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In the crystal structure of the title salt, C24H38N4 (2+)·2C24H20B(-), the C-N bond lengths in the central CN3 unit of the guanidinium ion are 1.3364 (13), 1.3407 (13) and 1.3539 (13) Å, indicating partial double-bond character. The central C atom is bonded to the three N atoms in a nearly ideal trigonal-planar geometry and the positive charge is delocalized in the CN3 plane. The bonds between the N atoms and the terminal methyl groups of the guanidinium moiety and the four C-N bonds to the central N atom of the (benzyl-dimethyl-aza-nium-yl)propyl group have single-bond character. In the crystal, C-H⋯π inter-actions between the guanidin-ium H atoms and the phenyl C atoms of the tetra-phenyl-borate ions are present, leading to the formation of a two-dimensional supra-molecular pattern parallel to the ac plane.

The asymmetric unit of the title hydrated salt, C15H37N6 (3+)·2Br(-)·OH(-)·H2O, contains one cation, three partial-occupancy bromide ions, one hydroxide ion and one water mol-ecule. Refinement of the site-occupancy factors of the three disordered bromide ions converges with occupancies 0.701 (2), 0.831 (2) and 0.456 (2) summing to approximately two bromide ions per formula unit. The structure was refined as a two-component inversion twin with volume fractions 0.109 (8):0.891 (8) for the two domains. The central C3N unit of the bis-amidinium ion is linked to the aliphatic propyl chain by a C-N single bond. The other two bonds in this unit have double-bond character as have the four C-N bonds to the outer NMe2 groups. In contrast, the three C-N bonds to the central N atom of the (di-methyl-aza-nium-yl)propyl group have single-bond character. Delocalization of the two positive charges occurs in the N/C/N and C/N/C planes, while the third positive charge is localized on the di-methyl-ammonium group. The crystal structure is stabilized by O-H⋯O, N-H⋯Br, O-H⋯Br and C-H⋯Br hydrogen bonds, forming a three-dimensional network.

The title hydrated salt, C7H18N3 (+)·OCN(-).1.5H2O, was synthesized starting from N,N,N',N',N'',N''-hexa-methyl-guanidinium chloride by a twofold anion-exchange reaction. The asymmetric unit contains two cations, two cyanate anions and three water mol-ecules. One cation shows orientational disorder and two sets of N-atom positions were found related by a 60° rotation, with an occupancy ratio of 0.852 (6):0.148 (6). The C-N bond lengths in both guanidin-ium ions range from 1.329 (2) to 1.358 (10) Å, indicating double-bond character, pointing towards charge delocalization within the NCN planes. Strong O-H⋯N hydrogen bonds between the crystal water mol-ecules and the cyanate ions and strong O-H⋯O hydrogen bonds between the water mol-ecules are present, resulting in a two-dimensional hydrogen bonded network running parallel to the (001) plane. The hexa-methyl-guanidinium ions are packed in between the layers built up by water mol-ecules and cyanate ions.

The reaction of the ortho-amide 1,1,1-tris-(di-methyl-amino)-4-methyl-4-(tri-methyl-sil-yloxy)pent-2-yne with bromine in benzene, yields the title salt, C15H33BrN3OSi(+)·Br(-). The C-N bond lengths in the amidinium unit are 1.319 (6) and 1.333 (6) Å, indicating double-bond character, pointing towards charge delocalization within the NCN plane. The C-Br bond length of 1.926 (5) Å is characteristic for a C-Br single bond. Additionally, there is a bromine-bromine inter-action [3.229 (3) Å] present involving the anion and cation. In the crystal, weak C-H⋯Br inter-actions between the methyl H atoms of the cation and the bromide ions are present.

In the title salt, C15H36N6 (2+)·2C24H20B(-), the three N-C bond lengths in the central C3N unit of the bis-amidinium ion range between 1.388 (3) and 1.506 (3) Å, indicating single- and double-bond character. Furthermore, four C-N bonds have double-bond character. Here, the bond lengths range from 1.319 (3) to 1.333 (3) Å. Delocalization of the positive charges occurs in the N/C/N and C/N/C planes. The dihedral angle between both N/C/N planes is 70.5 (2)°. In the crystal, C-H⋯π inter-actions between H atoms of the cation and the benzene rings of both tetra-phenyl-borate ions are present. The benzene rings form aromatic pockets, in which the bis-amidinium ion is embedded. This leads to the formation of a two-dimensional supra-molecular pattern along the ab plane.

