A 2D hydrogen-bonded dinuclear Zn(II) complex, [{Zn(H₂O) ₃ (bpe) ₂} ₂ (bpe)](NO₃) ₄・3bpe・14H₂O,1 (bpe = 4,4_-bipyridylethylene) containing coordination complex cations, [{Zn(H₂O) ₃ (bpe) ₂} ₂ (μ-bpe)] ⁴⁺and free bpe and lattice water molecules shows face-to-face, π ・ ・ ・ π stacking of two of the four free bpemolecules with coordinated bpe ligands. Out of eight bpe molecules, six are aligned in parallel fashion withshort C・ ・ ・ C distances of 3.663–3.814Å and they undergo photochemical [2+2] cycloaddition reaction. The photoreaction conducted on ground sample of 1 in the solid-state affords rctt-tetrakis(4-pyridyl)cyclobutane (rctt-tpcb) product in 75% yield. The molecular movement of free bpe molecules was tested by conducting thephotoreaction in ground sample and heated sample of single crystals. The photoreactivity study of 1 indicates that the free bpe molecules are locked between the cationic [{Zn(H₂O) ₃ (bpe) ₂} ₂ (bpe)] ⁴⁺ layers.

A novel organic salt, [bpeH].TFMS (1), of trans-1,2-bis(4-pyridyl)ethylene (bpe) was synthesized using trifluoromethane sulphonic acid (CF₃SO₃H, TFMS) by self-assembly and its crystal structure was determined by X-ray crystallography. Compound 1 forms hydrogen-bonded assembly of [bpeH]⁺ cations and CF₃SO⁻₃ anions which are held together by N–H· · ·N, C–H· · ·O and C–H· · ·F hydrogen-bonding interactions. An attempt has been made to orient the olefinic C=C bonds of bpe in the organic salt via weak hydrogenbonding interaction for photodimerization reaction in the solid state. The [bpeH]⁺ cations are in parallelorientation in the infinite one dimensional (1D) chain through N–H· · ·N hydrogen bonding. The olefinic C=C bonds of bpe are aligned in criss-cross orientation with a center-to-center distance of 4.97 Å. Even though the distance and the orientation of olefinic C=C bonds do not conform with the Schmidt topochemical criteria, compound 1 undergoes photodimerization reaction in solid state to produce stereo-specific rctt-tetrakis(4- pyridyl)cyclobutane (rctt-tpcb) (2) in 100% yield. The photoreactivity is expected to take place through cooperative movement of 1D chains and pedal-like motion of the pyridyl rings over the double bonds. The photodimerized product 2 undergoes acid-catalyzed isomerization to produce other cyclobutane isomers such as rcct-tpcb and rtct-tpcb. This strategy for synthesizing organic salts is a facile step for the synthesis of cyclobutanederivatives.

Two known Pb(II) metal-organic frameworks (MOFs), pseudo-supramolecular isomeric pairs synthesized namely, [Pb₃(BDC)₃(DMF)_3.5](1) and [Pb(BDC)(H₂O)] (2) (where BDC = benzenedicarboxylate) were synthesized and reexamined their structures to determine the topology of the networks. In that 1 displayed a 3D (10,3)-b linked network with having the ths topology whereas 2 shows a (6,3) 2D layers interconnected to a 3D framework structure. Remarkably, the desolvation of both 1 and 2 cause structural transformation to a known3D network structure of [Pb(BDC)]_n(3) as established by X-ray powder diffraction patterns. Photoluminescence studies in the solid-state at room temperature of 1–3 compounds exhibit interesting luminescence close to white light region due to ligand-to-metal charge-transfer (LMCT).