Distibines and dibismuthines

Unlike many distibines and dibismuthines, diarsines do not appear to exhibit thermochromic effects (105). 

Syntheses and Solid State Structures of Group 13-Distibine and -Dibismuthine Bisadducts... 

Structures 5 and 6 display the solid state structures of two representative distibine and dibismuthine adducts. The ligands bound to the central Sb and Bi atoms adopt a staggered conformation in relation to one another, with the bulky M(t-Bu)3 groups arranged in a trans-position. This is likely due to repulsive steric interactions. The central Sb—Sb [281.1(1) 32 283.9(1) pm 35] and Bi—Bi bond distances [298.3(1) 36 and 298.4(1) pm 37] are almost unchanged compared to the uncomplexed distibines and dibismuthines, as can be seen... 

An intermolecular analog of this inter-ring pnictogen bonding is found in the thermochromic distibines and dibismuthines.45 For example, 2,2, 5,5 -tetramethylbistibole (87) crystallizes so that the Sb atoms are aligned in chains with close contacts between the Sb atoms of adjacent molecules. It seems more than coincidental that the intermolecular contacts in 87 occur at virtually the same distance as the intramolecular contacts in 29. See Figure 3. 

Many distibines and dibismuthines have lighter colors in solutions or melts than in the solid state. Crystals of these thermochromic distibines or dibismuthines consist of linear chains of the dimetal compounds with short intermolecular metal-metal contacts. Delocalization of electrons along the chains is possibly responsible for the bathochromic shift between fluid and solid phases. Usually, the /raor-conformation is adopted by the tetraorganodimetal compounds in the solid state. (CF3)4As2 shows the /ra r-conformation also in the gas phase. Photoelectrospectroscopic measurements on Me4Sb2 revealed the presence of gauche- (12%) and trans- (88%) conformed in the gas phase.52... 

Nine other thermochromic distibines have been reported. All show a yellow melt, but the solid colors range from deep yellow to violet-blue. Seven thermochromic dibismuthines are known. The liquid colors are all red while solid colors are variable. The thermochromic distibines and dibismuthines are listed in Table II (7,10,17a,21,23-41) along with the melting points and colors of the crystals. Nonthermochromic dibismuthines are collected in Table III (20,29,32,42). 

On crystallization, nonthermochromic distibines and dibismuthines show little visual change. The solid colors of two nonthermochromic distibines (8 and 9) and two nonthermochromic dibismuthines (45 and 46) have been characterized by diffuse reflectance. In each case, only very modest changes in the absorption maxima were observed and between solid and solution. On the other hand, the intense colors shown by the solid phases of the thermochromic distibines are red shifted by 200-250 nm from their solution phase maxima (see Table IV) (7,25,29,33,34,37, 38b,40). The dibismuthines are red shifted even further. There is complete correspondence between dibismuthines and the analogous distibines, with the dibismuthines being red shifted by around 100 nm (see Fig. 1). 

Raman spectroscopy is extremely useful for characterization of distibines and dibismuthines, since the metal-metal stretching vibrations give rise to intense, easily identifiable peaks. Several thermochromic and nonthermochromic distibines have been examined as both solids and liquids (see Table VI) (7,40,49-51). With the exception of tetramethyldisti-bine, there are only small shifts in ysbsb between solid and liquid. Nor are there systematic differences between thermochromic and nonthermochromic distibines. The observed range of ySbSb appears to be predominantly... 

No diarsines or diphosphines show thermochromic behavior similar to that of the distibines and dibismuthines. For example, in the series of dipnictogen compounds A, B, and C illustrated in Scheme 6, the thermochromic distibines and dibismuthines correspond to nonthermochromic diarsines and diphosphines. Structural data are available to compare the three diarsines 51 (46), 52 (57), and 53 (5S) with the corresponding distibines 22 (25,26), 36 (37), and 30 (22). Diarsines 52 and 53 crystallize in gauche conformations as opposed to the trans-staggered conformation of the distibines. In neither case are there intermolecular As---As contacts shorter than 4 A. However, the lack of conformational correspondence makes any comparison tenuous. 

Distibines and dibismuthines (RjMMRj M = Sb, Bi) react with diarsines (R j AsAsRj) to give equilibrium mixtures of RjMAsR j (equation 93 ... 

Distibines and dibismuthines (R2MMR2 M = Sb, Bi) react with disulfides, diselenides and ditellurides (R EER E = S, Se, Te) to form R2MER (equation 103"°). The experimental procedure for the preparation of Me2SbTe(Tol-p)" has been described in detail. 

Diarsines (R2ASASR2) react easily with diphosphines, distibines and dibismuthines (R jMMR j M = P, Sb, Bi) to give equilibrium mixtures containing R2AsMR j (equation 146 3). 

Complexes with Sb-Sb and Bi-Bi Bonds 521 Table 15.1 Examples of reactions affording distibines and dibismuthines. 

The majority of Group 9 stibide and bismuthide complexes reported to date are cobalt derivatives [113,197,198]. Calderazzo and coworkers demonstrated that Co CO)g undergoes facile insertion into distibines and dibismuthines to afford their corresponding organostibide (66) and bismuthide (67) complexes (Scheme 15.20) [199]. Based on spectral data and parallel gas volumetric experiments, it was proposed that the antimony derivative is oligomeric, whereas the bismuth derivative is... 

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