Crystallographic and Spectroscopic Footprints of Hydrophobic and Hydrophilic Hydrogen Bonding within 2D Coordination Polymers

Abstract

In an aqueous solution, stability of the amphiphiles is attributed to the hydration of both polar and nonpolar groups. This study introduces a novel family of 2D tetracyanonickellate coordination polymers with unique crystallization properties, offering insights into simplified hydration shells and their spectroscopic signatures. The observed DMSO organization and water molecule arrangement in these structures provide a valuable model for understanding hydrophilic–hydrophobic interactions in complex systems. We present here crystallographic, thermogravimetric, and spectroscopic data on structural and vibrational differentiation of water in the vicinity of DMSO molecules at the atomic level. The new six 2D tetracyanonickellate coordination polymers, M[Ni(CN)₄], with M = Mn(1), Fe(2), Co(3), Ni(4), Zn(5), and Cd(6), achieved crystallization of the H₂O–DMSO mixture in the form of 1D assemblies. Hydrophilic and hydrophobic environments followed DMSO head-to-head and tail-to-tail organization driven by hydrogen bonds. Remarkably, the crystalline arrangement led to methyl and sulfoxide fragments, with only one water molecule fixed in their vicinity. The family of new solids crystallizes in the tetragonal space group (81), with average unit-cell parameters of a = b = 10.396(3), c = 7.980(4), and V = 862.9(3) (Z = 2) as determined by PXRD. Upon heating, DMSO and H₂O were simultaneously evacuated from crystalline solids as assessed by thermogravimetric analysis and mass spectrometry studies. Vibrational analysis of each sample was performed by means of MIR, FIR, and Raman spectra in the range of 4000–150 cm^–1. Both the ¹¹³Cd spectra of 6 and ¹³C SSNMR spectra of Zn (5) and Cd (6) are discussed.