Weakly coupled dinuclear system

A novel tridentate coordination mode for the carbonato-nickel(II) system was reported by Escuer and co-workers (61). The trinuclear compound [Ni2(p-C03)(dmpd)4(H20)][Ni(dmpd)2(H20)2](C104)4 H20 was obtained from the reaction of basic solutions of nickel(II) perchlorate and 2,2-dimethylpropane-1,3-diamine (dmpd) with atmospheric C02. The three nickel atoms show octahedral coordination with three different environments, №( 0 -0,0 )(dmpd)2, №( 0 -0 ) (dmpd)2(H20) and Ni(dmpd)2(H20)2. The carbonate anion acts as a bridge between two nickel ions whereas the [Ni(dmpd)2(H20)2]2 + subunit is linked by hydrogen bonds to the dinuclear group (Fig. 7). The dinuclear [Ni2(p-C03)(dmpd)4(H20)]2 + subunit shows a moderately weak antiferromagnetic coupling with a J value of —7.8 cm-1. 

In aU cases, the mononuclear square-planar cP complexes are very reactive. As a result, the least hindered complexes containing the porphyrins OEP (octaethylporphyrinato), TPP tetraphenylporphyrinato, TTP (tetratolylporphyr-inato), and TXP [tetrakis(3,5-dimethylphenyl)porphyrinato] easily dimerize (Fig. 42) to form diamagnetic metal-metal bonded dinuclear species (in which a description as M —is indistinguishable from a antiferromagnetically coupled M°—M system). The Rlu Rh bond is, however, rather weak, and allows thermal homolytic Rh—Rh bond splitting to study the reactivity of the... 

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