Structural and Spectroscopic Impact of Tuning the Stereochemical Activity of the Lone Pair in Lead(II) Cyanoaurate Coordination Polymers via Ancillary Ligands

Abstract

The reaction of Pb(ClO4)2 x xH2O, an ancillary ligand L, and two equivalents of Au(CN)2(-) gave a series of crystalline coordination polymers, which were structurally characterized. The ligands were chosen to represent a range of increasing basicity, to influence the stereochemical activity (i.e., p-orbital character) of the Pb(II) lone pair. The Pb(II) center in [Pb(1,10-phenanthroline)2][Au(CN)2]2 (1) is 8-coordinate, with a stereochemically inactive lone pair; all 8 Pb-N bonds are similar. The Au(CN)2(-) units propagate a 2-D brick-wall structure. In [Pb(2,2'-bipyridine)2][Au(CN)2]2 (2), the 8-coordinate Pb(II) center has asymmetric Pb-N bond lengths, indicating moderate lone pair stereochemical activity; the supramolecular structure forms a 1-D chain/ribbon motif. For [Pb(ethylenediamine)][Au(CN)2]2 (3), the Pb(II) is only 5-coordinate and extremely asymmetric, with Pb-N bond lengths from 2.123(7) to 3.035(9) A; a rare Pb-Au contact of 3.5494(5) A is also observed. The Au(CN)2(-) units connect the Pb(ethylenediamine) centers to form 1-D zigzag chains which stack via Au-Au interactions of 3.3221(5) A to yield a 2-D sheet. (207)Pb MAS NMR of the polymers indicates an increase in both the chemical shielding span and isotropic chemical shift with increasing Pb(II) coordination sphere anisotropy (from delta iso = -2970 and Omega = 740 for 1 to delta iso = -448 and Omega = 3980 for 3). The shielding anisotropy is positively correlated with Pb(II) p-character, and reflects a direct connection between the NMR parameters and lone-pair activity. Solid-state variable-temperature luminescence measurements indicate that the emission bands at 520 and 494 nm, for 1 and 2, respectively, can be attributed to Pb --> L transitions, by comparison with simple [Pb(L)2](ClO4)2 salts. In contrast, two emission bands for 3 at 408 and 440 nm are assignable to Au-Au and Pb-Au-based transitions, respectively, as supported by single-point density-functional theory calculations on models of 3.

Characterising Lone‐Pair Activity of Lead(II) by 207Pb Solid‐State NMR Spectroscopy: Coordination Polymers of [N(CN)2]− and [Au(CN)2]− with Terpyridine Ancillary Ligands

“…In contrast, holo-directional coordination occurs when the lone pair is inactive, resulting in a maximisation of the coordination sphere, and exhibiting symmetric bond lengths and higher point group symmetry. [13] We have previously reported the 207 Pb MAS (magic-angle spinning) NMR spectroscopic behaviour of [Pb-A C H T U N G T R E N N U N G (H 2 O){Au(CN) 2 } 2 ], [PbA C H T U N G T R E N N U N G (phen) 2 {Au(CN) 2 } 2 ] (phen = 1,10-phenanthroline), [PbA C H T U N G T R E N N U N G (bipy) 2 {Au(CN) 2 } 2 } (bipy = 2,2'-bipyridine) and [Pb(en){Au(CN) 2 } 2 ] (en = ethylenediamine) coordination polymers, [14,15] for which it was demonstrated that chem- Pb MAS NMR spectroscopy in order to characterise the structural and electronic changes associated with lead(II) lone-pair activity. Two new compounds, 2 and [Pb(4'-hydroxyterpy){Au(CN) 2 } 2 ] (6), were prepared and structurally characterised.…”

“…1 = 2 ) and can be used as an alternate method for the measurement of lonepair activity. [15] Of the four stable lead isotopes, only 207 Pb is NMR-active (I = 1 = 2 ), with a moderate resonance frequency (125.2 MHz at 14.1 T) and 22.1 % natural abundance. [19] 207 Pb has one of the largest NMR chemical shift ranges (>15 000 ppm versus 13 C % 300 ppm) and is highly anisotropic, [20] displaying great sensitivity to changes in electron density; [21][22][23][24] these are ideal properties for determining the effect of lone-pair activity within lead(II) coordination polymers.…”

Cyanide-bridged bimetallic multidimensional structures derived from organotin(IV) and dicyanoaurate building blocks: ion exchange, luminescence, and gas sorption properties

“…The unique ability of linear [Au(CN) 2 ] − anion to form Au-Au aurophilic interaction plays a key role in controlling the dimensionality and topology of these dicyanoaurate-based heterometallic polymers [4][5][6][7]. The cyanoaurate-based heterometallic polymers may exhibit unusual structural motifs and physical properties, such as luminescence [8][9][10][11], vapochromism [12,13], birefringence [14][15][16][17][18], colossal thermal expansion [19,20], magnetism [21][22][23][24][25] or ion exchange [26]. This dicyanoaurate anion also has significant importance in industrial and medical applications.…”

“…In this light, it seems surprising that literature describing cyanoaurate-based coordination polymers of main-group metals is unusually sparse. A series of lead(II) coordination polymers containing the dicyanoaurate(I) bridging ligands were prepared and structurally characterized [14][15][16][17][18]. Some of them are highly birefringent materials [14][15][16][17][18].…”

“…A series of lead(II) coordination polymers containing the dicyanoaurate(I) bridging ligands were prepared and structurally characterized [14][15][16][17][18]. Some of them are highly birefringent materials [14][15][16][17][18]. We have previously reported the construction and structural characterization of multidimensional structures containing the Au-CN-Sn link generated by the reaction of the hard Lewis acidic organotin R n Sn (4- [30].…”