Metal Complex Stacked

Most of the compounds listed in this class (Table 7) are tetraalkylammonium (R4N+) salts of metal dithiolene complexes. These salts generally exist in a 2 1 or 1 1 stoichiometry. The 2 1 salts, such as [ra-Bu4N]2[Cu(mnt)2]114) and [Et4N]2-[Cu(mnt)2]115,116) can exhibit interesting properties, but they will not be considered here since the transition-metal components are isolated from each other (d(M-M) 5 A). 

All of the 1 1 metal dithiolene systems listed in Table 7 are composed of a phos-phonium or ammonium cation and a metal111 bis-dithiolene monoanion. These compounds are structurally very similar, consisting of slipped stacks of metal dithiolene anions which are associated in pairs the stacks are surrounded by non-interacting cations. A view of a representative unit cell for this type of system is shown in Fig. 15. Only [n-Bu4N][Cu(mnt)2]92) displays a slightly different association of anion pairs in the 

As has been noted previously81, the structural parameters of metal dithiolene complexes are relatively insensitive to the overall charge on the complex, and the monoanionic dithiolene complexes generally retain the mmm (D2h) molecular symmetry found in both neutral and dianionic dithiolene complexes. The only notable structural trend is a lengthening of the M-S bond as the overall charge on the transition-metal complex increases. 

Electrical conductivity measurements have been made on a few of these metal dithiolene systems and show that they are, at best, poor semiconductors, with room-temperature conductivities of less than 10 6Q 1cm 1. This is not surprising as the molecules are in an integral oxidation state. Moreover, the existence of dimers destroys the crystallographic uniformity of the stacks and, as the magnetic studies have shown, the unpaired electrons tend to couple within the dimers rather than delocalize along the stacks. 

Another interesting compound in this class is [Ni(tatma)]2[Ni(edt)2]l07), which is structurally similar to [TTF]2[Ni(edt)2]87 (Sect. 3.2) and contains stacks of dimers, [Ni(tatma)+]2, connected by neutral Ni(tatma) molecules. These stacks are similarly 

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Ibers JA, Pace LJ, Martinsen ], Hoffmann BM (1982) Stacked Metal Complexes Structures and Properties. 50 1-55... 

Metal complexes of pteridine have provided 3D H-bonded networks containing H bonding between pteridine ligands and water molecules, and 7r-stacking and H bonding between adjacent pteridine ligands. The complex [ZnL(H20)2].2H20 has been prepared.267... 

In the early stage of the development of molecular conductors based on metal complexes, partially oxidized tetracyanoplatinate salts (for example, KCP K2 [Pt(CN)4]Br0.30-3H2O) and related materials were intensively studied [6], In this system, the square-planar platinum complexes are stacked to form a linear Pt-atom chain. The conduction band originates from the overlap of 5dz2 orbitals of the central platinum atom and exhibits the one-dimensional character. 

Noncovalent derivatization with metal complexes or nanoparticles is again based on van der Waals, electrostatic, H-bond and n-n stacking interactions. 

Heavier metal ions and metal complexes can find sites on nitrogen atoms of the nucleic acid bases. Examples are the platinum complex cisplatin and the DNA-cleaving antibiotic neocarzinostatin (Box 5-B). Can metals interact with the n electrons of stacked DNA bases A surprising result has been reported for intercalating complexes of ruthenium (Ru) and rhodium (Rh). Apparent transfer of electrons between Ru (II) and Rh (III) over distances in excess of 4.0 nm, presumably through the stacked bases, has been observed,181 as has electron transfer from other ions.181a Stacked bases are apparently semiconductors.182... 

Janiak, C., A critical account on 7t-7t stacking in metal complexes with aromatic nitrogen-containing ligands. J. Chem. Soc., Dalton Trans. 2000, 3885-3896. 

Karpishin, T. B. Stack, T. D. P. Raymond, K. N. Octahedral versus trigonal prismatic geometry in a series of catechol macrobicyclic ligand-metal complexes, J. Am. Chem. Soc. 1993,115, 182-192. 

Much attention is currently devoted to the synthesis and properties of shape-persistent macrocycles[l]. Such compounds are interesting for a variety of reasons including formation of columnar stacks potentially capable of performing as nanopores for incorporation into membranes or for the generation of nanowires[2]. Furthermore, in shape-persistent macrocycles incorporating coordination units, enc/o-cyclic metal-ion coordination may be exploited to generate nanowires[3], whereas e.ro-cyclic coordination can be used to construct large arrays of polynuclear metal complexes[4]. Shape-persistent macrocycles with reactive substituents may also be linked to other units to yield multicomponent, hierarchical structures. 

Contents J.A.Ibers, L.J.Pace, J.Martinsen, B.M.Hoffman Stacked Metal Complexes Structures and Properties. -M.J. Clarke, P.H.Fackler The Chemistry of Technetium Toward Improved Diagnostic Agents. - R.J.P. Williams The Chemistry of Lanthanide Ions in Solution and in Biological Systems. - C.K. Jorgensen, R.Reisfeld Uranyl Photophysics. 

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