ACr(C2O4)2(H2O)4 (A = Li or Na): two new coordination polymers of low dimensionality with different hydrogen-bond networks.

Single crystals of two new bimetallic oxalate compounds with the formula [ACr(C2O4)2(H2O)4]n (A = Li or Na), namely catena-poly[[diaqualithium(I)]-µ-oxalato-κ4O1,O2:O1',O2'-[diaquachromium(III)]-µ-oxalato-κ4O1,O2:O1',O2'], (I), and catena-poly[[diaquasodium(I)]-µ-oxalato-κ4O1,O2:O1',O2'-[di-aquachromium(III)]-µ-oxalato-κ4O1,O2:O1',O2'], (II), have been synthesized, characterized and their crystal structures elucidated by X-ray diffraction analysis and compared. The compounds crystallize in the monoclinic space group C2/m for (I) and in the triclinic space group P-1 for (II); however, they have somewhat similar features. In the asymmetric unit of (I), the Li and Cr atoms both have space-group-imposed 2/m site symmetry, while only half of the oxalate ligand is present and two independent water molecules lie on the mirror plane. The water O atoms around the Li atom are disordered over two equivalent positions separated by 0.54 (4) Å. In the asymmetric unit of (II), the atoms of one C2O42- ligand and two independent water molecules are in general positions, and the Na and Cr atoms lie on an inversion centre. Taking into account the symmetry sites of both metallic elements, the unit cells may be described as pseudo-face-centred monoclinic for (I) and as pseudo-centred triclinic for (II). Both crystal structures are comprised of one-dimensional chains of alternating trans-Cr(CO)4(H2O)2 and trans-A(CO)4(H2O)2 units µ2-bridged by bis-chelating oxalate ligands. The resulting linear chains are parallel to the [101] direction for (I) and to the [11-1] direction for (II). Within the two coordination polymers, strong hydrogen bonds result in tetrameric R44(12) synthons which link the metal chains, thus leading to two-dimensaional supramolecular architectures. The two structures differ from each other with respect to the symmetry relations inside the ligand, the role of electrostatic forces in the crystal structure and the molecular interactions of the hydrogen-bonded networks. Moreover, they exhibit the same UV-Vis pattern typical of a CrIII centrosymmetric geometry, while the IR absorption shows some differences due to the oxalate-ligand conformation. Polymers (I) and (II) are also distinguished by a different behaviours during the decomposition process, the precursor (I) leading to the oxide LiCrO2, while the residues of (II) consist of a mixture of sodium carbonate and CrIII oxide.

Intra- and supra-molecular inter-actions in cis,mer-diaqua-tris-(1H-imidazole-κN(3))(terephthalato-κO)cobalt(II) monohydrate.

In the title compound, [Co(C(8)H(4)O(4))(C(3)H(4)N(2))(3)(H(2)O)(2)]·H(2)O, the cisoid angles are in the range 85.59 (5)-93.56 (5)°, while two equal transoid angles deviate significantly from the ideal linear angle, the third being almost linear. One carboxyl-ate group is almost coplanar [1.23 (13)°] with the plane of its parent aromatic ring, although it has one O-atom donor involved in one coordination and one hydrogen bond as acceptor. The other carboxyl-ate group does not coordinate and is rotated out of this plane with a torsional twist of 17.27 (20)°. The coordination neutral entity, based on aqua ligands and two cyclic co-ligands seems, at first sight, monomeric. Strongly tight, via one intra-molecular hydrogen bond between aqua and carboxyl-ate O atoms, it brings out a quasi-planar six-membered ring around the Co(II) atom, turning the CoN(3)O(3) coordination octa-hedron into a new building block. The rigidity of this feature associated with several hydrogen-bonded arrays yields an extended structure. In the resulting supra-molecular packing, a binuclear hydrated Co(II) assembly, built up from triple strands driven by different heterosynthons, embodies the synergy of coordination, covalent and hydrogen bonds.

catena-Poly[[aquabarium(II)]-mu-aqua-bis(mu-2'-carboxybiphenyl-2-carboxylato)].

In the title compound, [Ba{HOOC(C(6)H(4))(2)CO(2)}(2)(H(2)O)(2)] or [Ba(C(14)H(9)O(4))(2)(H(2)O)(2)], the Ba atoms are coordinated by nine O atoms, six from two 2'-carboxybiphenyl-2-carboxylate (Hbpdc(-)) ligands and three from three coordinated water molecules, resulting in the formation of face-sharing distorted monocapped square antiprisms. The Hbpdc(-) ligands bridge the Ba atoms to form a one-dimensional helical polymer, with a Ba...Ba distance across the chain of 4.1386 (17) A. Adjacent chains are parallel to each other. The two independent ligands are tetradentate and have the same coordination mode, exhibiting mu-oxo bridges and eta(8)-chelation. The crystal structure is further stabilized by hydrogen bonds within each chain.

Sulfur-capped cyclodextrins: a new class of cavitands with extroverted as well as introverted donor functionalities.

Ansa-cyclodextrins were obtained in high yields by reaction of sodium sulfide with A,B-di- or A,B,D,E-tetramesylated alpha-CD precursors; the resulting thiocavitands are suitable for forming nanotubular molecules, as well as for hosting metal-organic fragments.

A new approach to A,B-difunctionalisation of cyclodextrins using bulky 1,3-bis[bis(aryl)chloromethyl]benzenes as capping reagents.

1,3-Bis[bis(4-tert-butylphenyl)chloromethyl]benzene and 1,3-bis[bis(4-anisyl)chloromethyl]benzene were employed as regioselective capping reagents for the preparation of C-6A,C-6B-bridged, permethylated alpha- and beta-CD derivatives; isolated yields up to 55% of proximally capped, methylated CDs were obtained, thus opening the way to the straightforward preparation of a wide range of A,B-functionalised CDs. As revealed by a single crystal X-ray diffraction study, the benzene-1,3-bis[bis(4-tert-butylphenyl)methyl] spacer is perfectly suited for A,B-capping of beta-cyclodextrin.