Acta Chim. Slov. 2001, 48, 147-158. 147 STRUCTURE REFINEMENT OF ZINC CONTAINING GALLOPHOSPHATE WITH THE ULM-5 STRUCTURE ' Maja Mraka, Madeleine Helliwellb, Alenka Ristić3, Nataša Zabukovec Logara, and Venčeslav Kaučičac ^National Institute of Chemistry, Ljubljana, Slovenia, University of Manchester, England, and ^University of Ljubljana, Slovenia f This paper is dedicated to the late Professor Drago Kolar Received 05-02-2001 Abstract A zinc containing microporous gallophosphate with the ULM-5 structure has been hydrothermally synthesised in the presence of fluoride ions and 1,6-diaminohexane as a structure-directing agent. It was characterised using single-crystal X-ray diffraction (R=5.3%) and EDAX elemental analysis. The compound crystallises in the orthorhombic space group P2|2|2 with unit cell parameters a = 24.814(13) Â, b = 18.458(5) Â, c = 10.2575(18) Â. EDAX analysis revealed up to 6(2) wt.% of zinc in the structure. The examination of Ga-O bond distances showed that zinc is preferentially located on one of the 5-coordinated gallium sites. No zinc was found on the extra-framework positions. The two 1,6-diaminohexane template molecules are well defined. The nitrogen atoms on both template molecules are ordered and hydrogen bonded to framework oxygen and fluorine atoms. Three of the twelve carbon atoms are disordered, each over two sites. Introduction Molecular sieves are crystalline materials with open framework structures, among which zeolites are the most representative group. They are widely used in gas separations, ion exchange and catalysis. Recently, many new zeolite-like structures such as aluminophosphates, ' gallophosphates ' and zincophosphates with new possible applications have been reported. Compared to zeolites, aluminophosphates and gallophosphates possess more complicated framework structures, which result from a variety of coordination possibilities of aluminium and gallium atoms. The introduction of small amounts of transition-metal atoms such as Co, Mn, Ni etc. on the aluminium or gallium framework sites create negative charges in otherwise neutral frameworks, which make this microporous materials potential solid-acid catalysts. ' M. Mrak, M. Helliwell, A. Ristić, N. Zabukovec Logar, V. Kaučič: Structure Refinement of Zinc... 148 Acta Chim. Slov. 2001, 48, 147-158. The amounts of incorporated metals depend on the structure type and chemical composition of the specific phosphate. Several papers about the synthesis, characterisation and catalytic properties of gallophasphates have been published until now, with the emphasis on the most well-known open-framework gallophasphate cloverite with supercages of 30 Â diameter and free aperture of 13.2 Â.9 However, few successful attempts have been reported on the incorporation of foreign atoms into framework or extra-framework sites of cloverite or other microporous gallophasphates. The first two examples were CoGaPO-LAU and CoGaPO-LTA,10 which were isolated from GaPC^ gels containing small amounts of cobalt. Low contents of heterometals (Zn, Si, Ti, Co, Ni, Fe and Mg) in the cloverite structure type have been reported, but have not yet been quantified. ' ' ULM-5 is a large pore microporous oxofluorinated gallophosphate with chemical composition of Gai6(P04)i4(HP04)2(OH)2F7, which was first synthesized and characterized in 1994 by Loiseau Ferey. It crystallises in an orthorhombic space group P22i2i with unit cell parameters a = 10.252(2) Â, b = 18.409(4) Â, and c = 24.639(7) Â. The three-dimensional network in which gallium atoms are four-, five-and also six-coordinated, contains 16-, 8- and 6-member ring channels. The diprotonated 1,6-diaminohexane molecules are located in the 16-member ring channels, whose free aperture is 12.20 x 8.34 Â. Here we report the synthesis and structure of a zinc containing gallophosphate with the ULM-5 structure type. Experimental Synthesis The synthesis was carried out hydrothermally in Teflon-lined autoclaves under autogeneous pressure. Gallium(III) oxide, orthophosphoric acid, and zinc(II) acetate were used as gallium, phosphorous and zinc sources (Table 1). Higher molar amount of zinc led to the formation of an unidentified zinc gallophosphate. M. Mrak, M. Helliwell, A. Ristić, N. Zabukovec Logar, V. Kaučič: Structure Refinement of Zinc... Acta Chim. Slov. 2001, 48, 147-158. 149 Table 1. Reaction gel molar composition Sample P^ Ga203 ZnÖ HF DAH* H^Ö ZnULM-5__________1________0.98 0.02 2________1_________100 *DAH=1,6-diaminohexane The reaction gel was prepared as follows: gallium(III) oxide and a solution of zinc(II) acetate were successively added to stirred diluted orthophosphoric acid solution. Then a dropwise addition of diluted HF and the templating agent, 1,6-diaminohexane was performed. The system was thoroughly stirred at room temperature, each time prior to the addition of the next component. The resulting gel was aged for 2 hours in the air and then the gel was loaded in Teflon-lined stainless steel autoclaves followed by heating at 170 °C under autogenous pressure for 24 hours. Table 2. Weight amounts of reagents used in synthesis gels for ZnULM-5 (g) Zn(CH3COO)2-2H20 Ga203 H3P04 H2N-(CH2)6-NH2 HF H20 0.09 3.92 4.92 2.48 2.21 36.39 After crystallisation, the autoclaves were cooled down to room temperature and the products were washed and dried at 80-100 °C. The pH of the initial gel raised from 1.5 before reaction to 4 at the end of the reaction. All masses of the reactants used are shown in Table 2. Characterisation A transparent crystal of 0.45 x 0.07 x 0.05 mm size was mounted on a glass fibre for room-temperature intensity data collection on a rotating-anode Rigaku AFC5R diffractometer with graphite-monochromated CuKa radiation (1.5418 Â). The orthorhombic cell constants were determined by least-squares refinement on the basis of 25 reflections. Lorentz, polarisation and empirical absorption corrections based on azimuthal scans were applied to the intensity data. Further details of the data M. Mrak, M. Helliwell, A. Ristić, N. Zabukovec Logar, V. Kaučič: Structure Refinement of Zinc... 150 Acta Chim. Slov. 2001, 48, 147-158. collection and reduction are contained in Table 3. Neutral atomic scattering factors were used for all atoms. The elemental analysis was carried out on five single crystals using an ED AX (energy dispersion analysis by X-ray) analytical system (TRACOR EDX), attached to a scanning electron microscope (JEOL JXA-840A). The amount of Zn varied from 3(2) to 6(2) wt. %. The variations in the zinc amount reflect an irregular distribution of zinc in the crystals. Table 3. Crystallographic parameters for ZnULM-5 Empirical formula Formula weight Crystal colour, habit Crystal system a(k) *(A) c(A) V(A3) z Space group Dc(Mgm-3) hkl data limits *-t/max^ ) 3 standard reflections for intensity change Intensity decay (%) Rim p(CuKa) (mm-1) Absorption correction T T 1 min? l max Total data Observed data (T>2cr(T)) Parameters R (on F2) Rw (on F2) Apmax (eA"3) Apmin (eA-3) C,2H36F3 5Ga7N4036P8Zn 1675.1 transparent, needle orthorhombic 24.814(13) 18.458(5) 10.2575(18) 4698(3) 4 P2,2,2 2.380 0