Linear metal chain compounds

In this chapter, we describe linear metal chain compounds, consisting of at least three metal ions, supported by ligand systems. Extended metal atom chains (EMACs) of Cr, Co, Ni, and Cu, supported by polypyridylamide ligands, are discussed. This is followed by linear and bent Pd chains sandwiched by unsaturated hydrocarbons. Unsupported linear metal chain compounds are discussed in subsequent sections. Because synthetic protocols and the bonding schemes are different for different metals, our discussion is classified according to metal ions. 

In Chapter 5, M. Majumdar and J. K. Bera describe the properties of and synthetic protocols for preparing extended linear metal (Cr, Co, Ni and Cu) chain compounds that contain at least three metal ions and are supported by ligand systems. In addition, they describe bent Pd chains that are sandwiched between unsaturated hydrocarbons and unsupported linear metal chain compounds. 

The spectacular iridium compound HH,HT,HH-[Ir6(/t-OPy)6(I)2(CO)i2] 231 containing an unprecedented almost linear metal chain made up of six iridium atoms has been prepared by Tejel et al. by oxidation of [Ir2(/t-OPy)2(CO)4] with iodine at 0°C in toluene. The formal oxidation state of the iridium atoms is 1.33. The new hexairidium compound has been characterized by X-ray diffraction analysis showing a linear array of iridium-bonded atoms with an HT-[Ir2(/t-OPy)2(CO)4] complex sandwiched in between two HH-[Ir2(/t-OPy)2(I)(CO)4] units (Figure 18). Complex 231 represents the longest polyiridium chain complex so far know. Other polyiridium species with as many as four iridium atom chain have been reported, see Ref 112,112a,l 12b... 

In this way we come to class III complexes, i.e. complexes in which the two sites are indistinguishable and the element has a non-integral oxidation state (delocalized valence). Usually one divides this class in two subclasses. In class IIIA the delocalization of the valence electrons takes place within a cluster of equivalent metal ions only. An example is the [NbgCli2] ion in which there are six equivalent metal ions with oxidation state + 2.33. In class IIIB the delocalization is over the whole lattice. Examples are the linear chain compound K2Pt(CN)4.Bro.3o. 3H2O with a final oxidation state for platinum of 2.30, and three-dimensional bronzes like Na WOg. 

Krogmann and Geserich showed these compounds to be linear metal atom chain compounds with short intrachain Ir—Ir separations of 2.86 A, and that they have related structures to the cation-deficient bis(oxalato)platinates.87 A detailed study of these compounds showed that the... 

Conducting halogenated linear metal atom chain systems were first reported in 195095 and are now known for Ni and/or Pd complexes of glyoxime (GLY), DPG and BQD. The compounds are usually produced by treating a hot solution of the neutral complex in o-C6H4C12 with I2 and lustrous coloured crystals of the NIOS compound are obtained on cooling the solution. The limited range of compounds studied is shown in Table 3 and all have metal-over-metal stacked structures. 

Oxford 1992, p. 31 (d) Extended Linear Chain Compounds, ed. J. S. Miller, Plenum Press, New York 1982 (e) Chemistry and Physics of One-Dimensional Metals, ed. FI. J. Keller, Plenum Press, New York 1977. 

Nickel(II), palladium(II) and platinum(II) form planar complexes with 1,2-diondioximato ligands. The compounds crystallize in columnar stacks with different angles of inclination between the molecular planes and the stacking direction. The metal-metal distances depend strongly on the electronic and steric properties of the ligands. Upon oxidation with molecular iodine mixed valence compounds can be obtained. The stacking direction becomes perpendicular to the molecular planes, in these solids and the metal-metal distances decrease considerably. I -anions are incorporated into the lattice to form linear arrays parallel to the metal chains (1). 

The widest columnar mesophase temperature ranges were obtained for the bis-[l,3-di-(substi-tuted-phenyl)-/3-diketonate] metal complexes bearing ten and twelve chains ((55) R = H or OC H2 +i). The ten-chain copper, palladium, and oxovanadium(IV) complexes ((55) M = Cu, Pd, VO R = H, = 6, 8, 10, 12, 14) were all mesomorphic and the enantiotropic mesophases were identified by optical texture and variable-temperature X-ray diffraction as columnar phases (Table 34). The copper and palladium complexes displayed a Coh phase for short chain length ( = 6, 8 for M = Cu = 6, 8, 10 for M = Pd), which transformed to a Coin phase as the chain length was increased. Surprisingly, no direct Cok-to-Colh phase transition was observed within the same compound, but weakly first-order Cok-to-Cok and Colh-to-Colh phase transitions were found for compounds with intermediate chain lengths. In contrast, the vanadyl complexes exhibited only one Coh mesophase. Infrared studies indicated that the VO complexes possessed a linear V=0—V=0 linear polymeric chain structure in the crystal phase, while no... 

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