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Beryllium fluoride has distinctive optical properties. In the form of fluoroberyllate glass, it has the lowest refractive index for a solid at room temperature of 1.275. Its dispersive power is the lowest for a solid at 0.0093, and the nonlinear coefficient is also the lowest at 2 × 10 −14.
The Be–F bond length is between 145 and 153 pm.The beryllium is sp 3 hybridized, leading to a longer bond than in BeF 2, where beryllium is sp hybridized. [11] In trifluoroberyllates, there are actually BeF 4 tetrahedra arranged in a triangle, so that three fluorine atoms are shared on two tetrahedra each, resulting in a formula of Be 3 F 9.
The fluorine–fluorine bond of the difluorine molecule is relatively weak when compared to the bonds of heavier dihalogen molecules. The bond energy is significantly weaker than those of Cl 2 or Br 2 molecules and similar to the easily cleaved oxygen–oxygen bonds of peroxides or nitrogen–nitrogen bonds of hydrazines. [8]
Structure of beryllium fluoride (BeF 2), a compound with a linear geometry at the beryllium atom. The linear molecular geometry describes the geometry around a central atom bonded to two other atoms (or ligands) placed at a bond angle of 180°.
The structure of the tetrafluoroborate anion, BF − 4. Tetrafluoroborate is the anion BF − 4. This tetrahedral species is isoelectronic with tetrafluoroberyllate (BeF 2− 4), tetrafluoromethane (CF 4), and tetrafluoroammonium (NF + 4) and is valence isoelectronic with many stable and important species including the perchlorate anion, ClO −
The structure of dimethylberyllium. The coordination number of Be in organoberyllium compounds ranges from two to four. [4] Dimethylberyllium and dimethylmagnesium adopts the same structure. [5] Diethylberyllium, however, does not structurally resemble diethylmagnesium (which has the same structure as dimethylmagnesium). [6]
The reaction with lithium hydride (in which the hydride ion is the Lewis base), forms sequentially LiBeH 3 and Li 2 BeH 4. [3] The latter contains the tetrahydridoberyllate(2-) anion BeH 2− 4. Beryllium hydride reacts with trimethylamine, N(CH 3) 3 to form a dimeric adduct with bridging hydrides. [11]
The reaction commences with the formation of the aquo adduct, H 2 O−BF 3, which then loses HF that gives fluoroboric acid with boron trifluoride. [22] 4 BF 3 + 3 H 2 O → 3 H[BF 4] + B(OH) 3. The heavier trihalides do not undergo analogous reactions, possibly due to the lower stability of the tetrahedral ions [BCl 4] − and [BBr 4] −.