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By a selective exchange of ligand Br by Cl, a series of nonstoichiometric bromo-chloro-pyridine- molybdenum(III) octahedral compounds of the type (cat)[MoBraCl(4-a)py2] (cat = pyH, a = 3–1 (1, 4, 7)); cat = [(C2H5)3NH], a = 2.744 (2); cat = Rb, a = 2.278 (5); cat =[(C6H5)4)As], a = 1.258 (8) and [MoBraCl(3–a)py3] (a = 2–1 (3, 6)) have been prepared and characterized. Owing to great similarity of the powder diffraction patterns and IR spectra of compounds mer- [MoBraCl(3-a)py3] (a = 3–0) with the known monoclinic modification in the space group P21/c and compounds [MoBraCl(3-a)py3] (a = 2-1 (3, 6)), the same type of crystal lattice was confirmed. Isostructurality was observed also for the orthorhombic trans-(pyH)[MoBr4py2]](Pnma) and compounds 1 and 4, while compound 7 is isostructural to trans-(pyH)[MoCl4py2]. X-ray crystallographic analyses of 2, 5 and 8, obtained by recrystallization of (pyH)[MoBraCl(4-a)py2] (a = 3–1) with different cations, were performed. In these compounds, MoIII is octahedrally coordinated with four halogenido ions at distances 2.4953(6)–2.5920(10) Å and two pyridine molecules at distances 2.195(4)-2.220(4) Å. Trans oriented pyridine rings in compounds 5 and 8 are co-planar, while deviation from co-planarity was noticed for compound 2 (8.9(3)°). The stoichiometry of four coordinated Br and Cl atoms in these compounds is not ideal, since the structure analysis results for 2, 5 and 8 show a mixed occupancy of crystallographic sites; thus, refined population parameters for both atoms (Br and Cl) were calculated., Selektivnom zamjenom bromovoga liganda klorovim dobijena je i karakterizirana serija nestehiometrijskih bromo-kloro-piridin-MoIII kompleksa tipa (cat)[MoBraCl(4–a)py2] (cat = pyH, a = 3–1 (1, 4, 7); cat = [(C2H5)3NH], a = 2.744 (2); cat = Rb, a = 2.278 (5); cat = [(C6H5)4As], a = 1.258 (8)) i [MoBraCl(3–a)py3] (a = 2–1 (3, 6)). Uslijed velike sličnosti difraktograma praha i IR spektara spojeva mer-[MoBraCl(3–a)py3] (a = 3–0) poznate monoklinske modifikacije u prostornoj grupi P21/c i spojeva [MoBraCl(3–a)py3] (a = 2–1 (3, 6)), potvr|en je isti tip kristalne re{etke. Opa`ena je izostrukturnost rompskoga trans-(pyH)[MoBr4py2] (Pnma) i spojeva 1 i 4, dok je spoj 7 izostrukturiran s trans-(pyH)[MoCl4py2]. Načinjena je rentgenska strukturna analiza spojeva 2, 5 i 8 dobijenih prekristalizacijom (pyH)[MoBraCl(4–a)py2] (a = 3–1) s različitim kationima. U tim je spojevima MoIII oktaedarski koordiniran s četiri halogenidna iona na udaljenostima 2.4953(6)–2.5920(10) Å i dvije molekule piridina na udaljenostima 2.195(4)–2.220(4) Å. Trans orijentirani piridinski prstenovi u spojevima 5 i 8 su koplanarni dok je kod spoja 2 ustanovljena devijacija od koplanarnosti (8.9(3)°). Strukturnom analizom utočnjeni su faktori zauzetosti četiri koordinirana atoma (Br, Cl) u spojevima 2, 5 i 8. Na|eno je da su navedeni kristalografski položaji zauzeti atomima Cl i Br u nestehiometrijskome omjeru.

ARKIVOC: vol. 2001, no. 5, (issn) 1551-7012, (dlps) 5550190.0002.511, This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 License. Please contact mpub-help@umich.edu to use this work in a way not covered by the license.

ARKIVOC: vol. 2001, no. 5, (issn) 1551-7012, (dlps) 5550190.0002.511, This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 License. Please contact mpub-help@umich.edu to use this work in a way not covered by the license.

In the last few years considerable effort has been directed at the targeted synthesis of zeolites and zeolite-like microporous materials with predetermined physical and catalytic properties. With new computational techniques, it has become possible to design templates for the synthesis of specific microporous structures with desired pore siže and connectivities. With regard to zeolite-like materials, much attention has been focused on transition metal containing systems, like zincosilicates, titanosilicates and various metalloaluminophosphates with a potential to generate specific redox conditions, in addition to Br0nsted and Lewis active catalytic centres. Experimental determination of subtle structural features such as the nature and position of the catalytically active metal sites, and the location, orientation and disorder of templates, metals or complexes within the microporous hosts has become possible using new characterisation techniques, mostly based on X-ray diffraction and the use of synchrotron and neutron radiation sources. In situ studies of the kinetics of nucleation, crystal growth and phase transitions or catalyst activation and operation at elevated temperatures have remarkably benefited from the new high-flux and well-collimated third-generation synchrotron radiation sources, and from the advances in the X-ray detector design and data handling.

