ABSTRACT
A series of M[Au(CN)(2)](2)(analyte)(x) coordination polymers (M = Co, Ni; analyte = dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF), pyridine; x = 2 or 4) was prepared and characterized. Addition of analyte vapours to solid M(µ-OH(2))[Au(CN)(2)](2) yielded visible vapochromic responses for M = Co but not M = Ni; the IR ν(CN) spectral region changed in every case. A single crystal structure of Zn[Au(CN)(2)](2)(DMSO)(2) revealed a corrugated 2-D layer structure with cis-DMSO units. Reacting a Ni(II) salt and K[Au(CN)(2)] in DMSO yielded the isostructural Ni[Au(CN)(2)](2)(DMSO)(2) product. Co[Au(CN)(2)](2)(DMSO)(2) and M[Au(CN)(2)](2)(DMF)(2) (M = Co, Ni) complexes have flat 2-D square-grid layer structures with trans-bound DMSO or DMF units; they are formed via vapour absorption by solid M(µ-OH(2))[Au(CN)(2)](2) and from DMSO or DMF solution synthesis. Co[Au(CN)(2)](2)(pyridine)(4) is generated via vapour absorption by Co(µ-OH(2))[Au(CN)(2)](2); the analogous Ni complex is synthesized by immersion of Ni(µ-OH(2))[Au(CN)(2)](2) in 4% aqueous pyridine. Similar immersion of Co(µ-OH(2))[Au(CN)(2)](2) yielded Co[Au(CN)(2)](2)(pyridine)(2), which has a flat 2-D square-grid structure with trans-pyridine units. Absorption of pyridine vapour by solid Ni(µ-OH(2))[Au(CN)(2)](2) was incomplete, generating a mixture of pyridine-bound complexes. Analyte-free Co[Au(CN)(2)](2) was prepared by dehydration of Co(µ-OH(2))[Au(CN)(2)](2) at 145 °C; it has a 3-D diamondoid-type structure and absorbs DMSO, DMF and pyridine to give the same materials as by vapour absorption from the hydrate.
ABSTRACT
Five isostructural dicyanometallate coordination polymers containing metallophilic interactions (In[M(CN)(2)](3) (M = Ag, Au), KCd[M(CN)(2)](3), and KNi[Au(CN)(2)](3)) were synthesized and investigated by variable-temperature powder X-ray diffraction to probe their thermal expansion properties. The compounds have a trigonal unit cell and show positive thermal expansion (PTE) in the ab plane, where Kagome sheets of M atoms reside, and negative thermal expansion (NTE) along the trigonal c axis, perpendicular to these sheets. The magnitude of thermal expansion is unusually large in all cases (40 x 10(-6) K(-1) < |alpha| < 110 x 10(-6) K(-1)). The system with the weakest metallophilic interactions, In[Ag(CN)(2)](3), shows the most "colossal" thermal expansion of the series (alpha(a) = 105(2) x 10(-6) K(-1), alpha(c) = -84(2) x 10(-6) K(-1) at 295 K), while systems containing stronger Au-Au interactions show relatively reduced thermal expansion. Thus, it appears that strong metallophilic interactions hinder colossal thermal expansion behavior. Additionally, the presence of K(+) counterions also reduces the magnitude of thermal expansion.
ABSTRACT
4,6-Di-2'-pyridylpyrimidine is employed as a bis(diimine) ligand bridging two cobalt bis(dioxolene) centers. The thermally induced valence tautomeric transitions of these two metal centers are coupled through the ligand. The result is that sequential switching from high-spin Co(II) to low-spin Co(III) of one center, followed by the onset of switching of the other center at lower temperature, is observed in a solid amorphous thin film by IR absorption spectroscopy.