3-(4-Pyridyl)-acetylacetone – a fully featured substituted pyridine and a flexible linker for complex materials

New Copper Complexes with N,O-Donor Ligands Based on Pyrazole Moieties Supported by 3-Substituted Acetylacetone Scaffolds

The new 3-monosubstituted acetylacetone ligands, 3-(phenyl(1H-pyrazol-1-yl)methyl)pentane-2,4-dione (HLacPz) and 3-((3,5-dimethyl-1H-pyrazol-1-yl)(phenyl)methyl)pentane-2,4-dione (HLacPzMe), were synthesized and used as supporting ligands for new copper(II) and copper(I) phosphane complexes of the general formulae [Cu(HLacX)2(LacX)2] and [Cu(PPh3)2(HLacX)]PF6 (X = Pz (pyrazole) or PzMe (3,5-dimethylpyrazole)), respectively. In the syntheses of the Cu(I) complexes, the triphenylphosphine coligand (PPh3) was used to stabilize copper in the +1 oxidation state, avoiding oxidation to Cu(II). All compounds were characterized by CHN analysis, 1H-NMR, 13C-NMR, FT-IR spectroscopy, and electrospray ionization mass spectrometry (ESI-MS). The ligands HLacPz (1) and HLacPzMe (2) and the copper complex [Cu(PPh3)2(HLacPz)]PF6 (3) were also characterized by X-ray crystallography. The reactivity of these new compounds was investigated and the new compounds 4-phenyl-4-(1H-pyrazol-1-yl)butan-2-one (7) and 4-(3,5-dimethyl-1H-pyrazol-1-yl)-4-phenylbutan-2-one (8) were obtained in basic conditions via the retro-Claisen reaction of related 3-monosubstituted acetylacetone, providing efficient access to synthetically useful ketone compounds. Compound 8 was also characterized by X-ray crystallography.

Metal halide coordination compounds with quinazolin-4(3H)-one

Three coordination compounds of quinazolin-4(3H)-one (quinoz; C8H6N2O) with divalent group 12 halides are reported. In all complexes, coordination occurs via the nitro-gen atom ortho to the quinazolinone carbonyl group. In the two chain polymers with composition [MX 2(quinoz)], viz. (M = Cd, X = Br), catena-poly[[[quinazolin-4(3H)-one-κN 3]cadmium(II)]-di-μ-bromido], [CdBr2(C8H6N2O)]n (I), and M = Hg, X = Cl, catena-poly[[[quinazolin-4(3H)-one-κN 3]mercury(II)]-di-μ-chlorido], [HgCl2(C8H6N2O)]n (II), the divalent cations are five-coordinate, with four bridging halide and one terminal quinoz ligand. The CdII atom in (I) has an almost trigonal-bipyramidal coordination environment, whereas the HgII atom in (II) has a more distorted coordination environment. Likewise, the halide bridges in (II) are significantly more asymmetric than in (I). In both (I) and (II), quinoz ligands at adjacent cations along each strand are oriented in opposite directions, and the organic ligands of neighboring strands inter-digitate with resulting π-π inter-actions. In contrast to the halide-bridged chain polymers (I) and (II), the adduct of quinoz with CdI2 is the tetra-hedral complex [CdI2(quinoz)2], di-iodido-bis-[quinazolin-4(3H)-one-κN 3]cadmium(II), [CdI2(C16H12N4O2)], (III). The CdII atom in this discrete complex is located on a twofold rotation axis. Disorder in (III) is reflected in an alternative minority orientation of the mol-ecules for which the iodine sites closely match the position of the majority orientation. In view of the low site occupancy of only 0.0318 (8) Å, only the CdII position for this alternative orientation was taken into account during refinement. In all three compounds, classical N-H⋯O hydrogen bonds with donor-acceptor distances of ca 2.9 Å occur; they link the polymer chains in (I) and (II) into di-periodic networks and connect adjacent discrete complexes in (III) to mono-periodic strands.

