Variable Combination of Mono- and Bidentate Ligands in Cu(I) (κ2-X1X2)(Y3) and Cu(I)(η2-X1X2)(Y3) Derivatives: Structural Aspects

This paper presents a structural analysis of a series of copper(I) complexes with the general composition Cu(κ2-X1X2)(Y3), in which bidentate (X1X2) and monodentate (Y3) donor ligands create a wide variety of inner coordination spheres. This study provides a rigorous structural classification and Continuous Shape Measures (CShM) analysis of twenty-nine three-coordinate copper(I) complexes featuring five-, six-, seven-, eight-, and eleven-membered metallacyclic rings. Within the five-membered metallacyclic series, encompassing varying donor sets (N,N; N,O; N,S; N,C; and P,P), the small ring size imposes severe steric demands. This causes the endocyclic X1–Cu–X2 angles to contract significantly below the ideal 120°, while the exocyclic X–Cu–Y3 angles expand up to 174.8°. CShM evaluation using the SHAPE 2.1 software shows that these derivatives split into two distinct structural regimes: one subgroup retains a highly strained, distorted trigonal planar geometry, whereas the other preferentially transitions into a non-planar pyramidal arrangement, adopting a fac-trivacant octahedral configuration. In contrast to these highly strained five-membered systems, the six-membered metallacycles—incorporating N,N; N,O; N,P; P,P; and O,S donor sets—allow for wider endocyclic angles (93.3° to 107.2°), which significantly mitigates structural strain, meaning this series is overwhelmingly dominated by highly ideal or only minimally distorted trigonal planar geometries. Finally, for the three-coordinate copper(I) complexes featuring expanded seven-, eight-, and eleven-membered metallacyclic rings, the enhanced stereochemical flexibility and low ring strain lead to the strong dominance of the virtually ideal trigonal planar arrangement.