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Chapter I Brief Introduction...
low UV-cut off and good mechanical properties. Many metal complexes of
urea and urea analogs have been explored [69]. Examples of these
complexes are zinc thiourea sulfate (ZTS), zinc thiourea chloride (ZTC),
bis(thiourea) cadmium chloride (BTCC) and copper thiourea chloride (CTC).
Bis(thiourea) cadmium chloride (BTCC) is a promising semi-organic NLO
material for second-harmonic generation[70-72]. BTCC crystals have very
high laser induced damage threshold values. In general, crystals of the type
M[tu]2X2 (where M = Cd, Co, Hg, Pb, Ti and Zn, tu is thiourea and X is a
halogen) have been found to exhibit good NLO properties [73]. In
organometalic category complexes of thiourea like, Bis(thiourea) cadmium
zinc chloride (BTCZC) [74] and bis(thiourea) cadmium formate [75] exhibit
good NLO property . The characteristics of ATMX (where AT = allylthiourea, M =
Cd or Hg, X = Cl or Br) were studied by Sun et al [76]. The second harmonic
generation efficiency of these materials is higher than that of urea. Recently,
Sun et al [77] have reported the crystal structure, optical and thermal
characterization of tri-allyl thiourea zinc chloride (ATZC) . ATZC shows
powder SHG efficiency comparative to urea.
The metal thiocyanantes and their Lewis-base adducts are one of the
interesting themes of structural chemistry [78]. As second order NLO
materials, the well known category of bimetallic thiocyanates such as
ZnCd(SCN)4, ZnHg(SCN)4, CdHg(SCN)4 and MnHg(SCN)4 (abbreviated as
ZCTC, ZMTC, CMTC and MMTC, respectively), exhibit efficient SHG at short
wavelengths. Cadmium mercury thicoyanate (CMTC) crystal is one of the
most efficient NLO crystals among complex crystals [79]. A novel NLO
organometallic complex crystal, Cadmium mercury thiocyanate dimethyl
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