Boron complexes anionic

Lopez Garcia et al. [2] have described a rapid and sensitive spectrophotometric method for the determination of boron complex anions in plant extracts and waters which is based on the formation of a blue complex at pH 1 - 2 between the anionic complex of boric acid with 2,6-dihydroxybenzoic acid and crystal violet. The colour is stabilised with polyvinyl alcohol. At 600 nm the calibration graph is linear in the range 0.3-4.5 xg boron per 25 ml of final solution, with a relative standard deviation of 2.6% for xg/l of boron. In this procedure to determine borate in plant tissues, the dried tissue is treated with calcium hydroxide, then ashed at 400 °C. The ash is digested with 1N sulfuric acid and heated to 80 °C, neutralized with cadmium hydroxide and then treated with acidic 2,6-dihydroxybenzoic acid and crystal violet, and the colour evaluated spectrophotometrically at 600 nm. Most of the ions present in natural waters or plant extracts do not interfere in the determination of boron complex anions by this procedure. Recoveries of boron from water samples and plant extracts were in the range of 97 -102%. 

Boric acid, fluoro-, 101 Boromycin, 96 Boron, 81-101 as ligand, 99 Boron complexes anionic, 90-97 antibiotics, 101 applications, 101 cationic, 97 chelates, 89... 

Pentamethylcyclopentadienyl substituted boron complexes arc obtamed by the reaction of the pentamethylcyclopentadienyl anion with boron tnfluonde [109] (Table 27) Similarly, the Gngnard reagent prepared from 3,5-bis(tnfluorometh-yl)iodobenzene reacts with sodium tetrafluoroborate to form the phase-transfer eatalyst 2 under anhydrous eonditions [110] (equation 87)... 

Lippard, S.J., Ucko, D.A. 1968. Transition metal borohydride complexes. II. Th reaction of copper(I) compounds with boron hydride anions. Inorg Chem 7 1051-1058. 

Tricoordinated boron compounds (boranes) are coordinatively unsaturated and their chemistry is dominated by reactions in which complexes are formed. These complexes are either neutral molecules (borane complexes), anions (borates) or boron cations. Space limitations mean that little or no attention will be paid to complexes containing several boron atoms and to species of the type L-BH3, [BH,]- and [L2BH2]+ (L = neutral ligand), discussed in detail in several books and reviews. Similarly, little attention will be paid to the plethora of metal borates and the cyclic and polymeric amino- and phosphino-boranes. 

G. R. Hill. Comparing the ratio of ionic charge to ionic radius is good for metals which form simple ions. For elements like boron, which exist always as complex anions, the ratio may not be meaningful. This may explain the anomalous position of boron in Figure 1. Do we have any information about the nature of the complexes formed by borates in plants ... 

Ogner [1] has described an automated analyser method for the determination of boron-containing anions in plants. This is based on the formation of a fluorescent complex between these anions and carminic acid at pH 7. The plant tissues are ashed at 550 °C and the residue dissolved in 0.5 N hydrochloric acid prior to adjustment to pH 6-7 with sodium carbonate solution. The solution is excited at 470 nm and fluorescence intensities measured at 585 nm. Interferences by the reaction of some cations with carminic acid are overcome by passing the solution through an ion exchange column to exchange the cations for sodium ions. Analytical recoveries of boron anions were in the range 98-104%. The detection limit of the method was 5 xg/l boron. 

Many other metal fluorides can homo- and heteroconjugate with related anions. Thus, boron fluoride gives readily the complex anions B2F7 and and... 

Besides the Methylene Blue, other spectrophotometric methods, based on ion-associates of anionic boron complexes with basic dyes are used. Extractable associates with BF4 are obtained with Nile Blue A (formula 4.32) [7,36,37], Capri Blue (formula 4.31) [38], Malachite Green (formula 4.26, with Me instead of Et), Chrompyrazole II (CHCI3, e = 6.7-10 at 595 nm) [40], etc. 

In addition to BF4 , other anionic boron complexes, also forming ion-associates with basic dyes, have been applied to determine boron, namely 2,4-dinitro-1,8-naphthalenediol and Brilliant Green (formula 4.26) (toluene, e = 1.0-10 at 637 nm [41 3], 2,6-dihydroxy-benzoic acid, and Malachite Green (chlorobenzene, e = 9.5-10 [5], 2,3-dihydroxy-naphthalene and Crystal Violet (benzene, e = 8.8-10 [44]), mandelic acid, and Malachite Green (benzene, e = 6.5-10 ) [45,46], pyrocatechol derivatives, and Ethyl Violet (toluene, e = 1.05-10 [47,48]. The ion-pair of the salicylate complex of boron with ferroin has also been proposed (CHCI3) [49]. 

Tetraphenylarsonium trichloro-stannate(ii) and germanate(ii) react with boron trifluoride to give a complex anion in which the tin or germanium is co-ordinated to boron trifluoride (74). The anions had a B shift of 19-0 1 p.p.m. [from (MeO)3B]. 

This has led to interesting phosphorus-boron complexes. Pentaphenyl phosphorus will donate a phenyl anion to triphenylborane ... 

There is an extensive and complex structural chemistry of boron-oxygen anionic species (polyborates), in aqueous or nonaqueous solution and in the melt or solid state, Six-membered ring formation dominates, but the structural chemistry of the species is complicated since boron exists in either 3- or 4-coordinate environments, or various combinations of these. Thus most polymeric species consist of (6—0)3 rings joined by boron atoms linked to an intervening oxygen atom, or y rings sharing a common boron atom. 

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