Structural and statistical investigation of the coordination behavior of the picolinate-based ligands using the CSD database

For statistical investigation of the coordination modes of all complexes containing the picolinate unit, a search run on the all CSD database complexes. This study revealed that there are 33 coordination modes for this class of compounds which can be divided up into four groups including: NO-Chelate Modes , Two Chelates Modes , O2-Chelate Modes and Non-Chelate Modes . 92% of all the structures contain a NO-chelate ring and (N,Oalcoholic) mode (Fig. 1) is the most observed coordination mode (56%) in which the picolinate unit acts as NO-donor and forms one chelate ring. Also the (N,O);O mode (Fig. 2) is the second most common mode of the CSD analogues (20%). In another comparison, the percentage of bridged and non-bridged structures was calculated. The data revealed that the picolinate unit commonly forms a non-bridged structure (87%). The picolinate unit can bridge 2−5 metal centers. In most cases the carboxylic moiety is deprotonated during the complexation process (94%), however deprotonation of the nitrogen atom in the pyridine ring is very rare (1%).