Supramolecular Isomerism of 2,2′‐Bipyrazine Complexes with cis ‐(NH 3 ) 2 Pt II : Ligand Rotational State and Sequential Orientation Determine the 3D Shape of Metallacycles

2,2′‐Bipyrazine (2,2′‐bpz) reacts with cis ‐(NH 3 ) 2 Pt II in water to give a variety of products, several of which were isolated and characterized by X‐ray analysis: cis ‐[Pt(NH 3 ) 2 (2,2′‐bpz‐ N 4) 2 ](NO 3 ) 2 ⋅ 3 H 2 O ( 1 ), [{ cis ‐Pt(NH 3 ) 2 (2,2′‐bpz‐ N 4, N 4′)} 3 ](PF 6 ) 5 NO 3 ⋅ 7 H 2 O ( 2 a ), [{ cis ‐Pt(NH 3 ) 2 (2,2′‐bpz‐ N 4, N 4′)} 3 ](BF 4 ) 2 (SiF 6 ) 2 ⋅ 15 H 2 O ( 2 b ), and [{ cis ‐Pt(NH 3 ) 2 (2,2′‐bpz‐ N 4, N 4′)} 4 ](SO 4 ) 4 ⋅ 22 H 2 O ( 3 ). In 1 , 2 b , and 3 the 2,2′‐bpz ligands adopt approximately C 2 h symmetries, hence the two pyrazine halves are in trans orientation, whereas in 2 a all three 2,2′‐bpz bridges are approximately C 2 v symmetric, with the pyrazine halves cis to each other. The topologies of the two triangular complexes 2 a and 2 b are consequently distinctly different, but nevertheless both cations act as hosts for anions. In 2 a a PF 6 − and a NO 3 − anion are associated simultaneously with the +6 cation, whereas in 2 b it is a BF 4 − anion and a water molecule, which are trapped in its cavity. There is no anion inclusion in case of the metallasquare 3 . In principle, 3 can exist in a large number of stereoisomers, depending on the rotational states of the bridging 2,2′‐bpz ligands. Isolation of a single rotamer form of 3 with C 2 h symmetric 2,2′‐bpz ligands and an overall meso form is proposed to be a consequence of a highly efficient self‐assembly process that starts from the precursor 1 and reaction with two cis ‐(NH 3 ) 2 Pt II units. This process leads to the isolated rotamer of 3 regardless of whether two cations 1 in head–head form react with two cis ‐(NH 3 ) 2 Pt II , or whether the Δ enantiomer of the chiral head–tail form of 1 combines with its Λ enantiomer through two cis ‐(NH 3 ) 2 Pt II entities.