Rosa D. Bailey

Cadmium(II) halide complexes of pyrazine

Abstract Pyrazine forms 1:1 complexes with cadmium(II) halides, CdX 2 · pyrazine (X = Cl, Br, I). The structures of all three members of this series have been determined by single-crystal X-ray diffraction. All of the complexes crystallize as infinite CdX 2 chains in which cadmium atoms are doubly bridged by pairs of halide atoms; pyrazine ligands complete the pseudo-octahedral coordination of the cadmium atoms and link the CdX 2 chains to form extended two-dimensional layers. While this type of coordination is fairly common for chloro and bromo derivatives, the iodo compound represents, to the best of our knowledge, the first example of an iodo derivative with this coordination. In each case the layers stack along the crystallographic a -axis to complete the structure. In the bromo and iodo complexes, which are isomorphous, the pyrazine ring planes are perpendicular to the plane of the layer. The chloro derivative has a very similar structure; however, the pyrazine rings are rotated by 19.3° away from perpendicular, bringing the ortho -CH groups into close proximity [2.89 (2) A] to a chloride atom.

Tetraiodoethylene: a supramolecular host for Lewis base donors

Abstract Tetraiodoethylene (TIE) forms charge transfer complexes with diazine donors through N···I interactions, in which the structure of the complex is very similar to that of TIE. In TIE, two unique molecules form distinct “layers”, and in the complexes the donor molecules take the place of TIE molecules in one of the layers. I···I interactions within the remaining layer of TIE maintain the structure of the layer and yet allow enough flexibility to accommodate a wide variety of donor molecules. Phenazine, quinoxaline, 1,4–dicyanobenzene, and 2,2′–bipyridine all form complexes with TIE which have very similar structures. Phenazine and 2,2′–bipyridine donors sit on the same inversion center as the TIE molecules they replace, and the donor·TIE chains run in the (1 1 0) direction. 1,4–Dcb·TIE has a very similar structure to that of the previously determined pyrazine·TIE complex, but the donor molecules span TIE acceptors in the (1 −2 1) direction rather than (1 1 1). The asymmetric environment of the donor sites in quinoxaline result in a very distorted layered structure, and the I···I interactions between neighboring TIE molecules are the weakest of those reported here. Decomposition of TIE in its reaction with 2,2′–bipyridine gave the side product, [2,2′–bipyridine(H)]I3·TIE, in which I···I interactions link TIE molecules and I3− anions to form a pseudo–polyiodide layer.

Structural and electronic properties of (2,2-trans)-dirhodium(II) tetrakis(N-phenylacetamidate)

Abstract We have synthesized and characterized the first known 2,2-trans isomer of the N-substituted dirhodium(II) tetrakisacetamidate, Rh2(RNAc)4, class of compounds. The bis benzonitrile adduct exhibits a unique orthogonal arrangement of the axial aromatic rings in the solid state. Structural and electronic features suggest the presence of π-backbonding.

The reaction of iodine with 9-methylacridine: formation of polyiodide salts and a charge-transfer complex

The reaction of iodine and 9-methylacridine in methylene chloride results not in the formation of a charge-transfer complex as with acridine, but in the iodine-rich salt [ICH2C13H8N–H]4(I8)(I5)2, 8, where a proton on the methyl group has been replaced by an iodine. In toluene, the reaction produces both a charge-transfer complex ICH2C13H8N–I2, 9, and a salt [CH3–acridine(H)]2(I7)(I5), 10. Polyiodide salt formation can be explained by the availability of a facile reaction pathway from the aryl radical cation which results from initial oxidation by I2.

Bis(Pyridyl)Cadmium(II) Iodide Complexes: Thermal, Inclusion, and Structural Behavior

Abstract Bis(4-cyanopyridine)cadmium(II) iodide ( 1 ) crystallizes as infinite CdI 2 chains, in which cadmium atoms are doubly bridged by pairs of iodine atoms; 4-cyanopyridine ligands occupy trans positions to complete an octahedral coordination about the cadmium. The chains are associated into layers through self-association of the cyano groups. The layer structure of 1 is essentially unchanged as mercury(II) iodide molecules are intercalated between the layers to form 2 . Bis(4-vinylpyridine)cadmium(II) iodide ( 3 ) crystallizes in a nearly isomorphous fashion with 1 ; however, lacking a donor site capable of binding to HgI 2 , it does not form an intercalation compound similar to 2 . Bis(2-vinylpyridine)cadmium(II) iodide ( 4 ) crystallizes as a molecular species with approximate tetrahedral coordination about the four-coordinate cadmium atom; steric interactions involving the vinyl groups prevent formation of extended chains. The 4-vinylpyridine complex undergoes a thermally-induced solid-state polymerization of the ligand that is not observed in 1 , 2 or 4 .

Synthesis of Polydiacetylene Charge-Transfer Complexes

Abstract Like 1,4-bis(3-quinolyl)buta-1,3-diyne, its structural isomer, 1,4-bis(4-isoquinolyl)buta-1,3-diyne, undergoes both photo- and thermal polymerization. Thermal polymerization of each material leads to more amorphous, less thermally stable polymers than are observed in the respective photopolymerization. The diacetylenes are found to react with certain organoiodines to give N-I charge-transfer complexes. Thermolysis of the complexes evolves the organoiodine species prior to polymerization of the diacetylene. The complexes fail to polymerize upon photolysis.

Synthesis, structure and thermal decomposition of tetra(2-pyridyl)pyrazine·I2 charge-transfer complexes

In both the solid state and in solution, 2,3,5,6-tetrakis(2′-pyridyl)pyrazine (tpp) reacts with iodine to form charge-transfer complexes. The solid state process results in the exclusive production of a mono-I2 adduct, 3, while the solution reaction can produce both 3 and a bis-I2 adduct, 4. The X-ray crystal structure of 4 is described and a structure for 3 is proposed based upon spectroscopic evidence and molecular orbital calculations. The thermal decompositions of 3 and 4 proceed by I2 evolution at very different rates and lead to different polymorphs of tpp. The mechanism of this process is described in terms of solid state reaction theory.

Dicarbonyl(η5-cyclopentadienyl)(pyrrolyl-N)iron(II)

The crystal structure of the title compound, [Fe(C 5 H 5 )-(C 4 H 4 N)(CO) 2 ], shows a discrete molecular structure with a distorted tetrahedral geometry about the Fe atom. The bond angles between the ligands in the tripod and the Fe-Cp centroid vector range from 121.9 to 123.7 (3)°, and the angles between the tripod ligands range from 90.5 (4) to 96.0 (4)°. The mean Fe-C carbonyl and Fe-C Cp distances are 1.776(4) and 2.098(16)A, respectively [Fe-Cp centroid 1.722(4)A], and the Fe-N pyrrole distance is 1.962(3)A. The Cp and pyrrole rings are both planar (maximum deviations of 0.007 and 0.006 A, respectively). The rotational orientation of the Cp ring with respect to the tripod ligands is approximately eclipsed with respect to the Fe-N pyrrole bond [N(1)-Fe(1)-Cp centroid -C(8) -3.1°]. The dihedral angle between the pyrrole ring and the N(1)-Fe(1)-Cp centroid plane is 73.7°.

Crystal engineering through charge transfer interactions; assisted formation of a layered coordination polymer (4-cyanopyridine)cadmium(II) iodide·diiodine

Formation of a layered coordination polymer (4-cyanopyridine)cadmium(II) iodide is assisted by n–ς* donor–acceptor interactions between coordinated iodine atoms of the layers and iodine molecules which bridge adjacent layers.