Modified Phenyl Groups on Pyrazin Groups to Synthesized Cobalt String Complexes

In the literature, ligand such as oligo-α-pyridylamines and oligo-naphthyridylamine are usually used in the linear metal string complex. In addition to all of the above, another series of ligand is synthesized by mixing two types of ligands. In other words, the type of ligand contains pyridyl and naphthyridyl groups. Permuting the possible permutation, we can find that symmetrical and the shortest ligand is 2,7-bis(α-pyridylamino)-1,8-naphthyridine (H2bpyany). Complexes contain bpyany2-, hexa-nickel or hexa-cobalt, axial ligands such as chloride and thiocyanate, and anions such as hexafluorophosphate and tetrafluoroborate were published1, 2. Another similar ligand that H2bpyany replaces pyridyl groups by pyrimidyl group is 2,7-bis(α-pyrimidylamino)-1,8-naphthyridine (H2bpmany). Hexanickel complexes with bpmany2- were also published3. According to the above, if we replace pyridyl group by pyrazin group, properties of complexes such as magnetic property, CV and resistance make a change. 2,7-bis(α-pyrazinamino)-1,8-naphthyridine (H2bpzany) and nickel or cobalt ions were reacted. We can get the signal in MALDI, but we cannot isolate the target. Because of this, we modified phenyl groups on pyrazin groups. By 2,7-bis(5-phenyl)-α-pyrazinamino-1,8-naphthyridine (H2bphpzany), [Co5(bphpzany)4(NCS)2] (1), [Co6(bphpzany)4(NCS)2](PF6)n (n=1 (2), n=2 (3)) have been synthesized and the crystal structures for complex 1–3 have been determined by X-ray crystallography. Three complexes are the similar component of four ligands, five or six cobalt ions, two thiocyanates as axial ligands, and hexafluorophosphate as counterions. The structural characterization is that the cobalt chain is helically wrapped by four bphpzany2–. Complex 1–3 have Co510+, Co612+ configurations, and all are air-stable.

Chirality control of the Quadruple helixes of the metal strings

Novel chiral pentadentate ligands with naphthyridine and camphorsulfonyl groups have been designed and used to control the chirality of quadruple helixes of metal strings directly:Δ-Ni5((-)camnpda)4 (1) and Λ-Ni5((+)camnpda)4 (2). Compound 1 is a Δ form metal string complex with H2(-)camnpda and 2 is Λ form one with H2(+)camnpda. By X-ray single-crystal diffraction, The structures of the compound 1 and 2 are both 2,2-trans form in the same monoclinic space group C2 and have the similar unit cell. Further, it demonstrates that two metal strings are chiral isomers each other by CD spectra. In theoretical computation, the local minimum (Λ-Ni5((+)camnpda)4 with the Δ form) becomes energetically unfavourable by about 100 kcal/mol due to the strong steric repulsion introduced by the camphor groups. Finally, the racemic crystal is obtained with a 1:1 mixture of compounds 1 and 2 in triclinic space group P-1. Both the external dinickel distance in 1 and 2, about 2.280 Å, and the SQUID experiment reveal mixed valence [Ni2]3+ characters and the magnetic behaviors are anti-ferromagnetic (J = -55.0 cm-1 for 1 and -63.3 cm-1 for 2). In the electrochemistry, the three reversible oxidation waves in 1 and 2 are -0.13, 0.20 and 0.97 V.