Zinc Borate Hydrolysis.

The crystalline zinc borate phase ZnB3O4(OH)3, known in commerce as 2ZnO·3B2O3·3.5H2O, is an important industrial material used as a fire-retardant synergist in polymers, a source of micronutrients in agriculture, and a preservative in building materials. It lends durability to wood composite building materials by inhibiting attack by wood destroying organisms. The hydrolysis chemistry of this zinc borate is relevant to its industrial use. ZnB3O4(OH)3 exhibits incongruent solubility, reversibly hydrolyzing at neutral pH to insoluble Zn(OH)2 and soluble B(OH)3. It is sparingly soluble with a room temperature solubility of 0.270 wt% in terms of its equivalent oxide components in solution, comprising 0.0267 wt% B2O3 and 0.003 wt% ZnO. Aspects of the hydrolysis chemistry of zinc borate under neutral pH conditions are discussed.

Hydrated Zinc Borates and Their Industrial Use.

Zinc borates are important chemical products having industrial applications as functional additives in polymers, bio-composites, paints and ceramics. Of the thirteen well documented hydrated binary zinc borates, Zn[B3O4(OH)3] (2ZnO∙3B2O3∙3H2O) is manufactured in the largest quantity and is known as an article of commerce as 2ZnO∙3B2O3∙3.5H2O. Other hydrated zinc borates in commercial use include 4ZnO∙B2O3∙H2O, 3ZnO∙3B2O3∙5H2O and 2ZnO∙3B2O3∙7H2O. The history, chemistry, and applications of these and other hydrated zinc borate phases are briefly reviewed, and outstanding problems in the field are highlighted.

Structure and Properties of Sodium Enneaborate, Na2[B8O11(OH)4]·B(OH)3·2H2O.

Millions of tons of sodium borates are used annually by global industries in diverse applications important to modern society. The Na2O-B2O3-H2O phase diagram in the 0-100 °C temperature range contains 13 unique hydrated crystalline sodium borates, including five important industrial products. Structures were previously reported for each of these except for that having the highest boron content, known as sodium enneaborate, Na4B18O29·11H2O or 2Na2O·9B2O3·11H2O (1). Here we report the single-crystal structure of 1, revealing the structural formula Na2[B8O11(OH)4]·B(OH)3·2H2O, and describe some of its properties and relationships to other sodium borates. The structure of 1 features linear polyborate chains composed of the repeating [B8O11(OH)4]2- fundamental building blocks with interstitial water and boric acid molecules integrated by extensive H bonding. Interstitial sodium cations occur in groups of four with interatomic distances of 3.7830(6) and 3.7932(8) Å. Upon heating, 1 initially becomes amorphous and then crystallizes as α-Na2B8O13 along with amorphous B2O3. Notably, α-Na2B8O13 contains octaborate fundamental building blocks that are topologically equivalent to those in 1. Compound 1 crystallizes in the monoclinic space group P21/n with a = 10.2130(8) Å, b = 12.940(1) Å, c = 12.457(1) Å, ß = 93.070(2)°, V = 1644.0(2) Å3, and Z = 2.

Solid-State Synthesis and Structure of the Enigmatic Ammonium Octaborate: (NH4)2[B7O9(OH)5]·3/4B(OH)3·5/4H2O.

The compound known since the 19th century as ammonium octaborate was structurally characterized revealing the ammonium salt of the ribbon isomer of the heptaborate anion, [B7O9(OH)5](2-), with boric acid and water molecules. Of composition (NH4)2B7.75O12.63·4.88H2O, it approximates the classical ammonium octaborate composition (NH4)2B8O13·6H2O and has the structural formula {(NH4)2[B7O9(OH)5]}4·3B(OH)3·5H2O. It spontaneously forms at room temperature in solid-state mixtures of ammonium tetraborate and ammonium pentaborate. It crystallizes in the monoclinic space group P21/c with a = 11.4137(2) Å, b = 11.8877(2) Å, c = 23.4459(3) Å, ß = 90.092(1)°, V = 3181.19(8) Å(3), and Z = 2 and contains well-ordered ammonium cations and [B7O9(OH)5](2-) anions and disordered B(OH)3 and H2O molecules linked by extensive H bonding. Expeditious solid-state formation of the heptaborate anion under ambient conditions has important implications for development of practical syntheses of industrially useful borates.

Synthesis and structure of a new heptaborate oxoanion isomer: B7O9(OH)5(2-).

