Structural and Spectral Features of 4'-Substituted 2'-Hydroxychalcones in Solutions and Crystals: Spectroscopic and Theoretical Investigations.

The article describes investigations of 2'-hydroxychalcone and its three derivatives bearing differently sized alkyloxy groups at position 4'. The compounds are investigated from the point of view of crystal structure, electronic absorption, fluorescence features in solutions and crystals using X-ray diffraction and electronic spectroscopy methods, and quantum chemistry calculations. In general, both in solutions and in the crystal phase, the influence of substituents on absorption spectra of chalcones was found to be insignificant. Exclusively in the case of 4'-(4-methoxybenzyloxy)-2'-hydroxychalcone, molecular packing influences the absorption features, which is because of the intermolecular interactions of substituent's phenyl ring and chromophore fragment of the neighboring molecules. The lack of fluorescence of the excited enol form of chalcones in solutions and crystals is mainly due to intersystem crossing and excited-state intramolecular proton transfer. Fluorescent properties of the phototautomer keto species formed by the proton transfer depend on molecular conformation. In solutions, the excited keto form is twisted and effectively deactivates nonradiatively due to conical intersection. In the crystal phase, the fixed planar geometry disables the conical intersection and the fluorescence of the keto form becomes detectable.

2-(4-Hy-droxy-phen-yl)-3-meth-oxy-4H-chromen-4-one.

In the title compound, C16H12O4, the substituent benzene ring and meth-oxy group are twisted relative to the 4H-chromene skeleton by 24.1 (1) and 61.3 (1)°, respectively. In the crystal, mol-ecules are connected by classical O-H⋯O and weak C-H⋯O hydrogen bonds, forming chains parallel to [201]. The 4H-chromene ring systems of adjacent mol-ecules are either parallel or inclined at an angle of 28.9 (1)°.

2,6-Dimethyl-phenyl acridine-9-carboxyl-ate.

In the title compound, C(22)H(17)NO(2), the acridine ring system and the benzene ring are oriented at a dihedral angle of 37.7 (1)°. The carboxyl group is twisted at an angle of 67.7 (1)° relative to the acridine skeleton. In the crystal, mol-ecules are arranged in stacks along the b axis, with all of the acridine rings involved in multiple π-π inter-actions [centroid-centroid distances in the range 3.632 (2)-4.101 (2) Å]. The acridine moieties are parallel within the stacks, but inclined at an angle of 52.7 (1)° in adjacent stacks.

Phenyl acridine-9-carboxyl-ate.

The acridine ring system and the benzene ring in the title compound, C(20)H(13)NO(2), are oriented at a dihedral angle of 6.4 (2)°. The carboxyl group is twisted at an angle of 83.6 (2)° relative to the acridine skeleton. The mol-ecules in the crystal are arranged in stacks along the b axis, with two of the acridine rings involved in multiple π-π inter-actions [centroid-centroid distances in the range 3.536 (2)-3.894 (2) Å]. Stacks arranged parallel are linked via C-H⋯π inter-actions, forming layers in the ac plane that are in contact with adjacent, inversely oriented layers via other C-H⋯π inter-actions, giving rise to double layers. The inversely oriented double layers inter-act dispersively. The acridine units are parallel within the parallel-oriented stacks, but inclined at an angle of 79.6 (2)° in the inversely oriented stacks.

2-(4-Fluoro-phen-yl)-2H-chromen-4(3H)-one.

In the crystal structure of the title compound, C(15)H(11)FO(2), mol-ecules form inversion dimers through pairs of weak C-H⋯O hydrogen bonds. Dimers oriented in parallel, linked by C-H⋯π contacts, are arranged in columns along the b axis. The fluoro-phenyl ring and the benzene ring of the 2H-chromen-4(3H)-one unit are inclined to one another by 70.41 (16)°. They are respectively parallel in a given column or almost perpendicular [oriented at an angle of 87.8 (1)°] in neighbouring (inversely oriented) columns, forming a herringbone pattern.

