Tris complex

Figure 1.18 Syntheses of ruthenium tris complexes of 1,10-phenanthroline ana z,z -oipynuyl.

Extended refluxing of hydrated RhCl3 with excess oxalate leads to the tris complex, the potassium salt crystallizing as orange-red crystals with Rh-O 2.000-2.046 A. 

Square planar coordination is general in these in the tris-complexes Au(S2CNR2)3, it is obtained by two dithiocarbamates being monodentate (the third is, of course, bidentate) [131], Such planar coordination in [Au(S2CNEt2)2]+SbF6 involves Au—S distances of 2.316-2.330 A [132]. 

Nickel and palladium react with a number of olefins other than ethylene, to afford a wide range of binary complexes. With styrene (11), Ni atoms react at 77 K to form tris(styrene)Ni(0), a red-brown solid that decomposes at -20 °C. The ability of nickel atoms to coordinate three olefins with a bulky phenyl substituent illustrates that the steric and electronic effects (54,141) responsible for the stability of a tris (planar) coordination are not sufficiently great to preclude formation of a tris complex rather than a bis (olefin) species as the highest-stoichiometry complex. In contrast to the nickel-atom reaction, chromium atoms react (11) with styrene, to form both polystyrene and an intractable material in which chromium is bonded to polystyrene. It would be interesting to ascertain whether such a polymeric material might have any catal3dic activity, in view of the current interest in polymer-sup-ported catalysts (51). 

The isothiazide ligand, (142), and its 3- and 5-methyl derivatives form the tris complexes IrCl3(isothiazole)3 in which isothiazole and the 5-methyl derivative bind through the S atom, whereas 3-methylisothiazole binds through the N atom.254... 

The bis- or tris-complexes of phenylcopper with triphenylphosphine react violently and exothermically with carbon disulfide, even at 0°C. Suitable control procedures are described. 

Dwivedi, B. K. et al., Indian J. Chem., 1987, 26A, 618-620 Twelve tris-complexes [Sn(C104)2.3L] between tin(II) perchlorate and Schifif bases derived from salicylaldehyde, anisaldehyde, or 2-hydroxy-l-naphthaldehyde and aromatic amines were investigated for thermal instability. 

FIGURE 5.7 Second-order hyperfine shift in the X-band EPR of the Cu(II)-Tris complex. The thin solid line is the experimental spectrum of 1.5 mM CuS04 in 200 mM Tris-HCl buffer, pH 8.0 taken at v = 9420 MHz and T = 61 K. Tris is tris-(hydroxymethyl)aminomethane or 2-amino-2-hydroxymethyl-l,3-propanediol. The broken lines are simulations using the parameters g = 2.047, gN = 2.228, Atl = 185 gauss. In the lower trace the second-order correction has been omitted. 

For five-membered heterocycles other than thiazole, (such as pyrazole [27], imidazole [28], and triazole [29]) the effect of replacement of just one pyridine moiety in 1 is greater and the [Fe N6]2+ derivatives in these instances show crossover behaviour. The [Fe N6]2+ derivative of 2-(pyridin-2-yl)imidazole 19 (Dq(Ni2+) 1150 cm-1 [22]) was shown relatively early on to be a crossover system [28]. In solid salts and in solution the transition is continuous and centred above room temperature. The dynamics for the 5T2— Ai relaxation for this system have been investigated by a number of techniques [30-32] and Beattie and McMahon have shown that in solution there is not only a spin equilibrium but also a ligand dissociation process, very reasonably ascribed to the high spin form of the tris complex [32]. 

As in the case of o-dioxolenes, the diimine derivatives also form tris-complexes. Figure 38 for instance shows the molecular structure of the benzoquinone diimino dication [Osn(bqdi)3]2 +. 50c... 

Among the other structurally characterized tris-complexes ([Fen(bqdi)3]2 +, 64 [Rum(bqdi)2(opda)]2 + 65) of known electrochemical behaviour,66 the only case we know in which structural data are available for redox couples is concerned with [Re o-C6H4(NH)2 3] + /[Re 0-C6H4(NH)2 3].67 Figure 39 shows the trigonal prismatic geometry of the monocation. 

Dithiolenes also form tris complexes of octahedral geometry. Limiting to M(dmit)3 complexes we can cite as a typical example the dianion [W(dmit)3]2-, the molecular structure of which is illustrated in Figure 44.81... 

Analogous methyl compoimds are iU-characterized and appear to be polymeric [129). The air-sensitive phenyl derivatives when first obtained from THF are soluble in benzene, but when dried completely are no longer soluble — apparently due to pol5unerization. The homoaryl complexes of the smaller scandium, and yttrium ions form only the tris complexes Sc(CeH5)3 and Y(C6H5)3 [129) It is apparent that the structure and stabihty of the homoaryls are dependent on the metal ionic radii and the steric bulkiness of the phenyl group. 

