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] in nickel(II) acetate chemistry has been investigated. Various synthetic procedures have led to the synthesis of complexes [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 [Ni4(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 magnetic properties of 4 have been modeled with three J values, and reveal competing antiferromagnetic and ferromagnetic coupling between the four N II ions.

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