Tetraaqua(4,4'-dimethyl-2,2'-bipyridine-κ2N,N')nickel(II) sulfate monohydrate: a simple molecule with an extremely complex hydrogen-bonding scheme.

The title ionic compound, [Ni(C12H12N2)(H2O)4]SO4·H2O, is composed of an Ni(II) cation coordinated by a chelating 4,4'-dimethyl-2,2'-bipyridine ligand via its two N atoms [mean Ni-N = 2.056 (2) Å] and by four aqua ligands [mean Ni-O = 2.073 (9) Å], the net charge being balanced by an external sulfate anion. The whole structure is stabilized by a solvent water molecule. Even though the individual constituents are rather featureless, they generate an extremely complex supramolecular structure consisting of a central hydrogen-bonded two-dimensional hydrophilic nucleus made up of complex cations, sulfate anions and coordinated and solvent water molecules, with pendant hydrophobic 4,4'-dimethyl-2,2'-bipyridine ligands which interact laterally with their neighbours via π-π interactions. The structure is compared with closely related analogues in the literature.

Two isomorphous transition metal complexes displaying a coordinated tetrathionate unit: bis(4,4'-dimethyl-2,2'-bipyridine-κ(2)N,N')(tetrathionato-κ(2)S,S')cadmium(II) dimethylformamide disolvate and the zinc(II) analogue.

The isomorphous title compounds, [Tr(S4O6)(C12H12N2)2]·2C3H7NO (Tr = Cd(II) and Zn(II)), consist of metal centres to which one tetrathionate and two 4,4'-dimethyl-2,2'-bipyridine chelating ligands bind. The structures are completed by two symmetry-related dimethylformamide solvent molecules. Each metal-centred complex is bisected by a twofold axis running through the metal centre and halving the chelating tetrathionate dianion through the central S-S bond. The ancillary symmetry-related 4,4'-dimethyl-2,2'-bipyridine ligands act as chelates. This results in a distorted six-coordinate geometry, with similar Tr-O/N distances but central angles differing substantially from 90 and 180°. Both ligands are basically featureless from a geometric point of view, with torsion angles in both coordinated tetrathionate groups suggesting a trend linking metal size (covalent radius) and ligand `openness'. Packing is directed by (C-H)aromatic···O bridges and π-π offset stacked interactions defining chains along [001], further linked by weaker (C-H)methyl···O bridges, some of them mediated by the dimethylformamide solvent molecules.

A new polymorph of bis[2,6-bis(1H-benzimidazol-2-yl-κN3)pyridinido-κN]zinc(II).

The title compound, [Zn(C(19)H(12)N(5))(2)], crystallizes in the tetragonal space group P4(3)2(1)2, with the monomer residing on a twofold axis. The imidazole N-bound H atoms are disordered over the two positions, with refined occupancies of 0.59 (3) and 0.41 (3). The strong similarities to, and slight differences from, a reported P4(2)2(1)2 polymorph which has a 50% smaller unit-cell volume [Harvey, Baggio, Muñoz & Baggio (2003). Acta Cryst. C59, m283-m285], to which the present structure bears a group-subgroup relationship, are discussed.

Tris(1,10-phenanthroline-κ(2) N,N')nickel(II) hexa-oxido-µ-peroxido-disulfate-(VI) N,N-dimethyl-formamide disolvate monohydrate.

The asymmetric unit of the title complex, [Ni(C12H8N2)3]S2O8·2C3H7NO·H2O, consists of a complex [Ni(phen)3](2+) cation and one isolated pds anion, with two DMF mol-ecules and one water mol-ecule as solvates (where phen is 1,10-phenanthroline, pds is the hexa-oxido-µ-peroxoido-di-sulf-ate dianion and DMF is dimethyl-formamide). The [Ni(phen)3](2+) cation is regular, with an almost ideal Ni(II) bond-valence sum of 2.07 v.u. The group, as well as the water solvent mol-ecule, are well behaved in terms of crystallographic order, but the remaining three mol-ecules in the structure display different kinds of disorder, viz. the two DMF mol-ecules mimic a twofold splitting and the pds anion has both S atoms clamped at well-determined positions but with a not-too-well-defined central part. These peculiar behaviours are a consequence of the hydrogen-bonding inter-actions: the outermost SO3 parts of the pds anion are heavily connected to the complex cations via C-H⋯O hydrogen bonding, generating an [Ni(phen)3]pds network and providing for the stability of the terminal pds sites. Also, the water solvent mol-ecule is strongly bound to the structure (being a donor of two strong bonds and an acceptor of one) and is accordingly perfectly ordered. The peroxide O atoms in the pds middle region, instead, appear as much less restrained into their sites, which may explain their tendency to disorder. The cation-anion network leaves large embedded holes, amounting to about 28% of the total crystal volume, which are occupied by the DMF mol-ecules. The latter are weakly inter-acting with the rest of the structure, which renders them much more labile and, accordingly, prone to disorder.

