Bis(μ-diisopropylhydoxylaminato)-κ2 O:N;κ2 O:O-bis[(diisopropylhydoxylaminato-κO)beryllium]

The title compound, [Be2(C6H14NO)4], was prepared from a solution of BeCl2 in diethyl ether and two equivalents of O-lithiated N,N-diisopropylhydoxylamine. The molecular structure is composed of a dinuclear unit forming a central five-membered planar Be—O—Be—O—N ring (sum of internal angles = 540.0°; r.m.s. deviation from planarity = 0.0087 Å). Both Be atoms show the unusual coordination number of three, with one Be atom coordinated by three O atoms and the other by two O atoms and one N atom, both in distorted trigonal–planar environments. The Be—O distances are in the range 1.493 (5)–1.600 (5) Å and the Be—N distance is 1.741 (5) Å.


Related literature
known up to date (Ullrich, 2007). Depending on the tendency of M to form ionic, covalent, or coordinative bonds to O and N atoms of the hydroxyl amine moiety, and also depending on the valency and the size of M, a comparably large variety of structure motifs and compositions is found. N,N-diisopropylhydoxylamine is probably the sterically most hindered hydroxylamine which is accessible. In continuation of our studies on Be coordination compounds (Berger, Hartmann et al., 2001;Berger et al., 2011;Berger, Schmidt et al., 2001;Dressel et al., 2003;Neumüller & Dehnicke, 2010), it was of special interest to investigate the reaction products formed from Be 2+ and deprotonated N,Ndiisopopylhydoxylamine.
In the dinuclear unit of the title compound, Be 2 (C 3 H 7 NO) 4 , the Be 2+ cations are bonded to O atoms and one N atom of the hydroxylamine moieties. The mononuclear subunit Be(ON i Pr 2 ) 2 is connected via an additional Be-O bond to an identical subunit. In addition, a Be-N bond to one of the four hydroxylamine moieties is observed. In this way, each of the two Be 2+ cations attains a threefold coordination. (Fig. 1) Such a coordination number is rarely found in Becontaining compounds and usually only in sterically demanding environments. Another striking feature of the molecular arrangement of the title compound is the planarity of the central Be-O-Be-O-N five-membered ring. This is underlined by the sum of 540.0° of the internal angles in the ring and a r.m.s. deviation from planarity of only 0.0087 Å.
Despite the planarity, no crystallographically imposed symmetry is found in the molecular unit of Be 2 (C 3 H 7 NO) 4 .

Experimental
A suspension of 1.282 g (4 mmol) Li(ON i Pr 2 ) in 15 ml of dry diethyl ether was slowly dropped to a solution of 159 mg BeCl 2 (2 mmol) in 5 ml diethyl ether. The reaction mixture was stirred for 6 h at room temperature and filtered using a syringe equipped with a Whatmann glass filter. The clear solution was reduced in vacuo to about 15 ml and stored at 243 K for two weeks. Clear colorless block-shaped crystals were collected from the solution under an argon atmosphere. The material is extremely water-and moist-sensitive and must be handled under inert gas.

Refinement
All H atoms were treated as riding with C-H distances of 0.97 (C-H), 0.98 (CH 3 ), and U iso (H) = 1.2 U eq (C) [1.5 U eq for methyl hydrogen atoms]. Riding methyl hydrogen atoms were allowed to rotate freely during refinement.

Figure 1
The dinuclear molecular unit of the title compound. Atoms are displayed with displacement ellipsoids at the 10% probability level. Hydrogen atoms have been omitted for clarity.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.