Structural studies isocyanide complexes

The subjects of structure and bonding in metal isocyanide complexes have been discussed before 90, 156) and will not be treated extensively here. A brief discussion of this subject is presented in Section II of course, special emphasis is given to the more recent information which has appeared. Several areas of current study in the field of transition metal-isocyanide complexes have become particularly important and are discussed in this review in Section III. These include the additions of protonic compounds to coordinated isocyanides, probably the subject most actively being studied at this time insertion reactions into metal-carbon bonded species nucleophilic reactions with metal isocyanide complexes and the metal-catalyzed a-addition reactions. Concurrent with these new developments, there has been a general expansion of descriptive chemistry of isocyanide-metal complexes, and further study of the physical properties of selected species. These developments are summarized in Section IV. 

The initial work in this field appeared as a communication in 1969 8), and this work was later expanded to a full paper (9). Badley et al. described the synthesis of m-Pt(PEt3)(CNCjH5)Cl2 from Pt2(PEt3)2Cl4 and the isocyanide the bromide complex could be obtained from this complex by addition of bromide ion. These complexes were then observed to react with various substances [Eq. (16)]. A crystal structure study on the complex... 

Isocyanide complexes. [Feroom temperature yields [Fe, (CNMe)6][FVi,CI4]2. Structural studies on this and [Fe(NCH)h][FeBr4], have been reported. 24 ... 

The luminescence properties of the gold(I) isocyanide complex [Au2(dmb)(CN)2] have been studied. The crystal structure of the complex showed an intramolecular gold-gold separation of 3.536A. The solid sample displayed an emission band at 456nm (tq = 0.59 ps) and a weaker broad emission band at around 600-700 nm. The... 

Extensive electrochemical studies of complexes of Type I were also reported (164-166). It was ascertained that [Rh2]2+ di-isocyanide complexes are more susceptible to oxidation than their dicarbonyl analogues, and that one-electron oxidations of the di-isocyanide complexes produce stable and isolable paramagnetic [Rh2]3+ species (165). In particular, paramagnetic complexes of the type [Rh2(/i-EE )2(f-BuNC)2(p-pz )](PF6)2 (EE = dppm, dapm, or dpam Hpz = Hpz, 4-MepzH, Hdmpz, 4-BrdmpzH, or 3,4,5-BrpzH) containing the [Rh2]3 + core were obtained via controlled potential electrolysis of the parent [Rh2]2+ species [Rh20i-EE )2(f-BuNC)2(/ -pz )](PF6). The X-ray crystal structure of [Rh2(/j.-dppm)2(r-BuNC)2(/x-dmpz)](PF6)2 showed a Rh- -Rh distance of about 2.83 A, which is consistent with a bonding order of 0.5 for the [Rh2]3 + core (166). 

Several different types of metal isocyanide complex exhibit solid state optical properties indicative of metal-metal interactions, but most exhibit low electrical conductivities. One series of salts [Rh(CNR)4]X , where R = phenyl, vinyl, ethyl or methyl and X = Cl, PFg, BF4 or CIO4, exhibit much hi er conductivities and Rh—Rh separations as short as 2.94 A. Single crystals of [Rh(CNCHCH2)4]C104 have a room temperature conductivity of 2 Q cm with an activation energy of 100 meV. An indication of a metallic state was observed below the decomposition temperature of 330 K but it was not possible to conclude whether the high conductivity was the result of partial oxidation, small band gap intrinsic semiconductor behaviour or extrinsic semiconductor behaviour due to Rh impurities . More recent studies indicate the existence of polynuclear species but a full structural study of an infinite metal atom chain compound wth isocyanide ligands has not been made, ... 

Several reports in the literature have suggested metal-metal interactions in the solid state for metal isocyanide complexes (53, 162, 220, 221, 282). Materials of the type Ma2(CNR)2(M = Pt, R = alkyl, aryl) have been prepared that exhibit different optical properties in the solid state than in solution. This phenomenon is generally indicative of metal-metal interactions. Since partial oxidation is not apparent from the stoichiometry, low conductivity is anticipated. The studies were limited to some vcifjt absorption (221) and reflectivity data (162) in the solid state. Structures SO, 31, and 32 (or mixtures thereof) fit the observed stoichiometry. 

In addition to the papers referenced above, crystallographic studies of a number of platinum isocyanide complexes have been undertaken, with stacking arrangements present in some structures,but absent in others. 

In order to prove this assumption, several trifluoromethyl isocyanide complexes with metals in low oxidation states have been synthesized, and their spectroscopic data, reactivity and structures have been studied. 

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