Zinc di(tert-butyl)phosphate complexes as precursors to zinc phosphates. Manipulation of zincophosphate structures

The reaction of ZnEt(2) with HO(O)P(O(t)Bu)(2) gives the insoluble polymer {Zn[O2P(O(t)Bu)(2)](2)}n (1). In the presence of slight amounts of water, this reaction produces good yields of the oxo-centered tetranuclear cluster Zn-4(mu(4)-O)[O2P(O(t)Bu)(2)](6) (2), which has been characterized by X-ray crystallography. Compound 2 is thermally labile and eliminates isobutene and water over the temperature range 130-220 degrees C. The ceramic yield at 900 degrees C corresponds to the theoretical yield for a Zn4P6O19 material, and the observed products at this temperature are alpha-Zn2P2O7 and beta-Zn(PO3)(2) (by XRD). When heated in ethanol at 85 degrees C for 30 h, 2 converts to polymer 1 and ZnO. This transformation is facilitated by acids, which allow the conversion to occur at room temperature. Polymer 1, characterized by X-ray crystallography, adopts a zigzag structure with zinc atoms linked alternately by one and then three bridging phosphate groups. This structure is therefore different from that adopted by the other two organozincophosphate {Zn[O2P(OR)(2)](2)}(n) polymers that are known, which exist as Linear chains with the zinc atoms bridged by two phosphate groups. Polymer 1 undergoes a quantitative pyrolytic conversion to beta-Zn(PO3)(2). Diffusion of a toluene solution of 2 into a dichloromethane solution of 1,6-hexanediamine produces a coordination network with the formula {Zn[O2P(O(t)Bu)(2)](2)[H2N(CH2)(6)NH2]}(n), (3), with elimination of ZnO. The network structure of 3 consists of {Zn[O2P(O(t)Bu)(2)](2)[H2N(CH2)(6)NH2]}(n) polymer strands interconnected via hydrogen bonds between the N-H and P=O groups to form layers stacked along the crystallographic b axis. Each polymer chain contains four-coordinate zinc atoms bonded to two monodentate di-tert-butylphosphate ligands and linked by 1,6-hexanediamine groups. Slabs of the layered structure are held together by a dense array of hydrogen bonds involving the N-H and P=O functionalities. These layers possess zinc phosphate/1,6-hexanediamine cores and are coated with tert-butyl groups such that there are only van der Waals interactions between layers. Thermogravimetric analysis and XRD studies show that 3 undergoes thermolysis to a mixture of crystalline alpha-Zn2P2O7 and beta-Zn(PO3)(2).