The nonmetal borate [H3N(CH2)7NH3][B7O9(OH)5].H2O (1) was prepared via a neat reaction of 1,7-diaminoheptane with excess boric acid under mild nonhydrothermal conditions. Single-crystal X-ray characterization of 1 revealed a new isomer of the heptaborate anion, B7O9(OH)5(2-). The heptaborate anion in 1 is comprised of four fused (BO)3 rings sharing three four-coordinate boron atoms and a single three-coordinate oxygen atom. This anion is a structural isomer of another recently described heptaborate anion, consisting of a chain of three (BO)3 rings. Compound 1 crystallized in the triclinic space group P1 with a=9.3266(17) A, b=10.1222(19) A, c=10.847(2) A, alpha=89.422(2) degrees, beta=82.349(2) degrees, gamma=75.158(2) degrees, V=980.7(3) A3, and Z=2.

Crystalline alcoholamine borates and the triborate monoanion.

The triborate and pentaborate compounds 3-hydroxy-2,2-dimethylpropylammonium triborate(1+), [HOCH2C(CH3)2NH3][B3O3(OH)4] (1), and 2-hydroxyethylammonium pentaborate(1-), [HOCH2CH2NH3][B5O6(OH)4].H2O (2), were prepared by crystallization from concentrated aqueous boric acid solutions containing the respective alcoholamines at a boric acid-alcoholamine mole ratio of 3.33:1.00. Compound 1 crystallized in the triclinic space group P1 with a = 5.9595(9) A, b = 6.3024(9) A, c = 15.594(2) A, alpha = 91.218(2) degrees , beta = 91.138(2) degrees , gamma = 118.034(2) degrees , V = 516.56(13) A (3), and Z = 2; 2 crystallized in the monoclinic space group P2 1/ n with a = 11.2469(8) A, b = 9.5091(6) A, c = 11.5422(8) A, beta = 90.175(1) degrees , V = 1234.41(15) A (3), and Z = 4. Compound 1 contains a rare example of a structurally characterized hydroxyl-hydrated triborate monoanion. Comparisons are made with other known examples of this anion.

(Trimethylsilyl)phosphine as a Versatile Reagent for Syntheses of New 4-Sila- and 4-Phosphaphosphorinanes.

(Trimethylsilyl)phosphine (Me(3)SiPH(2)) undergoes radical P-H bond addition to vinylphosphines and -silanes to form new 4-phospha- and 4-silaphosphorinanes [vinyl reagent]: [PhP(CH=CH(2))(2)], PhP(C(2)H(4))(2)PSiMe(3) diastereomers (9A/9B); [Et(2)NP(CH=CH(2))(2)], Et(2)NP(C(2)H(4))(2)PSiMe(3) (11); [Me(2)Si(CH=CH(2))(2)], Me(2)Si(C(2)H(4))(2)PSiMe(3) (14); [Si(CH=CH(2))(4)], (CH=CH(2))(2)Si(C(2)H(4))(2)PSiMe(3) (16) and [Me(3)SiP(C(2)H(4))(2)](2)Si (17). Reactions are accompanied by formation of only small quantities of the Markovnikov addition product phospholanes. Methanolysis of the new silylphosphines yields PhP(C(2)H(4))(2)PH diastereomers (10A/10B), Me(2)Si(C(2)H(4))PH (15), (CH=CH(2))(2)Si(C(2)H(4))(2)PH (18), and [HP(C(2)H(4))(2)](2)Si (19). Stepwise methanolysis of 11 yields the phosphorinanes Et(2)NP(C(2)H(4))(2)PH (12) and MeOP(C(2)H(4))(2)PH (13). Oxidation of 15 and 14 with O(2) or O(2)/H(2)O, respectively, yields the phosphine oxide Me(2)Si(C(2)H(4))(2)P(O)H (20) and the phosphinic acid Me(2)Si(C(2)H(4))(2)P(O)OH (21). New compounds were characterized by spectral ((31)P, (1)H, and (13)C NMR, IR, and MS) data. 21 was further characterized by a single-crystal X-ray analysis: monoclinic, P2(1)/c, a = 10.416(2) Å, b = 6.817(1) Å, c = 14.237(3) Å, beta = 106.32(2) degrees, Z = 4, V = 970.3(3) Å(3). The ring of 21 adopts a chair conformation with the P=O bond in an equatorial position. From spectral data, tentative isomeric and conformational structural assignments are made for the new phosphorinanes in solution.