Poly-imido analogues of various phosphorus oxo anions have gained recent attention in inorganic chemistry. Current methods to obtain these anions require strong organometallic deprotonating agents in reaction with phosphonium salt like [(NHPh)₄P]Cl or phosphoramides such as [(RNH)₃P=E] (E = NSiMe₃, O, S or Se) in non-polar solvents. Recently, employing salts of soft and reactive transition metal ions, we have developed methods to obtain these anions in polar and protic solvents. Herein, we have described a facile anion exchange route that stabilizes the highly labile tetrakis(2-pyridylamino)phosphonium cation as its nitrate salt, [P(NH²Py)₄]NO₃. This molecule exhibits a double chain structure mediated by H-bonding interactions of the pyridylamino segments (N-H...N). The phosphonium salt upon reaction with excess silver triflate results in a pentanuclear Ag(I) complex, {Ag₅[P(N²Py)₂(NH²Py)₂]}·(F₃CSO₃)₃, stabilized by two imido-phosphinate [P(N²Py)₂(NH²Py)₂]⁻ ligands. Formation of a similar penta-nuclear cluster has been observed before when AgClO₄ was used as a base. Our previous results with the related phosphate precursor, [PO(NH²Py)₃], in reaction with various Ag(I) salts have shown to yield complexes of the corresponding neutral, mono- and dianionic ligands. However, the stability of the Ag5-cluster within the mono-anionic casing of the [P(N²Py)₂(NH²Py)₂]⁻ ligand have seemingly overwhelmed the subtle reactivity changes offered by various Ag(I) salts.

Formation of cationic and neutral CuI cluster MOFs have been reported starting from tridentate phosphoramide ligands, [(NHR) ₃P = E] (L¹: R = 3-aminoquinolinyl (AQ), E = S; L²: R = 3-pyridyl (PY), E = S; L³: R = 3-aminoquinolinyl (AQ), E = O). By utilizing L¹, a cationic 2D-MOF {[(L¹) ₂ (Cu₆I₅)](OH) · 3DMF·4MeOH}n, 1 containing a rugby ball shaped discrete Cu₆I₅ cluster has been reported earlier. Formation of a new 3D-MOF {[(L²) ₂ (Cu₆I₄)](OH) ₂· 2DMF}n containing a Zintl type [(Cu₆I₄4) ² ⁺]n cluster chains is reported in this paper. A neutral cluster MOFs 3 with formula unit of {[Cu₄I₄L³ (CH₃CN)] · 2DMF · 3H₂O}n has been prepared from the ligand L³. Formation of the smaller Cu₄I₄ clusters in the MOF 3 is due to the presence of a MeCN ligation at one of the Cu(I) atoms which not only precludes the extension of the assembly in three dimension but also reduces the size of the obtained cluster. Unlike 1 which showed a ligand-assisted thermochromism, photophysical studies on the 3D-MOF 2 exhibited green phosphorescence at both 298 K and 77 K. The occurrence of the phosphorescence at 77 K in 2 is due to triplet cluster centered (³CC) excited state of the cluster as there is no ligand-centered transition observed at 298 K. The 2D-MOF 3 does not show any characteristic luminescence behavior as the presence of the acetonitrile coordination at one of the Cu(I) ion is believed to quench the emission by non-radiative pathways. Further, luminescence quenching experiments on 1 and 2 with aromatic nitro-analytes showed a very high sensing selectivity for picric acid (TNP) over other aromatic nitro-analytes.