The synthesis of coordination polymers using 4,4'-bipyridine (4,4'-bpy, 1) and transition metal ions has thus far produced several novel networks with a high degree of porosity. [1,2] Among all the networks, square-grid polymers are of particular importance due to their predictable pore sizes and selective inclusion of guest molecules. The first square-grid complex [{Zn(1) 2 (PF 6 ) 2 } n ] was reported by Robson et al. in 1990; it is interpenetrated and thus nonporous. [3] In 1994 we prepared the noninterpenetrated square-grid complex [{[Cd(1) 2 (H 2 O) 2 ](NO 3 ) 2 } n ]. [4] Despite the simple structural design, however, 1 has not been replaced by analogous structural units that are significantly longer. A few structures with a longer ligand Py-X-Py (Py 4-pyridyl, X CH 2 CH 2 , CHCH, or CC) have been reported; however, these ligands are longer than 1 by only 2 . [5] Herein we show that noninterpenetrated square-grid networks can be obtained with the larger ligand 2 , which is 8.5 longer than 1.
Treatment of 2 with Ni(NO 3 ) 2 (1:2 ratio) gives an extraordinarily big square-grid polymer with dimensions of about 20 Â 20 . Surprisingly, the grid framework thus obtained is so stable that the crystals after removal of the guest were analyzed by single-crystal X-ray diffraction. [6] The single crystals of the complex of 2 were grown by layering a solution of Ni(NO 3 ) 2 in MeOH over a solution of 2 in o-xylene and isolated in 80 % yield. The crystal structure of this complex revealed the formation of a noninterpenetrated square-grid polymer 3 . The Ni atom resides in a distorted [{[Ni(2) 2 (NO 3 ) 2 ] ´4(o-xylene)} n ] 3