## 4 Discussion  
Immbilized polyols can be phosphorylated with DECP in the presence of DMAP to form the monoprotic ligand. As noted earlier, the P=O band appears at 1265 cm\({}^{-1}\) in the diethyl phosphate. FTIR spectra of the monoprotic phosphates show that replacing one -OEt group with an acidic -OH affects band broadness and positions between 900 and 1250 cm\({}^{-1}\) (Figure 6); thus, for example, conversion to monoprotic pPentaM shifts the P=O from 1265 cm\({}^{-1}\) to 1224 cm\({}^{-1}\). The bands at 1124-1163 cm\({}^{-1}\) in DPA are assigned to P=O and those at 999 and 937 cm\({}^{-1}\) to the P-O(H). Though a phosphonate is being compared to phosphates, the additional downshift from two electron-withdrawing -OH groups is important to understanding the significance of the band positions when the acidic -OH group is proximate to the phosphoryl oxygen in the monoprotic phosphates (see below). Figure 5: Metal ion affinities among the polymers: pPentaM \(>\) pGlyM \(>\) pEG1M \(>\) DPA. Figure 6: FTIR spectra of monoprotic (pEG1M, pGlyM, pPentaM) and diprotic (DPA). Electron withdrawing groups shift the P=O band to higher frequency as seen in the shifts of soluble phosphates and phosphine oxides: The P=O band for tributyl phosphine oxide is at 1155 cm\({}^{-1}\) while that for triphenyl phosphine oxide is at 1190 cm\({}^{-1}\), an increase of 35 cm\({}^{-1}\) due to the electron withdrawing phenyl group [19]. The P=O in tributyl phosphate (TBP) is at 1282 cm\({}^{-1}\), while that for triphenyl phosphate (TPP) is at 1296 cm\({}^{-1}\), an increase of 14 cm\({}^{-1}\) since the inductive effect is attenuated by the intervening oxygen atom. Comparing phosphates to phosphine oxides shows the strong electron withdrawing effect of the -O- and its corresponding effect on P=O band positions. This affects the metal ion affinities of soluble complexants with phosphine oxides > phosphonates > phosphates [20]. Removal of one phenyl group from TPP to give the monoprotic (PhO)\({}_{2}\)P(O)(OH) lowers the P=O band by 110 cm\({}^{-1}\) to 1187 cm\({}^{-1}\) since an electron withdrawing group is removed (though the -O- remains bonded to the phosphorus). The decrease, however, is more intense than expected given the aforementioned attenuation. Moreover, removing one butyl group from TBP to give (BuO)\({}_{2}\)P(O)(OH) again results in a lowering of the P=O band position by 70 cm\({}^{-1}\) to 1212 cm\({}^{-1}\) despite removal of an electron donor. The -OH group must thus have an effect additional to its inductive effect since replacing it with the equally electron withdrawing -Cl to give (PhO)\({}_{2}\)P(O)Cl results in a shift to a much higher frequency (1308 cm\({}^{-1}\)). It is proposed that the dominant effect of the acidic -OH in the phosphates which shifts the P=O band to lower frequencies is hydrogen bonding to the phosphoryl oxygen. Hydrogen bonding between amines to P=O has been reported [21]. This is now suggested to occur between the P=O and the acid site in immobilized phosphates: replacing -OEt on the phosphate diethyl ester with -OH shifts the P=O to lower frequency by 35 cm\({}^{-1}\). Broadening around 1220 cm\({}^{-1}\) has been attributed to hydrogen bonding at the phosphoryl oxygen [22] and the broad bands associated with the P=O (Figure 6) support the presence of intra- and intermolecular hydrogen bonding. This P-OH\(\cdots\)O=P bonding in the monoprotic phosphates also decreases electron density in the phosphoryl bond, shifting the band from 1265 cm\({}^{-1}\) in the neutral diethyl phosphate to 1215-1230 cm\({}^{-1}\). Hydrogen bonding among soluble phosphonic acids has been observed [23; 24]. This bonding is strong, as indicated by the fact that the phosphonic acid remains a dimer even after one proton is exchanged for a metal ion. The metal ion affinities of pPentaM > pGlyM > pEG1M is the same as that for the corresponding neutral diesters (pPenta > pGly > pEG1). FTIR spectra show hydrogen bonding in the latter between its phosphoryl oxygen and the -OH groups on the neighboring glycol.