Use of the Di‐2‐pyridyl Ketone/Acetate/Dicyanamide “Blend” in Manganese(II), Cobalt(II) and Nickel(II) Chemistry: Neutral Cubane Complexes

The use of di‐2‐pyridyl ketone [(2‐py) 2 CO]/dicyanamide “blend” in cobalt( II ), manganese( II ) and nickel acetatechemistry has yielded neutral cubane clusters. The preparation of [Mn 4 (O 2 CMe) 2 {N(CN) 2 } 2 {(2‐py) 2 C(OH)O} 4 ] · 2(2‐py) 2 ‐CO · 4H 2 O ( 1 ) and [M 4 (O 2 CMe) 2 {N(CN) 2 } 2 {(2‐py) 2 C(OH)O} 4 ] · 10H 2 O [M = Ni ( 2 ), Co ( 3 )] was achieved by the reaction of [M(O 2 CMe) 2 ] · 4H 2 O with (2‐py) 2 CO and Na[N(CN) 2 ] in MeOH/H 2 O (1:5, v/v) at room temperature. The metal( II )‐mediated hydrolysis of (2‐py) 2 CO to give the coordinated monoanion of the hydrate gem ‐diol form involves a nucleophilic attack of H 2 O on the carbonyl group. In the case of the cobalt reaction system, there is a second product. Upon employing an excess of (2‐py) 2 CO, long reaction times, reflux conditions and high dilution, slow oxidation of Co II takes place leading to the isolation of the mononuclear cobalt( III ) complex [Co{(2‐py) 2 C(OH)O} 2 ][N(CN) 2 ] · 4H 2 O ( 4 ) in yields higher than 70 %. The structures of 1 , 2 and 4 have been solved by single‐crystal X‐ray diffraction studies, while a unit‐cell determination indicated that complex 3 is isostructural with 2 . The tetranuclear cluster molecules of 1 and 2 have cubane [M 4 (μ 3 ‐OR) 4 ] 4+ cores with divalent metal atoms and deprotonated oxygen atoms [originating from the(2‐py) 2 C(OH)O – ligands] occupying alternate vertices. The centrosymmetric [Co{(2‐py) 2 C(OH)O} 2 ] + cation of complex 4 has an octahedral structure with the (2‐py) 2 C(OH)O – ligands adopting the tridentate N , O , N ‐chelating coordination mode. The magnetic properties of 1 – 3 have been studied by variable‐temperature dc magnetic susceptibility techniques. The studies indicate weak antiferromagnetic coupling for 1 and ferromagnetic behaviour for 2 and 3 . A three‐ J model was found to be adequate for describing the thermal variation of the molar magnetic susceptibilities of 1 and 2 . The magnetochemical results have been compared with literature data. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)