Deciphering the H-Bonding Preference on Nucleoside Molecular Recognition through Model Copper(II) Compounds

The synthetic nucleoside acyclovir is considered an outstanding model of the natural nucleoside guanosine. With the purpose of deepening on the influence and nature of non-covalent interactions regarding molecular recognition patterns, three novel Cu(II) complexes, involving acyclovir (acv) and the ligand receptor N-(2-hydroxyethyl)ethylenediamine (hen), have been synthesized and thoroughly characterized. The three novel compounds introduce none, one or two acyclovir molecules, respectively. Molecular recognition has been evaluated using single crystal X-ray diffraction. Furthermore, theoretical calculations and other physical methods such as thermogravimetric analysis, infrared and UV-Vis spectroscopy, electron paramagnetic resonance and magnetic measurements have been used. Theoretical calculations are in line with experimental results, supporting the relevance of the [metal-N7(acv) + H-bond] molecular recognition pattern. It was also shown that (hen)O-H group is used as preferred H-donor when it is found within the basal coordination plane, since the higher polarity of the terminal (hen)O-H versus the N-H group favours its implication. Otherwise, when (hen)O-H occupies the distal coordination site, (hen)N-H groups can take over.

Crystal and molecular structures of dichloridopalladium(II) containing 2-methyl- or 2-phenyl-8-(diphenyphosphanyl)quinoline

The crystal structures of dichloridopalladium(II) complexes bearing 2-methyl- and 2-phenyl-8-(diphenylphosphanyl)quinoline, namely, dichlorido[8-(diphenylphosphanyl)-2-methylquinoline-κ2 N,P]palladium(II), [PdCl2(C22H18NP)] (1) and dichlorido[8-(diphenylphosphanyl)-2-phenylquinoline-κ2 N,P]palladium(II), [PdCl2(C27H20NP)] (2), were analyzed and compared to that of the 8-(diphenylphosphanyl)quinoline (PQH) analogue (3). In all three complexes, the phosphanylquinoline moiety acts as a bidentate P,N-donating chelate ligand. In the PQH complex (3), the PdII center has a typical planar coordination environment; however, both the methyl- and phenyl-substituted phosphanylquinoline (PQMe and PQPh, respectively) complexes (1) and (2) exhibit a considerable tetrahedral distortion around the PdII center, as parameterized by the τ4 values of 0.1555 (4) and 0.1438 (4) for (1) and (2), respectively. The steric interaction from the substituted group introduced at the 2-position of the quinoline ring enforces the cis-positioned Cl ligand to be displaced from the ideal coordination plane. Also, the ideally planar phosphanylquinoline five-membered chelate ring shows a large bending deformation by the displacement of the PdII center from the quinoline plane. In addition, in the phenyl-substituted complex (3), the coordinating quinolyl and the substituted phenyl rings are not co-planar to each other, having a dihedral angle of 33.08 (7)°. This twist conformation prohibits any intermolecular π–π stacking interaction between the quinoline planes, which is observed in the crystals of complexes (1) and (2).

Metal Complexes of π-Expanded Ligands (4): Synthesis and Characterizations of Copper(II) Complexes with a Schiff Base Ligand Derived from Pyrene

An innovative π-expanded ligand derived from salicylaldimine ligand representing pyrene ring as a substitute for benzene ring was synthesized in 5 steps from commercially available pyrene. This unique bidentate ligand (1) was coordinated to Cu(II) metal centre for affording complex 2, which was characterized by IR, elemental, X-ray diffraction analyses, and magnetic susceptibility. Its coordination geometry is a trans-square plane with an obvious stair-step structure which is formed by two pyrene moieties and the coordination plane (CuN2O2). In addition, the dihedral angle between the coordination plane and the pyrene ring is 34.9o and the plane of seven carbon atoms of the long alkyl chains were arranged nearly parallel to the pyrene rings. The electronic properties of this novel complex 2 were examined via cyclic voltammetry and absorption spectroscopy to show the narrower HOMO-LUMO gap than those of the complex 4. Moreover, the particular behavior of both complexes 2 and 4 was investigated through DFT studies.

Anagostic Interactions in Alkyl-Fluorenyl-Substituted N‐Heterocyclic Carbene Complexes of Palladium(II)

Two imidazolylidene (Im) complexes of the general formula trans-[PdX2(Im)(pyridine)] (X=Cl (2), Br (3)), in which the N-heterocyclic carbene ligand has one of its nitrogen atoms substituted by a bulky 9-propyl-9-fluorenyl group (PrF), have been prepared and fully characterised by spectroscopic methods and single-crystal X-ray structure analyses. In the solid state, the Im ring plane and the coordination plane of each complex are nearly orthogonal, thereby minimising the steric interactions between the N-substituents and the halide atoms. In both structures two methylenic C–H bonds sit near the dz2 axis point to the palladium atom, resulting in CH⋯Pd separations of 2.58/2.95Å in 2 and 2.74/2.74Å in 3. NMR measurements and DFT calculations indicate that these methylene groups are involved in anagostic CH⋯M interactions but not in significant H⋯X bonding.

trans-Dichloridotetrakis(pyridine-κN)rhodium(III) chloride methanol tetrasolvate

In the solvated title salt, [RhCl2(C5H5N)4]Cl·4CH3OH, the RhIIIatom lies on a special position of 2.22 site symmetry. Consequently, the cationic complex has molecularD2symmetry with atransdisposition for two equivalent Cl−and four equivalent pyridine ligands. The Rh—Cl and Rh—N bond lengths are 2.3452 (7) and 2.064 (2) Å, respectively. The planes of the coordinating pyridine ligands are tilted synchronously, with a dihedral angle of 40.76 (9)° between the least-squares pyridine plane and the coordination plane defined by the RhIIIand four pyridine N atoms. The chloride counter-anion is located on a crystallographic \overline{4}.. site, and is surrounded by four methanol molecules to which it is bound in a pseudo-tetrahedral arrangement by O—H...Cl hydrogen bonds.

