One-pot synthesis using a 2:2:1:2 molar ratio of Pb(OAc)₂·3H₂O, L, piperidinum terephthalate (ptp) and NaClO₄/NH₄PF₆ at room temperature affords two dinuclear compounds of the type [Pb₂(L)₂(𝜇- tp)](ClO₄/PF₆)₂ (1/2) [L=N,N'-(bis-(pyridin-2-yl)benzylidene)diethylenetriamine and tp = terephthalate dianion]. The compounds are characterized by microanalytical, spectroscopic, thermal and other physicochemical results. X-ray structural analyses of 1 and 2 reveal that each heptacoordinated lead(II) centre with a PbN₅O₂ chromophore are bound by five N atoms of L and connected through O atoms of a bis(bidentate) tp bridge. The arrangements of L and tp suggest a gap around the metal centre due to occupation of a stereo-active lone pair of electrons reflecting a hemidirected coordination around the metal centre. The complexes exhibit reasonable thermal stabilities with the tolerate temperatures ca. 255°C for 1 and 263°C for 2. The complexes display intraligand ($\pi-\pi^\ast$) fluorescence in the solid state and in DMF solutions at room temperature.

One mononuclear cobalt(II) compound of the type [Co(bnzd)₂(NCS)₂(OH₂)₂] (1) (bnzd = benzidine) has been isolated through a single-pot reaction of the molecular building components in MeOH-H₂O solvent mixture at room temperature and characterized by physico-chemical and spectroscopic methods. The crystal structure of complex 1 has an octahedral geometry with trans, trans, trans orientations in the order (N$^a$,N$^a$), (N$^t$,N$^t$), (O$^w$,O$^w$) [N$^a$ = N(amine), N$^t$ = N(thiocyanate) and O$^w$ = O(water)]. In crystalline state, individual units of 1 are associated by weak cooperative O-H…N, O-H…S and N-H…S hydrogen bonds resulting in a 3D network structure. The compound is redox active and shows luminescence in MeOH solution. Thermal decomposition pattern of 1 reveals the presence of two coordinated water molecules. Variabletemperature magnetic susceptibility measurement shows significant orbital contribution and numerical matrix diagonalization method gives the best fit parameters: 𝛼 = A^∗k = 1.43; 𝜆 = −130 cm^-1; 𝛥 = −864 cm^-1; TIP = 0.000975; R = $1.19 \times 10^{−4}$.

Two dinuclear mercury(II) iodide complexes of the types [(L1)Hg(𝜇-I)HgI₃] (1) and [Hg₂(L2) (I)₄]·H₂O (2) [L1 = tris(2-aminoethyl)amine and L2 = N,N'-(bis-(pyridin-2-yl)benzylidene)diethylenetriamine] have been synthesized and characterized usingmicroanalytical, spectroscopic, thermal and other physicochemical results. Structures of both the compounds are solved by X-ray diffraction measurements. Structural analyses show that one mercury (II) centre in 1 adopts a distorted tetrahedral geometry with an HgI₄ chromophore surrounded by four iodides, while the other has a distorted trigonal bipyramidal environment with an HgN₄I chromophore bound by four N atoms of L1 and one bridging iodide. Pentadentate Schiff base (L2) in 2 shows unusual binucleating bis(bidentate) behaviour to bind two different mercury(II) centres—Hg1 with an HgN₃I₂ chromophore in a distorted square pyramidal geometry and Hg2 with an HgN₂I₂ chromophore in a tetrahedral environment. Weak intermolecularN-H…I hydrogen bonds in 1 and cooperative C-H$\ldots$𝜋 and $\pi\ldots \pi$ interactions in 2 promote dimensionalities. The Schiff base complex, 2, shows intraligand ($\pi-\pi^\ast$) fluorescence in DMF solution at room temperature, whereas compound 1 containing tripodal amine is fluorescent-inactive.

A dinuclear compound [Mn₂(L)₂(𝜇-tp)](PF₆)₂·3.57H₂O (1) [L = N,N′-(bis(pyridin-2-yl)benzylidene)-1,3-propanediamine and tp = terephthalate dianion] has been isolated and characterized on the basis of microanalytical, spectroscopic and other physicochemical properties. X-ray structural study showed interesting bis(bidentate) bridging motif of tp in the dicationic dinuclear unit [Mn₂(𝜇-tp)]²⁺. Each manganese(II) centre adopts a rare distorted trigonal prismatic geometry with an MnN₄O₂ chromophore.Chelation of the tetradentate Schiff base (L) along with bis(bidentate) bridging of two O atoms of tp complete hexacoordination around each manganese(II) centre. The dinuclear units of 1 are associated through cooperative C-H$\cdots$F hydrogen bonds and $\pi^{\cdot} \pi$, C-H$^{\cdots} \pi$ and rare anion$^{\cdots} \pi$ interactions to promote the dimensionality in a graded manner. Variable temperature magnetic susceptibility measurement of 1 in the 2-300 K temperature range revealed weak antiferromagnetic interaction presumably due to long bridging arm of tp.

