![]() ![]() Chromium(III) tribromide hexahydrate was obtained from Aldrich Chemical Co. Īll chemicals were reagent-grade materials and used without further purification. It is confirmed that the 3+ moiety in compound (I) may be used as a potential receptor for Cr 2O 7 2− anions due to its high positive charge and the large number of hydrogen-bond donor groups of its six urea ligands. The O B-Cr B-O B bond angles in the two tetrahedral CrO 4 groups are between 105.21 (8) and 110.98 (10)°, indicating slight angular distortions. The Cr1 B-O7 B-Cr2 B bridging angle in the complex anion is 130.26 (10)°. In the structure of compound (I) it is in a nearly staggered conformation, whereas in K 2Cr 2O 7, the tetrahedral CrO 4 groups are in an almost eclipsed conformation (Brandon & Brown, 1968 ). It is of interest to compare the conformation of Cr 2O 7 2− with that found in other ionic crystals. The isolated Cr 2O 7 2− and Br − anions remain outside the coordination sphere of the cation. The C=O bonds are slightly longer than that in free non-coordinating urea (Guth et al., 1980 ). They are also comparable with the corresponding lengths determined for trans-ClO 4 (cyclam = 1,4,8,11-tetraazacyclotetradecane nic- O = O-coordinating nicotinate Choi, 2009 ), cis-ClO 4 (ox = oxalate Choi et al., 2004 a ), cis-(ClO 4) 2♰.5H 2O (acac = acetylacetonate Subhan et al., 2011 ), cis-NO 2 (Choi et al., 2004 b ) or cis- (edda = ethylenediamine- N,N'-diacetate Choi et al., 2012 ). The Cr A-O A bond lengths involving the urea ligand are in good agreement with the value of 1.9630 (17) Å for (BF 4) 3 (Górska et al., 2014 ). The Cr III ion is coordinated by six urea ligands through oxygen atoms with Cr A-O A bond lengths ranging from 1.9534 (13) to 1.9776 (12) Å, and with O A-Cr A-O A bond angles in the range 85.10 (5)–92.95 (5)°. Displacement ellipsoids are drawn at the 50% probability level. The molecular structures of the components in compound (I), showing the atom-numbering scheme. Within our broader study of Cr III complexes as industrial materials (Choi & Lee, 2009 Choi & Moon, 2014 Moon & Choi, 2015 ), we report herein the preparation and crystal structure of (Cr 2O 7)Br ![]() This complex crystallizes in the monoclinic space group P2/ n with four formula units in a cell of dimensions a = 13.782 (2), b = 10.393 (1), c = 17.794 (3) Å and β = 94. H 2O has been reported (Bondar et al., 1984 ).Previously, the crystal structure of (Cr 2O 7)Cl It was found that 3+ is suitable to target these oxoanions (Bala et al., 2013 ). Recently, the ionic reactions between hexaureachromium(III) and inorganic oxoanions (such as Cr 2O 7 2− or CrO 4 2−) in aqueous solution have been investigated. The dichromate ion is environmentally important due to its high toxicity (Yusof & Malek, 2009 ) and its use in many industrial processes (Goyal et al., 2003 ). On the other hand, Cr VI is toxic and recognized as a carcinogen to humans and wildlife. Cr III is an essential element in mammals for maintaining efficient glucose, lipid and protein metabolism. Chromium is usually found in trivalent and hexavalent oxidation states in soil, ground water and seawater (Cespon-Romero et al., 1996 ). The study of the anion or cation effect in octahedral metal complexes may be expected to yield a great variety of new structures and properties of both chemical and biological significance. Counter-ionic species in coordination compounds play important roles in chemistry, pharmacy, molecular assembly, biology and catalysis, as well as contributing significantly to environmental pollution however, their binding characteristics have not received much recognition (Martínez-Máñez & Sancenón, 2003 Fabbrizzi & Poggi, 2013 ). ![]()
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