3-Hy-droxy-1-methyl-2-[4-(piperidin-1-yl)phen-yl]quinolin-4(1H)-one.

There are two structurally similar but crystallographically independent mol-ecules (A and B) in the asymmetric unit of the title compound, C(21)H(22)N(2)O(2), which are linked via two O-H⋯O hydrogen bonds. An intramolecular O-H⋯O hydrogen bond also occurs in each molecule. In the crystal, the A and B mol-ecules are further linked through C-H⋯O inter-actions. The benzene ring is twisted at an angle of 69.9 (1) and 83.4 (1)° relative to the 1,4-dihydro-quinoline skeleton in mol-ecules A and B, respectively. Adjacent 1,4-dihydro-quinoline units of mol-ecules A are parallel, while mol-ecules A and B are oriented at an angle of 32.8 (1)°.

3-Hy-droxy-2-(4-hy-droxy-phen-yl)-4H-chromen-4-one.

In the title compound, C(15)H(10)O(4), the benzene ring is twisted at an angle of 20.7 (1)° relative to the 4H-chromene skeleton. In the crystal, adjacent mol-ecules are linked via a network of O-H⋯O and C-H⋯O hydrogen bonds. The mean planes of adjacent 4H-chromene moieties are parallel or oriented at an angle of 20.9 (1)° in the crystal structure.

2-(Furan-2-yl)-3-hy-droxy-4H-chromen-4-one.

In the crystal structure of the title compound, C(13)H(8)O(4), the inversely oriented mol-ecules form inversion dimers through pairs of O-H⋯O hydrogen-bonding inter-actions. An intramolecular O-H⋯O hydrogen bond occurs. In the packing of the mol-ecules, the nearly planar 2-(furan-2-yl)-4H-chromene units [dihedral angle between the chromene and furan rings = 3.8 (1)°] are either parallel or inclined at an angle of 80.7 (1)°.

3-Hy-droxy-2-(4-meth-oxy-phen-yl)-4H-chromen-4-one.

In the title compound, C(16)H(12)O(4), the benzene ring is twisted at an angle of 12.3 (1)° relative to the 4H-chromene skeleton, and an intramolecular O-H⋯O hydrogen bond occurs. The meth-oxy group is almost coplanar with the benzene ring [1.5 (1)°]. In the crystal, inversely oriented mol-ecules are arranged in double (A, A') columns, along the b axis, and are linked by a network of inter-molecular O-H⋯O hydrogen bonds (between A and A') and C-H⋯π contacts (within A or A'). The 4H-chromene cores are parallel within A or A', but make a dihedral angle of 88.6 (1)° between A and A'.

5-(4-Fluoro-phen-yl)-2-[2-(5-phenyl-1,3-oxazol-2-yl)phen-yl]-1,3-oxazole.

In the title compound, C(24)H(15)FN(2)O(2), the dihedral angles between the central benzene ring and the oxazole rings are 10.7 (6) and 64.1 (5)°. The dihedral angles between the oxazole rings and their pendant rings are 2.0 (3) and 24.3 (2)°. The F atoms are disordered over two sites with occupancies of 0.627 (3) and 0.373 (3) in the phenyl-ene-oxazol-yl-phenyl and in oxazol-yl-phenyl fragments, respectively. In the crystal structure, mol-ecules are linked through a network of C-H⋯F and weak π-π stacking inter-actions.

2-(4-Fluoro-phen-yl)-3-hy-droxy-4H-chromen-4-one.

In the crystal structure of the title compound, C(15)H(9)FO(3), inversely oriented mol-ecules form inversion dimers through pairs of O-H⋯O hydrogen bonds. The benzene ring is twisted at an angle of 12.0 (1)° relative to the 4H-chromene skeleton of the mol-ecule. Adjacent 4H-chromene units are parallel in a given column or oriented at an angle of 50.0 (1)° in neighboring, inversely oriented, columns, forming a herringbone pattern.

2,2-Difluoro-4-phenyl-1,3,2-dioxaborolo[4,5-c]chromen-5-ium-2-ide.

