Non-bonding interactions of anions with nitrogen heterocycles and phenyl rings: a critical Cambridge Structural Database analysisElectronic supplementary information (ESI) available: Distribution of short contacts in phenyl rings, distribution of structures with short C?Y contacts for various anions, distribution of ? interactions in different ring systems, examples of C?Y interactions and examples of anion?? interactions. See http://www.rsc.org/suppdata/ce/b3/b311000a/