Two novel two-dimensional cluster polymers {[NMe4]2[MOS3Cu3(μ2-I)3]} (M=Mo,W): synthesis, crystal structure and interesting optical alternation from self-defocusing to self-focusing

Two novel cluster polymers {[NMe4]2[MoOS3Cu3(μ2-I)3]} 1 and {[NMe4]2[WOS3Cu3(μ2-I)3]}n2 have been prepared. Bithiometalates MO2S22− (M=Mo,W), CuI, Me4NBr and 4,4′-trimethylene-dipyridine(tdp) reacted in solid state under low-heating temperature resulting in these two clusters. X-ray diffraction analysis reveals that the two polymers have the same two-dimensional network structures, which are formed from nest-shaped units along crystallographic b and c directions. I atoms take on a μ2-fashion in bridging all the units. An alternative view along crystallographic a direction shows that they are layered features. Their third-order non-linear optical (NLO) properties were determined by Z-scan techniques. Both compounds possess very strong NLO refractive effect with n2 value of −5.02 × 10−17 m2W−1 for 1 and 1.20 × 10−16 m2W−1 for 2, respectively. Different from routine work, there is an alternation from cluster polymer 1–2 in their optical properties: 1 shows self-defocusing behavior, while 2 gives self-focusing effect. Effective third-order NLO susceptibilities χ(3) were calculated to be 4.90 × 10−11 esu 1 and 1.48 × 10−9 esu 2. The corresponding hyperpolarizabilities γ are 3.39 × 10−28 and 1.02 × 10−26 esu, respectively.