This paper reports the synthesis and structures of two key
members, [(18C6)K][Cd(SCN)3] (1)
and
[(18C6)2Na2(H2O)2]1/2[Cd(SCN)3]
(2), of a new inorganic polymers with
organic spacers (IPOS) series with the
general formula [H−G][M−L], where the organic cation
[H−G]
q
+ is a host (H)−guest (G) complex
such as [(crown
ether)−(alkali metal)]+ and the inorganic anion
[M−L]
q
- is a metal (M)−ligand (L)
coordination polymer such as
[Cd(SCN)3
-]∞.
1 and 2 were prepared from 18C6, MSCN, and
CdSO4 where M = K+ (for 1) and
Na+ (for 2),
respectively. 1 crystallizes in an orthorhombic unit
cell of Cmc21 space group symmetry with lattice
parameters a
= 14.734(3) Å, b = 15.304(2) Å, c
= 10.625(3) Å; V = 2396(1) Å3,
and Z = 4. The structure was refined to
R
1
= 2.3% for 878 independent reflections (2θ ≤ 46°) with
I > 3σ. 2 crystallizes in a monoclinic
unit cell of P21/n
space group symmetry with lattice parameters a =
10.277(3) Å, b = 10.915(5) Å, c =
22.596(7) Å, β = 111.48(5)°;
V = 2359(5) Å3, and Z = 4.
The structure was refined to R
1 = 3.7%
for 2415 independent reflections (2θ ≤ 46°)
with I > 3σ. These crystals exhibit interesting
physical properties such as nonlinear optical effects (NLO).
The
novel features of this particular IPOS series, as exemplified by the
title compounds, as tailorable crystalline materials
are (1) the anions form isolated polymeric one-dimensional
zig-zag chains of
[Cd(SCN)3
-]∞ with
extended
π-conjugation system within the polymeric
−[MSC⋮N]M··· chain and high polarizabilities
(which are important
for NLO effects); and (2) the cationic host−guest complex
[(18C6)M]+ serves as a spacer/controller of the
crystal
structure and crystal symmetry. The most important characteristic
of the IPOS system reported herein is that it
allows concomitant but separate molecular and crystal
engineering (i.e., design of molecular structures and
crystal
packings in two independent controls). A detailed analysis of the
structures of 1 and 2 revealed
parallel and antiparallel
arrangements, respectively, of the infinite anionic
[Cd(SCN)3
-]∞ polymeric
zig-zag chains; such arrangements are
presumably dictated by the monomeric and dimeric host−guest
[(18C6)M]+ cations. General design strategies,
in
terms of symmetry control, as well as molecular and crystal
engineering, in terms of electronic and stereochemical
controls, are discussed. Furthermore, the structures of the title
crystals may be considered as “crystal host−guest
clathrates” in which the infinite anionic polymeric
[Cd(SCN)3
-]∞ chains form
an approximate square motif, creating
square channels which are filled by “molecular host−guest
complexes” such as [(18C6)K]+ (in 1) or
[(18C6)2Na2(H2O)2]2+ (in
2).
Aim Forest fragmentation is often accompanied by an increase in hunting intensity. Both factors are known drivers of species extirpations, but understanding of their independent effects is poor. Our goal was to partition the effects of hunting and fragmentation on bird species extirpations and to identify bird traits that make species more vulnerable to these two stressors.
Location Menglun, Yunnan, SW ChinaMethods We studied the landscape within 10 km radius of Menglun town, where forests have become highly fragmented by monoculture rubber plantations. We compiled data on birds recorded between 1954 and 1983 before forest loss and compared it with a checklist prepared between 2011 and 2014. We used countryside and matrix-calibrated species-area models (SAMs) to estimate the observed slope of forest bird extirpations in Menglun and compared it with the slope expected in the absence of hunting. We also investigated six ecological traits to determine those that best explained bird extirpation probability (EP).
ResultsWe found that 34% of the bird fauna had been extirpated from the study landscape, and the estimated slopes of countryside and matrix-calibrated SAMs for forest birds were around 1.4 and 1.7 times higher, respectively, than the 0.35 expected without hunting. Bird EP was strongly associated with size, and understorey insectivores that are known to be susceptible to fragmentation were less susceptible to hunting than frugivores. Given evidence of past and present hunting activity in the area, and the lack of support for alternative explanations, we suggest that hunting increased forest bird extirpations by around 1.3-to 1.6-fold.Conclusions This study highlights the importance of using species-area relationships to separate area effects from the impacts of hunting. Our results suggest that hunting substantially increases species extirpations in tropical fragmented landscapes and conservation interventions that only target deforestation will therefore be inadequate.
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