Antiferromagnetic square planar

Di-/-butyl-6-aminothiophenol gives complex (497) under strictly anaerobic conditions. In the presence of air, deep blue-violet solutions are obtained from which mixtures of solid deep blue-black cis/trans-(498) can be isolated.1345 For the square planar Ni complex, the cis-trans isomerization rate is fast. (498) is best described as a singlet diradical due to strong antiferromagnetic coupling of the benzosemiquinonate 7r-radicals.19, 134S... 

The structure of the pyrazine complex was suggested to contain polymeric square planar cations with bridging pyrazines and the magnetic properties (300-80K) were interpreted in terms of an antiferromagnetic exchange interaction. A Curie-Weiss constant of 84 K was calculated. At room temperature, the magnetic moment was found to be 1.61 BM. 

Sulfur-based Cr coordination compounds include a series of dithiocarbamates of the type [Cr(S2CNR2)2] (R = Me, Et or R2 = C4H8), which are antiferromagnetically coupled. The diethyl-substituted compound is an S-bridged dimer, making chromium five-coordinate. Square-planar Cr coordinated by sulfur occurs in the violet [NEt4]2[Cr(S2C2H4)2]. Finally, Thiourea and its derivatives form adducts with Cr halides, which are similar to the adducts with O-donors mentioned above. 

Type 2 Cu(II) weak absorption spectrum EPR spectrum characteristic of square-planar Cu(II) complexes Type 3 Cu(II) di-copper centre strong absorption in the near UV CXmax 330 nm) no EPR spectra, the two coppers are antiferromagnetically coupled. 

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... 

The alloys PrSns, NdSna, and SmSnj have the face-centred AuCua structure. All three show a Sn quadrupole splitting of 1 1 mm s in the temperature range 1 5-298 K because of the effectively square-planar coordination of tin to the rare-earth ion [235]. Although PrSnj and NdSna are known to order antiferromagnetically within this region, any induced field at the tin nucleus is below experimental resolution. 

---