Synthesis, characterization and structure determination of a new fluorogallophosphate (Mu-5) prepared in the presence of 1,4,8,11-tetraazacyclotetradecane

A new fluorinated gallophosphate has been synthesized in aqueous medium using the macrocycle 1,4,8,11-tetraazacyclotetradecane (cyclam) as the organic species. The material has been characterized using elemental analysis, X-ray diffraction and solid state NMR spectroscopy. Its structure was determined in the space group Pbcn (a = 13.373(2) Angstrom, b = 10.447(1) Angstrom, c = 18.538(2) Angstrom) from synchrotron powder diffraction data using a combination of direct methods and molecular modelling techniques. The structure, with the chemical formula [Ga20P16O64F8(OH)(4)] . 4C(10)H(24)N(4) per unit cell, consists of gallophosphate sheets of double 4-ring (D4R) units connected to one another to form 10-rings. Each D4R contains a fluoride ion, and each of the two Ga atoms in the D4R not connected to a neighboring D4R also has a terminal F- or OH- ion in its coordination sphere. F-19 solid-state NMR spectroscopy confirmed the presence of two types of fluoride ions. The sheets are connected to one another in an unusual manner via a Ga-cyclam complex. The cyclam molecule of this complex is further stabilized by hydrogen bonds to two terminal F- or OH- ions. All P atoms are tetrahedrally coordinated and 4-connected (i.e. form oxygen bridges to four Ga atoms), whereas the Ga atoms are 5- and 6-coordinated but only 2-, 3- and 4-connected to P atoms of the framework. This new gallophosphate exhibits low thermal stability, and becomes completely amorphous upon calcination at 350 degrees C. (C) 1998 Elsevier Science B.V. All rights reserved.