Polyhalide complexes

Os has a d" configuration and its coordination chemistry is dominated by polyhalide complexes. 

Polyiodides are specific polyhalides containing species such as I3", I7", Iq". Polyhalides often dissociate on heating the solid complexes. 

Dihalides are reduced by Cr(II) to the corresponding olefin ". Allylic and benzylic halides and polyhalides are reduced more readily than simple alkyl halides, but even the latter are readily reduced by an ethylenediamine complex ofCr(ri) . ... 

The synthesis of polyhalide salts, R4NX , used in electrophilic substitution reactions, are described in Chapter 2 and H-bonded complexed salts with the free acid, R4NHX2, which are used for example in acid-catalysed cleavage reactions and in electrophilic addition reactions with alkenes, are often produced in situ [33], although the fluorides are obtained by modification of method I.I.I.B. [19, 34], The in situ formation of such salts can inhibit normal nucleophilic reactions [35, 36]. Quaternary ammonium chlorometallates have been synthesized from quaternary ammonium chlorides and transition metal chlorides, such as IrClj and PtCl4, and are highly efficient catalysts for phase-transfer reactions and for metal complex promoted reactions [37]. 

Although chlorination, bromination and iodination of thiophenes by polyhalide salts require forcing conditions with the addition of zinc chloride [52], halogenation of acridine and acridone has been recorded to yield both 3-halo and 3,7-dihalo derivatives under relatively mild reaction conditions [53], However, whereas chloro-, bromo- and iodo-compounds are readily obtained from acridone, acridine only forms the bromo derivatives, as it produces stable complexes with the dichloroiodate and tetrachloroiodate salts [53]. 

Polyelectronic atom, 20-43 Polyhalide ions, 839-843 Polyhalogen cations, 848 Polymers, and phosphazene polymers, 773-775 Polynuclear carbonyl complexes, 633-639... 

Dioximes form bis complexes (35) where the ligand normally chelates through the nitrogen atoms.251-253 Detailed studies have been made of the partially oxidized compounds obtained from reaction of bis(diphenylglyoximato)- and bis(benzoquinone dioximato)-palladium with iodine254,255 and bromine.256 These complexes contain polyhalide anions and possess the high anisotropic electrical conductivity associated with many complexes which crystallize as stacked molecular units.257... 

Fluorine forms polyhalide anionic complexes including IFBr, IF Clt. BrFV. and lFf". which occur in salts of the higher alkalies, as well as catioits such as BrF .. which occurs in such salts as BrF ShF, BrFiAuFj, BrFvSOiF. etc. The dilluuriodatc ion. KFFj is also known in such salts as KIO F . 

Structural studies show thin ihc complex HICIi 4II () contains a positive irn alent iodine nioni, anti ihc planar ion ICH is one of the most stahle of Ihc polyhalide anions, as might he expeeied from consideration ot ihe large size ol the iodine atom and the small size of the chlorine atoms. 

The halides participate as terminal and bridge ligands and can be included in inner and external spheres of this kind of complex. A few examples of compounds with such terminal ligands are the boron ammines [BX3 NH3], [BX2(NH3)2]X, BX(NH3)3]X2, and [B(NH3)4]X3 (X = F, Cl, Br, I). Halides form part of many mixed-ligand carbonyl complexes, for example, Fe(CO)4I2 and polyhalide anions with various elements [4], In this respect, the structure of the anion [Re2Clx]2 provides important information the Re — Re bond is present and the chlorine atoms have a bridge function [4]. 

Carbonylmetalates will displace a halide from a metal halide complex to yield a metal-metal bonded species, Eq. (39). With di- and polyhalide... 

Preparation of Alkylidynetricobalt Nonacarbonyl Complexes by Reactions of Polyhalides with Dicobalt Octacarbonyl0... 

Van Arkel and De Boer originally considered the polyhalides, suchasl 3, ICl 2etc., as complexes consisting of an ion and a molecule. These complexes are stable, especially in... 

This approach has been used successfully to derive the stability constants of a number of ionic complexes such as NiS04 [105] and metal cation polyhalides [106, 107], as well as of molecular associations [108, 109]. Figure 4.11 shows the difference in the A.3 vs C variations for Niz+ perchlorate (no ion association) and NiS04 (ion association the sulfate anion has no action on t3) due to the lesser availability of the odd electrons of the metal ions, the Ps spin conversion reaction is less efficient when NiS04 ion pairs are present. 

The heat of solution is -4-68 Cal.,2 and the heat of formation 109-86 Cal.3 A saturated solution boils at 119-9° C. under 760 mm. pressure.4 Caesium chloride resembles the rubidium salt in forming a number of complex polyhalides.5 It is a useful agent in photomicrography, since it forms well-defined double salts with many metals among them—silver, gold, platinum, mercury, lead, copper, and many others.8 It has a decided toxic effect. 

Rubidium and caesium also form tribromides, and mixed trihalides, particularly of the MIClg type, are known in these the (Cl—I—Cl) ion is linear. The compounds KIBrCl and CsIBrF have also been isolated. All the alkali metals form stable orange-red polyhalides of the type MICI4, containing a square complex ion (p. 127). 

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