In the title salt, C16H34N5O3 (+)·C24H20B(-), the C-N bond lengths in the cation are 1.3368 (16), 1.3375 (18) and 1.3594 (17) Å, indicating partial double-bond character. The central C atom is bonded to the three N atoms in a nearly ideal trigonal-planar geometry and the positive charge is delocal-ized in the CN3 plane. In the crystal, weak C-H⋯O contacts are observed between neighbouring guanidinium ions and between guanidinium ions and tetra-phenyl-borate anions. In addition, C-H⋯π inter-actions involving guanidinium H atoms and aromatic rings of the anion are present. The phenyl rings form aromatic pockets, in which the cations are embedded. This leads to the formation of a two-dimensional supramolecular pattern along the ab plane.

In the cation of the title salt, C6H14NO(+)·C24H20B(-), the C-N bond lengths are 1.297 (2), 1.464 (2) and 1.468 (2) Å, indicating double- and single-bond character, respectively. The C-O bond length of 1.309 (2) Å shows double-bond character, pointing towards charge delocalization within the NCO plane of the iminium ion. In the crystal, C-H⋯π inter-actions between the iminium H atoms and the phenyl C atoms of the anion are present. The phenyl rings form aromatic pockets, in which the iminium ions are embedded.

The title compound, C8H12O6, was synthesized by de-acetyl-ation of 6-acetyl-1,2,3,4-di-O-methyl-ene-α-d-galactose with sodium methoxide. The central part of the mol-ecule consists of a six-membered C5O pyran-ose ring with a twist-boat conformation. Both fused dioxolane rings adopt an envelope conformation with C and O atoms as the flap. In the crystal, O-H⋯O and C-H⋯O hydrogen bonds are present between adjacent mol-ecules, generating a three-dimensional network.

In the title salt, C6H14NO(+)·C2H5SO4 (-), the C-N bond lengths in the cation are 1.2981 (14), 1.4658 (14) and 1.4707 (15) Å, indicating double- and single-bond character, respectively. The C-O bond length of 1.3157 (13) Å shows double-bond character, indicating charge delocalization within the NCO plane of the iminium ion. In the crystal, C-H⋯O hydrogen bonds between H atoms of the cations and O atoms of neighbouring ethyl sulfate anions are present, generating a three-dimensional network.

The asymmetric unit of the title salt, C10H20N3O2 (+)·C24H20B(-), contains two cations and two tetra-phenyl-borate ions. The C-N bond lengths in the central CN3 unit of the guanidinium ions range between 1.323 (2) and 1.381 (2) Å, indicating partial double-bond character. The central C atoms are bonded to the three N atoms in a nearly ideal trigonal-planar geometry and the positive charge is delocalized in the CN3 plane. The cationic six-membered rings are nonplanar, the dihedral angles between the N/C/N and C/C/C planes ranging from 45.8 (1) to 53.6 (1)°. In the crystal, C-H⋯π inter-actions are present between the guanidinium H atoms and the phenyl rings of the tetra-phenyl-borate ions. The phenyl rings form aromatic pockets, in which the guanidinium ions are embedded.

The title compound, C7H10O5, was synthesized by reaction of d-xylose with paraformaldehyde. In the crystal, the central part of the mol-ecule consists of a five-membered C4O ring with an envelope conformation, with the methine C atom adjacent to the O atom being the flap. The protected O atoms of both cyclic acetal groups are oriented so that the four chiral C atoms of the furan-ose part show an R configuration. C-H⋯O hydrogen bonds are present between adjacent mol-ecules, generating a three-dimensional network.

The C-N bond lengths in the guanidine unit of the title compound, C16H18N4O2, are 1.298 (2), 1.353 (2) and 1.401 (3) Å, indicating double- and single-bond character. The N-C-N angles are 115.81 (16), 118.90 (18) and 125.16 (18)°, showing a deviation of the CN3 plane from an ideal trigonal-planar geometry. In the crystal, C-H⋯O hydrogen bonds are observed between the methyl- and aromatic-H atoms and nitro-O atoms. One H atom of the phenyl ring and of the NMe2 group associate with the O atoms of the nitro group, giving chains along the a- and b-axis directions. Cross-linking of these two chains results in a two-dimensional network along bc.

In the title compound, C17H21N3O, the C-N bond lengths in the guanidine unit are 1.2889 (19), 1.3682 (19) and 1.408 (2) Å, indicating double- and single-bond character. The N-C-N angles are 115.10 (13), 119.29 (15) and 125.61 (14)°, showing a deviation of the CN3 plane from an ideal trigonal-planar geometry. In the crystal, non-classical C-H⋯O hydrogen bonds between methyl H atoms and meth-oxy O atoms are present, generating centrosymmetric dimers running in the [101] direction.

