Concomitance of octamolybdate isomers in metastable crystal structures isolated using homoleptic CoII/CoIII complexes as structure-directing templates

R. Atencio, A. Briceño, J. Bruno-Colmenarez, P. Silva, L. Rodríguez, E. Sosa, Erick Limones, Yesenia Pacheco, Julio Cáceres, Joel E. Vielma
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Abstract

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, α–β, γ–β or βcs–βgp stabilized by distinctive homoleptic [Co(bpy)3]n+ (bpy = 2,2′-bi­pyridine; n = 2 or 3) cations generated in situ: [Co(bpy)3]4[(α-Mo8O26)(β-Mo8O26)]·5H2O (1), [NH4][Co(bpy)3][(γ-Mo8O26)0.5(β-Mo8O26)0.5]·4H2O (2) and [Co(bpy)3]2[(βcs-Mo8O26)0.5(βgp-Mo8O26)]·12H2O (3). Solid 1 with the space group P21/n and unit-cell parameters a = 22.160 (6), b = 14.209 (3), c = 24.641 (4) A, β = 99.10 (2)° and V = 7661 (3) A3 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(β-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⋯O—Mo, C⋯H and H⋯H intermolecular contacts. A Hirshfeld surface analysis for 1 showed that the C⋯H and H⋯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.
用同感CoII/CoIII配合物作为结构导向模板分离亚稳晶体结构中八胺钼酸酯异构体的伴随物
利用水热条件提供的动力学域,可以分离出三种瞬态亚稳晶体结构,每种结构都带有伴随的八胺酸异构体对,即α -β, γ -β或βcs -β gp,它们由独特的同渗剂[Co(bpy)3]n+ (bpy = 2,2 ' -双吡啶稳定;n = 2或3)阳离子原位生成:[有限公司(bpy) 3] 4[(α-Mo8O26)(β-Mo8O26)]·5水(1),(NH4)[有限公司(bpy) 3][(γ-Mo8O26) 0.5(β-Mo8O26) 0.5]·4水(2)和[有限公司(bpy) 3] 2[(βcs-Mo8O26) 0.5(βgp-Mo8O26)]·12水(3)。固体P21和空间群1 / n,晶胞参数= 22.160 (6),b = 14.209 (3), c = 24.641(4),β= 99.10(2)°和V = 7661 (3) A3导致相同的晶体结构在不同条件下合成之前由Sun et al . [J。摩尔。结构。(2005), 741, 149-153]。通过对不同实验条件下获得的固体块体的PXRD谱图分析,监测了反应的产物组成和相稳定性等影响因素。混合相1 ~ 3的相对比例及其稳定性高度依赖于初始Co:Mo摩尔比和反应温度。特别是,温度的升高诱导1-3转变为由一维配位聚合物[Co(bpy)2(β-Mo8O26)0.5]n(4)和[(MoO3)(bpy)]n(5)形成的更热力学稳定的相。1-3的晶体结构对应于由C - H⋯O-Mo, C⋯H和H⋯H分子间接触自组装的分子盐。对1的Hirshfeld表面分析表明,C⋯H和H⋯H相互作用平均占总阳离子-阳离子分子间接触的51.8%。相比之下,这些相互作用在2(23.0%)和3(两种异构体平均28.5%)中大大减少。EPR实验表明,1和3的晶体结构为顺磁性,2的晶体结构为抗磁性。3的顺磁性源于在高自旋构型中[Co(bpy)3]3+的原位形成。本文还从晶体工程的角度描述了[Co(bpy)3]n+阳离子在伴随的八聚氰胺异构体的分离和自组装中的结构导向特性。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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