The ability to confine photoactive catalysts within metal organic framework (MOF) materials affords the opportunity to expand the functional diversity of these materials into solar-based applications. Here, two new Ru(II) tris(2,2'-bipyridine) (RuBpy)-based photoactive materials derived from reactions between Zn(II) ions and 1,3,5-tris(4-carboxyphenyl)benzene and templated by the presence of RuBpy (RWLC-1 and RWLC-2) are described with regard to structure and RuBpy photophysics. RuBpy cations have been successfully encapsulated within the cavities (RWLC-1) and channels (RWLC-2) of the new negatively charged frameworks, both of which are synthesized simultaneously in a single reaction vial. Single-crystal X-ray diffraction studies allowed for determination of the RuBpy position within crystal voids. RuBpy encapsulated in each of the two new MOFs exhibits biphasic triplet metal to ligand charge transfer ((3)MLCT) emission decay lifetimes (τRWLC-1-fast = 237 ns, τRWLC-1-slow = 1.60 μs, τRWLC-2-fast = 171 ns, and τRWLC-2-slow = 797 ns at 25 °C) consistent with two populations of RuBpy complexes, one being encapsulated in highly space-restricted cavities giving rise to a longer (3)MLCT lifetime, while the second is encapsulation within a larger nonperiodic pore or defect with a coencapsulated quencher giving rise to short emission lifetimes. Taken together, these results represent examples of the templating ability of RuBpy to produce novel materials with distinct photophysical environments of the encapsulated guests.

The 1:1 complex of 1,2-ethanediol with dimethyl sulfoxide was studied using density functional theory. A network of three hydrogen bonds holds the complex together, including two in which each methyl group donates to the same hydroxyl oxygen. Four lines of evidence support the existence of methyl-donated hydrogen bonds. The interaction energy is 36 +/- 5 kJ/mol using Becke's three parameter hybrid theory with the 1991 nonlocal correlation functional of Perdew and Wang, and a moderately large basis set (B3PW91/6-311++G**//B3PW91/6-31+G**). To determine the energy of each hydrogen bond, a relaxed potential energy scan was performed in a smaller basis set to break the weaker hydrogen bonds by forced systematic rotation of the methyl groups. Two cross-checking analyses show cooperative effects that cause individual hydrogen bond energies in the network to be nonadditive. When one methyl hydrogen bond is broken, the remaining interactions stabilize the complex by storing an additional 2-3 kJ/mol. With all hydrogen bonds intact, the O[bond]H...O[bond]S hydrogen bond contributes 26 +/- 2 kJ/mol stability, and each weak methyl bond stores 5 +/- 2 kJ/mol.

The development of effective sensor elements relies on the ability of a chromophore to bind an analyte selectively and then study the binding through changes in spectroscopic signals. In this report the ability of Zn(II) Tetraphenyl Porphyrin (ZnTPP) to selectively bind nitrite over nitrate ions is examined. The results of Benesi–Hildebrand analysis reveals that ZnTPP binds NO2 – and NO3 – ions with association constants of 739 ± 70 M–1 and 134 ± 15 M–1, respectively. Interestingly, addition of a pyridine ligand to the fifth coordination site of the Zn(II) center enhances ion binding with the association constants increasing to 71,300 ± 8,000 M–1 and 18,900 ± 3,000 M–1 for nitrite and nitrate, respectively. Density functional theory calculations suggest a binding mechanism through which Zn(II)–porphyrin interactions are disrupted by ligand and base coordination to Zn(II), with Zn(II) having more favorable overlap with nitrite orbitals, which are less delocalized than nitrate orbitals. Overall, these provide new insights into the ability to tune the affinity and selectivity of porphyrin based sensors utilizing electronic factors associated with the central Zn(II) ion.

No abstract

It has now been demonstrated that Ru(ii)tris(2,2'-bipyridine) (RuBpy) can be utilized to template the formation of new metal organic framework (MOF) materials containing crystallographically resolved RuBpy clusters with unique photophysical properties. Two such materials, RWLC-1 and RWLC-2, have now been reported from our laboratory and are composed of RuBpy encapsulated in MOFs composed of Zn(ii) ions and 1,3,5-tris(4-carboxyphenyl)benzene ligands (C. L. Whittington, L. Wojtas and R. W. Larsen, Inorg. Chem., 2014, 53, 160-166). Here, a third RuBpy templated photoactive MOF is described (RWLC-3) that is derived from the reaction between Zn(ii) ions and 1,4-dicarboxybenzene in the presence of RuBpy. Single Crystal X-ray diffraction studies determined the position of RuBpy cations within the crystal lattice. The RWLC-3 structure is described as a 2-fold interpenetrated pillared honeycomb network (bnb) containing crystallographically resolved RuBpy clusters. The two bnb networks are weakly interconnected. The encapsulated RuBpy exhibits two emission decay lifetimes (τ-fast = 120 ns, τ-slow = 453 ns) and a bathochromic shift in the steady state emission spectrum relative to RuBpy in ethanol.