Di-aqua-di-isothiocyanato-tin(II)-bis(18-crown-6), Sn(NCS)2·2(18-crown-6)·2H2O – A supramolecular compound of a low-valent main group element with bent sandwich architecture

Abstract

The crystal structure of the title compound, di-aqua-di-isothiocyanato-tin(II)-bis(18-crown-6), was determined by single crystal X-ray structure analysis. The compound crystallizes in the monoclinic space group C2/c with half a molecule of the point group C₂ in the asymmetric unit. The supramolecular arrangement of the three different building blocks, a bent Sn(NCS)₂ one, a water molecule, and an 18-crown-6 molecule exhibits a bent sandwich-like structure with an opening angle of 48.1(1)° referring to the least-squares planes through the oxygen atoms of the crown ether molecules. Bond lengths and angles within this aggregate indicate that the isothiocyanate groups bond to the central, bivalent tin atom via covalent 2e-2c-bonds based on two orthogonal p orbitals of the metal atom, and the oxygen atoms of the water molecules via a symmetrical 3c-4e bond by use of the third metal p orbital. The crown ether molecules do not have oxygen-tin contacts but are hydrogen-bonded to the water molecules. Their conformation has similarities with that of an ideal D_3d conformation.