An unusual two-dimensional hydrogen-bonding network in bis(2,9-dimethyl-1,10-phenanthrolin-1-ium) peroxodisulfate dihydrate.

The title compound, 2C(14)H(13)N(2)(+).S(2)O(8)(2-).2H(2)O, is a protonated amine salt which is formed from two rather uncommon ionic species, namely a peroxodisulfate (pds(2-)) anion, which lies across a crystallographic inversion centre, and a 2,9-dimethyl-1,10-phenanthrolin-1-ium (Hdmph(+)) cation lying in a general position. Each pds(2-) anion binds to two water molecules through strong water-peroxo O-H...O interactions, giving rise to an unprecedented planar network of hydrogen-bonded macrocycles which run parallel to (100). The atoms of the large R(8)(8)(30) rings are provided by four water molecules bridging in fully extended form (...H-O-H...) and four pds(2-) anions alternately acting as long (...O-S-O-O-S-O...) and short (...O-S-O...) bridges. The Hdmph(+) cations, in turn, bind to these units through hydrogen bonds involving their protonated N atoms. In addition, the crystal structure also contains pi-pi and aromatic-peroxo C-H...O interactions.

Di-µ-acetato-κO,O':O;κO:O,O'-bis-[(acetato-κO,O')(1,10-phenan-throline-κN,N')cadmium(II)].

The title compound, [Cd(2)(C(2)H(3)O(2))(4)(C(12)H(8)N(2))(2)], consists of dimeric units built up around a crystallographic symmetry centre. Each cadmium(II) unit is chelated by a 1,10-phenanthroline (phen) group and two acetate ligands, one of which also acts as a bridge, linking both seven-coordinated cadmium(II) centres. The crystal structure is governed by a single π-π inter-action between stacked phen groups [centroid-centroid distance 3.5209 (11) Å], leading to a planar structure parallel to (010).

Topological study of diverse hydrogen-bonded patterns found in a system of a nickel(II) complex and the sulfate anion.

A nickel(II) coordination complex, bis[2,6-bis(1H-benzimidazol-2-yl-κN3)pyridine-κN]nickel(II) sulfate, [Ni(C19H13N5)2]SO4 or [Ni(H2L)2]SO4, having four peripheral tetrahedrally oriented N-H donor units, combines with sulfate bridges to create hydrogen-bonded structures of varied dimensionality. The three crystal structures reported herein in the space groups P212121, I-4 and Pccn are defined solely by strong charge-assisted N-H...O hydrogen bonds and contain disordered guests (water and dimethylformamide) that vary in size, shape and degree of hydrophilicity. Two of the compounds are channelled solids with three-dimensional structures, while the third is one-dimensional in nature. In spite of their differences, all three present a striking resemblance to the previously reported anhydrous relative [Guo et al. (2011). Chin. J. Inorg. Chem. 27, 1517-1520], which is considered as the reference framework from which all three title compounds are derived. The hydrogen-bonded frameworks are described and compared using crystallographic and topological approaches.

Three phenanthroline-metal complexes with topologically similar but geometrically different conformations.

The structures of three related complexes of general formula M(pds)(nab)2 [pds is the peroxodi-sulfate anion and nab is an nitro-gen-containing aromatic base], viz. bis(2,9-dimethyl-1,10-phenanthroline-κ2N,N')(peroxodi-sulfato-κ2O,O')cadmium, [Cd(S2O8)(C14H12N2)2], (V), bis-(3,4,7,8-tetra-methy-1,10-phenanthroline-κ2N,N')(peroxodi-sulfato-κ2O,O')zinc, [Zn(S2O8)(C16H16N2)2], (VI), and bis-(3,4,7,8-tetra-methy-1,10-phenanthroline-κ2N,N')(peroxodi-sulfato-κ2O,O')cadmium, [Cd(S2O8)(C16H16N2)2], (VII), present the same topological coordination, with three chelating ligands in an MN4O2 polyhedron. The main difference resides in the fact that the first two complexes are bis-ected by a crystallographic twofold axis, thus providing a symmetrical environment to the cation, while in the third one this symmetry is disrupted into a clearly unsymmetrical disposition, probably by way of an unusually strong intra-molecular C-H⋯O hydrogen bond. The situation is compared with similar inter-actions in the literature. The structure of (V) is based on a redetermination in the correct space group C2/c of the structure originally described in the Cc space group [Harvey et al. (2001). Aust. J. Chem.54, 307-311; Marsh (2004 ▸). Acta Cryst. B60, 252-253].

The topotactic dehydration of monoclinic {[Co(pht)(bpy)(H2O)2]·2H2O}n into orthorhombic [Co(pht)(bpy)(H2O)2]n (pht is phthalate and bpy is 4,4'-bipyridine).