Other techniques, such as C.D. spectral change, have been used to demonstrate the presence of octa coordination for lanthanide ion in a system containing Eu(FOD)3 and alcohols or ketones (28). However, the anionic tetrakis complexes e.g. Eu(acac)i, Eu(benzac)i, Eu(DBM)i, Eu(BTFA)4, tend to dissociate into the tris-complex and L in alcoholic solution. The degree of dissociation depends on the complex as well as the polarity of the medium. In alcohol-DMF medium the dissociation is enhanced compared to the alcoholic solutions (29). The end product of these dissociation reaction may well be an octacoordinated species. Fluorescence emission from the coordinated europium ion was also helpful in estabhshing the nature of the species in solution 29). 

The tridentate diglycolate hgand, ( 00CCH20CH2C00 ), forms a 1 3 lanthanide complexes 199) in solution. Albertsson 200) was able to isolate the tris-complex as Na3[M(00CCH20CH2C00)3] 2 NaC104-6H20. He found... 

In a metal complex (102), five-membered chelate rings fonr d by 1,2-dia-mines exist in two puckered conformations, the enantiomeric X and 5 forms 36 and 37. For an achiral ligand in a bis or tris complex, steric interactions between rings are present, and the two conformations are no longer equivalent energetically. 

A basic solution with a large excess of acetylacetone is strong blue. Complexes have been studied (log Pi = 5.383, log j82 = 10.189, log / 3 = 14.704). A potential of —1.0 V vs. SHE was measured for the reduction of the VUI tris complex.84 Mixed complexes V(L)2(py)2(L= acac, trifluoroacetylacetonato or dibenzoylmethanato) isolated from solutions containing VS04 and the appropriate ligand97 show intense absorption in the region 700-300 nm. 

Aromatic polyalcohols act as strong coordinating agents and Table 17 summarizes reported formation constants. The complexes are quite stable this behaviour has been used for the qualitative and quantitative determination of vanadium (e.g. refs. 494 and 495). At pH 3-4, an initial vanadyl catechol complex slowly converts to a tris complex.496 In fact complexes with 1 3 metal-ligand stoichiometry have been isolated (see below), but since in the equilibrium (30) no protons are consumed or liberated, [VO(cat)2]2- and [V(cat)3]2 are not distinguishable by potentiometric studies. 

Attempts to prepare adducts directly from [VO(oxme)2] (138) were unsuccessful and a trigonal bipyramidal structure was suggested for this compound as for [VO(2-Me-oxine)2] (139).825 The [VO(oxine)2X] compounds were prepared by addition of V0S04 to an aqueous solution containing 8-hydroxyquinoline and the base X. For the adducts [VO(oxine)2X], a correlation was found between v(V=0) and the pK of the X ligand, except with bases with substituents where steric hindrance may be operating, and no evidence was obtained for the existence of both cis and trans isomers, unlike the case of [VO(acac)2] adducts (Section 33.5.5.4.ii). For the tris complexes [VO(oxine)3] , an octahedral structure in which one oxine ligand is unidentate and bonded to V was proposed.825... 

The tris and bis complexes of acetylacetone (2,4-pentanedione) (167) with chromium(III) have been known for many years (168,169).739 The tris compound is generally prepared by the reaction of an aqueous suspension of anhydrous chromium(III) chloride with acetylacetone, in the presence of urea.740 Recently a novel, efficient synthesis of tris(acetylacetonato)chromium-(III) from Cr03 in acetylacetone has been reported.741 The crystal structure of the tris complex has been determined.744 A large anisotropic motion was observed for one of the chelate rings, attributed to thermal motion, rather than a slight disorder in the molecular packing. 

The closely related tris complex of malonaldehyde (170) has been synthesized by the reaction of 1,1,3,3-tetramethoxypropane with anhydrous CrCl3 in an ether slurry.745 The complex was purified by sublimation and contains the simplest structural unit capable of enolizing to form a /3-ketoenolate chelate. 

Several unusual complexes containing neutral acetylacetonate have been reported.746 The complex [CrBr2(acac)(acacH)] was obtained from the reaction of HBr with [Cr(acac)3] [CrCl2(acac)(acacH)] was obtained from the reaction of CrCl3(THF)3 with acetylacetonate. Other unusual /3-diketonates include the tris(rhenaacetonates) (171).747,748 Two different forms of the tris complex of 2-nitroacetophenone with chromium(III) have been reported 749 these are probably geometric isomers. 

Camphorate complexes of chromium (III) have been studied. The four possible isomers of the tris complex of (+ )-3-acetylcamphorate (173) were isolated,752,753 and absolute configurations were tentatively assigned. The photoisomerization of these complexes has been investigated 754 quantum yields of the order of 10-3 were obtained with visible or ultraviolet radiation at temperatures around 100 °C. Bond-breaking processes were held to be important in the reactivity of cis isomers. 

---