Debasis Das

Solid-state trans → cis thermochromic isomerism in the n-propylethane-1,2-diamine complex of nickel(II) nitrate

Abstract The octahedral trans-[Ni(pren)2(NO3)2] 1 (pren = N-propylethane-1,2-diamine) has been synthesised. On heating, it isomerised endothermally to cis-[Ni(pren)2(NO3)] (NO3) la in the solid state accompanied by an irreversible blue-violet to deep blue (173–188°C, ΔH = 14.8 kJ mol1) thermochromism. On further heating, 1a melted at ca 211°C, and cooling to ambient temperature gave a metastable liquid. Copyright

Cis–trans isomerism in nickel(II)–diamine nitrite: synthesis and single crystal structure of an unusual cis-dinitronickel(II) complex, [NiL2(NO2)2] (L=1,2-diamino-2-methylpropane)

Abstract The complexes [NiL3](NO2)2·2H2O (violet, 1) and cis-[NiL2(NO2)2]·0.5H2O (pink, 1b) (L=1,2-diamino-2-methylpropane) have been synthesized from solution. The X-ray single crystal structure analysis of compound 1b has been carried out, but the presence of a water molecule cannot be detected. Upon heating, complex 1b undergoes dehydration followed by an endothermic phase transition to produce trans-[NiL2(NO2)2] (1d). The violet species (1) also undergoes dehydration upon heating with deamination resulting (1d).

SYNTHESES AND CHARACTERIZATION OF DIAMINE COMPLEXES OF NICKEL(II) TRIFLUOROACETATE : THERMOCHROMISM AND X-RAY SINGLE CRYSTAL STRUCTURE ANALYSES OF NI( PREN)2(CF3CO2)2 AND NI(IPREN)2(CF3CO2)2 (PREN = N-PROPYLETHANE-1,2-DIAMINE AND IPREN = N-ISOPROPYLETHANE-1,2-DIAMINE)

The complexes, [NiL 2 (CF 3 CO 2 ) 2 ] [L = N-methylethane-1,2-diamine (meen) , N-ethylethane-1,2-diamine (eten) , N-propylethane-1,2-diamine (pren) and N-isopropylethane-1,2-diamine (ipren) ] have been prepared and X-ray single crystal structures of [Ni (pren) 2 (CF 3 CO 2 ) 2 ] 3 and [Ni (ipren) 2 (CF 3 CO 2 ) 2 ] 4 are determined. Both 3 and 4 have slightly distorted trans -octahedral geometry with N 4 O 2 -chromophore around nickel (II) . The crystals are stabilized by H-bonds and this interaction is higher in 4 due to close proximity of methyl H-atoms of isopropyl group with oxygen atoms of trifluoroacetate groups. The complexes 3 and 4 exhibit blue to light-violet, irreversible discontinuous thermochromism. [Ni (meen) 2 (CF 3 CO 2 ) 2 ] 1 also shows thermochromism, blue-violet to blue but reverts on keeping in humid atmosphere. On the other hand, [Ni (eten) 2 (CF 3 CO 2 ) 2 ] 2 undergoes decomposition without showing any phase transition. However, thermochromism here is considered to be due to a decreased in-plane ligand field strength resulting from the conformational changes in diamine chelate rings.

Thermochromism in nickel(II) complexes: thermal, IR spectroscopic, solid-state 1H NMR and single crystal X-ray analysis of diaqua-bis(2,2-dimethyl-1,3-propanediamine) nickel(II) nitrate☆

Abstract The newly synthesized complex [Ni(dmtn) 2 (H 2 O) 2 ](NO 3 ) 2 (dmtn = 2,2-dimethyl-1,3-propanediamine) undergoes a reversible thermochromic phase transition in the range of 180–202°C ( ΔH = 10.4kJ mol −1 ) on heating after dehydration (dehydration temperature range 43–102°C). The complex has been characterized by X-ray crystallography at room temperature. The crystals are monoclinic, space group C2 m , a = 20.385(2), b = 6.9004(4), c = 6.9552(3) A , β = 102.60(5)°, V = 954.8(1) A 3 , Z = 2 and R = 0.046. The geometry of the nickel atom in the complex is tetragonally distorted octahedral with two H 2 O molecules coordinated at the trans position. The diamine chelate rings are in the trans chair-chair conformations. The broad-line 1 H NMR of partially deuterated [Ni(dmtn- d 4 ) 2 (NO 3 ) 2 ] (deuterated amine protons) indicates the onset of dynamic disorder of the diamine chelate rings at the phase transition temperature. The high temperature IR spectral measurement shows the complex retains its trans configuration after dehydration and phase transition with NO − 3 ions coordinated as a monodentate ligand.

Synthesis, IR and electronic spectroscopic and X-ray single crystal structural analysis of cis-[Ni(ipren)2(NO3)](NO3) (ipren = N-isopropylethane-1,2-diamine)

Abstract The deep blue complex [Ni(ipren)2(NO3)](NO3) has been synthesized, which is proposed to have cis-octahedral geometry on the basis of IR and electronic spectral studies and confirmed by single crystal X-ray analysis.

