© The Author(s) (published by International Union of Crystallography) Posted on May 6, 2015 by SCG DR Copyright Holders: © The Author(s) (published by International Union of Crystallography) Self-archiving policy Conditions Accepted version: √ Open Access Journal Published version: √ Open Access Journal Remarks: The Creative Commons Attribution Licence applies to all articles published in Acta Crystallographica Section E and IUCrJ. Verification Date: 05.05.2015