The borotellurates are heteropoly anion compounds which have tellurate groups attached to boron atoms. The ratio of tellurate to borate reflects the degree of condensation. In [TeO4(BO3)2]8- the anions are linked into a chain. In [TeO2(BO3)4]10− the structure is zero dimensional with isolated anions. These arrangements of oxygen around boron and tellurium can have forms resembling silicates. The first borotellurates to be discovered were the mixed sodium rare earth compounds in 2015.
The tellurate is of the form TeO6 in an octahedral arrangement. The borate is in the form BO3, with two oxygen atoms shared with two tellurate TeO6 groups.
Related compounds include boroantimonates, galloborates, borogermanates, borophosphates, boroselenates, boroselenites, and borosulfates.
Formation Borotellurates are formed by heating boric acid, and tellurium dioxide, with metal carbonates or oxides at over 800 °C. Lower temperatures can be used with a flux like potassium carbonate.
Reactions When heated to around 800 °C the borotellurates decompose by emitting TeO3 vapour and form a metal borate or metal tellurite.
List chemmwcrystal system space groupunit cell ÅvolumedensitycommentreferencesRb3BaTeB7O15837.02monoclinicP21/na=9.102 b=6.409 c=25.794 β=97.278 Z=41492.63.725actually this is a telluriteSr5TeO2(BO3)4832.94tetragonalP4/mnca= 7.6005 c=10.401 Z=2600.824.604colourless; birefringence is 0.048 at 1064 nmNa2Y2TeO4(BO3)2533.02monoclinicP21/ca=6.3073, b=9.9279, c=6.7219; β=104.26°; Z=2407.944.339barium tellurium borateBa4B8TeO191067.44monoclinicCca=11.512 b=6.667 c=19.700 β=105.734 Z=41455.34.872double layers; SHG 1×KH2PO4Ba2Mg2TeB2O10632.52orthorhombicCmcaa=6.177 b=10.383 c=12.956 Z=4830.95Na2Dy2TeO4(BO3)2680.20monoclinicP21/ca=6.3089, b=9.9808, c=6.7489; β=104.394°; Z=2411.625.488decompose 842.1Na2Ho2TeO4(BO3)2685.06monoclinicP21/ca=6.3060, b=9.9360, c=6.7339; β=104.230°; Z=2408.985.563decompose 844.2Na2Er2TeO4(BO3)2689.72monoclinicP21/ca=6.2964, b=9.9056, c=6.7089; β=104.110°; Z=2405.815.645decompose 850.5Na2Tm2TeO4(BO3)2693.06monoclinicP21/ca=6.2801, b=9.8594, c=6.6918; β=104.010°; Z=2401.895.727decompose 852.0Na2Yb2TeO4(BO3)2701.28monoclinicP21/ca=6.2631, b=9.8269, c=6.6741; β=103.972°; Z=2398.625.843decompose 871.0Na2Lu2TeO4(BO3)2705.14monoclinicP21/ca=6.2588, b=9.7998, c=6.6539; β=103.714°; Z=2396.485.907decompose 878.5Pb2Mg2TeB2O10772.22orthorhombicCmcaa=6.055 b=10.300 c=12.521 Z=4780.97
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