Synthesis and coordination to the coinage metals of a trimethylpyrazolyl substituted 3-arylacetylacetone

The ligand 3-(4-(1,3,5-trimethyl-1H-pyrazol-4-yl)phenyl)acetylacetone (1) combines a Pearson hard O,O′ chelating acetylacetone donor with a softer pyrazole N donor bridged by a phenylene spacer. Deprotonation and coordination to CuII leads to a square planar bis-acetylacetonato complex; interpreting the close proximity of an adjacent complex’s pyrazole moiety as an η 2 ${{\eta}}^{2}$ coordination to the axial CuII position leads to a two dimensional extended structure. The N donor capabilities are proven by coordination to AgPF6 and AuCl; for AgI a cationic linear bis-pyrazole complex as a toluene solvate is obtained with toluene-pyrazole π-interactions and an essentially uncoordinated PF 6 - ${{\mathrm{PF}}_{6}}^{-}$ anion. In the case of AuCl a neutral linear coordination compound with one chlorido and one pyrazole ligand 1 is obtained. Comparing the dihedral angles with a closely related but shorter ligand reveals a larger rotational degree of freedom in 1, allowing for richer architectures in emerging coordination polymers.

Argentophilic Interactions in Two AgI Complexes of 3-(2-(Pyridin-4-yl)ethyl)pentane-2,4-dione, a Promising Ditopic Ligand

Reactions of 3-(2-(pyridin-4-yl)ethyl)pentane-2,4-dione (HacacPyen) with AgPF6 and AgBF4 afforded cationic silver complexes [Ag(HacacPyen)2]+ with essentially linear coordination of the Ag I cation by two pyridine N atoms. Rather unexpectedly, the HacacPyen ligands in the PF6- salt 1 adopt the diketo form, in contrast to the uncoordinated HacacPyen molecule, whereas the corresponding BF4- salt 2 and the majority of 3-substituted acetylacetones crystallizes as the enol tautomer. In both compounds 1 and 2, complex cations aggregate via short Ag...Ag interactions to pairs. These contacts amount to 3 . 21 Å in 1 and 3 . 26 Å or 3 . 31 Å in 2. As they are unsupported by any additional bridging ligands and correspond to the closest interionic interactions between neighbouring complex cations, they may be addressed as argentophilic interactions. The PF6- anions in 1 and the BF4- counter ions in 2 are involved in long and presumably electrostatic Ag...F contacts of ca. 2 . 9 Å. Additional coordination between Ag I and keto O atoms of symmetry-equivalent ligands occurs in 1 and leads to an extended two-periodic supramolecular structure.

Proton disorder in a short intramolecular hydrogen bond investigated by single-crystal neutron diffraction at 2.5 and 170 K

The substituted acetylacetone 3-[2-(pyridin-4-yl)ethyl]pentane-2,4-dione, C₁₂H₁₅NO₂, (1), with an ethylene bridge between the acetylacetone moiety and the heteroaromatic ring, represents an attractive linker for mixed-metal coordination polymers. In the crystal, (1) adopts an antiperiplanar conformation with respect to the C-C bond in the central ethylene group and almost coplanar acetylacetone and pyridyl groups. The ditopic molecule exists as the enol tautomer, with proton disorder in the short intramolecular hydrogen bond. Single-crystal neutron diffraction at 2.5 K indicated site occupancies of 0.602 (17) and 0.398 (17). The geometry of the acetylacetone moiety is in agreement with such a site preference of the bridging hydrogen: the O atom associated with the preferred H-atom site subtends the longer [1.305 (2) Å] and the more carbonyl-like O atom the shorter [1.288 (2) Å] C-O bond. Based on structure-factor calculations for the alternative H-atom sites, reflections particularly sensitive for proton distribution were identified and measured in a second neutron data collection at 170 K. At this temperature, 546 independent neutron intensities were used to refine positional and isotropic displacement parameters for a structure model in which parameters for C and O atoms were constrained to those obtained by single-crystal X-ray diffraction at the same temperature. The site occupancies for the disordered proton do not significantly differ from those at 2.5 K.