Controlled heating of single crystals of the previously reported [Köferstein & Robl (2007). Z. Anorg. Allg. Chem. 633, 1127-1130] dihydrate {[Co(pht)(bpy)(H2O)2]·2H2O}n, (II) [where pht is phthalate (C8H4O4) and bpy is 4,4'-bipyridine (C10H8N2)], produced a topotactic transformation into an unreported diaqua anhydrate, namely poly[diaqua(µ2-benzene-1,2-dicarboxylato-κ(2)O(1):O(2))(µ2-4,4'-bipyridine-κ(2)N:N')cobalt(II)], [Co(C8H4O4)(C10H8N2)(H2O)2]n, (IIa). The structural change consists of the loss of the two solvent water molecules linking the original two-dimensional covalent substructures which are the `main frame' of the monoclinic P2/n hydrate (strictly preserved during the transformation), with further reaccommodation of the latter. The anhydrate organizes itself in the orthorhombic system (space group Pmn2(1)) in a disordered fashion, where the space-group-symmetry restrictions are achieved only in a statistical sense, with mirror-related two-dimensional planar substructures, mirrored in a plane perpendicular to [100]. Thus, the asymmetric unit in the refined model is composed of two superimposed mirror-related `ghosts' of half-occupancy each. Similarities and differences with the parent dihydrate and some other related structures in the literature are discussed.

The structure of {[Co(pht)(bpy)(H2O)]·3H2O}n (pht is phthalate and bpy is 4,4'-bipyridine) and the role of solvent water clusters in structure stability.

The Co(II) cation in poly[[aqua(µ-benzene-1,2-dicarboxylato-κ(3)O(1),O(2):O(1))(µ-4,4'-bipyridine-κ(2)N:N')cobalt(II)] trihydrate], {[Co(C8H4O4)(C10H8N2)(H2O)]·3H2O}n, is octahedrally coordinated by two N atoms of two 4,4'-bipyridine ligands, three O atoms from phthalate anions and a fourth O atom from a coordinated water molecule. The packing consists of planes of coordination polymers linked by hydrogen bonds mediated by three solvent water molecules; the linkage is achieved by the water molecules forming intricate oligomeric clusters which also involve the O atoms of the phthalate ligands.

A new simplifying approach to molecular geometry description: the vectorial bond-valence model.

A method to describe, analyze and even predict the coordination geometries of metal complexes is proposed, based on previous well established concepts such as bond valence and valence-shell electron-pair repulsion (VSEPR). The idea behind the method is the generalization of the scalar bond-valence concept into a vector quantity, the bond-valence vector (BVV), with the innovation that the multidentate ligands are represented by their resultant BVVs. Complex n-ligand coordination spheres (frequently indescribable at the atomic level) reduce to much simpler ones when analyzed in BVV space, with the bonus of a better applicability of the VSEPR predictions. The geometrical implications of the BVV description are analyzed for the cases of n=2 and 3 (n=number of ligands), and the validity of its predictions, checked for a large number of metal complexes.

Two Cd and Hg peroxodisulfate complexes with aromatic amines.

The crystal structures of two complexes containing the peroxodisulfate anion are reported, namely mu-peroxodisulfato-1kappaO:2kappaO'-bis[(acetato-kappa2O,O')aqua(2,2':6',2''-terpyridine-kappa3N,N',N'')cadmium(II)] heptahydrate, [Cd2(C2H3O2)2(S2O8)(C15H11N2)2(H2O)2].7H2O, (I), and catena-poly[[[bis(2,2'-bipyridine-kappa2N,N')mercury(II)]-mu-peroxodisulfato-kappa2O:O'] 0.4-hydrate], {[Hg(C10H8N2)2(S2O8)].0.4H2O}n, (II). In both structures, the anion behaves as a bridge, linking neighbouring coordination polyhedra in two different ways, either tightly bound to the heptacoordinated Cd2+ cation forming neatly separated dimeric entities in (I) or across a shorter O-S-O path producing weakly connected chains by way of 'semicoordination' to the Hg2+ cations in (II).

Bis[2,6-bis(1H-benzimidazol-2-yl-kappaN(3))pyridinato-kappaN]zinc(II).

The structure of [Zn(C(19)H(12)N(5))(2)], which is monomeric and consists of neutral Zn(bbip-H)(2) entities [bbip-H is the anionic form of bis(benzimidazolyl)pyridine, formed by the loss of one H atom], has been solved from a racemic twin. The Zn atom lies at a site with imposed 222 symmetry and the bbip-H ligand has imposed twofold symmetry. The imidazolyl H atom is disordered over two symmetry-related positions, thus raising the molecular symmetry as required by the space group. The angle between the planes of the two coordinated bbip-H ligands is 84.6 (3) degrees, so defining a distorted octahedral environment around the metal atom.