Conformational Flexibility of the Square‐Pyramidal Coordination Cap in a Series of Octahedral Nickel(II) Pentaamine Complexes – Magnetochemical Characterization of the Singly μ‐Cl‐Bridged Nickel(II) Dimer [(pyN 4 )Ni‐Cl‐Ni(pyN 4 )](PF 6 ) 3 [pyN 4 = 2,6‐Bis(1′,3′‐diamino‐2′‐methylprop‐2′‐yl)pyridine]

The architecture of the tetrapodal pentaamine ligand 2,6‐bis(1′,3′‐diamino‐2′‐methylprop‐2′‐yl)pyridine (pyN 4 , 1 ) allows it to coordinate to nickel(II) as a square pyramidal coordination cap. The pyridine nitrogen atom occupies an apical position of the coordination octahedron, while four equivalent pendent primary amino groups occupy the equatorial positions, with a sixth coordination site remaining for a monodentate ligand. Exchange of this ligand is facile, and a series of complexes [( 1 )NiX] n + (X = OH 2 , OClO 3 , NCS, N 3 , {Cl‐Ni(pyN 4 )}) has been prepared and characterised by elemental analysis, IR and UV/Vis spectroscopies (as applicable), and X‐ray structure determination. While the solid state structures show varying degrees of distortion of the ligand cap 1 from C 2v symmetry, a polynucleating coordination mode has not been observed. The ligand enables the synthesis of dinuclear nickel(II) complexes containing a single bridging ligand, as exemplified by the singly ‐chloro bridged complex [( 1 )Ni–Cl–Ni( 1 )](PF 6 ) 3 . This complex has an antiferromagnetically coupled ground state of total spin S T = 0, as determined from variable‐temperature magnetic susceptibility measurements.