(2-{[2-(Dimethylamino)ethyl]iminomethyl}benzenethiolato-κ3 N,N′,S)(4-methoxybenzenethiolato-κS)nickel(II)

In the title compound, [Ni(C11H15N2S)(C7H7OS)] or [Ni(NNImS)(4-OCH3PhS)] (NNImS = 2-{[2-(dimethylamino)ethyl]iminomethyl}benzenethiolato), the NiII cation is coordinated by a tridentate NNImS ligand and a monodentate thiolate ligand giving an N2S2 coordination set defining an almost square-planar environment. The Ni—Namine bond in the coordination plane is approximately 0.1 Å longer than the Ni—Nimine bond.

Crystal structure of a twisted-ribbon type double-stranded AgIcoordination polymer:catena-poly[[silver(I)-μ3-bis(pyridin-3-ylmethyl)sulfane-κ3N:N′:S] nitrate]

The asymmetric unit in the title compound, {[Ag(C12H12N2S)]·NO3}nor {[AgL]·NO3}n,L= bis(pyridin-3-ylmethyl)sulfane, consists of an AgIcation bound to a pyridine N atom of anLligand and an NO3−anion that is disordered over two orientations in an 0.570 (17):0.430 (17) occupancy ratio. Each AgIcation is coordinated by two pyridine N atoms from adjacentLligands to form an infinite zigzag chain along [110]. In addition, each AgIion binds to an S donor from a thirdLligand in an adjacent parallel chain, resulting in the formation of a twisted-ribbon type of double-stranded chain propagating along the [110] or [1-10] directions. The AgIatom is displaced out of the trigonal N2S coordination plane by 0.371 (3) Å because of interactions between the AgIcation and O atoms of the disordered nitrate anions. Intermolecular π–π stacking interactions [centroid-to-centroid distance = 3.824 (3) Å] occur between one pair of corresponding pyridine rings in the double-stranded chain. In the crystal, the double-stranded chains are alternately stacked along thecaxis with alternate stacks linked by intermolecular π–π stacking interactions [centroid-to-centroid distance = 3.849 (3) Å], generating a three-dimensional supramolecular architecture. Weak intermolecular C—H...O hydrogen bonds between the polymer chains and the O atoms of the nitrate anions also occur.

Crystal structure of unsymmetrical α-diimine palladium(II) complex cis-[{ArN=C(Me)–(Et)C=NAr}PdCl2] [Ar = 2,6-(iPr)2C6H3]

The unsymmetrical α-diimine ligand N-{2-[2,6-bis(propan-2-yl)phenylimino]pentan-3-ylidene}-2,6-bis(propan-2-yl)aniline, [ArN=C(Me)—(Et)C=NAr] [Ar = 2,6-(iPr)2C6H3], (I), and the corresponding palladium complex, cis-(N-{2-[2,6-bis(propan-2-yl)phenylimino]pentan-3-ylidene}-2,6-bis(propan-2-yl)aniline)dichloridopalladium(II) 1,2-dichloroethane monosolvate, [PdCl2(C29H42N2)]·C2H4Cl2 or cis[PdCl2{I}], (II), have been synthesized and characterized. The crystal and molecular structure of the palladium(II) complex have been established by single-crystal X-ray diffraction. The compound crystallized along with a 1,2-dichloroethane solvent of crystallization. The coordination plane of the PdII atom shows a slight tetrahedral distortion from square-planar, as indicated by the dihedral angle between the PdCl2 and PdN2 planes of 4.19 (8)°. The chelate ring is folded along the N...N vector by 7.1 (1)°.

Crystal structure of bis(2-{1-[(E)-(4-fluorobenzyl)imino]ethyl}phenolato-κ2N,O)palladium(II)

The asymmetric unit of the title complex, [Pd(C15H13FNO)2], contains one half of the molecule with the PdIIcation lying on an inversion centre and is coordinated by the bidentate Schiff base anion. The geometry around the cationic PdIIcentre is distorted square planar, chelated by the imine N- and phenolate O-donor atoms of the two Schiff base ligands. The N- and O-donor atoms of the two ligands are mutuallytrans, with Pd—N and Pd—O bond lengths of 2.028 (2) and 1.9770 (18) Å, respectively. The fluorophenyl ring is tilted away from the coordination plane and makes a dihedral angle of 66.2 (2)° with the phenolate ring. In the crystal, molecules are linked into chains along the [101] direction by weak C—H...O hydrogen bonds. Weak π–π interactions with centroid–centroid distances of 4.079 (2) Å stack the molecules alongc.

Crystal structure of dichlorido{4-[(E)-(methoxyimino-κN)methyl]-1,3-thiazol-2-amine-κN3}palladium(II)

In the title compound, [PdCl2(C5H7N3OS)], the PdIIatom adopts a distorted square-planar coordination sphere defined by two N atoms of the bidentate ligand and two Cl atoms. The mean deviation from the coordination plane is 0.029 Å. The methyl group is not coplanar with the plane of the metallacycle [torsion angle C—O—N—C = 20.2 (4)°]. Steric repulsion between the methyl group and atoms of the metallacycle is manifested by shortened intramolecular H...C contacts of 2.27, 2.38 and 2.64 Å, as compared with the sum of the van der Waals radii of 2.87 Å. The amino group participatesviaone H atom in the formation of an intramolecular N—H...Cl hydrogen bond. In the crystal, the other H atom of the amino group links moleculesviabifurcated N—H...(Cl,O) hydrogen bonds into chains parallel to [001].