The structure and thermal behaviour of sodium and potassium multinuclear compounds with hexamethylenetetramine

Sodium and potassium thiocyanate complex compounds of formulae [Na(hmta)(H2O)(4)] (2) (2+) center dot 2SCN(-) (1) and [K-2(hmta)(SCN)(2)] (n) (2) have been synthesized and characterised by IR spectroscopy, thermogravimetry coupled with differential thermal analysis, elemental analysis and X-ray crystallography. Each sodium and potassium cation is six co-ordinated, the sodium by one monofunctional hmta molecule, three terminal water molecules and two bridging water molecules, and the potassium by two bridging tetrafunctional hmta molecules and four bridging tetrafunctional thiocyanate ions. The coordination polyhedra of the central atoms can be described as distorted tetragonal bipyramids. The complex cations and anions of (1) are interconnected by multiple intramolecular O(water)-H center dot center dot center dot N(hmta/NCS) and O(water)-H center dot center dot center dot S hydrogen bonds to the three dimensional net. In each complex cation the intramolecular O-H center dot center dot center dot O hydrogen bonds link two terminal water molecules bonded to two metal cations. The compound (2) forms the three dimensional hybrid network in which the classical two-dimensional coordination polymers are linked by inorganic SCN- spacers to the third-dimension. Thermal analyses show that the compounds decompose gradually in three (for 1) and two (for 2) steps with formation of Na2SO4 and K2S as the final products, respectively, for 1 and 2.