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

Abstract

Abstract 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) A, b =10.447(1) A, c =18.538(2) A) from synchrotron powder diffraction data using a combination of direct methods and molecular modelling techniques. The structure, with the chemical formula [Ga 20 P 16 O 64 F 8 (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. 19 F 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°C.