N Donor substituted acetylacetones – versatile ditopic ligands

Acetylacetone (2,4-pentanedione) derivatives with N donor substituents represent ditopic ligands with coordination sites of distinctly different Pearson hardness. Deprotonation of the acetylacetone (Hacac) moiety leads to O,O′ chelating monoanionic (acac) ligands suitable for coordination to hard cations. The softer N donor site(s) preferably act as nucleophiles towards softer partners. When the organic molecules are employed as linkers and coordinate via either site, they are often selective and allow to synthesize well-ordered heterometallic solids. This review addresses the derivatives of 17 pentanediones with nitrile, pyridyl and pyrazolyl moieties as N donor substituents, with an emphasis on structurally characterized compounds. Depending on the N donor substituents and the cations, O,O′ or N coordination will dominate. The nitrile-substituted compounds essentially behave as acetylacetones; they may easily O,O′ coordinate to a wide range of cations whereas N coordination is limited to AgI, CuI or, in the case of less soft cations, to longer and presumably weaker contacts, e.g. to the more distant sites in Jahn–Teller distorted CuII. In contrast, pyridyl-substituted pentanediones act as N donor ligands, regardless whether their (H)acac site is chelating a cation or not. The still scarcely explored pyrazolyl derivative shows the most complex coordination pattern: it may be deprotonated both at the acetylacetone and the pyrazol site, the latter affording N,N′ bridging ligands. In addition to N donor nucleophilicity, the distance between the alternative coordination sites and their mutual orientation are relevant for crystal engineering applications.

Controlled stepwise synthesis of a Cu-MOF: Transmetallation of a magnesium precursor to a three-dimensional framework with very high solvent content

A copper metal-organic framework (MOF) was synthesized by transmetalation. The ditopic ligand 3-(3,5-dimethyl-pyrazol-4-yl)pentane-2,4-dione is introduced via its Mg precursor complex in which it is oxygen-coordinated. After transmetallation, the ligand acts as N,O,O′ linker between dinuclear, sulfato-bridged Cu(II) nodes. The resulting three-dimensional solid crystallizes in the chiral space group I213, with more than half of its cell volume occupied by disordered methanol and dichloromethane molecules: the coordination framework encloses a large solvent-filled region along [1 1 1] which coounts for 54.8% of the crystal volume. The structure collapses upon removal of the clathrated solvent. Sulfate-O atoms are exposed towards the solvent region and facilitate trapping of polar guest molecules. The framework topology corresponds to a lcv net with Vertex symbol 3·3·102·102·103·103.

3-(Pyridin-4-yl)acetylacetone: a donor ligand towards mercury(II) halides and a versatile linker for complex materials

The ditopic organic molecule 3-(pyridin-4-yl)acetylacetone (HacacPy) acts as a pyridine-type ligand towards HgX 2 (X = Cl, Br, I). The nature of the anion and the ligand-to-cation ratio dominate the outcome of the reaction. Two different coordination compounds form with HgCl2, namely a ligand-rich mononuclear complex, HgCl2(HacacPy)2, and a ligand-deficient one-dimensional chain polymer, [Hg(μ-Cl)2(HacacPy)]1 ∞, with five-coordinated HgII cations. Two compounds are also observed for HgBr2, a molecular complex isomorphous to the chloride derivative and a chain polymer with the composition [Hg(μ-Br)Br(HacacPy)]1 ∞, in which the cations are four-coordinated. The ligand-rich mononuclear and ligand-deficient polymeric chloride and bromide complexes may be interconverted via thermal degradation and mechanochemical synthesis. In contrast to the chloride and bromide compounds, the reaction product with HgI2 does not depend on the ligand-to-cation ratio but corresponds to [Hg(μ-I)I(HacacPy)]1 ∞, isomorphous to the bromide derivative. The N-coordinated HacacPy complexes could not be deprotonated and further crosslinked with a second cation. Synthesis of mixed-metal products could be achieved, however, by deprotonation of the acetylacetone moiety in HacacPy and formation of tris-chelated Fe(acacPy)3 and Al(acacPy)3 complexes in the first step. These mononuclear building blocks act as bridging poly(pyridine) ligands towards HgII halides and form two structure types. The first represents a one-dimensional ladder, with the tris(ligand) complexes acting as triconnected nodes and the HgII halides acting as linkers. In the alternative unprecedented product, both the tris(ligand) complexes and the [HgX 2(μ-X)HgX] groups act as equivalent triconnected nodes. They form a uninodal two-dimensional coordination network with vertex symbol 4.82 and fes topology.

