Humidity-Driven Reversible Transformation and Guest Inclusion in a Two-Dimensional Coordination Framework Tailored by Organic Polyamine Cation

Using a polyamine cation tetrenH55+ (tetren = tetraethylenepentaamine), we tailored the dynamic layered material (tetrenH5)1.6{CoII(H2O)2[MIV(CN)8]}4·xH2O (1, M = W, x = 12; 2, M = Mo, x = 11.2). 1 and 2 consist of strongly corrugated two-dimensional (2D) cyano-bridged monolayers {CoII(H2O)2[MIV(CN)8]}n2n– of square grid topology stacked in an alternate manner with cationic layers of tetrenH55+ and H2O molecules. The observed single-crystal-to-single-crystal (SCSC) transformation is due to the reversible dehydration of 1 and 2 to the respective monocrystalline materials (tetrenH5)1.6{CoII[MIV(CN)8]}4 (1deh and 2deh). Structural modifications consist of the change of coordination number (C.N.) of Co(II) from 6 to 4 and a degree of corrugation of the coordination skeleton resulting in changes of orthorhombic cell dimensions. The exposition of 1deh to vapors of H2O, MeOH, HCONH2, and MeCN gives 1reh, 1deh·5.6MeOH, 1deh·4HCONH2, and 1deh·2.4MeCN phases, respectively. 1reh reveals structural, physical, and physicochemical characteristics of 1, while 1deh·guest: 1deh·5.6MeOH, 1deh·4HCONH2, and 1deh·2.4MeCN evidently follow features of 1deh. When exposed to humidity, 1deh·guest phases reabsorb H2O to give respective mixed 1deh·guest·H2O phases. Structural changes are followed by single crystal and powder X-ray diffraction, magnetic measurements and IR, UV–vis–NIR, and electron spin resonance (ESR) spectroscopies. The values of the effective crystallographic volume for interlayer guest molecules and tetrenH55+ are estimated and discussed. The solid state–gas phase reactivity of 1, 1deh, and 1deh·guest is interpreted in terms of competition between Co(II)-guest coordination bonding and noncovalent interactions between guest molecules and interstitial molecules.