Three unique coordination geometries involving 1,2-dimethoxy-4,5-bis(2-pyridylethynyl)benzene

Abstract

Reaction of the new ligand 1,2-dimethoxy-4,5-bis(2-pyridylethynyl)benzene with different metal centers under similar reaction conditions led to three distinct structure formation processes: molecular ring closure, dimerization, and polymer formation.In synthetic, covalent organic chemistry the notion of conformers, oligomers and polymers are distinctly separated and irreconcilable. In supramolecular synthesis on the other hand this conception is less stringent. The utilized building blocks and the variety of binding forces that hold supramolecular assemblies together by arranging organic modules in the solid state makes the border of the very notions of conformers, cycles, and polymers more permeable. Here we wish to demonstrate that one organic module 1,2-dimethoxy-4,5-bis(2-pyridylethynyl)benzene 1 1 can form a supramolecular cycle, a dimer and polymer utilizing different inorganic connectors Cu(OAc) 2 , CoCl 2 and [Rh(OAc) 2 ] 2 .Single crystals suitable for X-ray diffraction † of Cu (1) O (maintaining the ligand to metal ratio) and ethanol was substituted for methanol (40% yield). These three systems each form a distinctly different structure and between them, demonstrate the importance of the free rotation of the pyridyl rings around the carbon-carbon bonds for facilitating the formation of the three structure types.Compound 2 demonstrates the preference of Cu 2+ for square planar coordination with copper positioned snugly between the two pyridyl rings. The resulting N-Cu-N (Cu-N 2.01 Å, NCu-N 172.98°) bonds close an eleven membered, triangular ring (Fig. 1), which is nearly identical to the structures reported by Bosch and Barnes for 1,2-bis(2-pyridylethynyl)benzene. 2 The square planar coordination of copper is completed by two trans oxygens from separate acetate groups.Compound 3 contains Co 2+ , which is found in typical tetrahedral coordination. 3 This tetrahedral preference, apparently, cannot be conveniently satisfied through a ring closure that would require a rotation of the pyridyl rings away from the 180° angle found in the copper complex. The result of such a rotation would be an elongated Co-N bond. Instead, the pyridyl rings rotate away from each other by 128° and bind to separate cobalt atoms with bond lengths of 2.03 Å, which is typical for Co-N bonds. The tetrahedral coordination in each case is completed by two chlorine atoms. The overall structure (Fig. 2) consists of two molecules of 1 bridging two cobalt atoms. An inversion center is located in the middle of the dimer.The polymeric structure of 4 (Fig. 3) results from the linear coordination preference of [Rh(OAc) 2 ] 2 . The structure consists This journal is

Unique 2:1 Complex with a trans-Chelating Bis-Pyridine Ligand

“…When the 1,2-dialkynylbenzene tether is used to link two diphenyl phosphine moieties, cis -ligation is still preferred, and a tetrahedal 2:1 complex is reported for Pd(0) , …”

Pyridine-Capped, Oligomeric (o-Phenyleneethynylene)s

“…The compound 1 19,20 and its parent 21,22 (without the methoxy groups) are suitable ligands for transition metals as they can coordinate in a trans-spanning fashion, forming monomeric complexes, or be the bridging part of a metal-organic coordination polymer. We present the synthesis and the structural characterization of the pyridine end-capped o-PEs 1-4 (Figure 1), which are potentially attractive as active layers in light emitting diodes and as building blocks for larger metal organic solid-state polymers.…”

Spacer Flexibility in Bis(pyridyl) Ligands: Chelating Organosilicon Pyridylethynyl Ligands

“…Ethynylpyridine ligands have been extensively utilized in the synthesis of organometallic nonlinear optical materials and supramolecular frameworks. − A ligand of particular recent interest is 1,2-bis(2-pyridylethynyl)benzene, known to form complexes with Cu(I), Pd(II), Ag(I), and even Br + . ,,− Due to the rigid nature of this ligand, complexes are generally formed in which the two pyridine rings are directly opposed. Conceivably, replacing the benzene ring spacer between the pyridylethynyl moieties could lead to different coordination modes and new metal complex geometries.…”