl (phenylacetenyl)phosphonite [PAP(OEt)(2)], tris(phenylacetenyl)phosphine [(PA)(3)P], and bis(diphenylphosphino)acetylene (DPPA). All complexes display two reversible one-electron oxidations at: 0.61 and 1.0 V vs SCE (1), 0.42-0.51 and 0.97-1.05 V [(PR(3))Ru(II)(CO)(DPP)], and 0.06-0.25 and 0.82-0.95 V [(PR(3))(2)Ru(II)(DPP)]. As predicted by EHMO calculations, the first oxidation is porphyrin or phosphorus centered, whereas the second one is ruthenium centered. Bulk electrolysis at the first oxidation potential yields stable monocations. Simulation of the cyclic voltammogram of (DPAP)Ru(II)(CO)(DPP) in CH(2)Cl(2) demonstrates the kinetic lability of the complex, and the association constant found (K = 1.27 x 10(6) M(-1)) is in accordance with the value determined by UV-vis titration (K = 1.2 +/- 0.3 x 10(6) M(-1)). Coordination of one phosphine ligand to Ru(II)(CO)(DPP) leads to a red shift in both the absorption and luminescence spectra. Shifts are typically 10 nm for the B- and Q-band absorptions and are not affected by the nature of the phosphorus ligand. The intense luminescence of (PR(3))Ru(II)(CO)(DPP), red-shifted by 21-28 nm compared to 1, can be attributed to originate from a (3)(pi,pi) excited state, and it exhibits lifetimes from 150 to 240 micros. In the bis-phosphine complexes (PR(3))(2)Ru(II)(DPP), the Q-band absorption is broadened and does not show any distinct peak. Judged from EHMO calculation, this could arise from a low-energy charge-transfer state involving the phosphorus ligand. The luminescence is efficiently quenched due to radiationless decay from a charge-transfer excited state, involving either the metal center or the phosphorus ligand; an unambiguous assignment could not be made.     

Supramolecular metal-polypyridyl and Ru(II) porphyrin complexes: photophysical, electron paramagnetic resonance, and electrochemical studies

A series of mixed-metal supramolecular porphyrin arrays in which the geometry of the central metal-polypyridyl moiety defines the spatial arrangement of two or more Ru(II)-porphyrin units through axial coordination have been prepared by employing self-assembly based protocols, and their photophysical and electrochemical properties have been studied. The electrochemical properties of the constituent parts of these arrays depend only on their own chemical environment, regardless of the nuclearity and the overall charge of the compound; in this way species with predetermined redox patterns can be obtained via the synthetic control of the self-assembly process. Interestingly, several of these arrays are luminescent both at room and at low temperatures, and in many cases core-to-periphery or periphery-to-core intramolecular energy transfer processes take place according to the nature of the central metal template.