In the crystal, the inversely oriented mol-ecules of the title compound, C(15)H(9)BF(2)O(3), form stacks along the a axis via π-π inter-actions between parallel phenyl-chromenium fragments. Linked by a network of C-H⋯F inter-actions, the stacks form layers in the ac plane that are dispersively stabilized in the crystal structure. Two F atoms bonded to the B atom are located in the plane perpendicular to the planar skeleton of the mol-ecule made rigid by two intra-molecular C-H⋯O inter-actions.

{2-[1-(2-Amino-2-methyl-propyl-imino)eth-yl]phenolato-κN,N',O}dioxidovanadium(V).

In the crystal structure of the title compound, [V(C(12)H(17)N(2)O)O(2)], the vanadium(V) centre is five-coordinate in a distorted square-pyramidal environment. The three atoms of the deprotonated Schiff base and a double-bonded O atom comprise the basal plane. N-H⋯O hydrogen bonds lead to a zigzag chain structure parallel to [001].

A monoclinic polymorph of di-µ-oxido-bis-({2-[2-(methyl-amino)ethyl-imino-methyl]phenolato-κN,N',O}oxidovanadium(V)).

A new monoclinic polymorph of the title compound, [V(2)(C(10)H(13)N(2)O)(2)O(4)], which is a centrosymmetric dimer, crystallizes in space group P2(1)/c, whereas the previously known polymorph crystallizes in the ortho-rhom-bic space group Pbca [Mokry & Carrano (1993 ▶). Inorg. Chem.32, 6119-6121]. Each V(V) atom is six-coordinated by one oxide group, two N atoms and one O atom from the Schiff base ligand, and by two additional bridging O atoms. The two methyl-ene groups are each disordered over two sites, with occupancy factors of 0.776 (14) and 0.224 (14). In the crystal structure, there are C-H⋯O hydrogen bonds and C-H⋯π inter-actions between the dimers.

Di-µ-oxido-bis-({2-[(R,R)-(-)-(2-amino-cyclo-hexyl)imino-meth-yl]-4-nitro-phenolato-κN,N',O}oxidovanadium(V)) dimethyl sulfoxide disolvate.

The title compound, [V(2)(C(13)H(16)N(3)O(3))(2)O(4)]·2C(2)H(6)OS, is a centrosymmetric dimeric complex solvated by two dimethyl sulfoxide mol-ecules. Each V(V) atom is six-coordinated by one oxide group, two N atoms and one O atom from the tridentate Schiff base ligand, and by two additional bridging O atoms in a distorted octa-hedral coordination geometry. Three atoms of the cyclo-hexane ring are each disordered over two sites, with occupancy factors of 0.501 (10) and 0.499 (10). C-H⋯O and N-H⋯O hydrogen bonds link the dimers and solvent mol-ecules into a supra-molecular network.

4-Meth-oxy-N-phenyl-aniline.

In the mol-ecule of the title compound, C(13)H(13)NO, the two benzene rings are oriented at a dihedral angle of 59.9 (2)°. In the crystal structure, the benzene rings of neighbouring mol-ecules are oriented nearly parallel or perpendicular, making dihedral angles of 2.8 (2) and 79.5 (2)°, respectively. The crystal structure is stabilized by a network of C-H⋯π and N-H⋯π inter-actions.

9-Ethyl-10-methyl-acridinium trifluoro-methane-sulfonate.

In the mol-ecule of the title compound, C(16)H(16)N(+)·CF(3)SO(3) (-), the central ring adopts a flattened-boat conformation, and the two aromatic rings are oriented at a dihedral angle of 3.94 (2)°. In the crystal structure, weak inter-molecular hydrogen bonds link the mol-ecules. There are π-π contacts between the aromatic rings and the central ring and one of the aromatic rings [centroid-centroid distances = 3.874 (2), 3.945 (2) and 3.814 (2) Å]. There is also an S-O⋯π contact between the central ring and one of the O atoms of the anion.