Concomitance of octamolvbdate isomers in meta-stable crystal structures isolated using homolentic CoII/CIII complexes as structure-directing templates

Exploiting the kinetic domain provided by hydrothermal conditions, it was possible to isolate three transient metastable crystal structures, each bearing concomitant pairs of octamolybdate isomers, namely, alpha-beta, gamma-beta or beta(cs)-beta(gp) stabilized by distinctive homoleptic [Co(bpy)(3)](n+)(bpy = 2,2'-bipyridine; n= 2 or 3) cations generated in situ: [Co(bpy)(3)](4) [(alpha-Mo8O26)(beta-Mo8O26)center dot 5H(2)O (1), [NH4][Co(bpy)(3)][(gamma-Mo8O26)(0.5) (beta-Mo8O26)(0.5)]center dot 4H(2)O (2) and [Co(bpy)(3)](2)-[(beta(cs)-Mo8O26)(0.5)(beta(gp)-Mo8O26)]center dot 12H(2)O (3). Solid 1 with the space group P2(1)/n and unit-cell parameters a = 22.160 (6), b = 14.209 (3), c = 24.641 (4) angstrom, beta = 99.10 (2)degrees and V = 7661 (3) angstrom 3 resulted in the same crystal structure as that synthesized previously under different conditions by Sun et al. [J. Mol. Struct. (2005), 741, 149-153]. Factors directing the reaction, such as product composition and phase stability, were monitored by analysis of the PXRD patterns of the bulk solids obtained under different experimental conditions. The relative proportions of the mixed phases 1-3 or their stabilization are highly dependent on the initial Co:Mo molar ratio and the reaction temperature. In particular, an increase in temperature induces the transformation of 1-3 into more thermodynamically stable phases formed by one-dimensional coordination polymers [Co(bpy)(2) (beta-Mo8O26)(0.5)](n) (4) and [(MoO3)(bpy)(n), (5). The crystal structures of 1-3 correspond to molecular salts self-assembled by C-H center dot center dot center dot O-Mo, C center dot center dot center dot H and H center dot center dot center dot H intermolecular contacts. A Hirshfeld surface analysis for 1 showed that the C center dot center dot center dot H and H center dot center dot center dot H interactions represent an average of 51.8% of the total cation-cation intermolecular contacts. In contrast, these interactions are vastly reduced in 2 (23.0%) and 3 (average 28.5% for both isomers). EPR experiments indicated that the crystal structures of 1 and 3 are paramagnetic, and that for 2 is diamagnetic. The paramagnetism of 3 stems from the in situ formation of [Co(bpy)(3)](3+) in a high-spin configuration. The structure-directing properties of the [Co(bpy)(3)](n+ )cations in the isolation and self-assembly of concomitant octamolybdate isomers are also described from the viewpoint of crystal engineering.

Automated summary

By exploiting hydrothermal conditions, three transient metastable crystal structures with octamolybdate isomers were isolated, each stabilized by distinctive [Co(bpy)(3)](n+) cations. Factors influencing the reaction, such as initial Co:Mo molar ratio and temperature, were found to significantly impact product composition and phase stability. The crystal structures of the isolated isomers were described, along with their magnetic properties and structural-directing role of [Co(bpy)(3)](n+) cations.