Krogmann complexes

Planar complexes containing metal-metal bonds. K. Krogmann, Angew. Chem., Int. Ed. Engl.,... 

One-dimensional complexes, 6,134 One-dimensional conductors, 6,134 One-dimensional metals Krogmann salts, 6, 136 Optical isomerism cobalt ammines, 1,12 history, 1,180... 

The ADtcp complexes are the most extensively studied series of Krogmann salts. In particular, the solid state properties of K2[Pt(CN)4]Br0.30 3.2H2O, KCP(Br), have been studied in great detail because of the availability of large high quality single crystals.30-32... 

K. Krogmann (2) confirms the same characteristic and stresses that the platinocyanides are the only compounds which are able to superpose their plane Pt(CN)4 at a shorter distance than 3.25 A. He notes that, when this distance is really shorter than 3.25 A, there is no isotypism of platinocyanides with the two analogue complexes of Pd and Ni. 

Some have tried to elucidate the matter by bringing in new experimental data. Thus, Krogmann (2) working on partially oxidized complexes (with Pt) found that the M—M distances were particularly contracted. 

The first compound widely noticed as a molecular inorganic conductor was KCP, K2[Pt(CN)4]Xo.3 H20 (X = Cl, Br), which was reported in 1968.KCP is a partially oxidised platinum complex, later called the Krogmann salt, and was prepared by oxidising a platinum(II) complex with halogen, or by electrochemical oxidation, or by mixing platinum(II) and platinum(IV) complexes. The KCP structure is characterised by... 

Recently Krogmann et al postulated a cation-deflcient, partially oxidized formulation for this material, K o.5lr(CO)2Cl2, and a columnar structure in the solid (16). This one-dimensional structure is consistent with the observed diamagnetism, stoichiometry, IR spectra, dc conductivity, and visual appearance of the complexes. Preliminary powder x-ray data support this formulation with a short 2.86 A Ir-Ir distance. This information sets a basis for the interpretation of detailed optical, electrical, and magnetic measurements that will help in further understanding of the chemistry and physics of one-dimensional inorganic complexes. 

In solution the cation-deficient species exhibit complex (273) pH-dependent equilibria (244, 245), which make purification difficult. Krogmann and Dodel (245) claim that in concentrated aqueous solution a blue-black polymer, (Pt-(ox)2] i , exists in equilibrium, Eq. 50, whereby... 

Krogmann et al. (516) have also reported the preparation of the isoelectron-ic mixed valent Ir2(C0)4Cl2(02CCH3) species from a mixture of hexachloro-iridate(IV) and formic and acetic acids. Preliminary powder x-ray data indicate that the dinuclear species possess extremely short Ir-Ir spacings of 2.78 A and a helical superstructure of 0.7 A in diameter. Further work is necessary to clarify the physical and chemical properties of these Ir - complexes in solution and the solid state. 

Since the first observations by X-ray diffuse scattering techniques of the structural features of the Peierls instability in ID conductors (Krogmann salt and TTF-TCNQ [25a]) a great number of experimental studies has been devoted to the physics of CDWs. It has been shown that metallic CT complexes with segregated stacks of donors and acceptors (see Figure 3.2) show low temperature CDW instabilities as theoretically predicted for ID electronic systems. Several experimental studies of this structural instability have been reviewed [475] (for some recent work see ref. [45], pp. 1255-1305). 

Almost a decade ago the first molecular superconductors based on the transition metal complex molecule (TTF)[Ni(dmit)2]2 was discovered (TTF = tetrathiafiilvalene, dmit = isotrithionedithiolate) [ 1 ]. Since then several M(dmit)2 superconductors have been found. Although most of the molecular metals currently studied are systems based on multi-sulfur (or selenium) 71 molecules, the first example of a metallic molecular crystal was a partially oxidized platinum complex. The discovery of the partially oxidized platinum complex is very old, about 150 years ago, but the physical meaning of the system had not been noticed until the crystal structure (by Krogmann and Hausen) revealed the existence of the extended linear Pt-Pt metal bonds [2]. The diffuse X-ray scattering experiments on this system (K2[Pt(CN)4]Bro.3 3H2O) by Comes et al. [3] convinced many people, who were interested in conducting crystalline molecular solids at that time, of the existence of one-dimensional metal electrons in molecular crystals for the first time, and so a new era of metallic molecular systems had been bom. 

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