Synthesis and characterization of [NiL2(OCOCF3)2] [L = 1-(2-aminoethyl) piperidine]: thermochromism and X-ray single crystal structure analysis

Abstract The complex [NiL2(OCOCF3)2] (1) [L = 1-(2-aminoethyl) piperidine] has been synthesized. Single crystal X-ray structure analysis of 1 reveals a trans-octahedral geometry having an N4O2 chromophore. 1 upon heating undergoes an irreversible endothermic phase transition (194–215°C; δH = 11.2 kJ mol−1) accompanied by a blue to reddish pink colour change retaining its trans-configuration. The thermochromism is proposed to be due to a decrease of in-plane ligand field strength resulting from conformational changes of the diamine chelate rings.

Syntheses and characterization of N,N′-dipropyl/diisopropylethane-1,2-diamine complexes of nickel(II) nitrate: Thermal studies and X-ray single crystal structure analysis of cis-nitratobis (N,N′-dipropylethane-1,2-diamine)nickel(II) nitrate

Abstract The blue complex cis-[Ni(dipren)2(NO3)](NO3) 1 and the greenish blue cis-[Ni(dipren)2(H2O2](NO3)2 · 2H2O2 (dpren/dpren = dipropyl/diisopropylethane-1,2-diamine) have been synthesized. Complex 2 upon heating loses four water molecules in a single step and undergoes melting accompanied with colour change, greenish blue to deep green, 2a. Configuration of the complexes 1,2 and 2a have been proposed to be cis-octahedral on the basis of magnetic, IR and electronic spectroscopic studies and confirmed in case of complex 1 by X-ray single crystal structure analysis. The role of steric factor of the alkyl groups on the selectivity of coordinating mode of nitrate ion is studied.

Thermal Studies of Nickel(II) Squarate Complexes of Triamines in the Solid State

Abstract[NiL2]C4O4·nH2O [where n=2 when L=diethylenetriamine(dien) and N-(3-aminopropyl)-1,3-propanediamine (dpt); n=3 when L=N-(2-aminoethyl)-1,3-propanediamine (aepn); n=0 when L=N2-methyldiethylenetriamine (medien)] and Ni(tmdien)C4O4·2H2O (where tmdien=1,4,7 trimethyl-diethylenetriamine) have been synthesised and investigated thermally in the solid state. Ni(dpt)C4O4·H2O has also been synthesised pyrolytically in the solid state from the corresponding bis complex. All the complexes possess octahedral geometry. The squarate anion takes part in coordination only in monotriamine species. [Ni(medien)2]C4O4 upon heating undergoes phase transition (270–285°C; ΔH=4.9 kJ mol−1) accompanied by colour change pink to grey. Thermal stability decreases with increase in chain length of the triamines.

Synthesis and crystal structure of selenocyanato bridged two dimensional supramolecular coordination compounds of cadmium(II)

Two novel 2D polymers of cadmium(II), [Cd(medien)(SeCN)2]n (1) (medien = N″-methyldiethylenetriamine) and [Cd2(iprdien)(SeCN)4]n (2) (iprdien = N′-isopropyldiethylenetriamine) have been synthesized and their molecular structure determined by X-ray crystallography. In complex 1 each octahedral cadmium(II) unit of a 1D coordination chain contains one pendant SeCN, binding through Se. These pendant SeCN form mutual relationships with other 1D chains through non-covalent interactions (H-bonding) giving rise to a 2D infinite sheet like structure. The molecular structure of 2 reveals a 2D infinite coordination polymer possessing alternating N-bonded octahedral and Se-bonded tetrahedral cadmium(II) centres exhibiting symbiotic phenomena. Both complexes undergo melting but complex 1 remains as a supercooled liquid in the temperature region 78–131 °C.

Thermal studies of 2-aminoethanol complexes of nickel (II) in the solid state

Abstract [NiL 3 ]X 2 (where L = 2-aminoethanol and X is Cl − , Br − , I − , NO 3 − , 0.5SO 4 2− or 0.5SeO 4 2− and [NiL 2 X 2 ] (X is Cl − , Br − , or SCN − ) have been synthesised from solution and their thermal study has been carried out in the solid phase. [NiL 3 ]I 2 and [NiL 3 ]SeO 4 undergo reversible endothermic phase transitions upon heating (63–93°C and 94–113°C, respectively, for heating and 94-65°C and 110–190°C, respectively, for cooling), whereas [NiL 3 ](NO 3 ) 2 exhibits two successive reversible endothermic phase transitions (10–38°C and 50–62°C for heating and 56-48°C and 19–(−8)°C for cooling). On the other hand, [NiL 3 ]SO 4 undergoes irreversible endothermic phase transition (99–112°C) in the solid state. All these transformations are assumed to be associated with the conformational changes of 2-aminoethanol chelate rings. [NiL 2 (NCS) 2 ] melts at ≈ 168°C and remains supercooled for a few days at ambient temperature. The initial temperatures of decomposition ( T i ) of these complexes have been compared with those of the corresponding ethane-1, 2-diamine complexes of nickel (II).