Accentuate the negative: Single‐network cadmium cyanide displays isotropic negative thermal expansion behavior of unprecedented magnitude over a large temperature range (see graph of unit cell parameter a versus temperature). Guest molecules in the pores of this framework block the transverse vibrational modes responsible for this behavior, causing the value of the linear coefficient of thermal expansion to increase with guest occupancy.

We report photoexcited-state crystal structures for two new members of the ͓Ru͑SO 2 ͒͑NH 3 ͒ 4 X͔Y family: 1 : X =H 2 O, Y = ͑ Ϯ ͒-camphorsulfonate 2 ; 2 : X = isonicotinamide, Y = tosylate 2 . The excited states are metastable at 100 K, with a photoconversion fraction of 11.1͑7͒% achieved in 1, and 22.1͑10͒% and 26.9͑10͒% at the two distinct sites in 2. We further show using solid-state density-functional-theory calculations that the excited-state geometries achieved are strongly influenced by the local crystal environment. This result is relevant to attempts to rationally design related photoexcitation systems for optical data-storage applications.

Tetramethylammonium copper(I) zinc(II) cyanide, which consists of N(CH(3))(4)(+) ions trapped within a cristobalite-like metal cyanide framework, has been studied by variable-temperature powder and single-crystal X-ray diffraction. Its coefficient of thermal expansion is approximately zero over the temperature range 200-400 K and comparable with the best commercial zero thermal expansion materials. The atomic displacement parameters, apparent bond lengths, and structure of a low-temperature, low-symmetry phase reveal that the low-energy vibrational modes responsible for this behavior maintain approximately rigid Zn coordination tetrahedra but involve significant distortion of their Cu counterparts.

The photoinduced O-bound coordination mode in RuSO(2) complexes, previously observed only at 13 K, has been generated at 100 K in tetraammineaqua(sulfur dioxide)ruthenium(II) (±)-camphorsulfonate. This coordination state, often denoted MS1, decays to the η(2)-bound MS2 state, with an estimated half-life of 3.4(8) h and a long-lived population of 2.9(4)% at 120 K.