Trigonal planar shape defined

Available structural details for these silicates, and for the wide range of other known species containing Mn" and silicate, are summarized in Table 23. Coordination numbers four (tetrahedral), five (both square pyramid and trigonal bipyramid and in-between structures), six (mainly octahedral and distorted, but including one trigonal prism), seven (of various shapes) and eight (dodecahe-dra and distorted rhombohedra) all are defined and there is evidence for three-coplanar in a zeolite the hydrated form is five-coordinate (3 x 2.28 A and 2 x 2.05 A) but, on dehydration of this Mn-exchanged zeolite, the solid contains planar three-coordinate Mn with Mn—O = 2.11 A, ... 

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