3-(Pyridin-4-yl)acetylacetone: CdII and HgII compete for nitrogen coordination

3-(Pyridin-4-yl)acetylacetone (HacacPy) acts as a pyridine-type ligand towards Cd^II and Hg^II halides. With CdBr₂, the one-dimensional polymer [Cd(μ-Br)₂(HacacPy)Cd(μ-Br)₂(HacacPy)₂]_∞ is obtained in which five- and six-coordinated Cd^II cations alternate in the chain direction. Reaction of HacacPy with HgBr₂ results in [Hg(μ-Br)Br(HacacPy)]_∞, a polymer in which each Hg^II centre is tetracoordinated. In both compounds, each metal(II) cation is N-coordinated by at least one HacacPy ligand. Equimolar reaction between these Cd^II and Hg^II derivatives, either conducted in ethanol as solvent or via grinding in the solid state, leads to ligand redistribution and the formation of the well-ordered bimetallic polymer catena-poly[[bromidomercury(II)]-μ-bromido-[aquabis[4-hydroxy-3-(pyridin-4-yl)pent-3-en-2-one]cadmium(II)]-di-μ-bromido], [CdHgBr₄(C₁₀H₁₁NO₂)₂(H₂O)]_n or [{HgBr}(μ-Br){(HacacPy)₂Cd(H₂O)}(μ-Br)₂]_∞. Hg^II and Cd^II cations alternate in the [100] direction. The HacacPy ligands do not bind to the Hg^II cations, which are tetracoordinated by three bridging and one terminal bromide ligand. The Cd^II centres adopt an only slightly distorted octahedral coordination. Three bromide ligands link them in a (2 + 1) pattern to neighbouring Hg^II atoms; two HacacPy ligands in a cis configuration, acting as N-atom donors, and a terminal aqua ligand complete the coordination sphere. Classical O-H...Br hydrogen bonds stabilize the polymeric chain. O-H...O hydrogen bonds between aqua H atoms and the uncoordinated carbonyl group of an HacacPy ligand in a neighbouring strand in the c direction link the chains into layers in the (010) plane.

A whole zoo of hydrogen bonds in one crystal structure: tris(isonicotinium) hydrogensulfate sulfate monohydrate

Depending on the reaction partner, the organic ditopic molecule isonicotinic acid (Hina) can act either as a Brønsted acid or base. With sulfuric acid, the pyridine ring is protonated to become a pyridinium cation. Crystallization from ethanol affords the title compound tris(4-carboxypyridinium) hydrogensulfate sulfate monohydrate, 3C₆H₆NO₂⁺·HSO₄^-·SO₄^2-·H₂O or [(H₂ina)₃(HSO₄)(SO₄)(H₂O)]. This solid contains 11 classical hydrogen bonds of very different flavour and nonclassical C-H...O contacts. All N-H and O-H donors find at least one acceptor within a suitable distance range, with one of the three pyridinium H atoms engaged in bifurcated N-H...O hydrogen bonds. The shortest hydrogen-bonding O...O distance is subtended by hydrogensulfate and sulfate anions, viz. 2.4752 (19) Å, and represents one of the shortest hydrogen bonds ever reported between these residues.

Neutral mixed-metal coordination polymers based on a ditopic acetylacetonate, Mg(ii) and Ag(i): syntheses, characterization and solvent-dependent topologies

In binary Mg/Ag framework compounds, the co-crystallized solvents decide topology.

Crosslinking of the Pd(acacCN)2 building unit with Ag(i) salts: dynamic 1D polymers and an extended 3D network

Pd(acacCN)₂ and Ag(i) salts aggregate to a 3D network or 1D chains. The latter topology provides an example for a tunable phase transition.