In the title solvated salt, C7H16NO(+)·C24H20B(-)·C2H3N, the C-N bond lengths in the cation are 1.2831 (19), 1.467 (2) and 1.465 (2) Å, indicating double- and single-bond character, respectively. The C-O bond length of 1.2950 (18) Å shows a double-bond character, pointing towards charge delocalization within the NCO plane of the iminium ion. The two C atoms of the n-butyl group are disordered over the two sites, with refined occupancy ratios of 0.890 (5):0.110 (5) and 0.888 (4):0.112 (4). In the crystal, C-H⋯π inter-actions occur between the methine H atom, H atoms of the -N(CH3)2 and -CH2 groups of the cation, and two of the phenyl rings of the tetra-phenyl-borate anion. The latter inter-action forms an aromatic pocket in which the cation is embedded. Thus, a two-dimensional pattern is created in the ac plane.

In the cation of the title salt, C4H8NO(+)·C24H20B(-), the C-N bond lengths are 1.272 (2), 1.4557 (19) and 1.4638 (19) Å, indicating double- and single-bond character, respectively. The C-O bond length of 1.3098 (19) Å shows that double-bond character and charge delocalization occurs within the NCO plane of the cation. In the crystal, a C-H⋯π inter-action is present between the methyl-ene H atom of the cation and one phenyl ring of the tetra-phenyl-borate ion. The latter forms an aromatic pocket in which the cation is embedded.

In the cation of the title salt, C4H10NO(+)·C24H20B(-)·C2H3N, the C-N bond lengths are 1.2864 (16), 1.4651 (17) and 1.4686 (16) Å, indicating double- and single-bond character, respectively. The C-O bond length of 1.2978 (15) Å shows double-bond character, pointing towards charge delocalization within the NCO plane of the iminium ion. C-H⋯π inter-actions are present between the methine H atom and two of the phenyl rings of the tetra-phenyl-borate ion. The latter forms an aromatic pocket in which the cation is embedded. The iminium ion is further connected through a C-H⋯N hydrogen bond to the aceto-nitrile mol-ecule. This leads to the formation of a two-dimensional supramolecular pattern along the bc plane.

In the title compound, C35H32N4, the C-N bond lengths in the guanidine part are 1.286 (3), 1.387 (2) and 1.414 (2) Å, indicating double- and single-bond character. The N-C-N angles are 114.48 (17), 118.78 (17) and 126.72 (17)°, showing a deviation of the CN3 plane from an ideal trigonal-planar geometry. The carbazole ring system is almost planar (r.m.s. deviation = 0.002 Å). In the crystal, mol-ecules are connected by weak C-H⋯N hydrogen bonds, generating a zigzag chain along the ac plane. Weak π-π inter-actions [centroid-centroid distance = 3.785 (1) Å] between two phenyl rings of the guanidine moiety are also present.

In the title molecular salt, C(14)H(22)N(3) (+)·Br(-), the ring incorporating the guanidinium grouping exhibits a half-chair conformation and the dihedral angle between the N-C-N and C-C-C planes is 55.0 (3)°. The C-N bond lengths in the central CN(3) unit are 1.333 (4), 1.338 (3) and 1.341 (4) Å, indicating partial double-bond character. The central C atom is bonded to the three N atoms in a nearly ideal trigonal-planar geometry and the positive charge is delocalized in the CN(3) plane. The distances between the N atom and the terminal methyl C atoms [1.453 (4)-1.461 (4) Å] are all close to a typical single C-N bond length.

Isolated guanidinium ions and tetra-phenyl-borate ions are present in the crystal structure of the title compound, C(11)H(22)N(3)O(2) (+)·C(24)H(20)B(-). In the guanidinium ion, the dihedral angle between the N/C/N and C/C/C planes being 49.9 (1)°. The six-membered ring exhibits a half-chair conformation. The C-N bond lengths in the cation range between 1.3335 (16) and 1.3552 (16) Å, indicating charge delocalization on the CN(3) plane. In the crystal, the cations are connected by C-H⋯O hydrogen bonds, generating a chain along the c axis.

