Bridged anion

Basic zirconium sulfate is also considered to be strands of [Zr(OH)2] joined by bridging sulfates (208). The resulting formula is Zr(OH) - (OH) (SO 3 -nH,0, wheie h are bridging anions and t are terminal anions. 

The methyl group of the free [MeB(C5F5)3] anion tends to give NMR signals at 8 0.5 ( H) and 5 = 10 ( C), whereas the methyl-bridged anion is found at about... 

Compounds of formula [M BgLj], where B is a bridging anionic donor and L a neutral one, may be considered as formally derived from M3X8 adducts by solvolysis. The reduction of Nbv in acid solutions has been used for its qualitative and quantitative determination, but the exact nature of the reduced species remains unknown. The red-brown salt obtained as early as 1912 by reduction of Nbv in aqueous H2S04 has been formulated as [K4(H502)][Nb302(S04)6(H20)3] 5H20 (48) on the basis of a recent X-ray structure... 

The [Cr(en)3]2+ and [Cr(pn)3]2+ salts have reflectance spectra (Table 11) resembling those of the hexaammines, and the six N donor atoms are assumed to complete tetragonally distorted octahedra around the metal. Stability constant measurements (Table 39) have shown that the ions [Cr(en)(aq)]2+ (vmax= 18 300 cm-1, e = 25 dm3 mol-1 cm-1) and [Cr(en)2(aq)]2+ (vma = 17 500 cm-1, e = 17 dm3 mol-1 cm-1) exist in aqueous solution, but that, as in the copper(II) system, the third ethylenediamine molecule is only weakly bound, and care is needed to prevent loss of en from tris(amine) complexes in the preparations. Several bis(amine) complexes, e.g. [CrBr2(en)2], have been isolated, and these are assigned trans structures because of IR spectral resemblances to the corresponding oopper(II) complexes. Since the spectrum of [Cr(S04)(en)2] also shows the presence of bidentate sulfate, this is assigned a trans octahedral structure with bridging anions. 

In the halides bridging anions lead to distorted CrXe octahedra sharing corners in which there are four short approximately equal Cr—X bonds and two long trans Cr—X bonds. There is also angular distortion of the octahedra. The fluoride has the tetragonal (distorted) rutile structure and the other halides chain-type structures. The mixed crystal (Mn, Cr)I2 is isotypic with monoclinic Crl2 (Table 34). 

By the stepwise thermal decomposition of the tris chelate, mono adducts of the type [NiX2(N—N)] (X = halides, NCS) were obtained.852-854 These complexes are polynuclear six-coordinate with bridging anions. In the thiocyanato derivative the nickel atoms are ferromagnetically coupled. 

With respect to the structures of these H-bridged anions, it is interesting to quote two comments (38-40). 

Ruff (71a) was also able to obtain halogen-bridged anionic complexes with different Group VIB metals, namely, [CrW(CO)i0Br] and [CrMo(CO)10I]. A little later, we used the same method to gain access to dinuclear NCS-bridged anions with heterometals and bent M—NCS —M bonds (72) ... 

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