Cyanide Lability and Linkage Isomerism of Hexacyanochromate(III) Induced by the Co(II) Ion

Abstract

Reactions between the [M(III)(CN)(6)](3-) (M = Fe and Co) anions and the mononuclear complex [Co(II)(dppe)(2)(H(2)O)][BF(4)](2) result in the formation of two isostructural trinuclear clusters {[Co(II)(dppe)(2)](2)[M(III)(CN)(6)]}(BF(4)). Surprisingly, reactions of [Co(dppe)(2)(H(2)O)](BF(4))(2) and [Co(triphos)(CH(3)CN)(2)](BF(4))(2) with [Cr(CN)(6)](3-) yield the mononuclear complexes [Co(dppe)(2)(CN)](BF(4)) and [Co(triphos)(CN)(2)], respectively. In the former case, an unusual pentanuclear intermediate complex {[Co(II)(3)(dppe)(4)(MeCN)][Cr(III)(CN)(6)](2)} was isolated. The reaction was probed by solution IR spectroscopy, which revealed a gradual conversion of the nu(C[triple bond]N) stretches of the starting materials to those of the CN-bridged intermediate and eventually to the single nu(C[triple bond]N) stretch of the final mononuclear product. The loss of carbon-bound CN(-) ligands from [Cr(CN)(6)](3-) occurs on a sufficiently slow time-scale for observation of varying degrees of cyanide linkage isomerism in the trigonal bipyramidal complex {[Co(tmphen)(2)](3)[Cr(CN)(6)](2)}; the study was aided by the use of different Co(II) starting materials. Results obtained by a combination of X-ray crystallography, infrared spectroscopy, and magnetometry provide unequivocal evidence that the presence of certain Lewis acids (e.g., Co(II) in this work and Fe(II) ions and BPh(3) in previously reported studies) promote the process of cyanide linkage isomerism, which, in the case of Co(II) species, leads to facile labilization of cyanide ligands from the [Cr(CN)(6)](3-) anion.

Design and Synthesis of Concentration Gradient Prussian Blue Analogues

“…The unequal hexacyanometalate ratio appears to be related to the relatively high solubility of the hexacyanochromate product, reducing its incorporation. The unusual behavior of [Cr­(CN) 6 ] 3– with some Lewis acids has been noted previously, where linkage isomerism, perhaps facilitated by redox processes, leads to enhanced lability of the hexacyanochromate ions …”

“…The unusual behavior of [Cr(CN) 6 ] 3− with some Lewis acids has been noted previously, where linkage isomerism, perhaps facilitated by redox processes, leads to enhanced lability of the hexacyanochromate ions. 46 ■ CONCLUSION Mixed-composition Prussian blue analogue particles with controlled concentration gradients have been prepared, and the synthetic conditions and component characteristics that lead to uniform gradients have been elucidated. The successful quenching of the kinetic gradient products primarily depends on the relative precipitation rates of the individual PBA species.…”

Boronated Cyanometallates

“…To compare the effects of ligand field strength on the electronic structures of cyanometallates, we synthesized the linkage isomer (TBA)3[Cr(NC-BPh3)6] (Cr-III-NC-BPh3) (cyanides are strong σdonors and weak π-acceptors). 39,63 When Cr-III was refluxed with BPh3 in MeCN, a dramatic color change from pale yellow to orange-red occurred. 39 Remarkably, the reaction triggered inversion of all six cyanide ligands, affording a borane-capped hexakiscyanoborate complex (Figure 2(d)).…”

Reaction mechanisms in solution

“…35 Reaction of [Co(dppe) 2 (H 2 O)](BF 4 ) 2 with [Cr(CN) 6 ] 3À yields the mononuclear complex [Co(dppe) 2 (CN)](BF 4 ) via an unusual pentanuclear intermediate which was isolated as {[Co II 3 (dppe) 4 (MeCN)][Cr III (CN) 6 ] 2 }. 36 Solution IR spectroscopy, revealed a gradual conversion of the n(CRN) stretches of the starting materials to those of the CN-bridged intermediate and eventually to the single n(CRN) stretch of the final mononuclear product. The loss of carbon-bound CN ligands from [Cr(CN) 6 ] 3À occurs on a sufficiently slow time-scale for observation of varying degrees of cyanide linkage isomerism in the trigonal bipyramidal complex {[Co(tmphen) 2 ] 3 [Cr(CN) 6 ] 2 }.…”