Two mononuclear compounds of the types pentacoordinated [Zn(L1)(OAc)]PF₆·H₂O (1) and hexacoordinated [Zn(L2)(OAc)]PF₆ (2) [L1 = N,N′-(bis(pyridin-2-yl)formylidene)-1,3-propanediamine; L2 = N,N′-(bis(pyridin-2-yl)benzylidene)-1,4-butanediamine] have been synthesized using one-pot reactions of a 1:1:1 molar ratio of Zn(OAc)₂.2H₂O, L1/L2, ammonium hexafluorophosphate in MeOH at room temperature. Compounds 1 and 2 are characterized on the basis of microanalytical, spectroscopic, thermal and other physicochemical results. Single crystal X-ray structural study reveals that the zinc(II) centre in 1 is coordinated by four N atoms of the Schiff base L1 and one O atom of terminal acetate with a ZnN₄O chromophore, whereas in 2, the zinc(II) centre is bound by four N atoms of the tailored Schiff base L2 and two O atoms of the chelated acetate. In the crystalline state, mononuclear units in 1 are engaged in weak cooperative intermolecular O-H⋯O and C-H⋯F hydrogen bonds affording a 1D chain. The individual units of 2 are packed by 𝜋 ⋯ 𝜋 and anion⋯ 𝜋 interactions to form a 2D sheet structure. The complexes show reasonable thermal stabilities and display intraligand 𝜋 $\to$ 𝜋^∗ fluorescence in solid state at room temperature.

The syntheses, characterizations and structures of a neutral 2D coordination polymer [Cd(bnzd)(NCS)₂]n (1) and a polycationic 3D coordination polymer isolated as perchlorate salt [Cd(bnzd)₃]n(ClO₄)₂n (2) (bnzd = benzidine) are described. X-ray structural analyses reveal that each hexacoordinated cadmium(II) center in 1 adopts a distorted octahedral geometry with a CdN₄S₂ chromophore bound by two N atoms of two different bnzd units and two N and two S atoms of symmetric doubly bridged end-toend NCS− units extended in a 2D sheet. Six N atoms of six different bridged bnzd units are bonded to each cadmium(II) in 2 in a non-ended fashion affording a 3D network structure. In the crystalline state, each 2D sheet structure in 1 is further stabilized by π· · ·π interaction which in turn affords a 3D network structure through multiple intermolecular N-H· · · S hydrogen bonds. On the other hand, the 3D network structure in 2 is stabilized by weak intermolecular N-H· · ·O hydrogen bonds and C-H· · ·π interactions. Bnzd, 1 and 2 display intraligand 1(π-π*) fluorescence in DMF solution at room temperature.

A neutral coordination polymer of chloridomercury(II) of the type[Hg(bzpy).μ−Cl/Cl]_n (1) and a dinuclear complex of bromidomercury(II) of the type [Hg(bzpy).μ − Br/ Br]₂ (2) (bzpy = 2-benzoylpyridine) were synthesized using a 1:1 molar ratio of HgCl₂/HgBr₂ and bzpy in methanolic solvent at room temperature and X-ray crystallographically characterized. Structural analyses show that each mercury(II) center in both the compounds adopts a distorted square pyramidal geometry with an HgNOX₃ [X = Cl in 1 and X = Br in 2] chromophore. Each mercury(II) center in the coordination polymer 1 is connected to two other metal(II) centers through two different chlorido bridges affording a zigzag one-dimensional (1D) chain. In the crystalline state, 1D chains in 1 are stabilized through weak non-covalent C−H···π interactions promoting to a 2D sheet structure,and these 2D sheets, in turn, are further associated through intermolecular C−H···O hydrogen bonds resulting in a 3D network structure. In 2, two bromide ions bridge two metal(II) centers to form a dinuclear entity. Thedinuclear units in 2 are packed through π · ·π stacking and intermolecular C−H · ·O hydrogen bonds to afford a 2D sheet structure. These 2D sheets self-assemble through intermolecular C−H···Br hydrogen bonds promoting to a 3D network structure. The thermally stable compounds 1 and 2 exhibit intraligand 1

¹(π−π^*)/fluorescence in DMF solutions at room temperature