Crystallographic Verification that Copper(II) Coordinates to Four of the Oxygen Atoms of Zeolite 6-Rings. Two Single-Crystal Structures of Fully Dehydrated, Largely Cu2+-Exchanged Zeolite Y (FAU, Si/Al = 1.56)

Abstract

Two single crystals of fully dehydrated, mostly Cu2+-exchanged zeolite Y were prepared by the exchange of Na75–Y (|Na75|[Si117Al75O384]-FAU, Si/Al = 1.56) with an aqueous stream 0.05 M in Cu(NO3)2, pH = 4.2, at 294 K for 18 and 24 h, respectively, followed by vacuum dehydration at 673 K and 1 × 10–6 Torr. Their crystal structures were determined by synchrotron X-ray diffraction techniques in the cubic space group Fd3m at 100(1) K and were refined to the final error indices R1/wR2 = 0.050/0.165 and 0.050/0.163, respectively, for |Cu32.6Na5.3H4.5|[Si117Al75O384]-FAU and |Cu33.0Na3.9H5.1|[Si117Al75O384]-FAU, respectively. Cu2+ ions occupy the 6-ring sites I′ and II, preferring I′; Na+ ions also occupy sites I′ and II; neither site is filled. All Cu2+ ions in these structures coordinate not only to three trigonally arranged oxygen atoms of their 6-rings, but also to a fourth oxygen atom of those 6-rings to achieve planar, severely distorted square, 4-coordination. This result is in agreement with DFT calcula...