In the last few years considerable effort has been directed at the targeted synthesis of zeolites and zeolite-like microporous materials with predetermined physical and catalytic properties. With new computational techniques, it has become possible to design templates for the synthesis of specific microporous structures with desired pore siže and connectivities. With regard to zeolite-like materials, much attention has been focused on transition metal containing systems, like zincosilicates, titanosilicates and various metalloaluminophosphates with a potential to generate specific redox conditions, in addition to Br0nsted and Lewis active catalytic centres. Experimental determination of subtle structural features such as the nature and position of the catalytically active metal sites, and the location, orientation and disorder of templates, metals or complexes within the microporous hosts has become possible using new characterisation techniques, mostly based on X-ray diffraction and the use of synchrotron and neutron radiation sources. In situ studies of the kinetics of nucleation, crystal growth and phase transitions or catalyst activation and operation at elevated temperatures have remarkably benefited from the new high-flux and well-collimated third-generation synchrotron radiation sources, and from the advances in the X-ray detector design and data handling.

Ammonium hydrogen maleate, NH4+C4Ha04- crystallizes in the orthorhombic system with a = 0.4616(1), b = 0.8085(2), c = 1.6410(5) nm, Z = 4 in space group Pbcm, and is isostructural with the analogous potassium salt. The crystal structure has been refined from diffracton1eter data to conventional R and Rw of 0.052 and 0.065 for 690 reflexions [I> 3 a (I)]. Minor changes in the crystal struc-· ture were observed due to formation of N-H · · · 0 hydrogen bonds.

The axial diadducts (pyH)2[Mo2(02CCHa)4X2], (py =pyridine, X = Br, I) were isolated from solutions of dimolybdenum tetra- • acetate in HX 1 : 1 after addition of pyridinium halide. (pyH)2 [Mo2(02CCHa)4Br2] (A) crystallizes in the space group I4/m with a= 0.9746(2) nm, c = 1.3948(2) nm, V = 1.32484 nma and Z = 2. Two modifications of the iodide analog were isolated. Triclinic modification (B) crystallizes in the space group Pl with a= 1.0016(1) nm, b = 1.0092(2) nm, c = 1.6325(2) nm, a = 74.75(1)0 , fJ = 71.38(2) 0 , r = 61.12(2)0 , V = 1.35747 nm3 mid Z = 2; tetragonal modification (C) in the space group I4/mcm with a = 1.3086(1) nm, c = 1.4712(1) nm, V = 2.51933 nm3 and Z = 4. The Mo - X (X = Br, I) distances, found in anions [Mo2(02CCH3)4X2]2-, 287.9(3) pm in A, 326.2(1) pm and 329.9(1) pm in B, and 320.4(1) pm in C are quite long, indicating only weak axial coordination. Accordingly, the Mo - Mo distances 210.2(1) pm in A, 210.3(1) pm in B, and 210.2(1) pm in C are only slightly longer than the Mo - Mo distance of 209.3(1) pm found in Mo2(02CCHa)4.

Ammonium hydrogen maleate, NH4+C4Ha04- crystallizes in the orthorhombic system with a = 0.4616(1), b = 0.8085(2), c = 1.6410(5) nm, Z = 4 in space group Pbcm, and is isostructural with the analogous potassium salt. The crystal structure has been refined from diffracton1eter data to conventional R and Rw of 0.052 and 0.065 for 690 reflexions [I> 3 a (I)]. Minor changes in the crystal struc-· ture were observed due to formation of N-H · · · 0 hydrogen bonds.

The axial diadducts (pyH)2[Mo2(02CCHa)4X2], (py =pyridine, X = Br, I) were isolated from solutions of dimolybdenum tetra- • acetate in HX 1 : 1 after addition of pyridinium halide. (pyH)2 [Mo2(02CCHa)4Br2] (A) crystallizes in the space group I4/m with a= 0.9746(2) nm, c = 1.3948(2) nm, V = 1.32484 nma and Z = 2. Two modifications of the iodide analog were isolated. Triclinic modification (B) crystallizes in the space group Pl with a= 1.0016(1) nm, b = 1.0092(2) nm, c = 1.6325(2) nm, a = 74.75(1)0 , fJ = 71.38(2) 0 , r = 61.12(2)0 , V = 1.35747 nm3 mid Z = 2; tetragonal modification (C) in the space group I4/mcm with a = 1.3086(1) nm, c = 1.4712(1) nm, V = 2.51933 nm3 and Z = 4. The Mo - X (X = Br, I) distances, found in anions [Mo2(02CCH3)4X2]2-, 287.9(3) pm in A, 326.2(1) pm and 329.9(1) pm in B, and 320.4(1) pm in C are quite long, indicating only weak axial coordination. Accordingly, the Mo - Mo distances 210.2(1) pm in A, 210.3(1) pm in B, and 210.2(1) pm in C are only slightly longer than the Mo - Mo distance of 209.3(1) pm found in Mo2(02CCHa)4.