A templated borate polymer from boric acid ‘flux’ synthesis: [Cu(en)2][B7O13H3]n

Molten boric acid ‘flux’ synthesis has been used to prepare pure [Cu(en)2][B7O13H3]n 1 in a 70% yield by heating Cu(NO3)2·3H2O, en and H3BO3 in a 1:6:13 ratio at 180°C for 3 days. Compound 1 is triclinic P-1, a=7.846(1), b=8.285(1), c=15.477(1) Å, α=99.14(1), β=96.05(1), γ=117.02(1)°, V=866.7 Å3. The coppers are square planar with two trans (en) chelates (Cu–N=2.00–2.03 Å). They have only weak axial interactions to hydroxyborates (Cu–O=2.50–2.57 Å). The [B7O13H3]n polymer component exists as anionic 2-D sheets, that associate through O–H–O hydrogen bond pairs to create an open 3-D shell about the structure-directing [Cu(en)2] counter-ions.