A Systematic Exploration of Nickel( II )/Acetate/Di‐2‐pyridyl Ketone Chemistry: Neutral and Cationic Tetranuclear Clusters, and a Novel Mononuclear Complex

The further use of di‐2‐pyridyl ketone [(2‐py) 2 CO] innickel( II ) acetate chemistry has been investigated. Various synthetic procedures have led to the synthesis ofcomplexes [Ni 4 (O 2 CMe) 2 {(2‐py) 2 C(OH)O} 4 (H 2 O) 2 ](ClO 4 ) 2 ( 1 ), [Ni(O 2 CMe){(2‐py) 2 C(OH) 2 }{(2‐py) 2 CO}](ClO 4 ) · H 2 O ( 2· H 2 O), [Ni 4 (O 2 CMe) 3 {(2‐py) 2 C(OH)O} 4 ](ClO 4 ) · 2H 2 O · 2EtOH ( 3· 2H 2 O · 2EtOH), [Ni 4 (O 2 CMe) 4 {(2‐py) 2 C(OH)O} 4 ] · 2MeCN ( 4· 2MeCN), and [Ni 4 (O 2 CMe) 3 {(2‐py) 2 C(OH)O} 4 ](O 2 CMe) · 6H 2 O · MeCN ( 5· 6H 2 O · MeCN). The Ni II ‐mediated hydrolysis of (2‐py) 2 CO to give the coordinated molecule (2‐py) 2 C(OH) 2 or the monoanion (2‐py) 2 C(OH)O – involves nucleophilic attack by H 2 O on the carbonyl group. The Ni II ion in 2· H 2 O is coordinated by one monodentate acetate, one N , N ′, O ‐tridentate chelating (2‐py) 2 C(OH) 2 molecule, and one N , N ′‐bidentate chelating (2‐py) 2 CO ligand. The tetranuclear cluster cation of 1 has a cubane {Ni 4 (μ 3 ‐OR) 4 } 4+ core with Ni II ions and deprotonated oxygen atoms occupying alternate vertices. The [Ni 4 (O 2 CMe) 3 {(2‐py) 2 C(OH)O} 4 ] + cations present in the complexes 3· 2H 2 O · 2EtOH and 5· 6H 2 O · MeCN have almost identical cubane structures that are different from the structure of the cation of 1 . The four metal ions in the centrosymmetric molecules of 4· 2MeCN are located at four vertices of a defect dicubane (with two missing vertices) and are bridged by six oxygen atoms. Characteristic IR bands are discussed in terms of the known structures of 1 – 5 . The magnetic data for the Ni II cubane 1 has been modeled with two J values, and shows that the coupling consists of two ferromagnetically coupled pairs that are antiferromagnetically coupled to give a diamagnetic ground state. The magneticproperties of 4 have been modeled with three J values, andreveal competing antiferromagnetic and ferromagneticcoupling between the four Ni II ions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)