Preparation and structure of barium decacyanodicobaltate(II) tridecahydrate, Ba3[CO2(CN)10].13H2O. Stereochemical analysis of the metal-metal bonded [Co2(CN)10]6- dimer

Abstract

The preparation of purple Ba3[Co2(CN)io] • 13H20 (an air-stable salt in striking contrast to the potassium salt) by reaction of an aqueous solution of Co(N03)2• 6H20 with Ba(CN)», and its subsequent characterization by single-crystal X-ray diffraction, not only has resolved all doubt regarding the architecture of the heretofore structurally elusive [Co2(CN)i0]6_ anion but also has furnished detailed structural parameters for comparison with those of related complexes. This binuclear cobalt anion (of crystallographic site symmetry C2 relating the two Co(CN)53halves to each other) was found to conform ideally to the Did-82m Mn2(CO)io-type structure stabilized by a Co(II)-Co(II) bond of length 2.798 (2) Á. An unexpected structural feature (which contrasts that in Mn2(CO)i0) is the Co-CN(ax) bond length of 1.961 (9) A being significantly longer by 0.075 Á than the average value of 1.886 (4) Á for the Co-CN(eq) distances which range from 1.876 (8) to 1.896 (8) A. A comparison of the metal-metal and metal-ligand bond lengths in the [Co2(CN)i0]6-anion with those in the electronically and structurally equivalent Mn2(CO)u> and the [Co2(CNCH3)h>]4+ cation is made, and the differences are rationalized in terms of bonding considerations. The fact that the C-N(ax) bond length of 1.125 (11) Á is 0.04 A shorter (on the borderline of statistical significance) than the average value of 1.165 (5) Á for the C-N(eq) bond lengths of range 1.159 (9)-1.178 (10) Á is utilized along with the intensity variations of the three infrared-allowed cyanide frequencies to provide a tentative vibrational assignment which is different from the known vibrational assignment of the corresponding infrared carbonyl bands in Mn2(CO)10. Ba3[Co2(CN)i0] • 13H20 crystallizes to give a monoclinic unit cell of dimensions a = 9.414 (1) A, b = 20.831 (4) A, c = 15.126 (2) A, ß = 93.457 (4)°, and of symmetry C2/c. The structural determination and least-squares refinement were based on 1761 independent data (/ > 2 (/)) collected by counter methods. Although the initial X-ray results indicated the formula as a dodecahydrate, the presence of the 13th water was shown both from complete elemental analysis and from density measurement (viz., pobsi = 2.305 (5) g cm-3 vs. Pealed = 2.295 g cm-3 for Z = 4) and subsequently substantiated from an anisotropic least-squares model (based on a statistical crystalline disorder of only this crystallographically independent 13th water oxygen atom) which yielded an unweighted Ri of 3.5% and a weighted i?2 of 5.3 %.The cyanocobalt(II) system in solution has generated widespread interest over a long period of time due to its remarkable catalytic properties in various hydrogenation reactions,2•3 to its facility in producing scission of small molecules such as H2,2-4 Br2,5 I2,5 H20,6 H202,7 HONH2,7 ICN,7 and various organic halides,8•9 and to its unusual ability in forming a variety of bridged complexes, [(NC)6Co-L-Co(CN)6]6-, by coordination with various reagents. Examples of the ligand-bridged species include L being peroxo,1011 cya...

Bridged and unbridged M2L10 complexes

“…The two bridging ligands are coupled next (remove dashed barrier in 12). 14 shows the four top (PH2)2 orbitals, those derived dering reversals in Re2Cl10 is to be found in the difference between the coupling units (Cl)2 vs. (PH2)2.…”

Metal–Metal (MM) Bond Distances and Bond Orders in Binuclear Metal Complexes of the First Row Transition Metals Titanium Through Zinc

“…The axially disubstituted tetracarboxylate complex 18 has a Co···Co distance of 2.83 Å indicating a weak MM interaction, possibly owing to the axial quinuclidine ligands. (Co 2 ) +4 complexes with long unsupported Co–Co bonds include the complex anion present in 19 , and the complex tetracation present in 20 , having R MM distances (Dahl, Raymond, and Cotton) of 2.798 (or 2.794) and 2.73(1) Å, respectively.…”

Photoredox Reactions of the Binuclear Complex Ions [(NC)5Co(III)NCM(II)(CN)5]6‐ (M = Fe and Ru)

“…A qualitative potential curve diagram (Fig. 6) with Co(II) in a low spin configuration as expected for a Co(II)-cyano complex [31]. The increase of the internuclear distance should reflect the strong Jahn-Teller distortion which is expected and has been observed to occur in low spin octahedral Co(II) complexes [32].…”