In the crystal structure of the title molecular salt, C(13)H(30)N(5)O(+)·C(24)H(20)B(-), discrete guanidinium cations and tetra-phenyl-borate anions are present. The C-N bond lengths in the CN(3) unit are 1.3427 (12), 1.3445 (12) and 1.3453 (13) Å, indicating double-bond character. The central C atom is surrounded in a nearly ideal trigonal-planar geometry by three N atoms and the positive charge is delocalized on the CN(3) plane. The bonds between the N atoms and the terminal C-methyl groups all have values close to a typical single bond [1.4595 (15)-1.4688 (12) Å]. In the crystal, cations are connected by C-H⋯O contacts generating a chain along the c axis.

The title compound, C(12)H(28)N(6), is located about an inversion center situated at the center of the -CH(2)-CH(2)- bond. The C-N bond lengths are 1.285 (2), 1.384 (2) and 1.395 (1) Å, indicating double- and single-bond character. The N-C-N angles are 114.1 (1), 119.3 (1) and 126.5 (1)°, showing a deviation of both CN(3) planes from an ideal trigonal-planar geometry.

A method for the preparation of the first acetylenedicarboxamidinium salt from a bis-orthoamide derivative of acetylenedicarboxyclic acid has been established. The salt reacted with cyclopentadiene and furan at room temperature to give bicyclic [4+2]-cycloaddition products. The solid compounds were characterized by solution NMR spectroscopy and by single-crystal X-ray diffraction. Quantum-chemical calculations of the isolated N,N,N',N',N'',N'',N''',N'''-octamethyl-acetylene-bis(carboxamidinium) ion showed very good agreement with the spectroscopic and diffraction data., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The reaction of 3,3,3-tris-(dimethyl-amino)-1-phenyl-prop-1-yne with bromine in pentane yields the title compound, C(13)H(17)N(2) (+)·Br(-). The acetyl-enic bond distance [1.197 (2) Å] is consistent with a C C triple bond. The amidinium C=N bonds [1.325 (2) and 1.330 (2) Å] have double-bond character and the positive charge is delocalized between the two dimethyl-amino groups.

In the crystal structure of the title compound, C(11)H(26)N(3) (+)·Cl(-)·C(4)H(4)N(4), the (2Z)-2,3-diamino-but-2-ene-dinitrile (Z-DAMN) mol-ecules are connected with the chloride ions via N-H⋯Cl hydrogen bonds, forming ribbons running along the a axis. The guanidinium ions are located in between the ribbons formed by Z-DAMN mol-ecules and chloride ions.

In the crystal structure of the title compound, C(5)H(10)N(2)O, mol-ecules are connected via pairs of strong N-H⋯O hydrogen bonds into centrosymmetric dimers, which are stacked along the a axis. The molecule is not planar, the dihedral angle between the N/C/N and C/C/C planes being 42.1(1)°.

The title compound, C(10)H(24)N(4) (2+)·2C(24)H(20)B(-)·2C(3)H(6)O, crystallizes with two acetone solvent mol-ecules per asymmetric unit. In the dication, both amidinium units are twisted about the central C-C single bond by 63.8 (3)° and the positive charges are delocalized over both N-C-N planes.

1H, 2H, and 11B NMR spectroscopy has been used to study the mechanism of the Fries rearrangement of aryl formates promoted by boron trichloride by monitoring both the substrate and the Lewis acid. DFT calculations were employed to investigate the energetics of several reaction paths and to calculate NMR chemical shifts of key intermediates and products. After the formation of a 1:1 substrate-Lewis acid adduct, the rearrangement proceeds in two steps, beginning with the cleavage of the ester bond and the release of formyl chloride in situ, which, in turn, acts as a formylating agent, introducing an aldehydic functionality into the aromatic ring. The high regioselectivity (only the ortho product is obtained) is also accounted for by the proposed intermolecular, Lewis acid-assisted mechanism.

A 7.4% power conversion efficiency at air mass (AM) 1.5 full sunlight was reached with a mesoscopic solar cell employing a new binary ionic liquid electrolyte composed of 1-propyl-3-methylimidazolium iodide and 1-ethyl-3-methylimidazolium tricyanomethanide in conjunction with the amphiphilic ruthenium complex NaRu(4-carboxylic acid-4'-carboxylate)(4,4'-dinonyl-2,2'-bipyridine)(NCS)(2), coded as Z-907Na. Ultramicroelectrode voltammetric, nanosecond laser transient absorbance, and photovoltaic measurements show that a high iodide concentration is required for dye regeneration to compete efficiently with charge recombination. A surprisingly fast reductive quenching process is turned on in pure iodide melts. This channel is unproductive, explaining the lower photocurrents observed under these conditions.