Second-Sphere Coordination Revisited

Since the concept of second-sphere coordination of transition metal complexes was introduced by Alfred Werner in 1913, the investigation of the phenomenon has emerged as a major thrust area - a significant part of which is based on the use of transition metal complexes as first coordination spheres as well as macrocycles as second-sphere ligands in promoting the assembly and dictating the main structural features of the second-sphere adducts. In this review, we first of all summarize the work carried out in our laboratory on the second-sphere coordination chemistry of transition metal complexes in the past three decades. Significant advances of relevance to the second-sphere coordination chemistry of square-planar gold complex anions with cyclodextrins are presented as the second part of this review.